Simple 3-transistor voltage regulator (with current limiting) 2011-12-17

[alec_t]

alec_t submitted a new article:

Simple 3-Transistor Voltage Regulator (with current limiting) - This article describes a simple 3-transistor voltage regulator with current limiting. It is based

This article describes a simple 3-transistor voltage regulator with current limiting. It is based on a conventional design of unknown origin. The component values quoted below were chosen to provide a stabilised 12V 40mA output from a 17V DC supply; but I show how they can be calculated for a customised output.

The circuit

View attachment 55887
Construction

A suggested layout is:-
View attachment 55889

How it works...

Read more about this article...

 

[nesma]

I want to layout the circuit>>but could you specify the zener diode model number..and also the transistor 2 and 3 models?/

 

[alec_t]

Examples are:
Zener BZX79-C5V6 or 1N5339BG,
Transistors BC184L, BC327 or 2N3704

 

[dougy83]

Doesn't C degrade the transient response? Won't it have poor load and line regulation? If the zener was in line with the base instead of the emitter, its current wouldn't change quite as much due to change of input voltage

 

[alec_t]

Doesn't C degrade the transient response?

Probably, but it was intended to make for smoother adjustment of the output voltage with the pot. Remove it if not needed.

Won't it have poor load and line regulation?

It's ok, not brilliant; but for better reg you'd need a more complex circuit if using discrete components rather than an IC.

If the zener was in line with the base instead of the emitter, its current wouldn't change quite as much due to change of input voltage

Not sure about that. For circuit simplicity some zener current change is inevitable wherever the zener is placed. If the zener were in line with the base then the current through it would be very small and its knee voltage would be less well defined (leading to poor regulation, hence current change) than with the zener in the emitter line. So its swings and roundabouts.

 

[Acquired Engineer Lucky]

Whats about the speed! How fast is the switching

 

[starlyte2]

I want to make a circuit, using a 3,7v input, output variable 3v to 6v, with 1,5 to 2,5 amps. It must be small, like 2cm by 3cm max. Does this sound possible with the circuit you've designed, obviously using the necessary values?

 

[joynal]

i want output 12-13v 10A load,when i load 11A load off.
and when battery low automatic cut off. which parts need to change. can u help me......