Replacing Optical Switch with Microswitch

[ChrisOfBristol]

I have a printer which uses an optical switch to control the paper feed. Unfortunately heat from the printer damages the switch. I have replaced it once, but it only lasted for a few pages. I am considering whether to replace it with a microswitch if I can find room and a way of attaching it.

The microswitch will have near zero resistance compared with the phototransistor's on resistance which will be appreciable. In order to avoid overloading the printer's electronics with a higher current, I could put a resistor in series with the switch - how about 1K?

Optical Switch

 

[Nigel Goodwin]

If your printer is killing optical switches, then you need to find out why - they are EXTREMELY reliable devices - and only lasting a few pages surely means there's something badly wrong.

What is dying?, the LED or the transistor? - according to that datasheet there's no other components there, so any current limiting needs to be external, was that the case with the original one?.

As for a microswitch, there's no need for a resistor, as the existing opto is just a transistor switch to ground and you could just replace it with the microswitch.

 

[ChrisOfBristol]

Nigel

I've read on the Internet that the opto-switch gets damaged by heat from the fuser, the max temperature it can take is 95C.

I'll have to find the original and test it.

I know how transistors work, but only in principle, not well enough to do calculations! I used the operating voltage and the maximum current to calculate the on-resistance of the transistor: R=20V/15mA. That wasn't valid as that figure isn't the on-current, it's the maximum allowable current. I assume you are saying that the on-resistance is virtually nothing, in which case I don't need a resistor to restrict the current.

 

[Nigel Goodwin]

Nigel

I've read on the Internet that the opto-switch gets damaged by heat from the fuser, the max temperature it can take is 95C.

I'll have to find the original and test it.

I know how transistors work, but only in principle, not well enough to do calculations! I used the operating voltage and the maximum current to calculate the on-resistance of the transistor: R=20V/15mA. That wasn't valid as that figure isn't the on-current, it's the maximum allowable current. I assume you are saying that the on-resistance is virtually nothing, in which case I don't need a resistor to restrict the current.

Correct.

 

[KeepItSimpleStupid]

I'll be wierd here:

Did the emitter or phototransistor die?

Can you replace just the photo-transistor? e.g. https://vetco.net/datasheets/OP803SL_datasheet.PDF

Can you engineer in a heat sink of some sort?

Replace, could mean dig it out. Use a thermally/electrically conductive epoxy. Use a different package? Install a heat reflector?