TWI569561B - Boost power converter circuit and controlling method of discontinuous current mode thereof - Google Patents

Description

Boost power conversion circuit and control method thereof for discontinuous current mode

The invention relates to a boosting power conversion circuit, in particular to a control method of a discontinuous current mode of a boosting power conversion circuit.

As shown in FIG. 4, it is a boosting power supply circuit 50a, which mainly includes a power integrated circuit 51 and an inductor L, a diode D, and an output capacitor Cout external to the power integrated circuit 51. And a voltage divider R1, R2. The power integrated circuit 51 includes a switch M1, a gate drive circuit 511, a pulse width modulation circuit 512, and a voltage comparison unit 513. The switch M1 is connected to an input voltage terminal through the inductor L. Vin is connected to the output capacitor Cout through the diode D. The voltage comparison unit 513 obtains the current output voltage Vout through the voltage dividers R1 and R2, and compares with a reference voltage Vref to output a comparison voltage signal to The pulse width modulation circuit 512 adjusts the corresponding pulse width modulation signal PWM to the gate driving circuit 511 according to the comparison voltage signal, and the gate driving circuit 511 is further configured by the gate driving circuit 511. The pulse width modulation signal PWM drives the switch M1 to be turned on or off.

When the switch M1 is turned on, the input voltage Vin charges the inductor L; when the switch M1 is not turned on, the inductor L provides the diode D with a forward voltage and is turned on, so that the inductor voltage is transmitted through the The output capacitor Cout provides an output voltage higher than the input voltage Vin to the voltage output terminal Vout.

As shown in FIG. 5, it is another boost power supply circuit 50b, which is substantially the same as the front boost power supply circuit 50a, except that the diode D externally connected to the power integrated circuit is replaced with another switch M2. The gate driving circuit 511 alternately drives the two switching switches M1 and M2 to be turned on or off according to the pulse width modulation signal, and also boosts the input voltage Vin to the voltage output terminal Vout.

Since the boosting power conversion circuit 50b provides a continuous current mode (CCM) and a discontinuous current mode (DCM) control mode according to the heavy load or light load of the load 60, the power conversion efficiency is better. Please cooperate with FIG. 6 , in the continuous current mode, the on-time of the two switches M1 and M2 is approximately equal to the cycle time of one pulse width modulation signal PWM_G1 and PWM_G2, so that the inductor current IL is continuously uninterrupted; When the switch is lightly loaded, the output voltage Vout is gradually increased. At this time, the comparison voltage signal Vcomp outputted by the voltage comparison unit 513 is relatively decreased. When the voltage is lower than a predetermined threshold voltage Vth, the pulse width modulation circuit is 512 corresponds to reducing the on-time of the two switch M1, M2; at this time, the inductor current IL will exhibit a discontinuous current; therefore, when the comparison voltage signal Vcomp output by the voltage comparison unit 513 is lower than a predetermined threshold voltage Vth When it enters the discontinuous current mode.

Since the boosting power conversion circuit 50b of FIG. 5 adds a switch M2, it is obvious that a voltage surge V_pon, V_poff is generated when the inductor voltage VL waveform corresponds to the time when the switch M2 is turned on and off. The waves V_pon and V_poff are caused by the switching loss of the switching switch, and the power conversion efficiency of the boosting power conversion circuit 50b shown in FIG. 5 in the discontinuous current mode is relatively poor, so that it is necessary to further improve.

In view of the technical problem that the conversion efficiency of the boost power conversion circuit in the discontinuous current mode is poor, the main object of the present invention is to provide a boost power conversion circuit and a control method thereof for the discontinuous current mode to improve light load. Power conversion efficiency.

The main technical means used to achieve the above purpose is that the boosting power conversion circuit includes: an inductor, a first MOS transistor, a second MOS transistor, an output capacitor, a gate driving circuit, and a pulse. a wide modulation circuit, a voltage comparison unit and a voltage divider; wherein the pulse width modulation circuit is preset with a first threshold voltage and a second threshold voltage lower than the first threshold voltage, and In the continuous current mode, the first and second MOS transistors are subjected to the following control steps according to the comparison voltage signal and through the gate driving circuit: the pulse width modulation circuit presets a first threshold voltage and a lower limit a second threshold voltage of the first threshold voltage, and in a discontinuous current mode, the first and second MOS transistors are subjected to the following control steps according to the comparison voltage signal and through the gate driving circuit: determining the voltage Comparing whether a comparison voltage output by the unit is lower than the first threshold voltage; if yes, entering a first-stage discontinuous current mode, and in each cycle of the pulse-wave modulation signal of the first-stage discontinuous current mode And alternately controlling the first and second MOS transistors to be turned on; wherein an on time of the first MOS transistor and a second MOS transistor on time are less than the cycle time; and determining the comparison voltage output by the voltage comparison unit Whether it is lower than the second threshold voltage; if yes, entering the second-stage discontinuous current mode, and controlling the first MOS transistor to be turned on during each cycle of the pulse-wave modulation signal of the second-stage discontinuous current mode And not conducting, turning off the second MOS transistor; if not, returning to the first stage discontinuous current mode.

The main technical means for achieving the above purpose is that the boosting power conversion circuit mainly comprises a first MOS transistor, a second MOS transistor and a voltage comparison unit; wherein the second MOS transistor system is serially connected to Between an inductor and an output capacitor, the voltage comparison unit obtains the current output voltage and outputs a comparison voltage signal after comparing with a reference voltage; wherein the control method of the discontinuous current mode of the boost power conversion circuit includes: Setting a first threshold voltage and a second threshold voltage; wherein the second threshold voltage is lower than the first threshold voltage; Determining whether a comparison voltage output by the voltage comparison unit is lower than the first threshold voltage; if yes, entering a first-stage discontinuous current mode, and each cycle time of the pulse-wave modulation signal of the first-stage discontinuous current mode And alternately controlling the first and second MOS transistors to be turned on; wherein an on time of the first MOS transistor and a second MOS transistor on time are less than the cycle time; and determining whether the comparison voltage output by the voltage comparison unit is Lower than the second threshold voltage; if yes, entering the second-stage discontinuous current mode, and controlling the first MOS transistor to be turned on during each cycle of the second-stage discontinuous current mode pulse-modulation signal Non-conducting, the second MOS transistor is turned off; if not, the first-stage discontinuous current mode is returned.

The control method of the boosting power conversion circuit of the present invention in a discontinuous current mode mainly comprises a two-stage discontinuous current mode. When the load is changed from light load to very light load, the required load current is sufficient. The self-diode of the second MOS transistor is supplied, so that the second MOS transistor is no longer turned on, and the self-diode is turned on, and the inductor current is output to the output capacitor to maintain the load supply; By reducing switching losses and improving power conversion efficiency at very light loads.

10‧‧‧Boost power conversion circuit

11‧‧‧ gate drive circuit

12‧‧‧ Pulse width modulation circuit

13‧‧‧Voltage comparison unit

20‧‧‧ load

50a, 50b‧‧‧ boost power conversion circuit

51‧‧‧Power Integrated Circuit

511‧‧‧ gate drive circuit

512‧‧‧ pulse width modulation circuit

513‧‧‧Voltage comparison unit

60‧‧‧ load

Figure 1: Circuit diagram of the boosting power conversion circuit of the present invention.

Figure 2 is a flow chart showing the control method of the discontinuous current mode of the present invention.

Figure 3: Figure 1 shows the voltage and current waveforms of the continuous current mode, the first phase discontinuous current mode, and the second phase discontinuous current mode.

Figure 4: Circuit diagram of a boost power conversion circuit.

Figure 5: Circuit diagram of another boost power conversion circuit.

Figure 6: Figure 5 shows the voltage and current waveforms in continuous current mode and discontinuous current mode.

The invention mainly aims at improving the control method of the boosting power conversion circuit in the discontinuous current mode, so that the conversion efficiency of the invention is better than that under the existing light load.

First, please refer to FIG. 1 , which is a circuit diagram of the boosting power conversion circuit 10 of the present invention, which includes an inductor L, a first MOS transistor M1, a second MOS transistor M2, an output capacitor Cout, and a gate. The pole drive circuit 11, a pulse width modulation circuit 12, a voltage comparison unit 13, and a voltage divider R1, R2. In a preferred embodiment, the first and second MOS transistors M1, M2, the gate driving circuit 11, the pulse width modulation circuit 12 and a voltage comparison unit 13 can be integrated in the same power integrated circuit. Medium, but not limited to this.

The first MOS transistor M1 is connected to an input voltage terminal Vin through the inductor L to be coupled to an input power source, and is connected to the output capacitor Cout through the second MOS transistor M2. The output capacitor Cout is connected. To a voltage output terminal Vout, the voltage output terminal Vout is connected to a load 20. In a preferred embodiment, the first MOS transistor M1 is an N-type transistor (such as an NMOS), and the second MOS transistor M2 is a P-type transistor (such as a PMOS). As shown, the drain D1 of the first MOS transistor M1 is connected to the inductor L, the source S1 is connected to a ground terminal, and the gate G1 is connected to the gate driving circuit 11. The drain D2 of the second MOS transistor M2 is connected to the inductor L, the source S2 is connected to the output capacitor Cout, and the gate G2 is also connected to the gate driving circuit 11.

The voltage comparison unit 13 obtains the feedback voltage VFB corresponding to the current output voltage Vout through the voltage dividers R1 and R2, and compares with a reference voltage Vref to output a comparison voltage Vcomp signal to the pulse width modulation circuit 12. The pulse width modulation circuit 12 adjusts the corresponding pulse width modulation signal PWM to the gate driving circuit 11 according to the comparison voltage signal Vcomp, and the gate driving circuit 11 drives the first according to the pulse width modulation signal PWM. The first and second MOS transistors M1, M2 are turned on or off. In a preferred embodiment, the voltage comparison unit 13 mainly includes an error amplifier with an inverted input terminal (-). Connected to the voltage dividers R1, R2, and the non-inverting terminal (+) is connected to the reference voltage Vref; therefore, as shown in FIG. 3, when the output voltage Vout is gradually increased, the output of the error amplifier is compared. The voltage signal Vcomp gradually decreases. Conversely, when the output voltage Vout gradually decreases, the comparison voltage signal Vcomp output by the error amplifier gradually rises.

When the load 20 is connected to the voltage output terminal Vout of the boosting power conversion circuit 10, and the load 20 is under heavy load, the boosting power conversion circuit 10 operates in a continuous current mode to provide a large load current IL. Next, as shown in Figure 3. When the load 20 is turned into a light load, the boost power conversion circuit 20 enters a discontinuous current mode. The control method of the discontinuous current mode of the present invention will be further described below with reference to FIG.

When the load 20 is turned into a light load, since a large current is not required, the output voltage Vout is gradually increased, and the voltage comparison unit 13 obtains the feedback voltage VFB corresponding to the output voltage Vout through the voltage dividers R1 and R2. After the reference voltage Vref is compared, the output voltage signal Vcomp is relatively reduced. Therefore, the pulse width modulation circuit 12 is preset with a first threshold voltage Vth1 and a second threshold voltage Vth2 (S10); wherein the second The threshold voltage is lower than the first threshold voltage.

When the comparison voltage signal Vcomp is lower than the first threshold voltage Vth1 (S11), the first-stage discontinuous current mode (S12) is first entered, that is, the pulse width modulation circuit 12 is alternately controlled by the gate driving circuit 11. The first and second MOS transistors M1 and M2 are turned on, but the pulse width modulation circuit 12 correspondingly reduces the on-time of the two MOS transistors M2, so that the first MOS transistor M1 is turned on and second. The on-time of the MOS transistor M2 is less than one cycle time of one pulse width modulation signal PWM_G1, PWM_G2. If the load 20 is switched back to the heavy load at this time, the continuous current mode is returned by determining that the comparison voltage signal Vcomp of the voltage comparison unit 13 is higher than the first threshold voltage Vth1 (S13).

On the other hand, if the load 20 is switched from light load to very light load, the output voltage Vout will continue to decrease, and the comparison voltage signal Vcomp of the voltage comparison unit 13 will decrease below the second threshold voltage Vth2; Determining whether the comparison voltage signal Vcomp of the voltage comparison unit 13 is lowered Up to the second threshold voltage Vth2 (S14); if so, enter the second-stage discontinuous current mode (S15), that is, the pulse width modulation unit 12 transmits the pulse width modulation signal PWM_G1 through the gate driving circuit 11. During the period of PWM_G2, only the first MOS transistor M1 is controlled to be turned on and off, and the second MOS transistor M2 is completely turned off. If the load 20 is switched back to light load at this time, the comparison voltage signal Vcomp of the voltage comparison unit 13 is judged to be higher than the second threshold voltage Vth2, but lower than the first threshold voltage Vth1, so that the first stage is returned. Discontinuous current mode (S12).

Since the current required for the load 20 to be extremely light load is relatively small, the on-current of the self-diode D of the second MOS transistor M2 is defined as the load current of the extremely light load, that is, the second transistor. The on-current current of the self-diode D of M2 is greater than or equal to the load current of the load 20 at a very light load. In a preferred embodiment, when the load current is less than 5 mA, the load 20 is determined to be extremely lightly loaded, and the second electrical boundary voltage Vth2 is set corresponding to the load current, so that the current is about 0.8 V; The voltage value can be adjusted according to actual circuit design requirements, and the invention is not limited thereto.

Referring to FIG. 3, when the comparison voltage signal Vcomp of the voltage comparison unit 13 is lower than the second threshold voltage Vth2, since the second MOS transistor M2 is completely turned off, the inductor voltage is second. The MOS transistor M2 is no longer turned on and off, and there is no switching loss. Therefore, in the second stage of the discontinuous current mode, the inductance voltage waveforms are compared with the corresponding inductor voltage waveforms shown in FIG. The wave (see the indication of Vp in Fig. 3); therefore, the conversion efficiency of the present invention is relatively improved compared to the power conversion efficiency of the discontinuous current mode as a whole in Fig. 6.

In summary, the control method of the discontinuous current mode of the present invention includes a two-stage discontinuous current mode. When the load is changed from light load to very light load, the required load current is sufficient by the second MOS. The self-diode of the transistor is supplied, so when the comparison voltage outputted by the voltage comparison unit is lower than the second threshold voltage, the load is extremely lightly loaded, and only the conduction and non-conduction control of the first MOS transistor is retained. And not controlling the second MOS transistor to be turned on, and the second MOS transistor is in direct conduction with the self-diode, and outputting the inductor current to the output capacitor to maintain the load supply; thus, In the two-stage discontinuous current mode, the inductor voltage will not cause a voltage surge due to the conduction and non-conduction switching losses of the second MOS transistor, so as to improve the power conversion efficiency at extremely light loads.

Claims (8)

A method for controlling a discontinuous current mode of a boost power conversion circuit, wherein the boost power conversion circuit includes a first MOS transistor, a second MOS transistor, and a voltage comparison unit; wherein the second MOS transistor system Connected between an inductor and an output capacitor, the voltage comparison unit obtains the current output voltage, and compares with a reference voltage to output a comparison voltage signal; wherein the control method of the discontinuous current mode includes: setting a first a threshold voltage and a second threshold voltage; wherein the second threshold voltage is lower than the first threshold voltage; determining whether a comparison voltage output by the voltage comparison unit is lower than the first threshold voltage; if yes, entering the first phase a continuous current mode, and alternately controlling the first and second MOS transistors to be turned on during each cycle of the pulse current modulation signal of the first stage discontinuous current mode; wherein the first MOS transistor is turned on and the first The second MOS transistor on-time is less than the cycle time; and determining whether the comparison voltage output by the voltage comparison unit is lower than the second threshold If yes, enter the second-stage discontinuous current mode, and control the first MOS transistor to be turned on and off in each cycle of the pulse-modulating signal of the second-stage discontinuous current mode to turn off the second MOS The transistor; if not, returns to the first stage discontinuous current mode. The method for controlling a discontinuous current mode according to claim 1, wherein the voltage output terminal of the boosting power conversion circuit is connected to a load, and the second threshold voltage is a load current corresponding to a load at a very light load. . The control method of the discontinuous current mode according to claim 2, wherein the first MOS transistor is an N-type transistor, and the second MOS transistor is a P-type transistor; wherein the P-type transistor is self-body The on current of the diode is greater than or equal to the load current when it is loaded at very light load. A boost power conversion circuit includes: an inductor, a first MOS transistor, a second MOS transistor, an output capacitor, a gate drive circuit, a pulse width modulation circuit, and a voltage a comparison unit and a voltage divider; wherein the first MOS transistor system is connected to an input voltage terminal through the inductor, and is connected to the output capacitor through the second MOS transistor, the output capacitor is connected to a voltage output terminal The voltage comparison unit obtains a feedback voltage corresponding to the current output voltage through the voltage divider, and compares with a reference voltage, and outputs a comparison voltage signal to the pulse width modulation circuit; the pulse width modulation circuit is configured according to the Comparing the pulse width modulation signal corresponding to the voltage signal adjustment to the gate driving circuit, wherein the gate driving circuit drives the first and second MOS transistors to be turned on or off according to the pulse width modulation signal; wherein: the pulse The wide modulation circuit is preset with a first threshold voltage and a second threshold voltage lower than the first threshold voltage, and in a discontinuous current mode, according to the comparison voltage signal and through the gate driving circuit The first and second MOS transistors perform the following control steps: determining whether a comparison voltage output by the voltage comparison unit is lower than the first threshold voltage; if yes, entering the first stage of discontinuous power a mode, and alternately controlling the first and second MOS transistors to be turned on during each cycle of the pulse current modulation signal of the first-stage discontinuous current mode; wherein the first MOS transistor is turned on and the second MOS The transistor on-time is less than the cycle time; and determining whether the comparison voltage output by the voltage comparison unit is lower than the second threshold voltage; if yes, entering the second-stage discontinuous current mode, and the second-stage discontinuous current mode During each cycle of the pulse-modulation signal, the first MOS transistor is controlled to be turned on and off, and the second MOS transistor is turned off; if not, the first-stage discontinuous current mode is returned. The boost power conversion circuit of claim 4, wherein the voltage output terminal is connected to a load, and the second threshold voltage is a load current corresponding to a load at a very light load. The boost power conversion circuit of claim 5, wherein: the first MOS transistor is an N-type transistor, the drain is connected to the inductor, and the source is connected to a ground, and the gate thereof And connected to the gate driving circuit; The second MOS transistor is a P-type transistor, the drain is connected to the inductor, the source is connected to the output capacitor, and the gate is also connected to the gate driving circuit; wherein the P-type transistor The on-state current of the autodiode is greater than or equal to the load current when it is loaded at very light loads. The boost power conversion circuit of claim 4, the voltage comparison unit includes an error amplifier having an inverting input coupled to the voltage divider and a non-inverting terminal coupled to the reference voltage. The boosting power conversion circuit according to any one of claims 4 to 7, wherein the first and second MOS transistors, the gate driving circuit, the pulse width modulation circuit and a voltage comparison unit are integrated A power integrated circuit.