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UC2844 output voltage drop a lot with load change

Sulyn ZHANG
Expert 8700 points
Other Parts Discussed in Thread: UC2844

Team,

My customer, key power automation in China is now using our UC2844. They use two-transistor forward with our UC2844, below is the principle of the topology:

With this topology, customer tested it and found that the output voltage will drop about 20% when the load current changed from 0 to full load suddenly, it seems the load transient is not good. Do you have some suggestion or solution for solving this problem? Thanks a lot for your support!

Best regards,

Sulyn Zhang

  • 0
    TI__Expert 5900 points
    Hi Sulyn,
    First customer need to confirm there are no fault was triggered. Below description is based on that the poor response was caused by the loop control.
    A cons for current mode control is its load transient response. When increasing the load suddenly, the current loop will response firstly. However due to current control, it will limit the duty cycle which will make make the output voltage drop worse.
    Improving voltage loop will help. Customer could try to increase the bandwidth of close loop.
    Increasing output cap will alleviate the output voltage drop also.

    Br
    Kening
  • 0 in reply to Kening Gao
    TI__Expert 8700 points
    Hi Kening,
    Many thanks for your support. As I feedback to customer, customer tried to change the loop bandwidth, but it seems no improvement. The duty cycle was limited to about 50% and the current change rate is about 0.2A/us. Do you have some idea about this or any parameters that needed to analysis this issue? I will ask customer for it asap, thanks a lot for your support!

    Best regards,
    Sulyn Zhang
  • 0 in reply to Sulyn ZHANG
    TI__Expert 5900 points
    Hi Sulyn,
    Has they increased the bandwidth? what is the bandwidth before and after the action?
    Could you share the schematic? you may send it to me via email, if you have concerns.

    Br
    Kening