Switching power supply and control circuit thereof

Abstract

The invention provides a switching power supply and a control circuit thereof. The switching power supply includes a power level circuit, a driving circuit and a control circuit. The control circuit includes a controller power on reset (POR) circuit, a post-controller POR signal generation circuit and a pulse width modulation (PWM) signal generation circuit. The post-controller POR signal generation circuit switches a post-controller POR signal to a ready level after a pre-controller POR signal is switched to a controller reset completion level and a driving signal starts to switch the level to operate a power switch. The PWM signal generation circuit adjusts the working ratio of a PWM signal to a preset minimum value before a pre-controller POR signal is switched to a controller reset completion level and a post-controller POR signal is switched to a ready level.

Description

technical field [0001] The present invention relates to a switching power supply and its control circuit, in particular to a switching power supply capable of confirming the operation state of the driving circuit therein. The invention also relates to a control circuit for use in a switching power supply. Background technique [0002] Figure 1A A prior art switching power supply (switching power supply 1 ) is shown. The switching power supply 1 converts the input voltage Vin to the output voltage Vout, and includes a control circuit 10 , a driving circuit 20 and a power stage circuit 30 . The control circuit 10 generates a pulse width modulation (PWM) signal PWM1 according to the feedback signal FB related to the output voltage Vo. The driving circuit 20 generates the driving signal Gate according to the PWM signal PWM1. The power stage circuit receives the driving signal Gate and operates at least one of the power switches to convert the input voltage Vin into the outpu...

AI Technical Summary

Problems solved by technology

[0008] The disadvantages of the prior art switching power supply are: firstly, when the controller POR rising threshold Vctl_R is lower than the driver POR rising threshold Vdrv_R, such as Figure 1B As shown, the time point t1 will be earlier than the time point t2, that is, the power-on operation of the control circuit 10 is earlier than the power-on operation of the driving circuit 20, which may cause the control circuit 10 to continuously increase the PWM speed before the power-on operation of the driving circuit 20 is completed. The working ratio of the signal PWM1 causes the inrush current flowing into the power stage circuit to be too high after the power-on operation of the driving circuit 20 is completed, and the circuit is damaged.

[0011] However, in this way, the voltage difference ΔV between the controller POR rising threshold Vctl_R and the driver POR rising threshold Vdrv_R must be considered. Within their respective error ranges, it is still necessary to keep the controller POR rising threshold Vctl_R set higher than the driver POR Rising threshold Vdrv_R, such as Figure 1C As shown, the voltage difference ΔV must be sufficient to ensure operation, the controller POR rising threshold Vctl_R is set higher than the driver POR rising threshold Vdrv_R, and there is a similar situation between the controller POR falling threshold Vctl_F higher than the driver POR falling threshold Vdrv_F

[0012] As a result, the default supply voltage Vcc must be high enough to provide the aforementioned correctness, which makes the default supply voltage Vcc unable to be lowered, causing the circuit to have higher power and consume higher power, which limits the energy-saving circuit. design development

Moreover, the setting ranges of the controller POR rising threshold Vctl_R, the driver POR rising threshold Vdrv_R, the controller POR falling threshold Vctl_F and the driver POR falling threshold Vdrv_F are also limited.

In addition, when the default controller supply voltage of the control circuit 10 is different from the default driver supply voltage of the drive circuit 20, the complexity of the circuit design is relatively high, which also limits the application range of the switching power supply 1

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