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current mode vs. voltage mode PWM control

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tdy

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current mode vs voltage mode

I am wandering why for the current control method there is a RS flip-flop be connected after the comparator before sending the driving signal to the swithing gate. But for voltage controller there is not such a block. Can anybody explain?
 

voltage mode vs current mode

A flip-flop is also used in many voltage mode controllers, e. g. classical 3524. It assures that only one output pulse is generated for each clock periode.
 

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    tdy

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voltage mode pwm

can u give some abnormal operation examples for the unintended driving signal?
 

flip flop pwm

If you don't use a flip-flop or some memory element, then you will suffer noise issues when you turn on the big power switches.

For example, if VM is only using a ramp and capacitor, then when the ramp exceeds the error voltage and you try to turn on the mosfet, switching noise can cause the comparator to flip back from 1->0.

If you have a flip-flop, we only care about the first comparator edge and we toggle the switch on/off cleanly. If you don't have a flip-flop, your converter can give several ON-OFF glitches at the start and end of each switching cycle.

A flip flop is cheap. You need to use one.
 
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current mode pwm controller

Your explanation is very helpful. Thank you verymuch.
 

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