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TIDA-00779: R38, R27, Current Limit Resistor Bypass Circuit

jaeyup jung
Intellectual 570 points
Part Number: TIDA-00779

hi 

i have a question.

There are two things I don't understand about Current Limit Circuit.
Q1) Are the device values of R38 (21k Ohm) and R27 (221k Ohm) correct?
R38(221k Ohm) and R27(21k Ohm) Isn't that what you should do???

Q2) I can't understand Switch On delay 0.2s.
In other words, I don't understand the circuit. Please help.

  • 0
    TI__Prodigy 420 points

    Hi jaeyup,

    Q1: The value of R38 is ok.

    Q2: Regarding the 0.2s delay, it is obtained by RC delay, simply you can observe the base voltage of Q5 using oscilloscope while PFC_ON no connected, the base voltage should rise to the ON thresh voltage of Q5 after power on 0.2s. Of course, this delay time should be related with input power voltage, we do not need to control a very precise time here, if your system has a MCU, you also can control the relay by MCU IO pin directly.

    Felix