Why transistor BC556 burns out frequently in this circuit?

Re: Why transistor BC556 burns out frequently in this circui

I say it could be an EMI issue because the whole thing works perfectly fine if I drive a resistive load on it.

Added after 1 minutes:

guptabhavesh said:

I say it could be an EMI issue because the whole thing works perfectly fine if I drive a resistive load on it.

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Okay just so there is no confusion yourdreamz and guptabhavesh are both my ids.

Re: Why transistor BC556 burns out frequently in this circui

What happens is when I drive the actuator forward, it works fine. When I drive it reverse it goes fine until the relay goes back to normal position to stop the drive voltage to the actuator. The microcontroller PIC16F887 hangs. Exactly when the relay's Common terminal separates from Normally Open (NO) terminal.

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I say it could be an EMI issue because the whole thing works perfectly fine if I drive a resistive load on it.

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to stop EMI from Actuator use RC Circuit close to Actuator.
if your PCB Design and power supply is not proper the micro will start malfunction/hang

you have not answered many questions earlier


P.Ashok Kumar

Re: Why transistor BC556 burns out frequently in this circui

to stop EMI from Actuator use RC Circuit close to Actuator.

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Thanks Ashok. Can you give a pointer to the R & C values here for a 24V, 3.6A (on full load) actuator.

if your PCB Design and power supply is not proper the micro will start malfunction/hang

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I don't doubt PCB design much because it is clean and done professionally, but I can still send some kind of jpg file of that area for review. It is double sided though.

About power supply, here is the attached circuit for that. Do you have any suggestions here? 220V AC to 24VDC is done by a SMPS (10A capacity). I checked on Oscilloscope, it is very clean.

you have not answered many questions earlier

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I am sorry about that Ashok, I'll do that now.

1)This fault only to particular PCB or all the PCB s??

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I have two PCBs assembled and ready. Problem persists in both of them.

2)from where your feeding the power supply (source of supply)

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I am using a 220VAC to 24VDC SMPS (10A capacity). I'm regulating 5VDC for uC power supply out of 24VDC using the attached circuit.

3)Sufficient filter capacitor connected on the PCB

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I think I have, you let me know.

3)what all the loads connected to PCB

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There is a provision for 6 such actuators actually at +24 side, but I have connected only one currently. On 5V side apart from the microcontroller there is a MAX485 chip, that's all.

4)How much is the load current

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The max load of each actuator is 3.6A. And not more than one actuator is operated at any given time. Though currently I have put almost no load on it. At peak sometimes it shoots up to 1.5A now.

5)Inductive loads are connected with reverse diode like relay coil

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Yes I made an arrangement for that (as shown in other attached schematic - D10 and D11), but didn't work. The uC still hangs.

Re: Why transistor BC556 burns out frequently in this circui

Try online Snuber Calculator Electronics Calculators

try this Schematic
you have to check the micro RESET and other INTERRUPT Inputs are sufficiently pulled high /low

P.Ashok Kumar