TL494: About the ouput transistor obout the TL494

Alvin Lin

Part Number: TL494

Hello, TI's Team:
Have a nice day.
When we use TL494, we have encountered a question and hope to get your help:
We found that there are two circuit about the output transistors like the below picture,And it make me comfused that the logic of the output duty cycle of these two circuits is not the opposite?
If I apply the circuit 2, would the higher the Vcomp voltage, the greater the duty cycle? If so, shouldn’t the design of the feedback circuit have to be reversed?
Thank you very much.

（PIN 13 is connected to Vref.）

over 3 years ago

0 Teng Feng over 3 years ago

TI__Genius 13660 points

Hello Alvin, I am OOO today, I will reply you tomorrow. Thanks.

0 Teng Feng over 3 years ago

TI__Genius 13660 points

Hello Alvin, It seems you are right that the polarity of these two circuit are opposite, but I didn't find the any reference schematic which applies secondary circuit. Could you show me a example? Thanks.

0 Alvin Lin over 3 years ago in reply to Teng Feng

Prodigy 110 points

Hi Teng,

I just saw the secondary circuit on the Internet.

Anyway,Is it ture that we have to apply the first circuit when I use the TL494 for a half bridge topology which have to limit the duty cycle below 50%?

And we have to concect the pin13 to Vref,right ?

+1 Teng Feng over 3 years ago in reply to Alvin Lin

TI__Genius 13660 points

Yes, you are right, the first circuitry is recommended, and connecting P13 to VREF pin for complementary mode. Thanks.

0 Alvin Lin over 3 years ago in reply to Teng Feng

Prodigy 110 points

Thank you very much.

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TL494: About the ouput transistor obout the TL494