DC-DC Converter High Voltage Power Supplies - Page 1
Forum section: electronics / beginners

author: Bob83
author_rank: Newbie
timestamp: June 23, 2016, 12:05:14 pm
content: Hey All!I'm new here. Been watching Dave's videos for some time and even though I don't really work in electronics or get involved with complex systems I've always found them entertaining. I thought I'd drop by and ask for some advice.I'm a bit of a valve/tube guitar amp enthusiast and I've been thinking about making some DC-DC converter high voltage supplies. Something like 12vdc to 300vdc and I'm thinking around 10mA should be fine. 12vdc will provide filament voltage and 300vdc@10mA (or around that) should give plenty of options for running common preamp valves.I've seen the nixie supplies that use 555 Timers or MAX1771 chips in boost converter setups and both will work for audio with some extra filtering, however I like the idea of putting together a small flyback converter. I think the isolation that type of circuit provides would be of an advantage if I made a valve preamp or pedal for example.Here are some controllers I've found.http://www.linear.com/product/LT3958http://www.linear.com/product/LT3748http://www.linear.com/product/LT3757The LT3958 contains a circuit that provides 300vdc@10mA but isn't specifically stated as providing isolation. The connections between the device and the transformer secondary are via ground though? The example circuit does not contain a switching transistor either.Other devices I've found that seem to deliver high voltages and currents are photo flash cap chargers. I've not looked into these much as I imagined they may not be ideal for my purposes. I imagine these may be better at charging caps at intervals rather than being used as continuous supplies.Just after some opinions from guys that know way more about this than myself! I've probably overlooked a lot of other solutions. Maybe some other SMPS topologies can be shrunk down to get what I'm after? I'm also looking into this with a view to practicing using LTspice and Eagle... both of which I'm very much a n00b at!Peace!

author: ebclr
author_rank: Super Contributor
timestamp: June 23, 2016, 04:54:46 pm
content: Don't need ic'shttp://www.talkingelectronics.com/projects/TheTransistorAmplifier/images/Fig96a.gif

author: Bob83
author_rank: Newbie
timestamp: June 27, 2016, 01:52:54 am
content: I don't recognise that type of circuit.What type of circuit is that?If its switching DC on the primary side, what is controlling the switching? A resonance involving the transformer and the caps?One advantage to the IC is high switching frequencies that aren't close to the audio band, unlike something like an LT1054 charge pump.

author: basinstreetdesign
author_rank: Frequent Contributor
timestamp: June 27, 2016, 05:51:26 am
content: Also called a Royer circuit.https://en.wikipedia.org/wiki/Royer_oscillator

author: Bob83
author_rank: Newbie
timestamp: June 27, 2016, 05:07:12 pm
content: Ah thanks guys!Thats given me some interesting reading. Including some stuff I had forgot from a while ago regarding LLC Resonant Converters.I also found some 555 timer based flyback style supplies and some push-pull supplies driven with the 555.Saying all that... the lack of an IC is something I like, although at least a 555 should remain in production for the foreseeable should I need to repair whatever I build! The 555 flyback/push-pull circuits I've found are not resonant circuits, so from my reading it looks like it requires heatsinks on the switching transistors and so on, while a resonant circuit stresses the transistors less due to zero voltage switching(?). Part count in non-resonant circuits also looks higher. I'm leaning towards LLC but searching out transformers and so on seems a bit of a wild ride. Also found a bunch of inverter circuits that look interesting.Right now you've got me spoilt for choice!

author: ebclr
author_rank: Super Contributor
timestamp: June 27, 2016, 05:16:01 pm
content: Instead of parts count do a USD count, 555 will also need a power stage and a heatsink, it's quite reliable

author: Bob83
author_rank: Newbie
timestamp: June 27, 2016, 06:01:10 pm
content: Some of the circuits i'm looking at only specify a source voltage, or have a battery symbol.In your opinion should I consider some extra protection besides maybe reverse polarity input and fusing?EDIT: I mean... if I use a supply like a 12v laptop/switchmode supply for exampleAlso, I very much appreciate the help!

author: ebclr
author_rank: Super Contributor
timestamp: June 28, 2016, 09:48:03 pm
content: I guess one PTC fuse and a reverse diode will be enough.