Hi:

Below I have a circuit where R6 is replaced by the actual led 3VDC at 100mA. 1N750 diode is a zener diode breaker down voltage of 3.8V or so to give constant 3VDC at the resistor R8 terminal. V2 varies from 0.1VDC to 1.5VDC. When V2 is above 0.5VDC the light shuts off and when V2 is equal to or below 0.5VDC light is on. V1 is constant either at 12VDC or 6VDC.

My problem is that the output at R8 is not coming to be constant 3.0 VDC. I get about 4VDC or above at the output. I blew one of BC5468 up actually popped. Maybe I wired something wrong or something not working.

Does anyone can test to see if the circuit works in real life? Maybe I wired it wrong somewhere. If it doesn't then how to correct it in real life?

 

One problem is the BC546 is only rated at 100ma continuous current.

 

One problem is the BC546 is only rated at 100ma continuous current.

How to resolve?

 

Use a higher current rated transistor.

 

Use a higher current rated transistor.

Which one? Such as?

 

BC639 or BD139 may be

 

BC639 or BD139 may be

Ltspice model?

 

Why do R1 and R2 have such low values?
What is providing the V2 voltage in the real world?

 

Why do R1 and R2 have such low values?
What is providing the V2 voltage in the real world?

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