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.

 

A schematic of the circuit in which the photo-transistor is being used would be helpful.

 

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.

 

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?

 

(Some text removed for clarity)
Likely you are overstressing the photo-transistor in some way.
Them facing each other would not do that.

Unless the laser is a lot more than the few milliwatts we imagine.

 

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

 

Here's the schematic. All is working fine except the photo transistor keeps going bad.

 

Here's the schematic. All is working fine except the photo transistor keeps going bad.

Don't see any reason why the phototransistor would be dying.

What is the part number?

 

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.

 

Hi John,
Does it fail when it's running continuously or when you switch the 5V supply On or Off?
E

 

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?

 

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

 

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?

 

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

 

Hello,

I think that @schmitt trigger the 3.3 uF and 100 k on the input of the opamp means.

Bertus

 

Hello,

I think that @schmitt trigger the 3.3 uF and 100 k on the input of the opamp means.

Bertus

That's the first 3.3uF and 100K. I can't get rid of it as its the HPF. How about I put a diode before it? So it only discharges through the GND?

 

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.

 

Put a 1kΩ resistor in series with the capacitor to limit any surge currents.
That won't appreciably affect the signal.

 

Put a 1kΩ resistor in series with the capacitor to limit any surge currents.
That won't appreciably affect the signal.

@crutschow Ok, will put a 1K in series. You didn't like my idea of a diode to prevent the cap discharging ever into the transistor?
@schmitt trigger yes, the 1/2 Hz HPF is basically just to take out DC.

 

Does the 10K resistor supplying the phototransistor actually measure 10K?