UC3844 Current sense problem

[baby_1]

Hello
Here as you see the internal Uc3844 block diagram , I have a question about current sense comparator.

if we assume the" C.S Comp" section is an op-amp what does the negative buffer pin do?
(it can reverse the zener voltage or not? if yes, it convert to zero or other values?)

thanks

 

[phobos1]

its the inverting terminal of the opamap..... there is no voltage reversal...

 

[baby_1]

Thanks for your response.
could you tell me if we set the "COMP" pin to ground what is "C.S Comp" section output?(and assume the current sense pin's voltage is approximately .5 volt) (it can't get negative value now what does it do?)

 

[baby_1]

As I test when I inject zero volt to "COMP" pin it shutdown PWM section.could you tell me about it(how it works?) on the internal circuit of uc3844?
Thanks

 

[phobos1]

if u make com 0 u make non inverting terminal high so at output u get a 1. so when s=1 output qbar is 0 and s=0 output qbar =1 leaving at 50% duty cycle so no pwm ........................

 

[goldsmith]

Hello
Here as you see the internal Uc3844 block diagram , I have a question about current sense comparator.

if we assume the" C.S Comp" section is an op-amp what does the negative buffer pin do?
(it can reverse the zener voltage or not? if yes, it convert to zero or other values?)

thanks

Hi
Do not try to analyze it's internally circuit because manufacturers won't publish it's real circuit diagram . a person which was analog IC designer noticed me about this issue .
you are not going to be an IC designer am i right ? so just learn how to use it . if the voltage of pin 3 reaches 1 volt thus the IC will shut down the PWM .
That's all and simple .

Good luck
Goldsmith