Post by thread:[EE]: Cheapest regulation circuit I've ever seen

I just got a board from a dead de-humidifier, which was powered straight from 220VAC. What at first looked like a custom DIP18 chip certainly seems to be a PIC judging by the pinout. No transformer for power input. No 7805. No nothing. The regulation consisted of a big 1uF unpolarised cap, some (smallish) inductors, a large resistor, diodes, and a couple Zener diodes (which I assume did the "regulation"). Is this reliable/safe? Certainly the most simplistic regulation circuit I've ever seen (+5V was tied almost straight to Neutral!). Wonder if it's cheaper than an off-the-shelf switched 5V supply though. Any thoughts on this? Is this actually in common use, and if so, is it safe or reliable? Were the designers completely crazy doing this? :) -- Hector Martin (spam_OUThectorTakeThisOuTmarcansoft.com) Public Key: http://www.marcansoft.com/hector.asc

Transformerless power supplies are not uncommon. Microchip has an app note that sheds some light on the subject: http://ww1.microchip.com/downloads/en/AppNotes/00954A.pdf And there've been countless threads here on the subject. They are allowed by UL and other safety regulations/organizations as "safe" as long as the user never comes in contact with any part of the circuit that's not isolated from the AC line. And yes, it's vastly cheaper than a switched power supply. The total cost for the power circuit is likely under $0.50 in small quantities. -Adam On 7/17/06, Hector Martin [PIClist] <hector+.....piclistKILLspam@spam@marcansoft.com> wrote: {Quote hidden}> I just got a board from a dead de-humidifier, which was powered straight > from 220VAC. What at first looked like a custom DIP18 chip certainly > seems to be a PIC judging by the pinout. No transformer for power input. > No 7805. No nothing. The regulation consisted of a big 1uF unpolarised > cap, some (smallish) inductors, a large resistor, diodes, and a couple > Zener diodes (which I assume did the "regulation"). Is this > reliable/safe? Certainly the most simplistic regulation circuit I've > ever seen (+5V was tied almost straight to Neutral!). Wonder if it's > cheaper than an off-the-shelf switched 5V supply though. > > Any thoughts on this? Is this actually in common use, and if so, is it > safe or reliable? Were the designers completely crazy doing this? :) > -- > Hector Martin (hectorKILLspammarcansoft.com) > Public Key: http://www.marcansoft.com/hector.asc > > -

Hector Martin [PIClist] wrote: > I just got a board from a dead de-humidifier, which was powered straight > from 220VAC. What at first looked like a custom DIP18 chip certainly > seems to be a PIC judging by the pinout. No transformer for power input. > No 7805. No nothing. The regulation consisted of a big 1uF unpolarised > cap, some (smallish) inductors, a large resistor, diodes, and a couple > Zener diodes (which I assume did the "regulation"). Is this > reliable/safe? Certainly the most simplistic regulation circuit I've > ever seen (+5V was tied almost straight to Neutral!). Wonder if it's > cheaper than an off-the-shelf switched 5V supply though. > > Any thoughts on this? Is this actually in common use, and if so, is it > safe or reliable? Were the designers completely crazy doing this? :) > No surprise. I have two designs that drive straight off of the AC mains. You need at least a CAP (300vDC for 115V, 450vDC for 230VAC) and at least ONE rectifier/diode, and a 5.1V zener diode. It works great to supply a few mA. In order to pass UL, you will need to insert a small fuse (50mA) to protect things from fire if the cap decides to short. You will also need to protect the circuit from lightning strikes, 'cause an overvoltage will take that cap out instantly. Generally speaking, the caps need to be plastic, not paper or electrolytics. While developing the code, using a scope, etc, make sure you use an ISOLATION TRANSFORMER to protect yourself and/or equipment from injury. --Bob

{Quote hidden}>-----Original Message----- >From: .....piclist-bouncesKILLspam.....mit.edu [EraseMEpiclist-bouncesspam_OUTTakeThisOuTmit.edu] >Sent: 17 July 2006 21:08 >To: Microcontroller discussion list - Public. >Subject: [EE]: Cheapest regulation circuit I've ever seen > > >I just got a board from a dead de-humidifier, which was >powered straight from 220VAC. What at first looked like a >custom DIP18 chip certainly seems to be a PIC judging by the >pinout. No transformer for power input. No 7805. No nothing. >The regulation consisted of a big 1uF unpolarised cap, some >(smallish) inductors, a large resistor, diodes, and a couple >Zener diodes (which I assume did the "regulation"). Is this >reliable/safe? Certainly the most simplistic regulation >circuit I've ever seen (+5V was tied almost straight to >Neutral!). Wonder if it's cheaper than an off-the-shelf >switched 5V supply though. > >Any thoughts on this? Is this actually in common use, and if >so, is it safe or reliable? Were the designers completely >crazy doing this? :) Odly enough I have been asked to fix a dead de-humidifier with what sounds like exactly the same circuit. A nearby lightning strike took out both of the zeners (a 5v1 and a 5v6 IIRC), though not got around to fixing it yet. Cheap and basicly crap, but it works "well enough" and lasts "long enough" for the manufacturer to save a few pennies on each unit. It's not "safe" in that there is no isolation from the mains, but on a double insulated appliance this shouldn't be a problem. Just don't go clipping your 'scope ground onto the circuit. They can be reliable is properly designed, but using a capacitor as the main dropping element means that the circuit is idealy designed to accept noise and transients which really punish the zeners, so there is usualy a series resistor to drop some of the voltage and limit current during transients. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. =======================================================================

Michael Rigby-Jones wrote: {Quote hidden}>> -----Original Message----- >> From: piclist-bouncesspam_OUTmit.edu [@spam@piclist-bouncesKILLspammit.edu] >> Sent: 17 July 2006 21:08 >> To: Microcontroller discussion list - Public. >> Subject: [EE]: Cheapest regulation circuit I've ever seen >> >> >> I just got a board from a dead de-humidifier, which was >> powered straight from 220VAC. What at first looked like a >> custom DIP18 chip certainly seems to be a PIC judging by the >> pinout. No transformer for power input. No 7805. No nothing. >> The regulation consisted of a big 1uF unpolarised cap, some >> (smallish) inductors, a large resistor, diodes, and a couple >> Zener diodes (which I assume did the "regulation"). Is this >> reliable/safe? Certainly the most simplistic regulation >> circuit I've ever seen (+5V was tied almost straight to >> Neutral!). Wonder if it's cheaper than an off-the-shelf >> switched 5V supply though. >> >> Any thoughts on this? Is this actually in common use, and if >> so, is it safe or reliable? Were the designers completely >> crazy doing this? :) >> > > > Odly enough I have been asked to fix a dead de-humidifier with what sounds like exactly the same circuit. A nearby lightning strike took out both of the zeners (a 5v1 and a 5v6 IIRC), though not got around to fixing it yet. > > Cheap and basicly crap, but it works "well enough" and lasts "long enough" for the manufacturer to save a few pennies on each unit. It's not "safe" in that there is no isolation from the mains, but on a double insulated appliance this shouldn't be a problem. Just don't go clipping your 'scope ground onto the circuit. They can be reliable is properly designed, but using a capacitor as the main dropping element means that the circuit is idealy designed to accept noise and transients which really punish the zeners, so there is usualy a series resistor to drop some of the voltage and limit current during transients. > > In my designs, I use a transorber (PK6X) in parallel with a 1 ohm resistor in series with the whole circuit. The fuse is just for UL, so I used the smallest possible size. The cap I used was a 1uF 400VDC non-polarized polyester cap. Mine was made in Germany. I then used 1N4005's as rectifiers. I used a 100uF @ 10V aluminum as a supply filter before applying it to the Zener for 5V regulation. I placed a small resistor before the zener, I think about 100 ohms,. None ever failed, though the client was in Tennessee, a very high-lightning area. The load was 5mA max, 2mA typical. The way UL works here is that if a fault occurs, the source must be tripped, and the load must not ignite. The PCB has to be FR4, etc. It was cheap, and dangerous to use if open, but this was completely potted and worked prefectly. --Bob {Quote hidden}> Regards > > Mike > > ======================================================================= > This e-mail is intended for the person it is addressed to only. The > information contained in it may be confidential and/or protected by > law. If you are not the intended recipient of this message, you must > not make any use of this information, or copy or show it to any > person. Please contact us immediately to tell us that you have > received this e-mail, and return the original to us. Any use, > forwarding, printing or copying of this message is strictly prohibited. > No part of this message can be considered a request for goods or > services. > ======================================================================= > >