Low side relay circuit issues

Other Hardware General Electronics
1

Hi Team, I hope you guys are doing well today. I'm facing a problem that below circuit is low-side switching

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before juming the problem, here are some details for you guys

  1. Relay details are below

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  1. input voltage is same (12 volts at 1A).

THE PROBLEM THAT I'M FACING

This circuit has been working fine for 3 days, but day 4 is not working after debugging found that the transistor is opened. Then I changed the transistor and it's working, so why is this happening and what is the correct way to consider the different things while designing these circuits?

2

But where is this relay in your diagram?

Please post a more complete schematic. Hand-drawn is ok, if it is neat.

Also, your diagram shows a 90V input, not 12V?

3

There are 4 different coils listed, which one do you have?
What is the voltage of RELAY_1?
What is the voltage of IN_90V?

4

A quick search for the data sheet for the PMBT2222 shows that it has a maximum collector - emitter voltage of 30V, so with 90V you can expect a 'problem'.

5

@PaulRB Hi, thanks for reply

I'm connecting the coil terminal one to 12v
and other to R1_GND to activate the transistor
RELAY_1 input volt is 3.3V via mcu

6

@jim-p Hi, thanks for replying below your answers
What is the voltage of RELAY_1?
answer—3.3V via MCU
What is the voltage of IN_90V?
answer input voltage is 12v
coil resistance is 225 ohm
so as per calculation, the current is 53.3 mA. Then why is it damaging the transistor?

7

@PerryBebbington Hi, thanks for reply
yes im uisng 12v as input

8

I don't see anything obviously wrong with the circuit. Perhaps someone else can see a problem I missed.

Failing that maybe there's something wrong with the way you have it wired, please post some photos.

Please in future post accurate information, posting a schematic was good but as I and others have pointed out it was incomplete and inaccurate.

9

There may be other unknown factors involved but one could be that you are not completely turning on the 2222 and it is overheating. I would change the base resistor from 1K to 330Ω

10

Hi,

@itsashutamar , can you please post a copy of your circuit, a picture of a hand drawn circuit in jpg, png?
Hand drawn and photographed is perfectly acceptable.
Please include ALL hardware, power supplies, component names and pin labels.

Can you post some images of your project?
So we can see your component layout.

What are you using as your power supply?

Thanks... Tom.... :smiley: :+1: :coffee: :australia: