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UC3525A: UC3525A

BJE
Prodigy 221 points
Part Number: UC3525A

Hi 

We have an application where we are regulating the input current to a non isolated 300W boost converter . The input voltage range is 3 to 60V . and the output voltage is 65V , We have an old design that is using a UC3535A PWM .  We were trying to modify this recently  to support a higher input current but we are seeing instability issues  above with an input voltage from about 8V to 12V . Then we found that US3525A PWM does not support slope compensation and this could be the cause of our problem .   The US3525A PWM as I understand it does not  have  support of slope compensation .  Can you recommend a suitable replacement current mode PWM  that supports slope compensation  ?Are there any recommended replacements of the UC3525A PWM ? Can you also recommend any suitable reference designs or application notes . 

  • 0
    TI__Mastermind 25570 points
    Eamonn - How are you !!! - long time no see and welcome to the TI e2e forum !

    Anyhow - to answer your question
    The duty cycle isn't a strong function of input voltage so if the design was working ok over the 3 to 60V range the duty cycle shouldn't get much wider over the 8V/12V range at the higher current - and in any case your design probably uses voltage mode control.

    What does the instability look like ?
    Is it due to something running out of control range ?
    Is it perhaps due to an input filter oscillation? increasing the current drawn from the source will reduce the impedance of the converter and this may trigger an input filter oscillation - try shorting the input filter - not the boost inductor of course.

    If you want to look at a different controller - there is a wide variety to choose from - the UCC2842 might suit.

    Let me know how you get on.

    Regards
    Colin