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UC2843: Output issuee

Part Number: UC2843

Hi Team,

i got this request from a customer:

I’m trying to do is to use two independent parallel circuits supplied from the same 15V source, but with common RC network to hopefully synchronize their operation.

The specification does not mention anything about the possibility of synchronization, but I would like to understand why this scheme does not work.

In order synchronize the operation of two UC2843 I thought it should be possible to use a common RC connected to RT/CT of both chips. Unfortunately it does not work like this.

In this case one of the chips outputs the PWM and the other outputs OV. I can’t understand why this happens considering that all other inputs are identical. What determines which chip operates and which does not?

Could you please comment in that?

Best Regards,
Alex

  • Hello Alex,

    I made a sample circuit to understand your customer's problem. Does the circuit below show what your customer is attempting to do? If so, the Vref on both circuits are shorted together. Since they are both outputs it is likely breaking one of the devices causing one of them to output 0V. The best way to sync the two devices is with an external sync as shown on page 17 of the datasheet.

    Regards,

    Jonathan Wong