This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TIDA-00779: Value of R39

Part Number: TIDA-00779

In schematic the value of R39 = 20k

in BOM R39 = 1k

You gave the answer to use 1k.

I'm pretty shure ( after recalculation ) it's wrong, 20k is the right value to get the required delay of 0.2sec.

Could you please check that?

Pepito

  • Hi,

    with R39 = 27k I can get the expected 200msec delay.
    Some assumptions for the calculation:

    1. relay coil resistance = 144 Ohm
    2. relay switch on time is 20msec @ 75% of the nominal coil voltage ( for 12V it's 9V )
    3. R25, R26, R38 ignored ( open )
    4. relay is on at the moment Vcoil is 9V or more

    If required, I can send you PDF with simulation results.

    Please let me know if I forgot anything ... and my calculation is wrong.

    Pepito

  • Hi Pepito,

    Firstly, please don't ignore the R25, R26 and R38, such resistors are used to set the delay time together with R27, C25, D9 and R31.

    To check the delay time, you can stop the PFC circuit firstly, means PFC_ON is disconnected with Bias, we hope the inrush current protection circuit works earlier than PFC.

    Actaully the R39 is not used for delay time setting, here just used to adjust the Q5's G-S voltage, the smaller value of R39, the higher voltage of G-S, and the smaller Ron for Q5 then.

    Felix

  • Hi Felix,

    thanks for quick response. I do not ignore R25, R26 and R38 in layout, only for delay calculation / simulation.

    Can provide PDF with results. With R39 = 27k I have the expected delay of 0.2sec.

    With R39=1k it's only 500usec + delay of the relay itself (Ton).

    Gate voltage of Q5 is e-function, after 5 R*C the voltage is always equal.

    Only the time is different.

    Have a good day

    Pepito

  • Hi Pepito,

    It seems we are not discussing the same issue?

    Please let me define the meaning of delay time we are talking, the delay time refers to the time from when the system is powered on to when the relay is switched on.

    The relay(K1) can be turned on by AC input power even there is no R39, the R39 and D10 circuit is only used to ensure that the relay is in the ON state when the PFC is working.

    Felix

  • Hi Felix,

    yes, we are talking about the same thing.

    Simulate the circuit on your own, then you can see the influence of R39. Watch Gate, Drain and Uc while power-on / off.

    Have a good day

    Pepito

  • Hi Pepito,

    It is ok, please send me your simulate result to felix-he@ti.com, I don't use simulation tools to analyze such issue.

    Felix