UC2844: UC2844 will not Start Up!

Ahmed Alzenk

Part Number: UC2844

Hello,

I have a power supply with PWM control, and I am encountering an issue where the input voltage fluctuates between 10V and 16V. However, it needs to be consistently at least 16V. Can you provide insights into what might be causing this problem? Any suggestions or troubleshooting tips would be greatly appreciated.

Thanks

Ahmed

over 1 year ago

0 Hong Huang over 1 year ago

TI__Guru 73325 points

Hi,

Where did you get your input voltage?

0 Ahmed Alzenk over 1 year ago in reply to Hong Huang

Prodigy 20 points

The device in question is from a customer, and it's currently not functioning properly. After the bridge rectifier, there are three resistors in series, each with a value of 56 kOhms. The voltage for the UC2844 is derived from the last resistor, and it should be 48V. Interestingly, when I desolder the UC2844, the 48V is present, but upon resoldering the IC, the voltage starts oscillating again.

I would appreciate any insights or suggestions you may have to address this issue.

0 Hong Huang over 1 year ago in reply to Ahmed Alzenk

TI__Guru 73325 points

Hi,

Please provide the circuit you are talking about. It sounds like the series resistors caused the problem to have too much voltage drop. When I can see your circuit I can provide some more comments.

0 Ahmed Alzenk over 1 year ago in reply to Hong Huang

Prodigy 20 points

I don’t have any Circuit! I have to repair it without circuit .

but I don’t think that the problem is from the resistors, because if I remove the controller the 48 volt present

+1 Hong Huang over 1 year ago in reply to Ahmed Alzenk

TI__Guru 73325 points

Hi,

If you remove the controller, the previous controller needed current is 0 so no volage drop on your series resistors.

I am not able to understand the issue without the circuit. But I think the series resistors are the root cause when the IC needs current to work then the voltage drops. For example, if the current is 1mA, each resistor voltage drop is 56V.

0 Ahmed Alzenk over 1 year ago in reply to Hong Huang

Prodigy 20 points

hi,

i solved the Problem. ich had to give the Board an external 24VDC.

thank u for ur help

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UC2844: UC2844 will not Start Up!