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TL494: Technical issues

Zhonghui Xu
Expert 5445 points
Part Number: TL494

Hi team,

I got a question from customer.

I use TL494 to make a 12-16.8v input, 110V / 100W / 60Hz output correction wave inverter. The test found that the output voltage difference between no-load and load is about 10V.

Attached is my schematic diagram, please have a look, is there any parameter need to be adjusted?

DC TO AC..pdf

Thank you very much for your help.

Best regards,

  • 0
    TI__Mastermind 33115 points

    Hi,

    10V, 9% variation on 110V is not too bad using TL494. I expect that when tested over production, the variation will most likely be worse due to temp, tolerance, process. Specifically have you considered the oscillator and reference voltage variation? The refence is 4.75V<VREF<5.25V, contributing a 10% contribution from this one parameter alone. Your schematic looks electrically correct but a few comments for possibly improving the accuracy issue you are seeing:

    1. Use 0.1% setting resistor for RT
    2. Use NPO dielectric for CT capacitor and make sure the voltage rating on all ceramic caps is at least 2x or more compared to the applied voltage
    3. The gate resistors on your AC switching MOSFETs, Q22-23, Q24-25 are very large - is this intentional because this causes a very long turn-on delay that is not accurately managed when you consider the non-linear dynamic switching behavior of a MOSFET 

    Regards,

    Steve M

  • 0 in reply to Steven Mappus1
    TI__Expert 5445 points

    Hi Steven,

    Thank you very much for your support.

    Now the capacitance I use on CT is 50V / 5%. The resistance of RT is 1% error.

    As for MOS transistor, can you recommend some models q22-23 and q24-25 to me?

    Best regards,

  • 0 in reply to Zhonghui Xu
    TI__Mastermind 33115 points

    Hi,

    I appreciate your response but TI support for this case will be limited to the controller and it's functionality within your application. TL494 is used in many inverter applications and I expect it will perform well with he specifications you've provided so far. As you are working through the debug of your design, try and identify areas that might be contributing to regulation inaccuracy. I've tried to highlight a few and the timing of your MOSFET rectifier stage could be one. If you identify issues with timing, non-linear effects, etc, you should also be consulting with the MOSFET manufacturer to receive their advice on device selection. 

    Steve