Efficient voltage stabilization - Page 1
Forum section: electronics / beginners

author: Sigmoid
author_rank: Frequent Contributor
timestamp: October 23, 2013, 06:49:33 pm
content: Hey,I'm quite familiar with the voltage stabilizer designs based on Zener diodes, but I'm a bit confused by their power implications...Say, I have a voltage source (battery), which will provide me with "something around 12V". The battery charge degrades over time, and I need stable 5 Volts for sensitive stuff.So I implement a voltage regulator with a 5V Zener. Now, this involves adding a resistor to the positive terminal of the battery, in order to limit the Zener current, and create the voltage divider... but this seems like an issue.If I make the resistance too low, I'll be bleeding Watt-hours from my ass (sorry), and have a bad heat problem to boot. If I make the resistance too high, I won't have enough current for the actual load!Is there a more efficient way of regulating voltage?

author: mariush
author_rank: Super Contributor
timestamp: October 23, 2013, 06:55:39 pm
content: Yes, use a low quiescent current low drop linear regulator if your sensitive stuff only needs a few mA.Use a high efficiency switching regulator if you need more current.

author: IanB
author_rank: Super Contributor
timestamp: October 23, 2013, 07:00:07 pm
content: What mariush said, but why are you even considering a zener diode for this application? The immediate thought should be "voltage regulator" and then look up a part like the 7805 or equivalent...

author: awallin
author_rank: Frequent Contributor
timestamp: October 23, 2013, 07:00:54 pm
content: don't mix these two:a) voltage regulator: reasonably stable voltage, meant for supplying current to a deviceb) voltage reference: very stable voltage, but almost no current sourcing capacitya Zener might sometimes be OKish for use b) but very seldom for a)

author: edavid
author_rank: Super Contributor
timestamp: October 23, 2013, 08:35:37 pm
content: Quote from: mariush on October 23, 2013, 06:55:39 pmAren't those kind of expensive? A zener is a simple and cheap solution if your load is in the 1-20mA range. That's especially true if you need to create a split supply from a single supply... just stack 2 zeners.

author: c4757p
author_rank: Super Contributor
timestamp: October 23, 2013, 08:41:45 pm
content: On one hand, I'm squarely of the belief that Zeners are hugely underrated. They're quite good little regulators when you have a small-ish, constant-ish load, and they're cheap as, well¸ diodes. "Small-ish, constant-ish loads" are common in analog applications.On the other hand, this is a battery application, perhaps a low quiescent current series regulator would be better.On the gripping hand, we don't know what kind of battery this is, perhaps a quiescent handful of milliamps through the diode is nothing at all.5V to me suggests digital, though. Consider a low quiescent current buck converter.

author: Sigmoid
author_rank: Frequent Contributor
timestamp: October 23, 2013, 10:10:18 pm
content: Quote from: AcHmed99 on October 23, 2013, 07:34:04 pmThanks, this design seems quite adequate, as in not bleeding power all over the place, and being reasonably cheap as well:http://electriciantraining.tpub.com/14179/css/14179_210.htmThere's a lot of these practical cookbook designs that I don't know.

author: madires
author_rank: Super Contributor
timestamp: October 23, 2013, 11:04:30 pm
content: Quote from: Sigmoid on October 23, 2013, 10:10:18 pmAdding a cap in parallel to CR1 would improve the regulation.

author: sleemanj
author_rank: Super Contributor
timestamp: October 23, 2013, 11:50:31 pm
content: Quote from: Sigmoid on October 23, 2013, 06:49:33 pmA buck converter (step down DC-DC converter).Search eBay for LM2596 you'll find very cheap modules (like this one, just the first one that came up:http://www.ebay.com/itm/1pcs-DC-DC-Buck-Converter-Step-Down-Module-LM2596-Power-Supply-Output-1-23V-30V-/251066005460), your 12v goes in one end, twiddle the pot until you get 5v out the other.Far far FAR more efficient than a linear regulator (or zener shunt), which is quite important if you're running off battery.

author: txescientist
author_rank: Regular Contributor
timestamp: October 27, 2013, 08:08:06 pm
content: Hi,Why don't you use low dropout regulator like LF50CV. It is much better than 7805 in battery operated circuits in case you don't want switching regulator.http://www.datasheetcatalog.com/datasheets_pdf/L/F/5/0/LF50CV.shtml