TWI893421B - Switching power supply control chip and control method - Google Patents

Abstract

The present invention provides a control chip and control method for a switching power supply. The switching power supply includes a first switch, a first resistor, and a transformer. One end of the first switch is grounded through the first resistor, a second end of the first switch is connected to the transformer, and a third end of the first switch receives a control signal from the control chip. The control chip includes: a demagnetization module that detects the demagnetization condition of the switching power supply's transformer to generate a demagnetization signal, detects the voltage at the second end of the first switch to generate a resonant valley conduction signal, and detects the operating mode of the switching power supply to generate an operating mode signal; a first control unit that generates a first signal based on the demagnetization signal and the voltage across the first resistor; a second control unit that generates a second signal based on the demagnetization signal and the operating mode signal of the switching power supply; and control logic that generates a control signal for turning the first switch on and off based on the first signal, the second signal, and the resonant valley conduction signal.

Description

Switching power supply control chip and control method

The present invention relates to the field of circuit technology, and more specifically to a control chip and control method for a switching power supply.

A switching power supply, also known as a switching power supply or switching converter, is a type of power supply. Its function is to convert a voltage level into the voltage or current required by the user through various topologies (for example, flyback, buck, or boost).

A power controller is a device that controls a controlled switching power supply. Traditional power controllers are limited by the topology of the controlled switching power supply and produce power frequency ripple in the output current, resulting in low efficiency.

One aspect of the present invention provides a control chip for a switching power supply, wherein the switching power supply includes a first switch, a first resistor, and a transformer, one end of the first switch is grounded through the first resistor, a second end of the first switch is connected to the transformer, and a third end of the first switch receives a control signal from the control chip, the control chip including: a demagnetization module for detecting the demagnetization condition of the transformer of the switching power supply to generate a demagnetization signal, and detecting the voltage at the second end of the first switch to generate a demagnetization signal. A resonant valley conduction signal is generated, and an operating mode of the switching power supply is detected to generate an operating mode signal; a first control section generates a first signal based on the demagnetization signal and the voltage across the first resistor; a second control section generates a second signal based on the demagnetization signal and the operating mode signal of the switching power supply; and a control logic generates a control signal for controlling the on and off state of the first switch based on the first signal, the second signal, and the resonant valley conduction signal.

One aspect of the present invention provides a control method for a switching power supply executed by a control chip, wherein the switching power supply includes a first switch, a first resistor, and a transformer, one end of the first switch being grounded via the first resistor, a second end of the first switch being connected to the transformer, and a third end of the first switch receiving a control signal from the control chip. The control method includes: detecting demagnetization of the transformer of the switching power supply to generate a demagnetization signal, detecting a voltage at the second end of the first switch to generate a resonant valley conduction signal, and detecting an operating mode of the switching power supply to generate an operating mode signal; generating a first signal based on the demagnetization signal and the voltage across the first resistor; generating a second signal based on the demagnetization signal and the operating mode signal of the switching power supply; and generating a control signal for turning the first switch on and off based on the first signal, the second signal, and the resonant valley conduction signal.

The switching power supply control chip and control method of this invention are no longer limited by the topology of the controlled switching power supply. They offer efficient constant current precision control and can eliminate power frequency ripple in the output current, achieving optimal efficiency.

100: Power on/off

200,400: Control chip

201: Demagnetization module

202,6031,8031: Timing module

203: First comparison module

204,6034,8033: Edge-triggered module

205: Second comparison module

206,405,604,804: Control Module

2DEM_on: Double demagnetization time signal on.

401, 601, 801: Demagnetization module

402,6021,8021: Sampling module

403,6022,8022: Error current control module

404: Compare Module

602,802: First Control Section

6023,8023: First comparison module

603,803: Second Control Section

6032: Valley Lock Module

6033,8032: Second comparison module

800: Control chip

AC, Vs: voltage source

B1: Register

C, _Co , C1, C21, C41, C61, C62, C63, C81, C82: Capacitors

comp: comparison result signal

comp1: First comparison result signal

comp2: Second comparison result signal

D1, D2, D3, D4, D5, D6: diodes

DEM: Demagnetization signal

fre: operating frequency

gate: control signal

I1, Ic: First current source

I2, Id: Second current source

I _o : output current

I _p : primary side peak current

K: Predetermined ratio

Lp: Primary side inductance

N _p ,N _s : Number of turns

ON&DCM: The first switch S1 is on.

QR_on: Resonance valley conduction signal

R _cs : First resistor

R1: resistor

S1: First switch

S21, S22, S41, S42, S61, S62, S63, S64, S65, S66, S67, S68, S81, S82, S83, S84, S85: Switch

T: Transformer

T _ON ,T _DCM ,T _DEM : time

V1: voltage source

VC1, VC2, V _error : output (voltage)

V _cs ,V _ds : voltage

V _dc : Bias voltage source

VH: Upper threshold value

VI ₀ : First input voltage

VL: Lower threshold value

V _Led : output voltage

V _ref : reference voltage

_Vt : charge and discharge starting level

Vt: voltage source

V _th : threshold voltage

Aspects of the present invention are best understood from the following detailed description when read in conjunction with the accompanying drawings. Note that, in accordance with standard industry practice, various features are not necessarily drawn to scale. In the drawings, like numerals describe similar components. Similar numerals with different letter suffixes may represent different instances of similar components. In the drawings:

Figure 1 shows a schematic diagram of the topology of a switching power supply.

Figure 2 shows a schematic diagram of a traditional control chip for controlling a switching power supply;

Figure 3 shows the key operating waveforms of the control chip in Figure 2 controlling the switching power supply;

Figure 4 shows a schematic diagram of a conventional control chip for controlling a switching power supply.

Figure 5 shows the key operating waveforms of the control chip in Figure 4 controlling the switching power supply;

Figure 6 shows a schematic diagram of a control chip according to an embodiment of the present invention;

Figure 7 shows the key operating waveforms of the control chip in Figure 6 controlling the switching power supply;

Figure 8 shows a schematic diagram of a control chip according to an embodiment of the present invention; and

Figure 9 shows the key operating waveforms of the control chip in Figure 8 controlling the switching power supply.

The following describes in detail the features and exemplary embodiments of various aspects of the present invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention can be practiced without some of these specific details. The following description of the embodiments is intended merely to provide a better understanding of the present invention by illustrating examples thereof. The present invention is in no way limited to any specific configuration and algorithm set forth below, but rather encompasses any modifications, substitutions, and improvements to the elements, components, and algorithms without departing from the spirit of the present invention. Well-known structures and techniques are not shown in the drawings and the following description to avoid unnecessarily obscuring the present invention.

Figure 1 shows a schematic diagram of the topological structure of a switching power supply. As shown in Figure 1, the switching power supply 100 includes a first switch S1, a first resistor _Rcs , and a transformer T. The first switch S1 can be a metal-oxide-semiconductor field-effect transistor (MOSFET). The first terminal (source) of the first switch S1 is grounded via the first resistor _Rcs . The second terminal (drain) of the first switch S1 is connected to the transformer T ( _Np and _Ns represent the number of turns of the primary and secondary windings of the transformer T, respectively). The third terminal (gate) of the first switch S1 receives a control signal (gate) from the control chip.

It should be understood that the switching power supply 100 may also include other components and their connections. For example, as shown in Figure 1, the second end of the first switch S1 is specifically connected to the primary side of the transformer T and is also connected to the filtering circuit of the switching power supply 100 (including resistor R1 and capacitor C1) via diode D1. The secondary side of the transformer T is connected to the output circuit via diode D2. This output circuit includes a light-emitting diode (LED) load and a capacitor _C0 connected in parallel with the load. In Figure 1, the switching power supply 100 also includes a voltage source AC, a rectifier bridge formed by four diodes D3-D6, and a capacitor C. In Figure 1 , V _cs represents the voltage at the first terminal of the first switch S1, which is also the voltage across the first resistor R _cs ; V _ds represents the voltage at the second terminal of the first switch S1 ; V _Led represents the output voltage; and I _o represents the output current. While the figure illustrates the above components and their connections, the topology of the switching power supply 100 of the present invention is not limited thereto.

Figure 2 shows a schematic diagram of a conventional control chip for controlling a switching power supply. The control chip in Figure 2 implements flyback double demagnetization time control.

As shown in Figure 2, the control chip 200 includes a demagnetization module 201 that detects the demagnetization condition of the transformer T of the switching power supply 100 to generate a demagnetization signal DEM, and detects the operating mode of the switching power supply 100 to generate an operating mode signal.

The control chip 200 includes a timing module 202 that generates an output VC1 according to the demagnetization signal DEM and the working mode signal. As shown in FIG. 2 , the timing module 202 includes: a first current source I1 and a second current source I2 connected in series, wherein one end of the first current source is grounded; switches S21 and S22 corresponding to the first current source I1 and the second current source I2, respectively, wherein the switch S21 is controlled by a demagnetization signal DEM. For example, when the demagnetization signal DEM is high, indicating that the transformer T of the switching power supply 100 is demagnetized, the switch S21 is turned on; the switch S22 is controlled by an operating mode signal. For example, the switch S22 is turned on when the operating mode signal indicates that the switching power supply 100 is in discontinuous conduction mode (DCM) and the first switch S1 is turned on (indicated by ON&DCM in the figure); and a capacitor C21 connected between the connection point of the first current source I1 and the second current source I2 and ground. The output provided by the timing module 202 is the voltage across capacitor C21.

The control chip 200 also includes a first comparator module 203, which compares a first input signal with a second input signal to generate a first comparison result signal, comp1. As shown in Figure 2, the first input terminal of the first comparator module 203 is connected to the junction of the first current source I1 and the second current source I2. The first input signal is the output VC1 of the timing module 202. The second input terminal of the first comparator module 203 is connected to ground via a voltage source V1. The second input signal is the voltage threshold of the voltage source V1. The voltage source V1 also provides an initial voltage for the capacitor C21.

The control chip 200 also includes an edge-triggered module 204 that outputs a double demagnetization timer on signal 2DEM_on based on the first comparison result signal comp1 generated by the first comparator. For example, when the output VC1 rises to the voltage value of the voltage source V1, the double demagnetization timer on signal 2DEM_on output by the edge-triggered module 204 transitions to a high level.

As shown in FIG2 , the control chip 200 further includes a second comparison module 205. The second comparison module 205 compares the voltage _Vcs across the first resistor _Rcs with a threshold voltage _Vth to generate a second comparison result signal comp2.

The control chip 200 further includes a control module 206 that generates a control signal (gate) to turn the first switch S1 on and off based on the double demagnetization timer on-signal 2DEM_on generated by the edge trigger module 204 and the second comparison result signal comp2 generated by the second comparison module 205. For example, when the voltage _Vcs across the first resistor _Rcs is greater than the threshold voltage _Vth , the control module 206 generates the control signal (gate) to turn the first switch S1 off. When the double demagnetization timer on-signal 2DEM_on is high, the control module 206 generates the control signal (gate) to turn the first switch S1 on.

Specifically, when the control signal gate is high, it turns on the first switch S1, increasing the transformer primary current and the voltage _Vcs across the first resistor _Rcs . When _Vcs reaches _Vth , the control signal gate goes low, turning off the first switch S1. While the first switch S1 is on, the second current source I2 charges the capacitor C21. After the first switch S1 is turned off, the first current source I1 discharges the capacitor C21 during the demagnetization period of the transformer T. When the demagnetization module 201 detects the completion of demagnetization, the capacitor C21 discharges, and the second current source I2 resumes charging the capacitor C21. When the voltage VC1 on the capacitor C21 is charged to the voltage value of the voltage source V1, the double demagnetization counter on-time signal 2DEM_on output by the edge triggered module 204 turns high, the control signal gate becomes high, and the first switch S1 is turned on again.

Figure 3 shows the key operating waveforms of the control chip in Figure 2 controlling the switching power supply. In Figure 3, gate represents the control signal for the switching power supply generated by control module 206; V _ds represents the voltage at the second terminal (drain) of first switch S1; VC1 represents the output of edge-triggered module 204, namely, the voltage across capacitor C21; and 2DEM_on represents the double demagnetization timer on-time signal.

In double demagnetization time control, the current of the first current source I1 is equal to the current of the second current source I2. Therefore, the time T _ON + T _DCM = T _DEM , where T _ON represents the time when the control signal gate is at a high level, T _DCM represents the time when the control signal gate is at a low level and the switching power supply 100 is in discontinuous conduction mode (DCM), and T _DEM represents the time when the control signal gate is at a low level and the transformer T of the switching power supply 100 is demagnetized. Under ideal conditions, the current in the load LED lamp is:

Due to the internal comparator switching delay and the turn-on/off delay of the first switch S1, the actual current will be higher than the ideal state. This deviation is also affected by the chip and the first switch S1. This deviation is related to the input voltage and the primary inductance of the transformer T. Therefore, the constant current accuracy of the double demagnetization time control is poor. In addition, the voltage _Vds at the end of the double demagnetization is uncertain, which may cause the first switch S1 to turn on at the resonance peak, resulting in poor efficiency. However, the output current of the double demagnetization time control is minimally affected by the input voltage, so the power frequency ripple is extremely small. The peak value of the primary current of the transformer T varies little with the input voltage, and the operating frequency is basically the same under high and low input voltages. Therefore, double demagnetization time control has both advantages and disadvantages.

Figure 4 shows a schematic diagram of a conventional control chip for controlling a switching power supply. The control chip 400 in Figure 4 implements closed-loop, quasi-harmonic valley conduction control.

As shown in FIG4 , the control chip 400 includes a demagnetization module 401 for detecting the demagnetization of the transformer T of the switching power supply 100 to generate a demagnetization signal DEM and a voltage at the second terminal of the first switch S1 to generate a resonant valley conduction signal QR_on; and a sampling module 402 for detecting the peak voltage _Vcs across the first resistor _Rcs .

The control chip 400 also includes an error current control module 403, which differentially integrates a first input voltage _V10 at the reverse input terminal and a reference voltage _Vref at the forward input terminal to provide an output _Verror . The first input voltage is the peak voltage of the voltage _Vcs across the first resistor _Rcs or ground. As shown in Figure 4, the error current control module 403 is connected to ground via switch S41 and to the sampling module 402 via switch S42. When the demagnetization signal DEM generated by the demagnetization module 401 is high, indicating that the transformer T is demagnetizing, switch S42 turns on and switch S41 turns off. At this point, the first input voltage _V10 is the peak voltage of the voltage _Vcs across the first resistor _Rcs . When the demagnetization signal DEM generated by the demagnetization module 401 is low, indicating that the transformer T has completed demagnetization, switch S42 is closed and switch S41 is closed. At this time, the first input voltage is at a low level, such as 0. As shown in Figure 4 , capacitor C41 is connected between the output of the error current control module 403 and ground. Therefore, the output V _error of the error current control module 403 is also the voltage across capacitor C41.

The control chip 400 further includes a comparison module 404 that compares the output V _error of the error current control module 403 with the product of the voltage V _cs across the first resistor R _cs and a predetermined ratio K to generate a comparison result signal comp; and a control module 405 that generates a control signal gate for controlling the on and off of the first switch S1 based on the resonant valley conduction signal QR_on generated by the demagnetization module 401 and the comparison result signal comp generated by the comparison module 404.

Specifically, when the control signal gate is high, the first switch S1 is turned on, increasing the transformer primary current and the voltage _Vcs across the first resistor _Rcs . When _Vcs reaches K* _Vcs , which is greater than the voltage of the comparison result signal comp, the control signal gate goes low, turning the first switch S1 off. After the first switch S1 is turned off, the transformer T enters demagnetization. When the demagnetization module 401 detects the resonant valley of the voltage at the second terminal of the first switch S1 after demagnetization, the resonant valley conduction signal QR_on flips to a high level, turning the first switch S1 on again.

Figure 5 shows the key operating waveforms of the control chip in Figure 4 controlling the switching power supply. In Figure 5, gate represents the control signal for the switching power supply generated by the control module 405; V _ds represents the voltage at the second terminal (drain) of the first switch S1; and QR_on represents the resonant valley conduction signal QR_on generated by the demagnetization module 401.

In the flyback closed-loop quasi-resonant valley conduction control, the first switch S1 is turned on when the demagnetization module 401 detects that the voltage V _ds has resonated to its lowest value after demagnetization. This minimizes switching losses during each switching operation, reducing switching losses. Furthermore, by sampling the output current to generate the voltage V _error to control the on-time of the first switch S1, constant current accuracy is improved. However, in this flyback closed-loop quasi-resonant valley conduction control, when the input voltage of the switching power supply increases, the rising slope of the primary-side current of the transformer T increases during the on-time of the first switch S1. Consequently, the on-time of the first switch S1 decreases, resulting in an increase in the operating frequency. The operating frequency at high input voltage is significantly higher than that at low input voltage. Therefore, although the single-shot switching loss is lower than that of the double demagnetization time control, the significantly higher operating frequency at high voltage causes the switching loss of the flyback closed-loop quasi-harmonic valley conduction control to increase at high voltage. In addition, due to the higher operating frequency at high voltage, according to the input power formula:

Where Lp is the primary inductance of transformer T, _Ip is the primary peak current of transformer T, and fre is the operating frequency. At high voltage, the primary peak current _Ip of transformer T is lower than at low voltage. Therefore, transformer T utilization decreases when the input _voltage is high. Although the input is filtered by capacitors after the rectifier bridge, the voltage still exhibits power frequency fluctuations. The peak primary current required for valley-conduction constant current control will vary. Due to the limited response speed of the internal loop, the output current cannot instantly follow the constant current value. It can only ensure that the average output current follows the constant current control value, resulting in power frequency fluctuations in the output current. Therefore, the closed-loop quasi-harmonic valley conduction control with flyback has both advantages and disadvantages.

The embodiments of this invention propose a simple implementation method that simultaneously leverages the advantages of double demagnetization time control and flyback closed-loop quasi-harmonic valley conduction control while avoiding their shortcomings. This method achieves high constant current accuracy and resonant valley conduction while ensuring that high and low voltage operating frequencies are essentially the same. This improves HV transformer core utilization, reduces HV switch losses, and eliminates power-frequency ripple in the output current.

FIG6 shows a schematic diagram of a control chip according to an embodiment of the present invention. As shown in FIG6 , the control chip includes a demagnetization module 601 that detects the demagnetization condition of the transformer T of the switching power supply 100 to generate a demagnetization signal DEM, detects the voltage at the second terminal of the first switch S1 to generate a resonant valley conduction signal QR_on, and detects the operating mode of the switching power supply 100 to generate an operating mode signal; a first control unit 602 that generates a first signal based on the demagnetization signal DEM and the voltage across the first resistor _Rcs ; a second control unit 603 that generates a second signal based on the resonant valley conduction signal and the operating mode signal; and a control module 604 that generates a control signal for turning the first switch S1 on and off based on the first signal generated by the first control unit 602 and the second signal generated by the second control unit 603.

As shown in FIG6 , the first control unit 602 includes a sampling module 6021 for detecting the peak voltage of the voltage V _cs across the first resistor R _cs ; an error current control module 6022 for differentially integrating a first input voltage V ₁₀ at the reverse input terminal and a reference voltage V _ref at the forward input terminal to provide an output V _error , where the first input voltage is either the peak voltage of the voltage V _cs across the first resistor R _cs or ground; and a first comparison module 6023 for comparing the output V _error of the error current control module 6022 with the product of the voltage V _cs across the first resistor R _cs and a predetermined ratio K to generate a first comparison result signal comp1.

As shown in Figure 6, the error current control module 6022 is grounded via switch S61 and connected to the sampling module 6021 via switch S62. When the demagnetization signal DEM generated by the demagnetization module 601 is high, indicating that the transformer T is demagnetizing, switch S62 is turned on and switch S61 is turned off. At this time, the first input voltage _VI0 is the peak voltage of the voltage _Vcs across the first resistor _Rcs . When the demagnetization signal DEM generated by the demagnetization module 601 is low, indicating that the transformer T has completed demagnetization, switch S62 is turned off and switch S61 is turned on. At this time, the first input voltage is low, such as 0. As shown in FIG6 , capacitor C61 is connected between the output terminal of the error current control module 6022 and ground. Therefore, the output V _error of the error current control module 6022 is also the voltage on capacitor C61 .

The first signal of the first control part 602 is the first comparison result signal comp1.

As shown in FIG6 , the second control part 603 includes: a timing module 6031, which generates an output VC2 according to the demagnetization signal DEM and the working mode signal. As shown in FIG6 , the timing module 6031 includes: a first current source Ic and a second current source Id connected in series, wherein one end of the second current source Id is grounded; switches S63 and S64 corresponding to the first current source Ic and the second current source Id, respectively, wherein the switch S63 is controlled by the working mode signal. For example, the switch S63 is turned on when the working mode signal indicates that the switching power supply 100 is in the discontinuous conduction mode (DCM) and the first switch S1 is in the conducting period (shown as ON&DCM in the figure). Switch S64 is controlled by the demagnetization signal DEM. For example, when the demagnetization signal DEM is high, indicating that the transformer T of the switching power supply 100 is demagnetized, switch S64 is turned on. Capacitor C62 is connected between the junction point of the first current source Ic and the second current source Id and ground. The timing module 6031 provides output VC2, which is the voltage across capacitor C62. A voltage source Vt is connected between the junction point of the first current source Ic and the second current source Id and ground, as well as switch S65. Voltage source Vt provides an initial voltage value for capacitor C62.

The second control unit 603 also includes a valley lock module 6032, which is used to provide the threshold voltage for the current switching cycle by subtracting the bias voltage source V _dc from the voltage across capacitor C62 immediately before the first switch S1 was turned on in the previous switching cycle. As shown in FIG6 , the valley lock module 6032 includes a register B1 for buffering the voltage threshold, a bias voltage source V _dc , a capacitor C63 connected between the junction of register B1 and the bias voltage source V _{dc (} closest to the timing module 6031) and ground, and a voltage source Vs connected between the bias voltage source V _dc (farthest from the timing module 6031) and ground. When capacitor C62 is charged to the voltage value of voltage source Vt, the double demagnetization timer on-signal 2DEM_on goes high. If the resonant valley conduction signal QR_on then goes high, switch S66, connected between register B1 and bias voltage source _Vdc, briefly turns on to sample the voltage across capacitor C63 minus a small bias voltage provided by _bias voltage source _Vdc , generating a new threshold voltage _Vth as the output of valley lock module 6032. When _Vth falls below the lower threshold VL or exceeds the upper threshold VH, the operating frequency is outside the acceptable range for the double demagnetization time control. At this point, the double demagnetization timer on-off signal 2DEM_on flips high. The voltage threshold is provided by the voltage source Vs via switch S68. This voltage can be a fixed value close to the charge/discharge start level _Vt , or a voltage closer to _Vt calculated from _Vth . This locks the number of valleys during the turn-on phase of the first switch S1 to the same value as during the previous switching cycle. By switching the number of valleys, the operating frequency is kept closer to twice the demagnetization time, preventing high power-frequency ripple in the output current caused by valley switching due to power-frequency ripple in the input capacitor voltage.

The second control unit 603 also includes a second comparison module 6033, which compares the first input signal and the second input signal to generate a second comparison result signal comp2. As shown in Figure 6, the first input terminal of the second comparison module 6033 is connected to the connection point of the first current source Ic and the second current source Id. The first input signal is the output VC2 of the timing module 6031. The second input terminal of the second comparison module 6033 is connected to the valley lock module 6032 to receive the variable threshold voltage _Vth via the switch S67. The second input signal is the variable threshold voltage _Vth from the valley lock module 6032.

The second control unit 603 also includes an edge-triggered module 6034 that outputs a double demagnetization counter on-time signal 2DEM_on based on the second comparison result signal comp2 generated by the second comparison module 6033. For example, when VC2 rises to the threshold Vt, the double demagnetization counter on-time signal 2DEM_on output by the edge-triggered module 6034 transitions to a high level.

Based on the first comparison result signal comp1, the double demagnetization time on-time signal 2DEM_on, and the resonant valley conduction signal QR_on, the control module 604 generates a control signal gate for turning the first switch S1 on and off. Specifically, when the first comparison result signal comp1 indicates that the product of the voltage _Vcs across the first resistor _Rcs and the predetermined ratio K is greater than the output _Verror of the error current control module 6022, the control module 604 generates the control signal gate for turning the first switch S1 off. Specifically, the gate signal is set to a low level. When the double demagnetization time-on signal 2DEM_on turns high and then the resonance valley conduction signal QR_on turns high, the control module 604 generates a control signal gate for controlling the first switch S1 to turn on, that is, the gate signal is high.

Figure 7 shows the key operating waveforms of the control chip in Figure 6 controlling the switching power supply.

In Figure 7, gate represents the control signal for the switching power supply generated by control module 604; _Vds represents the voltage at the second terminal (drain) of first switch S1; VC2 represents the output of timing module 6031, namely the voltage across capacitor C62; 2DEM_on represents the double demagnetization timing turn-on signal; QR_on represents the resonant valley conduction signal; and Vt represents the starting value for the charge and discharge of capacitor C82 during each switching cycle.

As shown in Figure 7, when the control signal gate is high, the first switch S1 is turned on, and the first current source Ic charges capacitor C62 until the control signal gate goes low. Then, the second current source Id discharges capacitor C62 until the demagnetization module 601 detects the end of transformer T demagnetization. At this point, the first current source Ic starts charging capacitor C62 again until the voltage across capacitor C62 exceeds the threshold _Vth , and the double demagnetization timing on-signal 2DEM_on transitions to a high level. If the demagnetization module 601 detects the resonant valley conduction signal QR_on transitioning to a high level, the voltage across capacitor C62 minus the bias voltage source _Vdc is sampled and used as the threshold voltage _Vth for the next switching cycle. Then, the control signal gate goes high, turning on the first switch S1 again. Simultaneously, the voltage across capacitor C62 is reset to its initial value, Vt, by briefly turning on switch S65, restarting charging. This prevents the input voltage's power-frequency ripple from causing a change in the number of resonant valleys, which in turn would cause frequency fluctuations and, consequently, power-frequency fluctuations in the output current.

If the input voltage is large enough, close to DC voltage, or DC voltage, then the valley locking portion of this embodiment is unnecessary, and control can be achieved using the implementation method of the following embodiment.

Figure 8 shows a schematic diagram of a control chip according to an embodiment of the present invention.

As shown in FIG8 , the control chip includes a demagnetization module 801 that detects the demagnetization condition of the transformer T of the switching power supply 100 to generate a demagnetization signal DEM, detects the voltage at the second terminal of the first switch S1 to generate a resonant valley conduction signal QR_on, and detects the operating mode of the switching power supply 100 to generate an operating mode signal; a first control unit 802 that generates a first signal based on the demagnetization signal DEM and the voltage across the first resistor R _cs ; a second control unit 803 that generates a second signal based on the resonant valley conduction signal and the operating mode signal; and a control module 804 that generates a control signal for turning the first switch S1 on and off based on the first signal generated by the first control unit 802 and the second signal generated by the second control unit 803.

As shown in Figure 8, the first control unit 802 includes a sampling module 8021 for detecting the peak voltage of the voltage _Vcs across the first resistor _Rcs ; an error current control module 8022 for differentially integrating a first input voltage _V10 at the reverse input terminal and a reference voltage _Vref at the forward input terminal to provide an output _Verror , where the first input voltage is the peak voltage of the voltage _Vcs across the first resistor _Rcs or ground; and a first comparison module 8023 for comparing the output _Verror of the error current control module 8022 with the product of the voltage _Vcs across the first resistor _Rcs and a predetermined ratio K to generate a first comparison result signal comp1.

As shown in Figure 8 , the error current control module 8022 is grounded via switch S81 and connected to the sampling module 8021 via switch S82. When the demagnetization signal DEM generated by the demagnetization module 801 is high, indicating that the transformer T is demagnetizing, switch S82 is turned on and switch S81 is turned off. At this time, the first input voltage _VI0 is the peak voltage of the voltage _Vcs across the first resistor _Rcs . When the demagnetization signal DEM generated by the demagnetization module 801 is low, indicating that the transformer T has completed demagnetization, switch S82 is turned off and switch S81 is turned on. At this time, the first input voltage is low, such as 0. As shown in FIG8 , capacitor C81 is connected between the output terminal of the error current control module 8022 and ground. Therefore, the output V _error of the error current control module 8022 is also the voltage on capacitor C81 .

The first signal of the first control part 802 is the first comparison result signal comp1.

As shown in Figure 8 , the second control unit 803 includes a timing module 8031 that generates an output VC2 based on the demagnetization signal DEM and the operating mode signal. As shown in Figure 8 , the timing module 8031 includes a first current source Ic and a second current source Id connected in series, with one end of the second current source Id being grounded; and switches S83 and S84 corresponding to the first current source Ic and the second current source Id, respectively. Switch S83 is controlled by the operating mode signal. For example, switch S83 is switched on when the operating mode signal indicates that the switching power supply 100 is in discontinuous conduction mode (DCM) and the first switch S1 is conducting (indicated as ON & DCM in the figure). Switch S84 is controlled by the demagnetization signal DEM. For example, when the demagnetization signal DEM is high, indicating that the transformer T of the switching power supply 100 is demagnetized, switch S84 is turned on. Capacitor C82 is connected between the connection point of the first current source Ic and the second current source Id and ground. Output VC2 provided by the timing module 8031, i.e., the voltage across capacitor C82, is connected between the connection point of the first current source Ic and the second current source Id and ground. Voltage source Vt is connected between the connection point of the first current source Ic and the second current source Id and ground, as well as switch S85.

The second control unit 803 also includes a second comparison module 8032, which compares the first input signal with the second input signal to generate a second comparison result signal comp2. As shown in Figure 8, the first input terminal of the second comparison module 8032 is connected to the junction of the first current source Ic and the second current source Id. The first input signal is the output VC2 of the timing module 8031. The second input terminal of the second comparison module 8032 is connected to ground via the voltage source Vt. The second input signal is the fixed voltage from the voltage source Vt.

The second control unit 803 also includes an edge trigger module 8033, which outputs a double demagnetization counter on-time signal 2DEM_on based on the second comparison result signal comp2 generated by the second comparator. For example, when VC2 rises to the threshold Vt, the double demagnetization counter on-time signal 2DEM_on output by the edge trigger module 8033 transitions to a high level.

Based on the first comparison result signal comp1, the double demagnetization time on-time signal 2DEM_on, and the resonant valley conduction signal QR_on, the control module 405 generates a control signal gate for turning the first switch S1 on and off. Specifically, when the first comparison result signal comp1 indicates that the product of the voltage _Vcs across the first resistor _Rcs and the predetermined ratio K is greater than the output _Verror of the error current control module 8022, the control module 804 generates a control signal gate for turning the first switch S1 off. This gate signal is set to a low level. When the double demagnetization meter on-time signal 2DEM_on turns high and then the resonance valley conduction signal QR_on turns high, the control module 804 generates a control signal gate for controlling the conduction of the first switch S1, that is, the gate signal is high.

Specifically, when the control signal gate is high, the first switch S1 is turned on, increasing the transformer primary current and the voltage _Vcs across the first resistor _Rcs . When _Vcs reaches K* _Vcs , which is greater than _Verror , the control signal gate goes low, turning the first switch S1 off. While the first switch S1 is on, the first current source Ic charges the capacitor C82. After the first switch S1 is turned off, the transformer T enters demagnetization. During the demagnetization period, the second current source Id discharges the capacitor C82. When the demagnetization module 801 detects the end of demagnetization, capacitor C82 stops discharging, and the first current source Ic continues to charge capacitor C82. When the voltage VC2 of capacitor C82 reaches the fixed threshold Vt, the double demagnetization timer on-signal 2DEM_on flips to a high level. If the resonant valley conduction signal QR_on flips to a high level, the first switch S1 turns on again.

Figure 9 shows the key operating waveforms of the control chip in Figure 8 controlling the switching power supply. In Figure 9, gate represents the control signal for the switching power supply generated by control module 804; _Vds represents the voltage at the second terminal (drain) of first switch S1; VC2 represents the output of timing module 8031, namely the voltage across capacitor C82; 2DEM_on represents the double demagnetization timing turn-on signal; and QR_on represents the resonant valley conduction signal. Vt represents the starting value for the charge and discharge of capacitor C82 during each switching cycle.

As shown in Figure 9, when the control signal gate is high, the first switch S1 turns on, and the first current source Ic charges capacitor C82. Charging stops when the control signal gate goes low. Subsequently, the second current source Id discharges capacitor C82 until the demagnetization module 801 detects the end of demagnetization. At this point, the first current source Ic returns to charge capacitor C82 until the voltage VC2 across capacitor C82 exceeds its initial value Vt, causing the double demagnetization timing on-signal 2DEM_on to transition high. Subsequently, if the demagnetization module 801 detects the resonant valley conduction signal QR_on transitioning high, the control signal gate goes high, turning the first switch S1 on again. Simultaneously, the voltage across capacitor C82 is reset to its initial value Vt by briefly turning on switch S85, and charging resumes. In this way, the power-frequency ripple of the input voltage will not cause a change in the number of resonant valleys, thereby causing frequency abrupt changes and thus power-frequency fluctuations in the output current.

The switching power supply control chip and control method of the present invention combine the advantages of double demagnetization time control and flyback closed-loop quasi-harmonic valley conduction control while avoiding their shortcomings. This achieves high constant current accuracy and resonant valley conduction while ensuring nearly identical high and low voltage operating frequencies. This improves HV transformer core utilization, reduces HV switch losses, and eliminates power-frequency ripple in the output current.

The figures illustrate control chips and control methods according to various embodiments of the present invention. It should be understood that the present invention is not limited thereto and may be implemented in other forms without departing from the spirit and essential characteristics of the present invention. The present embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the appended claims rather than the foregoing description, and all modifications coming within the meaning and range of equivalents of the claims are intended to be embraced therein.

2DEM_on: Double demagnetization time signal on.

800: Control chip

801: Demagnetization module

802: First Control Section

8021: Sampling Module

8022: Error Current Control Module

8023: First comparison module

803: Second Control Section

8031: Timing module

8032: Second comparison module

8033: Edge-triggered module

804: Control Module

C81, C82: Capacitors

comp1: First comparison result signal

comp2: Second comparison result signal

DEM: Demagnetization signal

gate: control signal

Ic: First current source

Id: Second current source

K: Predetermined ratio

ON&DCM: The first switch S1 is on.

QR_on: Resonance valley conduction signal

S81, S82, S83, S84, S85: Switches

VC2, V _error : output (voltage)

V _cs : voltage

VI ₀ : First input voltage

_Vt : charge and discharge starting level

Vt: voltage source

V _ref : reference voltage

Claims (24)

A control chip for a switching power supply, wherein the switching power supply includes a first switch, a first resistor, and a transformer, one end of the first switch is grounded through the first resistor, a second end of the first switch is connected to the transformer, and a third end of the first switch receives a control signal from the control chip, the control chip including: a demagnetization module for detecting the demagnetization condition of the transformer of the switching power supply to generate a demagnetization signal, and detecting the voltage at the second end of the first switch to generate a A resonant valley conduction signal is detected, and an operating mode of the switching power supply is detected to generate an operating mode signal; a first control section generates a first signal based on the demagnetization signal and the voltage across the first resistor; a second control section generates a second signal based on the demagnetization signal and the operating mode signal of the switching power supply; and control logic generates a control signal for controlling the on and off state of the first switch based on the first and second signals and the resonant valley conduction signal. The control chip for the switching power supply as claimed in claim 1, wherein the first control section comprises: a sampling module for detecting the peak voltage of the voltage across the first resistor; an error current control module for differentially integrating a first input voltage and a reference voltage to provide an output, wherein the first input voltage is the peak voltage of the voltage across the first resistor or a ground voltage; and a first comparison module for comparing the output of the error current control module with the product of the voltage across the first resistor and a predetermined ratio to generate a first comparison result signal as the first signal. The control chip for a switching power supply as described in claim 2, wherein the first control section further includes a second switch and a third switch, the error current control module is connected to the sampling module via the second switch and to ground via the third switch, and the output of the error current control module is connected to ground via a first capacitor. Furthermore, when the demagnetization signal indicates that the transformer is demagnetizing, the second switch is turned on and the third switch is turned off, and the first input voltage is the peak voltage of the voltage across the first resistor. Furthermore, when the demagnetization signal indicates that the transformer has completed demagnetization, the second switch is turned off and the third switch is turned on, and the first input voltage is ground voltage. The control chip of the switching power supply as claimed in claim 2 or 3, wherein when the first comparison result signal indicates that the product of the voltage across the first resistor and a predetermined ratio is greater than the output of the error current control module, the control logic generates a control signal to turn off the first switch. The control chip for a switching power supply as claimed in claim 1, wherein the second control section comprises: a timing module that generates an output based on a demagnetization signal and an operating mode signal; a second comparison module that compares the output of the timing module with a threshold voltage to generate a second comparison result signal; and an edge trigger module that generates a double demagnetization timing turn-on signal as the second signal based on the second comparison result signal. The control chip for a switching power supply as claimed in claim 5, wherein the current source module comprises: a first current source and a second current source connected in series; a second capacitor connected between a connection point between the first current source and the second current source and ground, the second capacitor being charged and discharged based on the demagnetization signal and the operating mode signal; a voltage source connected between a connection point between the first current source and the second current source and ground; and a fourth switch, wherein the initial voltage of the second capacitor and the initial value of the threshold voltage are provided by the voltage source. The control chip for a switching power supply as described in claim 6, wherein the current source module further comprises: a fifth switch between the first current source and a connection point between the first current source and the second current source; and a sixth switch between the second current source and a connection point between the first current source and the second current source, wherein the fifth switch is turned on and off according to the operating mode signal, and the sixth switch is turned on or off according to the demagnetization signal. The control chip of the switching power supply as claimed in claim 7, wherein when the operating mode signal indicates that the switching power supply is in a discontinuous conduction mode and the first switch is in a conducting period, the fifth switch is turned on and the second capacitor is charged; and when the demagnetization signal indicates that the switching power supply is in a demagnetization period, the sixth switch is turned on and the second capacitor is discharged. The control chip for a switching power supply as claimed in claim 5, wherein when the second comparison result signal indicates that the output of the timing module has risen to the threshold voltage, the double demagnetization timing turn-on signal generated by the edge trigger module switches to a high level. The control chip for the switching power supply as claimed in claim 5, wherein when the double demagnetization counter turn-on signal is at a high level and the resonance valley conduction signal flips to a high level, the control module generates a control signal to control the conduction of the first switch. The control chip of the switching power supply as claimed in claim 10, wherein, after the control module generates a control signal to control the first switch to be turned on, the fourth switch is turned on to reset the second capacitor to the threshold voltage. The control chip of the switching power supply as described in claim 5 further includes a valley lock module for subtracting a bias voltage from the voltage output by the timing module before the first switch is turned on in the previous switching cycle of the switching power supply to provide the threshold voltage for the current switching cycle. The control chip for a switching power supply as described in claim 12, wherein, when the threshold voltage is lower than a lower threshold limit or exceeds an upper threshold limit, the valley lock module adjusts the threshold voltage to a value close to the initial value of the threshold voltage. A control method for a switching power supply executed by a control chip, wherein the switching power supply includes a first switch, a first resistor, and a transformer, one end of the first switch being grounded via the first resistor, a second end of the first switch being connected to the transformer, and a third end of the first switch receiving a control signal from the control chip. The control method includes: detecting demagnetization of the transformer of the switching power supply to generate a demagnetization signal, detecting a voltage at the second end of the first switch to generate a resonant valley conduction signal, and detecting an operating mode of the switching power supply to generate an operating mode signal; generating a first signal based on the demagnetization signal and the voltage across the first resistor; generating a second signal based on the demagnetization signal and the operating mode signal of the switching power supply; and generating a control signal for turning the first switch on and off based on the first and second signals and the resonant valley conduction signal. The switching power supply control method of claim 14 further includes: detecting a peak voltage of the voltage across the first resistor; differentially integrating a first input voltage and a reference voltage to provide an output, wherein the first input voltage is the peak voltage of the voltage across the first resistor or a ground voltage; and comparing the output with a product of the voltage across the first resistor and a predetermined ratio to generate a first comparison result signal as the first signal. The switching power supply control method of claim 15, wherein when the demagnetization signal indicates that the transformer is demagnetizing, the first input voltage is the peak voltage of the voltage across the first resistor, and when the demagnetization signal indicates that the transformer has completed demagnetization, the first input voltage is the ground voltage. In the switching power supply control method of claim 15 or 16, when the first comparison result signal indicates that the product of the voltage across the first resistor and a predetermined ratio is greater than the output, a control signal is generated to turn off the first switch. The switching power supply control method of claim 14 further comprises: utilizing a timing module of the control chip to generate an output based on a demagnetization signal and an operating mode signal; comparing the output with a threshold voltage to generate a second comparison result signal; and generating a double demagnetization timing turn-on signal as the second signal based on the second comparison result signal. The control method of a switching power supply as described in claim 18 further comprises: when the operating mode signal indicates that the switching power supply is in a discontinuous conduction mode and the first switch is in a conduction period, charging the capacitor of the timing module; and when the demagnetization signal indicates that the switching power supply is in a demagnetization period, discharging the capacitor of the timing module. The method for controlling a switching power supply as claimed in claim 18, wherein when the second comparison result signal indicates that the output of the timing module has risen to the threshold voltage, the double demagnetization timing on/off signal is switched to a high level. The method for controlling a switching power supply as claimed in claim 18, wherein, after the double demagnetization time turn-on signal is at a high level, when the resonant valley conduction signal flips to a high level, a control signal for controlling the conduction of the first switch is generated. The method for controlling a switching power supply as claimed in claim 21, wherein after generating a control signal for controlling the first switch to be turned on, the capacitance of the timing module is reset to the threshold voltage. The control method for a switching power supply as described in claim 18 further includes: subtracting a bias voltage from a voltage output by the timing module before the first switch is turned on in a previous switching cycle of the switching power supply to provide the threshold voltage for the current switching cycle. The switching power supply control method of claim 14 further comprises: if the threshold voltage is lower than a lower threshold limit or exceeds an upper threshold limit, adjusting the threshold voltage to an initial value close to the threshold voltage.