Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Switching Vs. Zener controlled supply

Switching Vs. Zener controlled supply

Switching Vs. Zener controlled supply

What are the pros an cons of a Switching mode power supply Vs. a zener controlled power supply (also known as emitter follower voltage regulator) ?

Everyone knows the first one. Here's a picture of the second one: http://www.radio-electronics.com/info/data/semicon...

RE: Switching Vs. Zener controlled supply

Switching is typically more efficient.

This is because the switching device is either on (low voltage drop, thus low power dissipation), or off (no current, thus low power dissipation).

In contrast, the linear regulator uses voltage drop over the transistor to control the output voltage. So high current and voltage drop at the same time, power dissipated as heat.

RE: Switching Vs. Zener controlled supply

Linear supplies are inherently quieter, whereas switchers can be made fairly quiet through careful design.

RE: Switching Vs. Zener controlled supply

Zener based supplies are becoming rare these days. They are neither accurate because of
transistor gain or zener tolerance. They can easily be replaced by a single part of the
78XX type that are offered in a variety of voltages and currents. They can also be adjusted
to any voltage above the base voltage by the addition of two resistors. Low drop out varieties
also allow a smaller differential between input and output voltages. If going the zener route,
consider using a LM431 as a replacement for the zener. Last couple hundred I bought only cost
about 3 cents each.

RE: Switching Vs. Zener controlled supply

Of course, switchers are more efficient. But efficiency is not everything. For low power applications where you need a measly few hundred microamps at 3.3 V or so, a zener supply is OK. Even if you need one mA with occasional short pulses of higher current. And, yes, the LM431 is great. Doesn't cost much, is stable and low noise (which you can't say about zeners) and can easily be made to deliver any voltage at or above base voltage.

Gunnar Englund
Half full - Half empty? I don't mind. It's what in it that counts.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close