Current limit module and control module for power converters and associated method

Patent metadata

Field	Value
Publication number	US-9401648-B2
Application number	US-201414318632-A
Country	US
Kind code	B2
Filing date	Jun 28, 2014
Priority date	Jun 28, 2013
Publication date	Jul 26, 2016
Grant date	Jul 26, 2016

Abstract

A power converter having a current limit module and a method for controlling the power converter. The power converter converts an input voltage to an output voltage based at least on driving a main switch to switch on and off and regulates the output voltage through regulating a duty cycle of the main switch. The current limit module is configured to compensate a first current limit threshold indicative of a maximum allowable value of a peak value of a switching current of the main switch with a threshold compensation signal indicative of the duty cycle to provide a second current limit threshold. The second current limit threshold is used to limit the maximum value of the peak value, so that a maximum allowable output power of the power converter is substantially uninfluenced by the variation in the duty cycle.

First claim

I claim:

1. A current limit module for a power converter, wherein the power converter comprises a main switch and is configured to convert an input voltage to an output voltage based on driving the main switch to switch on and off in response to a pulse width modulated signal, and wherein a switching current flows through the main switch, and wherein the percentage of the on time of the main switch in a switching cycle is referred to as a duty cycle, the current limit module comprising:
a threshold compensation circuit having a first compensation input terminal, a second compensation input terminal and a compensation output terminal, wherein the first compensation input terminal is configured to receive a first current limit threshold indicative of a maximum allowable value of a peak value of the switching current, and wherein the second compensation input terminal is configured to receive a threshold compensation signal indicative of the duty cycle, and wherein the threshold compensation circuit is configured to superpose the threshold compensation signal with the first current limit threshold to provide a second current limit threshold at the compensation output terminal; and
a current limit comparison circuit having a first comparison input terminal, a second comparison input terminal and a comparison output terminal, wherein the first comparison input terminal is configured to receive a second current sense signal indicative of the switching current with ramp compensation, and wherein the second comparison input terminal is configured to receive the second current limit threshold, and wherein the current limit comparison circuit is configured to compare the second current sense signal with the second current limit threshold to generate a second comparison signal at the comparison output terminal, and wherein the second comparison signal triggers the pulse width modulated signal to turn the main switch off when the second current sense signal exceeds the second current limit threshold.

2. The current limit module of claim 1 , wherein the threshold compensation signal increases with the increase of the duty cycle and decreases with the decrease of the duty cycle, and wherein the threshold compensation circuit is configured to superpose the threshold compensation signal with the first current limit threshold by adding the threshold compensation signal to the first current limit threshold.

3. The current limit module of claim 1 , wherein the threshold compensation signal decreases with the increase of the duty cycle and increases with the decrease of the duty cycle, and wherein the threshold compensation circuit is configured to superpose the threshold compensation signal with the first current limit threshold by subtracting the threshold compensation signal from the first current limit threshold.

4. The current limit module of claim 1 further comprising:
a ramp compensation module, configured to receive a first current sense signal generated by sensing the switching current and a ramp compensation signal having a predetermined slope, and further configured to add the first current sense signal with the ramp compensation signal to provide the second current sense signal.

5. The current limit module of claim 1 further comprising:
a compensation signal generator configured to generate the threshold compensation signal, wherein the compensation signal generator comprises:
a compensation coefficient regulator configured to receive the pulse width modulated signal which carries the duty cycle information, and further configured to apply a compensation coefficient in response to the pulse width modulated signal to provide a coefficient regulation signal, wherein the coefficient regulation signal carries the information of the compensation coefficient and the duty cycle; and
a filter configured to receive the coefficient regulation signal, and further configured to filter the coefficient regulation signal to provide the average of the coefficient regulation signal as the threshold compensation signal.

6. The current limit module of claim 5 , wherein the power converter has an independent current limit threshold regulation pin; and wherein the threshold compensation circuit is configured to add the threshold compensation signal to the first current limit threshold; and wherein the compensation coefficient regulator comprises:
a controllable current source having a control terminal and an output terminal, wherein the control terminal is configured to receive the pulse width modulated signal, the output terminal is electrically coupled to the current limit threshold regulation pin and is configured to output a substantially constant current in response to the pulse width modulated signal during the main switch is on, and is further configured to cut the constant current off in response to the pulse width modulated signal during the main switch is off; and
a coefficient regulation resistor coupled between the current limit threshold regulation pin and a reference ground, wherein the coefficient regulation resistor is user programmable, and wherein the coefficient regulation signal is provided at the current limit threshold regulation pin.

7. The current limit module of claim 5 , wherein the power converter has an independent current limit threshold regulation pin; and wherein the pulse width modulated signal is triggered to turn the main switch on with a clock signal and is triggered to turn the main switch off with an off trigger signal; and wherein the threshold compensation circuit is configured to add the threshold compensation signal to the first current limit threshold; and wherein the compensation coefficient regulator comprises:
a controllable current source having a control terminal and an output terminal, wherein the control terminal is configured to receive the pulse width modulated signal, the output terminal is electrically coupled to the current limit threshold regulation pin and is configured to output a ramp current with a predetermined slope in response to the pulse width modulated signal during the main switch is on, and is further configured to cut the ramp current off in response to the pulse width modulated signal during the main switch is off;
a coefficient regulation resistor coupled between the current limit threshold regulation pin and a reference ground, wherein the coefficient regulation resistor is user programmable; and
a sample-hold circuit having a sample control terminal, a sample input terminal and a sample output terminal, wherein the sample control terminal is configured to receive the off trigger signal, and wherein the sample input terminal is electrically coupled to the current limit threshold regulation pin, and wherein the sample-hold circuit is configured to sample a voltage at the current limit threshold regulation pin at the moment when the main switch is turned off in response to the off trigger signal, and is further configured to hold the sampled voltage and provide that held sampled voltage at the sample output terminal as the coefficient regulation signal.

8. The current limit module of claim 5 , wherein the power converter has a current sense pin coupled to a reference ground through a sense resistor, the current sense pin is used in meanwhile as a current limit threshold regulation pin; and wherein the threshold compensation circuit is configured to subtract the threshold compensation signal from the first current limit threshold; and wherein the compensation coefficient regulator comprises:
a controllable current source having a control terminal and an output terminal, wherein the control terminal is configured to receive the pulse width modulated signal, the output terminal is electrically coupled to the current sense p

Assignees

• Chengdu Monolithic Power Sys

Inventors

• Li Yike

Classifications

• H02M3/33507 Primary

  with automatic control of the output voltage or current, e.g. flyback converters (H02M3/33561, H02M3/33569 take precedence) · CPC title

• H02M2001/0038

  Electricity · mapped topic

• H02M1/32

  Means for protecting converters other than automatic disconnection · CPC title

• H02M1/0038

  Circuits or arrangements for suppressing, e.g. by masking incorrect turn-on or turn-off signals, e.g. due to current spikes in current mode control · CPC title