12v DC to 24v 50Hz AC square-wave <500mA: transformer & transistors? - Page 1
Forum section: electronics / projects

author: NeverEtched
author_rank: Newbie
timestamp: July 31, 2021, 02:28:01 am
content: I want to make this 12v DC to 12v AC circuit, but substitute the chassis transformer with one that doubles the 12v AC to 24v AC (i.e. x2, or a 1:2 transformer).Two questions:1: the video uses CTC1351 transistors. I can't find these on sale (in the UK). Can anyone recommend a transistor/mosfet, or indicate what I should search for?2: I can't find a suitable chassis transformer: don't know if a low voltage/current 1:2 transformer exists, or what search term to use to find one.Advice appreciated.Thanks

author: BrokenYugo
author_rank: Super Contributor
timestamp: July 31, 2021, 05:51:33 pm
content: That's a super crude way of doing things and wont give you 50Hz. If I'm understanding correctly it will give you whatever frequency it decides to oscillate at based on the inductance and stray capacitance of the transformer winding.

author: Benta
author_rank: Super Contributor
timestamp: July 31, 2021, 07:20:12 pm
content: Aka Royer Converter.Extremely primitive and very noisy (EMI). The "50 Hz" you can forget all about."mrelectron" indeed. More like mrplumber.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 31, 2021, 07:27:26 pm
content: Here's a better way to go from 12V DC to 24V AC: boost 12V to about 32V, send that through a H bridge. You can do that fairly easily with a microcontroller, can even vary the boost voltage to get something closer to a sine wave.

author: Zero999
author_rank: Super Contributor
timestamp: July 31, 2021, 09:26:04 pm
content: Yes, you need a boost converter followed by an H-bridge. You could use this crude circuit and a 12V-0-12V mains transformer, with the 230V winding rewound for 24V, but a boost converter + h-bridge is much more efficient.Something like this:https://www.google.com/shopping/product/15204545902766272836?q=12v+24v+boost+converter&client=firefox-b-d&biw=1920&bih=920&prds=eto:594997339594865079_0&sa=X&ved=0ahUKEwjkxs3dlo7yAhUHAcAKHR9ZCoQQ8wIIkgcConnected to a self-oscillating H-bridge.

author: BrokenYugo
author_rank: Super Contributor
timestamp: July 31, 2021, 10:39:24 pm
content: The simplest solution if you just need 24VAC@50 and aren't picky about waveform is to get a small 240V inverter for auto use and connect a common 240-24 transformer with a capacity of something like 40-50VA to be one the safe side.

author: NeverEtched
author_rank: Newbie
timestamp: August 02, 2021, 11:01:55 pm
content: Thanks for the posts, chaps.I've already got a small inverter (300w) for 12v to 230v and a stepdown chassis transformer to 24v, which I will hook up and test out tomorrow, so thanks to BrokenYugo for that observation.I was hoping to construct something smaller and dedicated to this specific purpose, so I am still interested in Zero999's circuit diagram. I'd not heard of an H-bridge, so bear with me... As I understand it, it can switch the output polarity from a dc input, and I assume this can be fast, e.g. 50x per sec.A couple of questions, please:The input voltage is at V1 (?), but I can't see where the output is*.Also, I'm not familiar with the downward pointing triangle symbols are, as shown connected to the emitters of the npn transistors (*is that the output?) and the V1 input. I'm supposing it can't be common, earth or chassis? What is it, please?Thanks for the tips!Much appreciated.

author: Zero999
author_rank: Super Contributor
timestamp: August 03, 2021, 07:51:06 am
content: Quote from: NeverEtched on August 02, 2021, 11:01:55 pmThe output is across RL.The downward pointing symbols mean ground i.e. the 0V rail.It is the simple astable multivibrator, but with a couple of extra transistors for the high side. D1 and D2 protect Q1 and Q2's bases from the reverse voltage, when the opposite transistor turns on and the capacitor's positive plate is connected to 0V.https://en.wikipedia.org/wiki/Multivibrator#Astable_multivibrator

author: NeverEtched
author_rank: Newbie
timestamp: August 04, 2021, 11:33:39 am
content: Excellent, Zero999, thank you.I'd not seen that symbol for common/0v/earth.If I may, what does 'RL' stand for, or '48R' for that matter (and what does the rectangle symbol represent)?I've ordered a small 100w inverter, 12v DC to 240v AC, which I will disembowel and hook up to that 240-24v transformer (having checked the LED lights work when I put the output of my 300w inverter through it). Seems somewhat inelegant, but it it does the trick, I'll be happy with that.BTW, made my first multivibrator in about 1970, for the sounds it could make... Haven't really progressed more than that, really.Thanks for the words of wisdom, chaps.

author: Zero999
author_rank: Super Contributor
timestamp: August 04, 2021, 12:34:37 pm
content: Quote from: NeverEtched on August 04, 2021, 11:33:39 amRL stands for ResistorloadThe rectangle is the resistor symbol.https://www.google.com/search?q=resistor+symbol&client=firefox-b-e&source=lnms&tbm=isch&sa=X&ved=2ahUKEwibhefprpfyAhVih_0HHd_cARYQ_AUoAXoECAEQAw&biw=1263&bih=872Why not use 12VDC LEDs lights?For future reference, these sorts of questions, belong in the begnners section.

author: Terry Bites
author_rank: Super Contributor
timestamp: August 04, 2021, 12:39:17 pm
content: There are very few low voltage transformers arround. But 230V torriods with 2x 12V windings abound. Carefully run a pair of cheapo transformers back to back on the 230V side.. You get a 230V inveter as free gift too.You might want slightly differing ratio transformers. Fiddle with the mains taps to get to overcome some of the inefficiencies. Or use a lower volage on the input trafo. Say 10V windings.Royer-50Hz-you'll need a special trafo. Nah.My first multivibrator used snot filled PNP black glass tranistors....

author: NeverEtched
author_rank: Newbie
timestamp: August 04, 2021, 06:30:26 pm
content: Thanks Terry & Zero.Beginner's section comment noted."Why not use 12VDC LEDs lights?" Because I can't find any. You'd think that wouldn't be difficult, but after months of searching for a long run (10m+) of outdoor 12v dc static led lights (i.e. without 'modes' or timer), I found these really nice sets of lights (12m), which turned out to be 24v AC, so that became my 'easier' option.Thanks for the RL definition, and I didn't know the old zig-zag symbol for resistor had been updated.Interesting torroidal stuff, thanks & noted, but I think I'm going to stick with the inverter/transformer inelegance for now. (BTW, I don't suppose it has to be 'exactly' 50hz for this application.)I remember those glass transistors! And you've reminded me about the white 'snot'...Cheers!