UC2901: UC2901 as feedback controller

Karthik Venkateshaiah

Part Number: UC2901

Hi,

I am designing a DC-DC converter without Opto-coupler feedback. To achieve Isolation i am using UC2901 IC with 1:1 transformer instead of Opto-coupler. For reference attaching the rough circuit. I am facing a problem that at PIN 4 and PIN 5 of UC2901 no pulses are coming to drive transformer. Please let me know if anything wrong i did in the circuit.

Thanks & Regards,

Karthik K V

over 2 years ago

0 Hong Huang over 2 years ago

TI__Guru 50935 points

Hi,

If you compare yours and Fig 5, it looks pin 2 should be open - so you may try this. Also compare other connections to make sure correct.

If confirmed connection ok on schematics while still not working, you may need to check your physical connections. You may need first probe VREF and CT to make sure they are ok. Also need to check all components of their connections and values used to be correct.

0 Karthik Venkateshaiah over 2 years ago in reply to Hong Huang

Prodigy 130 points

Hi,

I have made the changes as you suggested, Pin 2 i kept open and cross checked for VREF but still the result is same. In datasheet wave form at IC pins has not given could you please share if TI has wave form details of IC pins.

0 Hong Huang over 2 years ago in reply to Karthik Venkateshaiah

TI__Guru 50935 points

Hi,

It would be better to use TINA TI simulation model to check each pin waveform. The model can be downloaded from ti.com where you search uc2901. The Tina software is free to download from ti.com.

0 Hong Huang over 2 years ago in reply to Hong Huang

TI__Guru 50935 points

Hi,

Here are a few waveforms based on the simulation.

0 Hong Huang over 2 years ago in reply to Hong Huang

TI__Guru 50935 points

Hi,

Please also compare your circuit to the below simulation. Notice several NC pins connection.

0 Karthik Venkateshaiah over 2 years ago in reply to Hong Huang

Prodigy 130 points

Hi,

Thanks a lot.

0 Karthik Venkateshaiah over 2 years ago in reply to Karthik Venkateshaiah

Prodigy 130 points

HI,

As per the circuit you sent before i connected and it is working thanks for that but still i have a doubt that in the datasheet it is given that 1.5V at PIN 11 is sufficient to enable drive signals at PIN4 and PIN5 but it is not working at 1.5V instead working at 2.2V. Also in the circuit you sent earlier the voltage at PIN 11 is 2.21V.

Please clarify

Thanks & Regards,

Karthik K V

+1 Hong Huang over 2 years ago in reply to Karthik Venkateshaiah

TI__Guru 50935 points

Hi,

I think it depends on COMP pin sink current caused voltage drop with additional margin to make sure always ok.

0 Karthik Venkateshaiah over 2 years ago in reply to Hong Huang

Prodigy 130 points

HI,

Got it. Mr. Hong I need to trouble you further more , now my power supply is working good in CV mode. With the same feedback (with UC2901 without opto-coupler) can i achieve CC/CV output.