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LM555: Suitability for Push-Pull Converter

Jejomar Ildefonso
Expert 8590 points
Part Number: LM555

Hi Team,

Our customer is designing a push-pull converter and they intend to use the LM555, but it will with no feedback and no dead time. Would this be suitable for this use case? Are there any potential risks of having open-loop and no dead-time for the push-pull converter?

Below are the push-pull converter specifications:
Vin: 24v
Vout1: +15V, 0.2A
Vout2: -15V, 0.2A

Thanks in advance!


Kind Regards,

Jejomar

  • 0
    TI__Guru* 93105 points

    Hello Jejomar,

    It is not completely clear from your description how the LM555 will be applied within the push-pull converter circuit. You mention that Vin is 24 V, and the outputs are +/-15 V. The LM555 has a maximum supply voltage 18 V so not sure if it would fit in this application.

    Can you provide a concept circuit showing how the LM555 would be used in the push-pull converter circuit? That would be helpful for formulating an answer to this inquiry.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    TI__Mastermind 48116 points

    Hi Jejomar,

    In addition to Thom's comments. We will need to know your Push-Pull converter's switching frequency. Gate to source capacitance of switching transistor and Vgs voltage, assumed transformers are driven by mosfets. 

    For a Push Pull Converter, your output voltage is fixed, but your application load may not. Thus the Duty Cycle of the Push Pull converter will have to change. If you are running open loop in the Duty Cycle, you need to resolve Cross Conduction issues in the power transistors, which switching transistors may get damaged if the issues are not taken care of. In addition, your input voltage may not be a constant either. If the output load is changing, you have to compensate the voltage or current feedback with PWM frequency due to changes in converter's efficiency, input voltage, changes in load etc.. 

    Best,

    Raymond.