# How to deal with fluctuating input voltage?

1. Jun 20, 2011

### naiht

I am doing a tacho-meter of a single 12V power supply, it is meant for a car engine.
However in real life the power supply from an real vehicle fluctuates between 10-14V.

In this situation it is clear that some form of power supply regulation is needed.

I am currently considering a Zener diode (zener regulation); but if so the breakdown voltage (or the zener value) has to be lower than 10V, which does not meet the 12V supply requirement.

Are there any more suitable power supply regulation that can deal with the fluctuation?
Say, make 10V to 12V and make 14V to 12V?

Hope you understand my questions!
Thanks all!

2. Jun 20, 2011

### Floid

What you want to do is run off a voltage less than what your lower limit is going to be... say 5V and then get a voltage regulator to handle getting you the 5Vs from your varying range of input voltages.

Just do a google search for voltage regulator and find one that fits your needs.

3. Jun 20, 2011

### Dmytry

You can use
http://en.wikipedia.org/wiki/Buck–boost_converter
type circuit.
There are integrated circuits for this sort of regulator. It is also highly efficient (more efficient than resistor+zener).

4. Jun 21, 2011

### naiht

Dmytry, if efficiency is not concerned, will this one http://ecelab.com/circuit-regulator-opamp.htm work?
I am not really familiar with converters and the circuit looks complicated with those RLC...

I am trying to do comparisons to find the most suitable way for my project :)

5. Jun 21, 2011

### naiht

Oh and one more thing, the regulator's circuits have +ve & -ve terminal, while I only need a single +12V voltage supply... How should I connect the regulator?

6. Jun 21, 2011

### Dmytry

The circuit you linked can only step down the voltage I'm afraid. It's a linear regulator, dropping the voltage on the transistor.
What is the current consumption?
For the regulation that can step it up as well as down, you absolutely need complicated-looking circuit with energy storing elements (capacitors, inductances). It is not necessarily complicated to build through.
One example.