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Insulation required for pri/sec windings ...........Vout = 250V flyback

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grizedale

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Hello

We do flyback, V(in) = 12V, Vout = 250V.

It is only low power (2W) so we do 1:1 transformer with DCM.

Anyway, since enamelled copper wire has 1000 Volts of insulation on it....do we need to put a layer of tape between the prinary and secondary layers?

And , also, could we actually wind the primary and secondary wires in bifilar, and not have to woory about insulation between the primary and secondary wires which are enamelled copper wire.
 

o we need to put a layer of tape between the prinary and secondary layers?
Click to expand...
Hi grizedale
Of course you will need . it is for more safety .
Best Wishes
Goldsmith
 
turns ratio is 1:1 is not reasonable for the transformer.
Advise to add more than two layer of tape between primary and secondary windings, keep enough safe distance
If parallel wound, must be using Triple insulation wire for two windings.

- - - Updated - - -

turns ratio is 1:1 is not reasonable for the transformer.
Advise to add more than two layer of tape between primary and secondary windings, keep enough safe distance
If parallel wound, must be using Triple insulation wire for two windings.
 
Hi again
Yes i'm agree with szhighstar . 1:1 is not good . because as you probably know maximum allowed D.C for a fly back converter can't exceed from 50 percent . thus you will have 311/2 when D.C is maximum . so feedback loop will try to decrease D.C . until the minimum D.C is given ! thus the efficiency can decrease too , because the voltage across the GS , will be like a spike . ( such as trigger pulse of a triac ! ) . so at a little time your mosfet will be at linear region . and of course when your out put current is ( for example ) around 5 A , thus the input current will be around 5.5 A ! it is not a proper design .
 
Ok thanks,

OK i go to 1:2 (pri:sec) but no more or else the reverse voltage on the diode gets too high.

This is a DCM flyback.......it never goes into ccm.

I dont think i need insulation, why should i, ...standard enamelled copper wire gives 1000v of insulation.

The tranformer is contained inside an enclosure so nobody can touch any electrical parts.

If you think of a buck-boost converter with vin = 12V and Vout = 250V, well theres 238V difference between some of the buckboost inductors windings, but we never saw flashover from that.......so why in the flyback is it different?

TWO PIECES OF ENAMELLED COPPER WIRE will not flash over due to having a few hundred voltage difference between them...........so why do i bother with the tape...it just decreases coupling.
 

Hi again
Did you understand why isolation needed really ? ( in transformer ) . do you know what will happen if your primary short to the secondary ? nothing ! just a big bang !
OK i go to 1:2 (pri:sec) but no more or
Sorry , i thought your out put is 12 volts if your out put is 250 volts , your transformer should be at least 511 volts ( before filtering ) . you understand ? at least ! i think 600 volts will be ok . 600/2=300 it can compensate the effect of loading as well .
 

why will it short?...ECW 9enam copp wire) has insulation of 1000v

my cct is very low power
 

Just consider that temperature increases because of each reason . and insulator destroys ! what will happen ? a designer should consider high value of safety in design .
 
please see EN61558 and EN60950 and EN60065, you will understand why you must add insulation tape.
 
Even if it seems like the insulation isn't necessary, many regulations will force you to use tape anyways, so that you have a minimum creepage distance. You need to find out what safety specs you need to pass.
 
This is not to contradict safety guidelines...

Nevertheless I have used a Radio Shack 6.3V 300mA transformer to heat a hi-V tube in my old oscilloscope. The secondary winding is in direct electrical contact with 1000 VDC.

This means 1000 V is riding the secondary inside the R.S. unit.

I was getting arcing with the original multiple tapped transformer. I solved the problem by installing a separate transformer.

However arcing developed with the first R.S. transformer. This was after the scope had been stored in a hi-humidity basement. The arcing did not go away even when I moved the scope where the air was dry.

So I replaced it with an identical R.S. unit. Years later I have not had a recurrence of the problem.

I do not know specifically what construction is used in the transformer.
 
your transformer is raise voltage part, if secondary rises 1000v voltage , HI-POT of wire must meet 1000V, it is reinforce insulation wire,there are maybe many turns in secondary winding, so wire and wire are very easy to short.
Addition it must have enough satety between primary and secondary windings.

- - - Updated - - -

your transformer is raise voltage part, if secondary rises 1000v voltage , HI-POT of wire must meet 1000V, it is reinforce insulation wire,there are maybe many turns in secondary winding, so wire and wire are very easy to short.
Addition it must have enough satety between primary and secondary windings.
 
this is just a xenon beacon, so saftey requirements are not needed.

As long as prying fingers cant touch the internal high voltage then alls good.....and they cant because its in a plastic case.
 

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