How to build a stiff voltage source using an emitter follower

Picture of How to build a stiff voltage source using an emitter follower
This instructable will teach you how to make a great voltage source using a few resistors, a voltage source, and a transistor. Only a minimal knowledge of electronics is required!

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Step 1: Motivation

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In simple terms, we can think of a voltage (or more specifically, potential difference) as the source of energy in a circuit. Whatever your load may be (iPhone, speakers, etc.), you will need to provide voltage for it to function.

Say you have a voltage source, but it isn’t adjustable and your load requires a smaller voltage. The simplest way to remedy this is with a set of two resistors, which will make up a voltage divider. If you know how voltage dividers work, you will know how a large part of electronic circuits work!

Step 2: How a voltage divider works - an example

Picture of How a voltage divider works - an example
The voltage divider works by outputting a fraction of input voltage. This fraction is determined by the relationship between two resistors. Kirchoff’s Laws tell us that, in a circuit consisting of some input voltage Vin and two resistors R1 and R2, the voltage dissipated across R2 will be


If we hook up our load in parallel with R2, we may give it whatever voltage (less than Vin) with good choice of R1 and R2 values.

For example, if Vin is 15 Volts and R1 and R2 are both 100 ohms (as in the attached file voltage-divider.pdf), Vout=15*(100)/(200)=7.5 V. Thus we can get an output of 7.5 Volts from a fixed 15 Volt source!

WWC2 years ago
This is some great info for a DIYer such as my self. Thanks for the ible as i didn't know about this.
You have more to follow?
jonex (author)  WWC2 years ago
This was for our electronics class, if you want more check out our group page!