I have 12VDC power supply at 30watts. I want stable voltage source that outputs 3.3vdc with output current of 1A.

The stable voltage source would be turned on or off depending upon motion sensor.



I thought about using below circuit but if I have hfe of 40 then I would get 25ma plus 20ma required by didoe total of 45ma. It is fine when load is on but when load is off fry the diode.




Does anyone have any other stable circuit configuration using transistors, capacitors, indictors, resistors and diodes only? Also does anyone know how I can edit the above circuit?

 

A 12VDC, 30W, supply can max output current is 30W / 12V = 2.5A, so you can't get 3A out with that circuit.
Also, Q1 would be dissipating (12V-3.3V) * 2.5A = 21.75W of power so would require a large heat-sink.

Much better is to buy an efficient switching buck-regulator from Ebay or Amazon, that can give you the 3A output and only dissipate a watt or so.

 

A 12VDC, 30W, supply can max output current is 30W / 12V = 2.5A, so you can't get 3A out with that circuit.
Also, Q1 would be dissipating (12V-3.3V) * 2.5A = 21.75W of power so would require a large heat-sink.

Much better is to buy an efficient switching buck-regulator from Ebay or Amazon, that can give you the 3A output and only dissipate a watt or so.

Sorry typo I mean output current of 1A.

 

High power zener diodes were available many years ago when people were designing simple linear voltage converters like your design.
Yours is not a regulator since it is missing an error amplifier with negative feedback.

 

I would recommend a LMR38010. It is easy to use. There is an enable input. The output is stable, if perhaps not quiet.
But whatever you do, don't cheap out on input supply decoupling, otherwise it won't work.

 

I would recommend a LMR38010. It is easy to use. There is an enable input. The output is stable, if perhaps not quiet.
But whatever you do, don't cheap out on input supply decoupling, otherwise it won't work.

No ics please

 

No ics please

That's going to make an accurate output voltage tricky.
No TL431s, no LM4040 or other bandgap references.

Dees the motion sensor have any ICs in it?

 

Does anyone have any other stable circuit configuration using transistors, capacitors, indictors, resistors and diodes only?

Why have you started a 3rd thread on essentially the same circuit?

The circuit you posted in post #43 in this thread is better than what you posted here (which will not give you a stable voltage because you have a base-emitter junction in the output).

Your requirements are still suspect. The voltage regulator will need to dissipate up to 8.7W.

LM317 could easily do this with 2 resistors and a couple capacitors and a big heatsink. TL431 could also do it, but you need a big output cap because it generates a lot of ripple (didn't know that until yesterday when I breadboarded a circuit with a MOSFET for your other thread).

 

LM317 could easily do this with 2 resistors and a couple capacitors and a big heatsink. TL431 could also do it, but you need a big output cap because it generates a lot of ripple (didn't know that until yesterday when I breadboarded a circuit with a MOSFET for your other thread).

Are you sure it was ripple? I bet it was unstable. How much capacitance did you have between cathode and adj?