Calaculate ZVS Driver flyback voltage - Page 1
Forum section: electronics / projects

author: AutogolazzoJr
author_rank: Regular Contributor
timestamp: November 04, 2017, 12:45:26 pm
content: Hello,I am designing a high voltage power supply using an ac flyback transformer and a zvs driver. I am trying to calculate the voltage output. I will apply 12v dc to the zvs driver, and the flyback transformer will have a 5+5 turn center tapped primary coil and a 2400 turn secondary coil. When calculating the output voltage, I am using this formula.When substituting numbers into the formula, do I set primary turns to 5 turns or 10 turns?

author: AutogolazzoJr
author_rank: Regular Contributor
timestamp: November 04, 2017, 03:24:05 pm
content: I don't know if you are allowed to bump, but kinda need this to be answered. Thanks!

author: Buriedcode
author_rank: Super Contributor
timestamp: November 04, 2017, 03:35:36 pm
content: Because the primary consists of two coils, that are switched on alternately, you treat it as having 5 primary turns.However.It isn't quite as simple as Ns/Np * Vin. The primary voltage will be much larger than Vin, and so the output voltage will be higher. If there are built-in diodes in the transformer (as many tv/crt flybacks have) then for half the switching cycle, energy will be stored in the core. It is also somewhat dependent on switching frequency and the characteristics of the transformer. For the most part you simply treat the output as 'being high voltage'. It would be very difficult to calculate the actual voltage with any sort of precision, as it is also dependent of spark gap length.The fact you're asking this is worrying as you could well be dealing with lethal high voltage without know the basics of how the circuit works. I understand wanting to make cool sparks (I too have built lots of high voltage stuff) but there are plenty of things that can go wrong, which, at best, will mean the circuit simply doesn't work/oscillate. At worst, you blow up components.

author: AutogolazzoJr
author_rank: Regular Contributor
timestamp: November 04, 2017, 03:44:07 pm
content: Thanks. I'll be using an ac flyback transformer, so no complications with diodes. I am kinda scared about high voltages. I'll probably use a wrapping paper tube with a paper clip attached or something like that for measuring arc length and stuff. I am not using it for sparks, and I have some knowledge of relatively hv (guitar tube amps) but not much knowledge about zvs drivers. I am using it to experiment with x rays from common half-wave rectifiers (obviously lead shielding will be used).

author: Buriedcode
author_rank: Super Contributor
timestamp: November 04, 2017, 03:51:49 pm
content: One thing I don't often see when experimenting with HV transformers is .. a safety spark gap. I'd start with 10mm for now, you can always widen it later.This isn't so much safety for the operator, but for the transformer itself. If the secondary is left open, then it will always arc - just not necessarily from the wires coming from the transformer, but between the windings in the secondary (internal breakdown), which will quickly burn the insulation a lower the voltage required for further internal breakdown - effectively reducing your maximum output voltage to significantly less (essentially fatal for the transformer). Whilst a ZVS circuit isn't really a 'flyback converter' (you said no diode on the output), it is still very possible to generate a secondary output potential much higher than the breakdown voltage.This is one of the reasons stun guns have a spark gap. Marketing says its for intimidation, but its really to provide a maximum output voltage to prevent the transformers internal breakdown.

author: AutogolazzoJr
author_rank: Regular Contributor
timestamp: November 04, 2017, 04:42:58 pm
content: Oh goodness, I'll have to sound like an idiot again. I haven't even seen spark gaps mentioned in any high voltage power supplies I''ve seen, but I get what you mean. NOOB QUESTION ALERTwould I put the spark gap in parallel with my circuit, or series? I am guessing parallel across the transformer...ThanksAlso, so if I run my flyback transformer with no load (open circuit) it will cause internal breakdown? I haven't heard that before.

author: AutogolazzoJr
author_rank: Regular Contributor
timestamp: November 04, 2017, 06:36:32 pm
content: bump

author: strawberry
author_rank: Super Contributor
timestamp: November 04, 2017, 09:44:27 pm
content: Vin * pi = Vprim pk-pkTo prevent from insolation breakdown use sectioned secondary winding or some fancy insolation between layersAnd high frequency can cause breakdown due to winding capacitance and standing wave in windingOutput in series with some ~100k resistor otherwise self oscillating ZVS could stop going short

author: AutogolazzoJr
author_rank: Regular Contributor
timestamp: November 05, 2017, 04:43:06 pm
content: Thanks. Another question. As you know, I am feeding a zvs driver into the AC flyback transformer, and then into a multiplier cascade.This is the product:http://highvoltageshop.com/epages/b73088c0-9f9a-4230-9ffc-4fd5c619abc4.sf/de_DE/?ObjectPath=/Shops/b73088c0-9f9a-4230-9ffc-4fd5c619abc4/Products/ZVS_Driver_kit_ACShould I connect the half of the flyback transformer that goes into the ground part of the cascade to earth ground? A.k.a mains earth referencing? Or will that short the circuit?This guy does it here:

author: prasimix
author_rank: Unknown
timestamp: November 05, 2017, 10:39:11 pm
content: Quote from: AutogolazzoJr on November 05, 2017, 04:43:06 pmNo, that will not short the circuit. You have at least two possibility: to ground one end of the secondary and connect another to the voltage multiplier or to use two multipliers one to get positive and another for negative output.