Power supply using Voltage multiplier (Diodes) - Page 1
Forum section: electronics / projects

author: GoatZero
author_rank: Regular Contributor
timestamp: October 07, 2013, 02:44:03 am
content: So i need a 24v 220mA power supply for my led strip, and i didnt want to go out today, so i decided try to apply what i saw on class this week (voltage multipliers) and i also saw the video that dave had made about the topic to understand it as best as i could, so now i decided to make oneI started with a 12 V 500mA transformer that i had lying around, made a rectifier bridge using 4 x 1N4001 i did place a 25V 1000uF Capacitor to filter and i finally got my rectified signal tested on the osciloscopeNow this is where im getting confused im placing my capacitors and diodes, and it doesnt matter how many i add up, the voltages are not getting multiplied im measuring 20.4v across all the capacitors, even when they are rated to 25v and yes i also meassured from the 1st red node to the last node (pic related)any help? im quite confused about whats going oni already tried several type of capacitors, electrolitic and film ones, rated from 25v to 50v and from 500nF to 1000uF with no luckcant voltage multipliers be used in DC?Next thing im about to try is switch the voltage multiplier before the rectifier bridge i just did the circuit and i get al pulsant signal however, im having troubles rectifing the half waveThe second picture i just added its what im trying to do instead of the 1st picture

author: mariush
author_rank: Super Contributor
timestamp: October 07, 2013, 03:26:16 am
content: A 12v transformer will give you about 15.5-16v after rectification using the 4 diodes, and taking out the forward voltage on the two diodes that are always on in the bridge rectifier. For 1n4001 diodes the forward voltage should be about 0.6-0.8v.So 12v x 1.414 = 17v, - 0.6-0.8 x 2 = 15.8-16vAt 200mA (0.2A), the ripple on the output with a 1000uF capacitor will be about Current / 2 x MainsFrequency x C ( in Farads) = 0.2 / 2 x 60Hz (assuming US) x 0.001F= 1.6vSo at 0.2A, after the capacitor, you'll get a dc voltage that goes between about 14.2v and 16v . (Now of course, if you want 24v @ 220mA, the actual current used to generate this will be much higher, so you'll have much higher ripple)If you actually tried to use a voltage doubler scheme to get 24 volts... forget it, those voltage doublers are only good for low currents... not 220mA. You're better off using a switching regulator in the boost mode configuration, like MC34063 (dave did a video about it and there are "calculators" online which give you all the component values) and for a led strip, you don't need super accurate voltage, as long as you get it around 24v you'd be fine.

author: GoatZero
author_rank: Regular Contributor
timestamp: October 07, 2013, 05:31:52 am
content: So i was looking for more info about the topic and and apparently this circuit (see picture)Actually rectifies the signal DC without the bridgethe multilayer voltage circuit will give DC because of the diodes rectifing little by littleIt sounds right however at class they didnt say it and i dont recall Dave saying that at the video he made about the topic, so i will watch it again...Edit: looks like he says it right at the start .... so i might attemp to make the circuit once again after im done with the videoIt makes sense to me however i dont have that many caps from the same value i might get the tomorrow however, Can anyone confirm this?

author: mariush
author_rank: Super Contributor
timestamp: October 07, 2013, 06:12:11 am
content: Using this type of circuit for a few mA is one thing, using it to get 220 mA is another thing. You'd need very big capacitors to sustain so much current, and maybe more powerful diodes.Not to mention the output will not be that smooth - you'd get dc voltage with a lot of ripple .. unless you add more capacitors or some kind of filtering to smooth everything out.Anyway, test, even if you fail you'll learn something. But when you're done, have a look at dave's video about switching power supplies:

author: tszaboo
author_rank: Super Contributor
timestamp: October 07, 2013, 06:24:00 am
content: Ok, making a switching PSU with 50 or 60 hertz is just not going to work, as you would need stupid big capacitors to solve this. I just don't understand why you act like "if I have a hammer everything is a nail". Use a one way rectifier to make bipolar (+/-) power supply and don't use the ground, and your problem solves itself with less component, than the original.

author: GoatZero
author_rank: Regular Contributor
timestamp: October 07, 2013, 06:43:45 am
content: if i handt tried or asked how to do it i wouldnt have known it cant be done that easily, so i guess its for the sake of learning, i guess i will end up buying a 24V transformer tomorrow to make a normal PSU with no multipliers

author: tszaboo
author_rank: Super Contributor
timestamp: October 07, 2013, 06:07:03 pm
content: Quote from: GoatZero on October 07, 2013, 06:43:45 amSorry, I was a bit harsh. As I said, you dont need to buy a new transformer, just use your circuit a bit differently. Please read:http://nandblog.com/bipolar-power-supply-neccecarily-center-tapped-transformer/

author: GoatZero
author_rank: Regular Contributor
timestamp: October 07, 2013, 08:00:35 pm
content: Quote from: NANDBlog on October 07, 2013, 06:07:03 pmi have been reading your blog, it seems that you have quite a lot of experience dealing with electronics, i might dive a bit more in your old entries, actually i was wondering (Hoping dave doesnt kill me) why dont you start your own video blog?All the entries talk about something quite usefull or informative and i bet you could make 5-8 min videos about each