I’m trying to resolve a problem with this latch and release break beam circuit

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Barbados1993

Joined Sep 7, 2021
1
Help Needed!!

I’m trying to resolve a problem with this latch and release break beam circuit – with PNP transistor amplifier It works fine for a few minutes then consistently breaks down – as though the transistor is getting overheated?

It works again after about 20 mins.. It’s driving me nuts!

I’m not very clued up on transistor selection.. and mainly using what’s been available in a liitle selection pack.. then I have pages of scrawling’s which have lead me to arrive at resistor values – I’ve tried lots of transistors and different resistors but any combination which works still seems to fade away after repeated use.

It was suggested that I add a flyback diode – which I tried (in blue) this made no difference

Any help or advice greatly appreciated.
 

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ericgibbs

Joined Jan 29, 2010
13,825
hi B,
Welcome to AAC
A PNP with a +V collector supply will fail, it should be NPN type.

E
What is the output levels of the IR.?
 

MisterBill2

Joined Jan 23, 2018
9,463
First, it certainly looks like either the transistor Emitter and collector are reversed, or the supply polarity is wrong. Certainly a 470 ohm or 47 ohm base pull-up resistor is far to low a value. in any case.
So without a correct circuit drawing, no solution.
In addition, there also needs to be a resistor to limit base current from the IR device, because excess base drive will allways cause problems.
 
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