Phototransistor going bad regularly

Thread Starter

JohnSnow16041992

Joined Jun 2, 2023
62
I have an IR sensor which is basically an IR emitter and a IR photo transistor. I have got a problem with it. I am powering it up via 5V. I have done slight modification, I have taken the emitter and photo-transistor apart and set them in a way that they are continuously facing each other.

Now my problem is that every few days/weeks the photo transistor goes bad and I have to replace it with a new one. I want to understand why this is happening. Is it because I am making them face each othr? Thanks.
 

crutschow

Joined Mar 14, 2008
34,048
Likely you are overstressing the photo-transistor in some way.
Them facing each other would not do that.

Post a complete schematic of your circuit.
 

dl324

Joined Mar 30, 2015
16,691
Now my problem is that every few days/weeks the photo transistor goes bad and I have to replace it with a new one. I want to understand why this is happening. Is it because I am making them face each othr?
What did you do besides make them face each other? Did you modify the circuit?
 

Reloadron

Joined Jan 15, 2015
7,452
Less a schematic good luck. Does the transistor run hot? Common source of transistor failure is excessive current. Less a schematic I have no clue what is going on with your modified design of a circuit.

Ron
 

Thread Starter

JohnSnow16041992

Joined Jun 2, 2023
62
i
Don't see any reason why the phototransistor would be dying.

What is the part number?
the sensor datasheet does not mention which photo transistor they use. Could the capacitor next to the photo transistor be causing any troubles? Would a diode in the signal line to the cap help? Or could the noise in the power supply be having an impact? Even though the power supply is well regulated, when the power is switched on their is a one time spike in the output from the photo transistor.
 

Thread Starter

JohnSnow16041992

Joined Jun 2, 2023
62
Hi John,
Does it fail when it's running continuously or when you switch the 5V supply On or Off?
E
I can't be sure. Earlier I was supplying the 5V via SMPS and it was going bad faster. Now I supplied it via linear regulator, and it took longer time to go but go it did. I have no way of knowing for sure whether its going bad at on off or while in use, but if I have to put my money I'd say on off has to do something with it. Can it just be a quality issue?
 

schmitt trigger

Joined Jul 12, 2010
843
EDITED:
Get rid of the 3.3 uF and 1 Meg. Couple it directly.
The capacitor may cause a large spike on the phototransistor upon power down.
Otherwise, I don’t see any electrical condition which could make it fail
 
Last edited:

Thread Starter

JohnSnow16041992

Joined Jun 2, 2023
62
which 3.3uF you want me to remove? And I haven't got any 1Meg in there!
You are saying that cap right after the phototransistor is to blame? So a diode in line would help?
 

twohats

Joined Oct 28, 2015
429
Hi,
Can you move the phototransistor further away from the IR transmitter, to see if that will increase its lifespan?
Good luck..........
 

schmitt trigger

Joined Jul 12, 2010
843
High pass filter??
Are you operating the photo transistor in linear mode?
If so, what is your required cutoff frequency? Those components are giving a -3dB of 1/2 of a Hertz.
 
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