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TL494 stop switching condition

Andy Kim35968
Prodigy 10 points
Other Parts Discussed in Thread: TL494

Hi,

One of my customer wants to know what voltage for Feedback (pin 3) pin can make TL494 stop switching. In other words, he wants to kinow how much voltage level (please refer to TL494 spec page 2) of feedback pin and next point of Error Amplifier1,2 can be recognized as "H" for PWM Comparator.

Thanks in advance. .

  • 0
    TI__Mastermind 25130 points

    Andy,

    I do not believe that a condition where the voltage needed on the FB pin to cause a sessation of switching has been defined.

    At the same time if you look at page 7 of SLVA001D you wil see that the Ct peak voltage is defined as 3 volts and in the spec for the TL494 (SLVS074E) there is a 0.7 volt level shift from the Ct voltage to the PWM comparator. From these two it would indicate that a voltage above 3.7 volts on the FB pin should work. I would expect that there are tolerances involved and that a voltage slightly above 4 volts would work better. Since the error amplifier output is powered from the internal rail it would be wise to keep that votlage as the upper DO NOT EXCEED limit of the voltage on the feedback pin.

    A better method in my opinion would be to use the error amplifiers themselves to drive the FB output high. Pulling the positive input of the error amplifier high or the negative input low or a combination of both should work better than trying to bias the output FB rail.

    John