Voltage regulator

Why don't you just purchase one? A linear or switching regulator should be able to handle those input voltage requirements. How much current will the regulator need to supply?

If you need both boost and buck capability, then you probably need a switching supply. National, MicroLinear and dozens of others make suitable single-chip solutions usually requiring an inductor and little else. Even more companies make complete power supplies.

If this is an automotive application, there are a lot of solutions ready to roll as well.

DspDad

Thank you, melone & dspdad. Actually I want to design a Zener regulator which is giving an output voltage of 6.3 when the input varies from 4 to 14 volt. The load current required is 150mA. Can you give a complete picture?

Is this possible?

The boost/buck switcher is the only circuit I can think of that will supply a regulated 6.3V for an input range of 4V to 14V.

A linear regulator will give something less than 4V with a 4V input, always assuming it hasn't dropped out and reduced its output to zero.

I suppose one of the adjustable Low Dropout linear regulators would probably work down to 4V, but you'd have to test it and you still wouldn't be getting 6.3V.

Why 6.3V anyway? Sounds like a tube filament voltage to me.

rgds
Zeit.

Siril-
For what you want, you will have to use some type of buck/boost design. Suitable switchmode regulating devices are available from a variety of companies such as Linear Tech, Maxim, and National Semiconductor.

I went to the National Semiconductor website, and to their online "Power" design tool. I entered Vmin=4 and Vmax=14 with Vout of 6.3 at 0.2A. The tool suggest a design using the National LM2585-ADJ part. I didn't persue this any further, but you can use this online design tool to design and simulate what you need (within limits). Linear Tech also has some downloadable software that is spice-based.

A zener regulator is not going to give you 6.3V when the input is below around 7volts. It is not an amplifier.
Zeners require a minimum amount of current too maintain regulation as well. This is large in comparison to your load needing 150mA. I avoid zeners generally because of the poor regulation and unnecessary wasted power as compared to say a 7805 regulator. For your application a switcher will likely be the best solution.