JP2012139003A - Switching power supply device - Google Patents

Abstract

To provide a switching power supply device capable of realizing a stable start-up when a power source is turned on while providing a control circuit for controlling a switching element on the secondary side.
In a switching power supply device 1 provided with a switching element 13 for controlling a current flowing in a primary winding 12 of an insulating transformer 10, and for controlling switching of the switching element 13 based on an output voltage Vout on a secondary side. A primary-side control IC 14 that operates with an input voltage Vin input to the primary side and outputs a PWM signal Sp1 that controls switching of the switching element 13 when the power is turned on. A secondary-side control IC 25 that operates at the output voltage Vout and outputs a PWM signal Sp2 that controls the switching of the switching element 13, and the primary side based on the PWM signal Sp1 of the primary-side control IC 14 when the power is turned on. When the current of the winding 12 is controlled and the secondary side control IC 25 starts outputting the PWM signal Sp2 The was configured to control the current of the primary winding 12 based on the PWM signal Sp2.
[Selection] Figure 1

Description

  The present invention relates to an insulating switching power supply device.

Conventionally, a switching power supply device is known as a power supply device. The switching power supply apparatus includes a switching element and a control IC that controls the operation of the switching element, and the control IC generates a PWM signal having a duty ratio corresponding to an input voltage to turn on / off the switching element. By executing control (PWM: Pulse Width Modulation), a predetermined output voltage is generated with high efficiency.
As the switching power supply device, an insulating switching power supply device in which an insulating transformer is provided in the voltage converter and the primary side and the secondary side are insulated is known. The insulation type switching power supply device is highly efficient and excellent in insulation, and a multi-output power supply device can be easily configured by providing a plurality of secondary windings in an insulation transformer. Widely used for conversion to output voltage.

  By the way, in the insulated switching power supply device, in order to feedback control the output voltage, a tertiary winding (feedback winding) for detecting the output voltage is provided on the primary side, and the voltage induced in the tertiary winding is set to the voltage. A configuration for adjusting the duty ratio of the PWM signal based on this is known. However, in this configuration, since feedback control is performed with the voltage detected on the primary side, the change in the output voltage due to the load fluctuation on the secondary side is not detected, and this cannot be dealt with.

Therefore, a voltage detection circuit for detecting the output voltage is provided on the secondary side, and feedback control is performed by feeding back the output of the voltage detection circuit to the primary side and inputting it to the control IC. By directly detecting the voltage, it is possible to satisfactorily control the output voltage that changes according to the load fluctuation.
In particular, in a switching power supply device that detects an output voltage on the secondary side, a control IC including a voltage detection circuit is provided on the secondary side, and the output voltage is detected by the control IC to generate a PWM signal. Is known to transmit to the primary side (see, for example, Patent Document 1).
According to this configuration, the output voltage can be detected and feedback controlled by the voltage detection circuit included in the control IC without separately providing a voltage detection circuit on the secondary side. In addition, compared to a configuration in which the output voltage is fed back to the primary side, the control loop is not band-limited due to the phase delay of the feedback signal, and in particular, the transient response is not affected by the phase delay. There are benefits.

JP-T-2003-523711

By the way, when the control IC is provided on the secondary side, the control IC on the secondary side is surely connected when the power is turned on so that the control IC on the secondary side can operate at the timing of the input voltage input start (power on) to the primary side. It is necessary to supply voltage.
If a spare power supply is separately provided for the control IC on the secondary side, the control IC can be reliably operated at the power-on timing, but the cost is increased by the spare power supply. In particular, when the switching power supply device is configured as a multi-output type and a control IC is provided for each output, a spare power supply is required for each output, resulting in an increase in cost.

On the other hand, in the technique of the above-mentioned Patent Document 1, a standby power supply is not required by providing a pulse transformer in the primary winding to generate the operating power of the control IC on the secondary side.
However, if the input voltage is not sufficient at the power-on timing, the voltage output to the control IC may be insufficient and startup may fail. For this reason, as shown in Patent Document 1, a resonance circuit that resonates when the power is turned on is provided on the primary side in order to prevent startup failure, and a plurality of switching elements are provided when the power is turned on by resonance of the resonance circuit. A separate configuration is required for reliably starting the control IC by turning it on repeatedly. However, when the switching power supply device is configured as a multi-output type by providing a switching element for each of a plurality of outputs, the resonance of the resonance circuit is mainly parasitic in the switching system for each output. Can not be provided. For this reason, since it is necessary to provide a resonance circuit for each output, the circuit configuration becomes complicated and the apparatus cost increases.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a switching power supply device capable of realizing stable start-up when the power is turned on while providing a control circuit for controlling the switching element on the secondary side. And

  In order to achieve the above object, the present invention provides a switching element for controlling a current flowing in a primary winding of an insulated transformer, and controls switching of the switching element based on an output voltage on a secondary side. In the apparatus, a primary side control circuit that operates with an input voltage input to the primary side and outputs a first control signal that controls switching of the switching element when the power is turned on, and a secondary side circuit are provided. A secondary side control circuit that operates at the output voltage and outputs a second control signal for controlling switching of the switching element, and the power supply is turned on based on the first control signal of the primary side control circuit. When the secondary control circuit starts outputting the second control signal by controlling the current of the secondary winding, the current of the primary winding is controlled based on the second control signal. It is characterized in.

  According to the present invention, the output voltage can be output to the secondary side by controlling the current of the primary winding based on the first control signal of the primary side control circuit at the power-on timing. The secondary side control circuit provided on the secondary side can be reliably started to operate. When the secondary control circuit starts outputting the second control signal, the current of the primary winding is controlled based on the second control signal of the secondary control circuit provided on the secondary side. Control with reduced delay becomes possible.

  According to the present invention, in the above switching power supply device, a first switching element that operates according to a first control signal of the primary side control circuit, and a second switching element that operates according to a second control signal of the secondary side control circuit; The switching element for controlling the current of the primary winding is switched between the first switching element and the second switching element to control the current of the primary winding. The control based on the first control signal of the side control circuit is switched to the control based on the second control signal of the secondary side control circuit.

  According to the present invention, the switching element for controlling the current of the primary winding is switched between the first switching element and the second switching element, so that the control of the primary side control circuit is controlled to the control of the secondary side control circuit. Therefore, the operation reliability is improved as compared with the configuration in which the signal input to the single switching element is switched between the first control signal and the second control signal.

  According to the present invention, in the switching power supply device, the control of the current of the primary winding is based on the second control signal of the secondary control circuit from the control based on the first control signal of the primary control circuit. When switching to control, switching is performed with a period in which no current flows after a period in which current flows in the primary winding based on the first control signal.

  According to the present invention, at the time of switching, the period in which current flows in the primary winding based on the first control signal and the period in which current flows in the primary winding based on the second control signal do not continue. Therefore, instantaneous overvoltage can be prevented.

  According to the present invention, in the switching power supply device, when the control of the current of the primary winding is switched to the control based on the second control signal of the secondary control circuit, the primary control circuit is stopped. It is characterized by doing.

  According to the present invention, when switching to the control based on the second control signal of the secondary side control circuit, the primary side control circuit is stopped, so that power saving is achieved.

  Further, the present invention provides the above switching power supply apparatus, wherein a plurality of the primary windings are provided on the primary side, the switching elements are provided on the primary windings, and the primary windings are provided on the secondary side for each primary winding. A secondary winding is provided to form a multi-output type, and the secondary side control circuit for controlling the corresponding primary side switching element is provided for each output.

  According to the present invention, since the secondary side control circuit for controlling the corresponding primary side switching element is provided for each output, the output voltage is feedback controlled for each output, and the load of each output is mutually controlled. It is possible to suppress the occurrence of cross regulation when it fluctuates independently.

  According to the present invention, in the switching power supply device, each of the switching elements is controlled by a common primary side control circuit.

  According to the present invention, since each of the plurality of switching elements is controlled by the common primary side control circuit, the apparatus cost can be suppressed and the ratio of the primary side control circuit in the circuit scale can be reduced.

According to the present invention, the output voltage can be output to the secondary side by controlling the current of the primary winding based on the first control signal of the primary side control circuit at the power-on timing. The secondary side control circuit provided on the secondary side can be reliably started to operate. When the secondary control circuit starts outputting the second control signal, the current of the primary winding is controlled based on the second control signal of the secondary control circuit provided on the secondary side. Control with reduced delay becomes possible.
The present invention further includes a first switching element that operates according to a first control signal of the primary side control circuit, and a second switching element that operates according to a second control signal of the secondary side control circuit, The switching element for controlling the current of the secondary winding is switched between the first switching element and the second switching element so that the current of the primary winding is controlled by the first control circuit of the primary side control circuit. If the control based on the control signal is switched to the control based on the second control signal of the secondary side control circuit, the signal input to the single switching element is transferred between the first control signal and the second control signal. Operation reliability is improved as compared with the switching configuration.
In the present invention, when switching the control of the current of the primary winding from the control based on the first control signal of the primary side control circuit to the control based on the second control signal of the secondary side control circuit, If a configuration is adopted in which the current is not passed through the primary winding based on the first control signal and then the current is not passed, the primary winding is switched based on the first control signal at the time of switching. Since the period in which the current flows and the period in which the current flows in the primary winding based on the second control signal do not continue, it is possible to prevent an instantaneous overvoltage from occurring.
Further, in the present invention, when the control of the current of the primary winding is switched to the control based on the second control signal of the secondary control circuit, the primary control circuit is stopped. Since the primary side control circuit is stopped when switching to the control based on the second control signal of the secondary side control circuit, power saving is achieved.
In the present invention, a plurality of primary windings are provided on the primary side, the switching elements are provided on the primary windings, and the secondary windings are provided on the secondary side for each primary winding. If the secondary side control circuit for controlling the corresponding primary side switching element is provided for each output, the corresponding primary side switching element is provided for each output. Since the secondary side control circuit to be controlled is provided, the output voltage is feedback controlled for each output, and the occurrence of cross regulation when the load of each output fluctuates independently of each other can be suppressed.
Further, in the present invention, if each of the switching elements is controlled by the common primary side control circuit, each of the plurality of switching elements is controlled by the common primary side control circuit. In addition, the ratio of the primary side control circuit to the circuit scale can be reduced.

It is a circuit diagram which shows the structure of the switching power supply device which concerns on 1st Embodiment of this invention. It is a circuit diagram of a secondary side control IC. It is a circuit diagram of a switching circuit. It is a circuit diagram which shows the structure of the switching power supply device which concerns on the modification of 1st Embodiment. It is a circuit diagram concerning the modification of the power system slave of a 1st embodiment. It is a circuit diagram of the switching circuit in the modification. It is a circuit diagram which shows the structure of the switching power supply device which concerns on 2nd Embodiment of this invention. It is a figure which shows the structure of a starting detection circuit and a switching circuit. It is a timing chart which shows the switching operation of a PWM signal. It is a circuit diagram concerning the modification of the switching circuit of a 2nd embodiment. It is a timing chart which shows the switching operation | movement of the PWM signal in the modification. It is a circuit diagram concerning other modifications of a change circuit of a 2nd embodiment. It is a timing chart which shows the switching operation | movement of the PWM signal in the modification.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<First Embodiment>
FIG. 1 is a circuit diagram of an insulating switching power supply device 1 according to the present embodiment.
The switching power supply apparatus 1 is connected to an inverter circuit that drives a three-phase drive motor for driving a vehicle as a load, and is configured as a separately excited type and flyback type DC-DC converter as shown in FIG. Insulated transformer 10 is provided. The primary side of the insulated transformer 10 is connected to an ignition power source IG of a vehicle that is a DC power source. When the ignition switch of the vehicle is turned on, an input voltage Vin is input from the ignition power source IG to the primary side. . The switching power supply device 1 converts the input voltage Vin input to the primary side, and outputs a plurality of output voltages Vout having a predetermined voltage level to the secondary side. Specifically, the switching power supply device 1 outputs the output voltage Vout to each of the six gate drive circuits UH, UL, VH, VL, WH, WL provided for each gate terminal of the six IGBTs included in the inverter circuit. The so-called multi-output type is configured.

The configuration of the switching power supply device 1 will be described in detail. The primary side of the insulating transformer 10 includes a plurality of (seven in this embodiment) primary windings 12 connected in parallel to each other and the primary winding. And a switching element 13 that is connected in series and controls the current flowing through the primary winding. Further, on the primary side, a primary-side control IC 14 that controls the switching by outputting the PWM signal Sp1 to each switching element 13 is provided. Although this primary side control IC 14 can be provided for each switching element 13, in the present embodiment, the primary side control 14 is provided in common to each switching element 13, and thereby the primary side occupying the circuit scale. The ratio of the control IC 14 is reduced.
The primary side control IC 14 is a circuit that operates with the input voltage Vin, and starts outputting the PWM signal Sp1 when the input voltage Vin starts to be input (power-on).

On the other hand, a secondary winding 15 provided corresponding to each primary winding 12 and an output circuit 18 provided for each secondary winding 15 are provided on the secondary side of the insulating transformer 10. The output circuit 18 is provided with a voltage detection circuit 22, and the remaining output circuit 18 is provided with a secondary control IC 25.
The output circuit 18 includes a diode 16 and a smoothing capacitor 17. The output circuit 18 is induced in each of the secondary windings 15 according to a current change generated in each primary winding 12 as the switching element 13 is switched. The power is rectified and smoothed by the diode 16 and the smoothing capacitor 17 to output the output voltage Vout.
In this embodiment, the output voltage ratings of the output circuit 18 connected to the gate drive circuits UH, UL, VH, VL, WH, WL are all the same. 1 is connected to the output HVcc in FIG. 1 as a load, and the remaining six output circuits 18 are connected to gate drive circuits UH, UL, VH, VL, WH, and WL are connected as loads.

The high voltage side microcomputer 21 detects the temperature and voltage of the gate drive circuits UH, UL, VH, VL, WH, WL, etc. under the control of an ECU (engine control unit) which is a host vehicle computer, and outputs it to the ECU. It is an electronic circuit that constantly consumes substantially constant power. That is, in the output circuit 18 to which the high-voltage side microcomputer 21 is connected, the output voltage Vout is stable because there is almost no load fluctuation caused by the high-voltage side microcomputer 21, and the voltage detection circuit 22 is provided in the output circuit 18 for output. By detecting the voltage Vout, the secondary output voltage Vout is stably detected.
The voltage detection circuit 22 receives a divided voltage Vdet obtained by dividing the output voltage Vout by the resistors R1 and R2, and outputs a feedback signal Sa indicating a comparison result between the divided voltage Vdet and the reference constant voltage Vref (FIG. 2). To do. The reference constant voltage Vref is a voltage value defined according to the rated voltage of the output voltage Vout. That is, when the divided voltage Vdet exceeds the reference constant voltage Vref, the output voltage Vout exceeds the rated voltage. Conversely, when the divided voltage Vdet is lower than the reference voltage, It is shown that Vout is below the rated voltage.
The voltage detection circuit 22 sets the feedback signal Sa to the high level when the output voltage Vout exceeds the rated voltage, and sets the feedback signal Sa to the low level when the output voltage Vout is lower than the rated voltage. . Note that, when the output voltage Vout is equal to the rated voltage, it is arbitrary whether the feedback signal Sa is set to the high level or the low level.

The feedback signal Sa of the voltage detection circuit 22 is fed back to the primary side control IC 14 via the insulating element 23 such as a photocoupler. Based on the feedback signal Sa of the voltage detection circuit 22, the primary side control IC 14 generates a PWM signal Sp 1 whose duty ratio is adjusted so that the output voltage Vout is close to the rated voltage, and is supplied to the switching element 13 via the buffer circuit 24. input.
Specifically, when the feedback signal Sa is at a high level (excess state of the output voltage Vout), the primary side control IC 14 sets the duty ratio of the PWM signal Sp1 to the minimum duty ratio, and conversely, the feedback signal When Sa is at the low level (insufficient state of the output voltage Vout), the duty ratio of the PWM signal Sp1 is set to the maximum duty ratio. Thereby, the output voltage Vout is feedback-controlled. As described above, each primary-side switching element 13 is controlled by the primary-side control IC 14, and the output voltage Vout is output to each corresponding output circuit 18.

On the other hand, each of the output circuits 18 to which the gate drive circuits UH, UL, VH, VL, WH, WL are connected as loads is connected to the secondary control IC 25 in place of the voltage detection circuit 22. .
The secondary side control IC 25 operates at the output voltage Vout of the corresponding output circuit 18, and outputs the PWM signal Sp <b> 2 that controls switching to the primary side switching element 13 that forms a pair with the output circuit 18. The signal is output via the switching circuit 26.
The switching circuit 26 is a circuit that is provided before the switching element 13 and switches a signal input to the switching element 13 between the PWM signals Sp1 and Sp2.
Specifically, the switching circuit 26 is configured to output 1 until the output voltage Vout exceeds the operation start voltage of the secondary side control IC 25 when the power is turned on and the PWM signal Sp2 starts to be output from the secondary side control IC 25. The PWM signal Sp1 of the next-side control IC 14 is output to the switching element 13, and the PWM signal Sp2 is output to the switching element 13 after the output of the PWM signal Sp2 is started.
Thereby, in the switching power supply device 1, when the power is turned on, it operates under the control of the primary side control IC 14, and after the secondary side control IC 25 starts the operation, the secondary side control IC 25 is controlled. It will switch and operate.

  In the following description, the power supply system in which the secondary output circuit 18 includes the voltage detection circuit 22 and the output voltage Vout is feedback-controlled based on the feedback signal Sa of the voltage detection circuit 22 is referred to as the power supply system master Bm. A power supply system provided with a secondary-side control IC 25 in the secondary-side output circuit 18 and feedback-controlled by the secondary-side control IC 25 is referred to as a power-system slave Bs, and each is distinguished as necessary. .

The secondary side control IC 25 and the primary side control IC 14 have the same circuit configuration. The configuration of the secondary side control IC 25 will be described as a representative.
FIG. 2 is a circuit diagram of the secondary side control IC 25.
The secondary side control IC 25 includes a built-in voltage detection circuit 30, an oscillation circuit 31, a PWM comparator 32, and a buffer circuit 33.
The built-in voltage detection circuit 30 outputs a feedback signal Sa indicating whether or not the output voltage Vout is exceeded, similarly to the voltage detection circuit 22 provided in the power supply system master Bm. That is, the built-in voltage detection circuit 30 includes a constant voltage source 35 that outputs the reference constant voltage Vref, and a comparator 36 that compares the divided voltage Vdet of the output voltage Vout with the reference constant voltage Vref and outputs a feedback signal Sa. When the divided voltage Vdet exceeds the reference constant voltage Vref (excess state of the output voltage Vout), a high level feedback signal Sa is output, and when the divided voltage Vdet is lower than the reference constant voltage Vref (output voltage) When Vout is insufficient, a low-level feedback signal Sa is output, and this feedback signal Sa is input to the PWM comparator 32.
Since the secondary control IC 25 incorporates the built-in voltage detection circuit 30, whether or not the output voltage Vout is exceeded (excess or deficiency) can be provided on the secondary side of the power supply system slave Bs without providing the voltage detection circuit 22 separately. Detection and feedback control becomes possible.
When the secondary side control IC 25 shown in the figure is used as the primary side control IC 14, it is connected to a feedback signal Sa indicating the level of the output voltage Vout.

The oscillating circuit 31 generates a triangular wave having a fixed period that becomes a base signal of the PWM signal Sp <b> 2 and outputs the triangular wave to the PWM comparator 32.
The PWM comparator 32 generates a PWM signal Sp2 whose duty ratio is varied according to the signal level of the feedback signal Sa, and supplies the PWM signal Sp2 to the gate terminal of the switching element 13 via the buffer circuit 33.
Specifically, the triangular wave signal St generated by the oscillation circuit 31 and the feedback signal Sa from the built-in voltage detection circuit 30 are input to the PWM comparator 32, and the PWM comparator 32 receives the signal level of the feedback signal Sa. The PWM signal Sp2 is generated by adjusting the duty ratio of the triangular wave signal St between the maximum duty ratio and the minimum duty ratio according to the difference between the output voltage Vout and the reference constant voltage Vref.
The PWM signal Sp2 is input to the insulating element 23 via the buffer circuit 33, transmitted to the primary side, and input to the switching circuit 26 of the corresponding switching element 13.

FIG. 3 is a circuit diagram of the switching circuit 26.
As described above, the switching circuit 26 outputs the PWM signal Sp1 of the primary side control IC 14 until the output of the PWM signal Sp2 from the secondary side control IC 25 is started, and after the output of the PWM signal Sp2 is started, the PWM signal Sp2 Is a circuit that outputs.
Specifically, the switching circuit 26 roughly includes a waveform shaping circuit 40, a NOR circuit 41, a signal cutoff circuit 42, a NOT circuit 43, and a delay circuit 44.
The waveform shaping circuit 40 is for shaping the waveform of the PWM signal Sp2 transmitted to the primary side via the insulating element 23. The waveform shaping circuit 40 includes a pull-up resistor 45 and an open collector transistor 46, and includes a NOR circuit 41. Output a PWM signal Sp2.

The signal blocking circuit 42 blocks the input of the PWM signal Sp1 to the NOR circuit 41 when the PWM signal Sp2 is output from the waveform shaping circuit 40. That is, the signal cut-off circuit 42 is turned on in response to the high level signal input of the PWM signal Sp2, the transistor 47 that connects the input terminal of the PWM signal Sp1 of the NOR circuit 41 to the ground potential, and the high level of the PWM signal Sp2. The capacitor 48 is charged by a signal input and holds the ON voltage of the transistor 47, and a backflow preventing diode 49 is provided.
Since the High level signal is included in the PWM signal Sp2 in a short cycle, the capacitor 48 is kept charged while the PWM signal Sp2 is being output, and the transistor 47 is continuously turned on. The input of the PWM signal Sp1 to the circuit 41 is continuously cut off.

Under such a configuration, while the PWM signal Sp1 is not blocked by the signal blocking circuit 42, that is, while the PWM signal Sp2 is not output, the signal level of the PWM signal Sp2 input to the NOR circuit 41 is Low level. Therefore, the NOR circuit 41 outputs an inverted signal of the PWM signal Sp1.
On the other hand, when the signal blocking circuit 42 blocks the PWM signal Sp1, that is, when the PWM signal Sp1 is output, the signal level of the PWM signal Sp1 input to the NOR circuit 41 becomes the low level. The NOR circuit 41 outputs an inverted signal of the PWM signal Sp2.

The NOT circuit 43 is a circuit that inverts and outputs the output of the NOR circuit 41. Thus, the PWM signal Sp1 is output from the switching circuit 26 while the PWM signal Sp2 is not input, and the PWM signal Sp2 is output. While the signal is input, the PWM signal Sp2 is output.
In the power supply system slave Bs, when the PWM signal Sp2 is output from the switching circuit 26, the switching element 13 is switched based on the PWM signal Sp2, whereby the feedback control of the output voltage Vout is performed on the primary side control. The IC 14 is switched to the secondary control IC 25.

However, if the signal output from the PWM signal Sp1 to the PWM signal Sp2 is suddenly switched by the switching circuit 26, the High level (ON period) of the PWM signal Sp1 and the High level (ON period) of the PWM signal Sp2 are changed at the time of switching. As a result, a pulse signal having a large duty ratio may be input to the switching element 13, which causes an instantaneous overvoltage.
Therefore, in the present embodiment, the delay circuit 44 is provided in the switching circuit 26. In other words, the delay circuit 44 provides a time difference between the output stop of the PWM signal Sp1 and the output start of the PWM signal Sp2, and creates an off period in which no current flows through the primary winding 12, so that the PWM signal Sp1 is output. This circuit prevents the on period and the on period of the PWM signal Sp2 from continuing.
Specifically, the delay circuit 44 starts inputting the PWM signal Sp <b> 2 to the NOR circuit 41 after a time has elapsed since the input of the PWM signal Sp <b> 1 to the NOR circuit 41 is blocked by the signal blocking circuit 42. That is, the delay circuit 44 includes a transistor 50 that connects the input terminal of the PWM signal Sp2 of the NOR circuit 41 to the ground, a capacitor 51 that keeps the ON voltage of the transistor 50 and continuously turns on the transistor 50, and this capacitor 51 is discharged with the input of the PWM signal Sp2 to turn off the transistor 50, and the transistor 52 for inputting the PWM signal Sp2 to the NOR circuit 41 is provided.

As a result, when the PWM signal Sp2 is input to the switching circuit 26, the input of the PWM signal Sp1 to the NOR circuit 41 is blocked by the signal blocking circuit 42, and the capacitor 51 of the delay circuit 44 starts to discharge. Then, the input of the PWM signal Sp2 to the NOR circuit 41 is started at the timing when the transistor 50 is turned off by the discharge.
As a result, the signal input to the switching element 13 is stopped until the delay due to the discharge of the capacitor 51 elapses from the timing when the output of the PWM signal Sp1 is stopped, and the off period during which no current flows through the primary winding 12, Thereafter, the output of the PWM signal Sp2 is started. Therefore, a pulse signal having a large duty ratio is not input to the switching element 13, and an instantaneous overvoltage does not occur at the time of switching.

As described above, according to the present embodiment, the control of the switching element 13 is performed when the operation of the secondary control IC 25 starts with the increase of the output voltage Vout by the control of the primary control IC 14 when the power is turned on. Is switched from the primary side control IC 14 to the secondary side control IC 25.
With this configuration, the primary-side control IC 14 operates at the power-on timing, so that the output voltage Vout can be reliably output to the secondary side, and the secondary-side control IC 25 can be activated by this output voltage Vout. After the secondary side control IC 25 is activated, the control signal for the switching element 13 is generated on the secondary side, so that feedback control of the output voltage without feedback delay is realized.

  According to the present embodiment, when the control of the switching element 13 is switched from the primary side control IC 14 to the secondary side control IC 25, when the output of the PWM signal Sp1 from the primary side control IC 14 to the switching element 13 is stopped. Since the PWM signal Sp2 of the secondary side control IC 25 is output to the switching element 13 after a certain period of time, a period during which no current flows through the primary winding 12 is always provided at the time of switching. This reliably prevents a pulse signal having a large duty ratio from being input to the switching element 13, and an instantaneous overvoltage does not occur at the time of switching.

  Further, according to the present embodiment, since the secondary side control IC 25 for controlling the corresponding primary side switching element 13 is provided for each of the plurality of secondary side output circuits 18, the output voltage Vout is Feedback control is performed, and cross regulation when the load of each output circuit 18 fluctuates independently of each other can be suppressed.

  In addition, according to the present embodiment, since each of the plurality of switching elements 13 is controlled by the common primary side control IC 14, the device cost can be reduced and the ratio of the primary side control IC 14 to the circuit scale can be reduced. .

In the first embodiment, the following modifications are possible.
<Modification 1-1>
In the above-described embodiment, as shown in FIG. 1, the power supply system master Bm is configured to provide the voltage detection circuit 22 on the secondary side and perform feedback control of the output voltage Vout. However, the present invention is not limited to this. That is, as shown in FIG. 4, a tertiary winding (feedback winding) 122A for detecting an output voltage is provided on the primary side of the switching power supply apparatus 100, and the voltage induced in the tertiary winding 122A is supplied to the primary side. A configuration may be adopted in which the primary side control IC 14 adjusts the duty ratio of the PWM signal Sp1 based on the voltage input to the control IC 14.

<Modification 1-2>
In the above-described embodiment, in the power supply system slave Bs, the control by the primary side control IC 14 and the secondary side control IC 25 are configured so as to exclusively supply any one of the PWM signals Sp1 and Sp2 to the same switching element 13. Although it is configured to switch between control, the present invention is not limited to this.
That is, as shown in FIG. 5, a switching element 213A whose switching is controlled by a PWM signal Sp1 and a switching element 213B whose switching is controlled by a PWM signal Sp2 are connected in parallel to the primary winding 12, and PWM By providing a switching circuit 226 that exclusively enables each of the switching elements 213A and 213B depending on whether or not the signal Sp2 is output, the switching element 213A, which controls the current flowing through the primary winding 12, is provided. It may be configured to switch between control by the primary side control IC 14 and control by the secondary side control IC 25 by switching between 213B.

FIG. 6 is a circuit diagram of the switching circuit 226 in this modification.
The switching circuit 226 includes a buffer circuit 261, a signal cutoff circuit 242, and a delay circuit 244. The buffer circuit 261 functions as a waveform shaper for the PWM signal Sp <b> 2 input via the insulating element 23. The signal cut-off circuit 242 cuts off the input of the PWM signal Sp1 to the switching element 213A when the PWM signal Sp2 (its high level) is output. That is, the signal cutoff circuit 242 has substantially the same configuration as the signal cutoff circuit 42 of the first embodiment, and is turned on in response to the high level signal input of the PWM signal Sp2 and the input of the PWM signal Sp1 of the switching element 213A. The transistor 47 is connected to the ground potential, a capacitor 48 that is charged by a high level signal input of the PWM signal Sp2 and holds the on-voltage of the transistor 47, and a backflow prevention diode 49. .

  The delay circuit 244 inputs the PWM signal Sp2 to the switching element 213B with a time from when the PWM signal Sp1 is cut off, so that both the switching elements 213A and 213B are switched when switching from the PWM signal Sp1 to the PWM signal Sp2. Prevents momentary overvoltages from occurring due to overlapping of ON periods. That is, the delay circuit 244 includes a transistor 250 that connects the input terminal of the PWM signal Sp2 of the switching element 213B to the ground, a capacitor 251 that maintains the ON voltage of the transistor 250 and continuously turns on the transistor 250, and this capacitor And a diode 252 for preventing a backflow from 251. The high potential side of the capacitor 251 is connected to the input terminal of the switching element 213A. When the transistor 47 is turned off with the input of the PWM signal Sp2, the capacitor 251 is connected to the ground and starts discharging.

Therefore, when the PWM signal Sp2 is input to the switching circuit 226, the signal blocking circuit 242 blocks the input of the PWM signal Sp1 to the switching element 213A, and the switching of the switching element 213A stops. At the same time, in the delay circuit 244, the capacitor 251 starts discharging, the input of the PWM signal Sp2 to the switching element 213B is started at the timing when the transistor 250 is turned off by the discharging, and the switching element 213B starts switching.
As a result, the switching element 213B operating on the PWM signal Sp2 starts its operation when the delay due to the discharge of the capacitor 251 has elapsed from the timing when the switching element 213A operating on the PWM signal Sp1 is stopped. The periods during which both 213B are turned on do not overlap, and an instantaneous overvoltage does not occur at the time of switching.

  Thus, according to this modification, the switching element that controls the current of the primary winding 12 is switched between the switching elements 213A and 213B, and the control of the primary control IC 14 is changed to the control of the secondary control IC 25. Since the control is switched, the operation reliability is improved as compared with the configuration in which the signal input to the single switching element is switched between the PWM signals Sp1 and Sp2.

Second Embodiment
In the first embodiment described above, the multi-output type switching power supply device 1 has been exemplified. However, in the present embodiment, a mode of one output will be described.
FIG. 7 is a circuit diagram showing a configuration of the switching power supply apparatus 300 according to the present embodiment.
As shown in this figure, in the switching power supply device 300, a tertiary winding (feedback winding) 322A for detecting an output voltage is provided on the primary side, and the voltage Va of the tertiary winding 322A is supplied to the primary side control IC 14. And the primary side control IC 14 adjusts the duty ratio of the PWM signal Sp1 based on the voltage Va to perform feedback control of the output voltage Vout. Further, the start detection circuit 370 and the start detection The configuration is different from that of the first embodiment in that it includes a switching circuit 326 that operates based on the output of the circuit 370.

FIG. 8 is a diagram illustrating the configuration of the activation detection circuit 370 and the switching circuit 326.
The activation detection circuit 370 is a circuit that switches a signal to be output in response to activation of the secondary side control IC 25 (that is, output start of the PWM signal Sp2). That is, the activation detection circuit 370 includes a detection circuit 373 having a capacitor 375, a diode 372 for preventing backflow from the capacitor 375, and buffer circuits 371 and 374, and High or Low depending on the charging voltage of the capacitor 375. The level signal is output as the switching instruction signal Sc and the stop signal Sb. The stop signal Sb is a signal that instructs the primary control IC 14 to stop the operation.

  The capacitor 375 is charged by a high level signal input of the PWM signal Sp2, and since the high level signal is included in the PWM signal Sp2 in a short cycle, the capacitor 375 is output while the PWM signal Sp2 is being output. 375 is maintained in a charged state. Therefore, the startup detection circuit 370 outputs a high level signal by charging the capacitor 375 while the PWM signal Sp2 is being output. Conversely, while the PWM signal Sp2 is not being output, When the capacitor 375 is discharged, a low level signal is output.

  The switching circuit 326 exclusively outputs either the PWM signal Sp1 or the PWM signal Sp2 in accordance with the signal level of the switching instruction signal Sc of the activation detection circuit 370. That is, while the signal level of the switching instruction signal Sc is Low level, the PWM signal Sp1 is output, and during the High level, the AND circuit 380 that outputs Low level, and while the signal level of the switching instruction signal Sc is High level, An AND circuit 381 that outputs the PWM signal Sp1 and outputs the Low level during the Low level, an OR circuit 382 that outputs a logical sum of the AND circuits 380 and 381, and a buffer circuit 383 are provided.

Under this configuration, as shown in FIG. 9, the stop signal Sb and the switching instruction signal Sc transition to the high level at the timing ta when the PWM signal Sp2 of the secondary side control IC 25 is input to the start detection circuit 370. Among these, the stop signal Sb is input to the primary side control IC 14, and the primary side control IC 14 stops the output of the PWM signal Sp1. Further, when the switching instruction signal Sc becomes High level, the switching circuit 326 switches the output signal from the PWM signal Sp1 to the PWM signal Sp2 at the timing ta and outputs it to the switching element 13.
Thereby, the control of the switching element 13 is switched from the primary side control IC 14 to the secondary side control IC 25. Further, after the switching, the primary side control IC 14 stops, so that power saving can be achieved.

Thus, according to this embodiment, in addition to the effects described in the first embodiment, the following effects can be obtained.
That is, according to this embodiment, since the primary side control IC 14 is stopped when the control is switched to the control based on the PWM signal Sp2 of the secondary side control IC 25, power consumption can be suppressed.

  The switching power supply device 300 according to the present embodiment can be modified as follows.

<Modification 2-1>
In the second embodiment, the switching circuit 326 switches the output signal from the PWM signal Sp1 to the PWM signal Sp2 at the timing ta when the PWM signal Sp2 of the secondary side control IC 25 is input to the activation detection circuit 370. .
In this configuration, as shown in FIG. 9, when switching is performed when the pulse Pu1 of the PWM signal Sp1 is at a high level, the pulse Pu2 of the PWM signal Sp2 is continued to the pulse Pu1, and the ON period Wt. Is output to the switching element 13, and an overvoltage is instantaneously generated.
Therefore, in the present modification, as shown in FIG. 10, the switching circuit 426 is provided with a latch unit 444 for preventing the ON period of the PWM signal Sp1 and the PWM signal Sp2 from continuing at the time of switching. In FIG. 10, the same members as those in FIG.

  The latch unit 444 is configured to be able to switch permission / stop of the output of the switching circuit 426 by switching the signal level of the signal input to the AND circuit 483 provided at the output terminal of the switching circuit 426. Specifically, the latch unit 444 includes a latch circuit 491 and an AND circuit 490 that inputs a set signal to the latch circuit 491. The AND circuit 490 outputs a set signal to the latch circuit 491 when both the PWM signal Sp1 and the PWM signal Sp2 output from the switching circuit 426 are at a high level, that is, when both inputs to the OR circuit 382 are at a high level. To do. The latch circuit 491 holds the output state to the AND circuit 483 in the low level state by the input of the set signal, and is unlatched when the PWM signal Sp2 becomes the low level.

As a result, as shown in FIG. 11, at the timing ta when the pulse Pu2 of the PWM signal Sp2 of the secondary control IC 25 is input to the activation detection circuit 370, the pulse Pu1 of the PWM signal Sp1 of the primary control IC 14 is at a high level. In this case, the latch unit 444 operates to stop the output of the switching circuit 426, and then the latch is released at the timing tb when the PWM signal Sp2 transitions to the low level.
As a result, when the pulse Pu1 of the PWM signal Sp1 is at a high level at the switching timing ta, an off period (that is, a period in which no current flows through the primary winding 12) is always provided. A long pulse signal is not output to the switching element 13, and the occurrence of an instantaneous overvoltage can be prevented.

<Modification 2-2>
In the above-described modified example 2-1, the configuration using the latch circuit 491 is illustrated to prevent the on periods of the PWM signal Sp1 and the PWM signal Sp2 from continuing, but the present invention is not limited to this.
That is, as shown in FIG. 12, the switching instruction signal Sc2 for allowing the output of the PWM signal Sp2 is delayed by the delay circuit 595 with respect to the switching instruction signal Sc1 for stopping the output of the PWM signal Sp1. It is good also as a structure which inputs into H.326.
As a result, as shown in FIG. 13, after the output of the PWM signal Sp1 is stopped by the switching instruction signal Sc1 at the switching timing ta, the switching instruction signal Sc2 at the timing tc when the delay time by the delay circuit 595 has elapsed. Since the output of the PWM signal Sp2 is started, an off period (that is, a period in which no current flows through the primary winding 12) is always provided between the PWM signal Sp1 and the PWM signal Sp2. As a result, a pulse signal having a long ON period Wt is not output to the switching element 13, and an instantaneous overvoltage can be prevented from occurring.

  The first and second embodiments described above merely show one aspect of the present invention, and can be arbitrarily modified and applied without departing from the spirit of the present invention.

For example, in each of the embodiments described above, the secondary control IC 25 is not limited to the configuration in which the built-in voltage detection circuit 30 is built, and may be configured to be provided outside the secondary control IC 25.
Further, for example, the switching circuits 326 and 426 described in the second embodiment and the modified example of the second embodiment may be used for the switching circuit 26 of the first embodiment.

1, 100, 300 Switching power supply device 18 Output circuit 10 Insulated transformer 12 Primary winding 13 Switching element 14 Primary side control IC (primary side control circuit)
15 Secondary winding 18 Output circuit 22 Voltage detection circuit 25 Secondary side control IC (secondary side control circuit)
26, 226, 326 switching circuit 30 built-in voltage detection circuit 44, 244 delay circuit 122A, 322A tertiary winding 213A switching element (first switching element)
213B switching element (second switching element)
370 Start detection circuit 444 Latch unit 595 Delay circuit Bm Power supply system master Bs Power supply system slave Sp1 PWM signal (first control signal)
Sp2 PWM signal (second control signal)
Vin input voltage Vout output voltage

Claims (6)

In the switching power supply apparatus which provides a switching element for controlling the current flowing in the primary winding of the insulation transformer and controls the switching of the switching element based on the output voltage on the secondary side.
A primary control circuit that operates with an input voltage input to the primary side and outputs a first control signal that controls switching of the switching element when the power is turned on;
A secondary side control circuit that is provided on the secondary side, operates at the output voltage, and outputs a second control signal for controlling switching of the switching element,
When the power is turned on, the current of the primary winding is controlled based on the first control signal of the primary side control circuit, and when the secondary side control circuit starts outputting the second control signal, the second control signal A switching power supply device that controls the current of the primary winding based on A first switching element operated by a first control signal of the primary side control circuit;
A second switching element that operates according to a second control signal of the secondary side control circuit,
The switching element for controlling the current of the primary winding is switched between the first switching element and the second switching element to control the current of the primary winding of the primary side control circuit. 2. The switching power supply device according to claim 1, wherein the control is switched from control based on a first control signal to control based on a second control signal of the secondary side control circuit. When switching the control of the current of the primary winding from the control based on the first control signal of the primary side control circuit to the control based on the second control signal of the secondary side control circuit, the first control signal The switching power supply according to claim 1, wherein the switching is performed with a period in which no current is passed after a period in which the current flows in the primary winding based on the above.   4. The primary side control circuit is stopped when the current control of the primary winding is switched to control based on a second control signal of the secondary side control circuit. The switching power supply device according to any one of the above. A plurality of primary windings are provided on the primary side, the switching elements are provided on the respective primary windings, and the secondary windings are provided on the secondary side for each primary winding, thereby providing a multi-output type. Configure
5. The switching power supply device according to claim 1, wherein the secondary-side control circuit that controls a corresponding primary-side switching element is provided for each output. 6. The switching power supply according to claim 5, wherein each of the switching elements is controlled by the common primary side control circuit.

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