[SOLVED] 3V DC buffer using transistors

[Faddei]

Hi all,

I want to convert 5V (USB) to 3V to power a microcontroller. I generate the 3V using a voltage divider and want to buffer this voltage. So i need a DC buffer.

I know it is possible to implement this using an opamp. But i was wondering what kind of topologies are there based on transistors (BJT's or FET's).

Thank you in advance.

 

[crutschow]

You want a low current linear voltage regulator. An LM317 is commonly used for that. A voltage divider from the regulator output to the ADJ pin determines the output voltage.

 

[Faddei]

You want a low current linear voltage regulator. An LM317 is commonly used for that. A voltage divider from the regulator output to the ADJ pin determines the output voltage.

Thank you crutschow for your fast reaction. I am sorry i did not mentioned that i also know it is possible to do so using a voltage regulator. But i am really wondering about a transistor based solution.

 

[godfreyl]

The simplest way is to start with a resistive voltage divider giving about 3.6V, then add an emitter follower to the output.

 

[Faddei]

Thanks godfreyl. That is what i was looking for.

 

[BradtheRad]

Here is a schematic illustrating the method in Godfrey's post #4.

I added a zener diode to show how to obtain tighter regulation if necessary.

 

[Faddei]

Here is a schematic illustrating the method in Godfrey's post #4.

I added a zener diode to show how to obtain tighter regulation if necessary.

Thank you BradtheRad!