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Hot!Protect PIC

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2019/08/18 22:47:55 (permalink)
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Protect PIC

I'm designing a WS2811 pixel driver PCB.Using PIC16F15XX series.
In the pcb there is a 3pin header that directly you can connect the driver to the string.Power to the PIC is coming from that same header. My question is for reliability matters what improvements can I do?

Ex: *users will give supply from unbranded cheap 5V power supplies.Will the spikes damaged the PIC?
*Do I need additional caps to the PIC power rail?
*Do I need a series resister with the dataout line? etc...

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#1

9 Replies Related Threads

    PStechPaul
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    Re: Protect PIC 2019/08/19 12:07:53 (permalink)
    +1 (1)
    A 5 volt TVS across the capacitor would help protect the device. But be advised that the cheap 5V "wall-wart" adapters are often unregulated and can output as much as 10 volts open circuit. In that case you would need to add a regulator.

     
    #2
    Gort2015
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    Re: Protect PIC 2019/08/19 13:03:31 (permalink)
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    Why not use the WS2412B, they have the driver already inside ready to take the wave formed signal.
    Not much hardware needed for these, just 1 pin.
     
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    mpgmike
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    Re: Protect PIC 2019/08/19 13:11:46 (permalink)
    +1 (1)
    I have used cheap walwarts in the past, add a 5 volt regulator (LM7805 is common).  Usually I spec a 9 volt power supply just in case someone uses a good regulated version (the LM7805 needs <6.5 volts or so input to produce 5.0 volts output).

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    Re: Protect PIC 2019/08/19 17:52:39 (permalink)
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    Hi thanks All.
    I' m driving 200 Pixels so giving 5V/10A power supplies.
    #5
    ric
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    Re: Protect PIC 2019/08/19 18:03:54 (permalink)
    +1 (1)
    Do you really need 50mA per pixel?
    Edit: I guess you do. If all three are flat out, 3x 18.5 = 55.5mA.
    post edited by ric - 2019/08/19 18:17:54

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    NKurzman
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    Re: Protect PIC 2019/08/19 18:08:12 (permalink)
    +1 (1)
    5V 10A? Crap supplies? I hope you are not planning to Warrantee that. You can add a TVS and a series resistor to the PIC. Or a TVS and a regulator. But is they are way to high it can fry. The pixel drivers will also be unhappy. A TVS can help with spikes but not continued over voltage.
    #7
    PStechPaul
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    Re: Protect PIC 2019/08/19 18:17:25 (permalink)
    +2 (2)
    Consider using a PTC thermal fuse, or a standard fuse, or a circuit breaker, in conjunction with the TVS. A crowbar circuit using an SCR across the output of the PSU is another option. Once triggered the SCR will be essentially a short circuit with less than a volt, and can easily handle 30 amps or more long enough for primary protection in the PSU to actuate.

     
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    Re: Protect PIC 2019/08/19 20:14:40 (permalink)
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    You all correct.Most probably many will give supply from unbranded metal cage supplies.I'm planning to add a low dropout regulator to power the PIC.Not sure I can find a TVS in my area with a common part number :(
    #9
    acharnley
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    Re: Protect PIC 2019/08/20 01:25:21 (permalink)
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    TVS in 5V will have a higher max breakdown point that will likely be higher than what the pic can withstand (a resistor in series will help). PTC are slow, both methods generate heat and TVS has long term reliability issues if it's constantly getting very hot.

    I'd measure what current your PIC is drawing and use a resistor to limit it to that x 1.5 margin at 5V (don't use the margin if you're happy for the PIC to drop to ~3.3V on current surge), then a 4.7v zener in line with the PIC input. Use the characteristics of your power draw to your advantage rather than ignoring them.
    post edited by acharnley - 2019/08/20 01:31:24
    #10
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