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Flyback controller for 200-700 VAC input, 5 VDC 500 mA output, high-temperature automotive environment

user4359238
Prodigy 90 points
Other Parts Discussed in Thread: PMP7668, UCC28704

I need to design a power supply that can convert up to 700 VAC input with a 5V 500 mA output. This is going to be operating in an environment that will be at 85C continuously with peak operating temperatures of 125C. This device will be physically isolated inside of a motor casing so isolated or not does not really matter.  

I had previously used this design: PMP7668 http://www.ti.com/lit/an/slua721/slua721.pdf as a starting point for a supply that operated up to 525 Vrms. With some small modifications and a simple DC/DC buck supply at the output I was able to get the required 500 mA at 5V DC, but now of course the bosses say we need to push the input range up a bit. I went back to try and redesign this to work with 700 Vrms, and I have run into some problems.

For one, my rectified DC Voltage is going to be up to 1000 V. Since this design uses BJTs, this seems to limit my choice in transistors to those which can only withstand 200 mA max or are too large for my application.

I have been looking at using one of the flyback controllers in the UCC2870x series with a SiC MOSFET. I have seen a number of reference designs with the input voltage range of 85-265 VAC. I am looking for a recommendation on a reference design that could be modified to fit my required voltage range. Suggestions on which components to change would be very much appreciated as well. 

  • 0
    TI__Expert 8210 points

    Unfortunately we don't have any reference designs that run at 1kV, but the UCC2870x series is a good fit for this application.  I also recommend looking at our newer UCC28704, which has a separate datasheet.  

    If you're ok with using a flyback topology the typical application that many of these designs are shown in will work with only a few modifications.  The voltage rating of the components on the input side need increased high enough to withstand the max input voltage (with margin), the startup resistor will need to be increased to keep the current constant at the higher voltages, the transformer will need to be redesigned with a new turns ratio/isolation voltage and the output rectifier diode will need to be selected so that it's able to withhold the reflected input voltage plus the output voltage.  I do not recommend using an existing EVM to hack this solution into since the HV spacing of copper traces may not be sufficient.  Also depending on the FET selected there is a chance you may need to have an external gate driver to turn the FET on since the internal driver only sources 32mA.  This can be achieved with a gate driver IC or a BJT push/pull amplifier.

  • 0 in reply to Eric Faraci
    Prodigy 90 points
    Thank you Eric. I think I will start from the design procedure shown in the UCC28704 datasheet.