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I am designing a flyback converter, input 170V output 1200V at 2mA.

I am having trouble finding an appropriate transformer, most do not have a high enough N. Current transformers seem to have ranges in 1:500, so I could work with that.

Is it proper to use a current transformer as a conventional step up voltage transformer?

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  • \$\begingroup\$ Most likley no. What switching frequency are you planning to run your converter at? \$\endgroup\$ – winny Mar 8 '18 at 11:14
  • \$\begingroup\$ Probably it will work this way or another. Shat about all available transformers, so the secondary winding would be your primary? Then you just take a transformer from 170v to 24v supply \$\endgroup\$ – Gregory Kornblum Mar 8 '18 at 11:15
  • \$\begingroup\$ Please note that current transformers usually have low number of turns. For example, one I'm using in one of my projects has 50:5:5 turns. The ones having 1:500 ratio will not be quite different. So using one may be impossible, or at least problematic. \$\endgroup\$ – Rohat Kılıç Mar 8 '18 at 11:22
  • \$\begingroup\$ The standard switching frequency I have seen for control ICs is 66 kHz to 132 kHz. \$\endgroup\$ – A.S. Mar 8 '18 at 11:47
  • \$\begingroup\$ Sure, but what are YOU designing for? The current transformers, which frequency are they made for? \$\endgroup\$ – winny Mar 8 '18 at 14:44
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Unfortunately, a current transformer is built as a transformer, which means it has very high inductance, high permeability, so stores very little magnetic energy for its weight and cost. In fact, a transformer specifically designed as a 'current transformer' is going to be even higher permeability and lower energy storage than your average power supply transformer.

A flyback transformer, although it has 'transformer' in the name, is built on a low permeability core, so it can store far more energy per weight than its high permeability cousin.

As long as you don't mind the transformer having a very low power throughput for its weight, then you can use a current transformer as a flyback, or any transformer for that matter, as long as the insulation is OK for your purposes. This may be OK for a quick 'proof of principle' lash-up on the bench, but for a proper product, you should really use a proper flyback, it will be cheaper, lighter, and smaller.

Keep the primary current below saturation, there's nothing to be gained and much to be lost trying to run it into saturation.

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    \$\begingroup\$ I am having trouble finding a proper transformer for my application, specifically with the output voltage rating. My input voltage could be 120 Vac rectified -170 Vdc, so an N = 15 would be adequate when running at 50% duty cycle. Able to point to any transformers which I could use for this application? \$\endgroup\$ – A.S. Mar 8 '18 at 12:26
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    \$\begingroup\$ Also, is there another way to generate a high voltage which I could look into? \$\endgroup\$ – A.S. Mar 8 '18 at 12:28
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Is it proper to use a current transformer as a conventional step up voltage transformer?

Almost certainly not - a CT is intended to have its output winding connected to a resistive burden of a few ohms and this will limit the output voltage to a few volts so, why should a CT manufacturer ensure that the varnish on the secondary windings is capable of withstanding a thousand volts.

Also, with the burden in place the core is largely prevented from magnetic saturation so how could anyone know what current could be put into the "primary" before saturation occured?

If you want an output of 1200 volts then use a large ferrite transformer and hand-build it. Stack about a thousand windings for the secondary in layers that are well insulated from each other to prevent breakdown. This sort of build is not for the faint hearted or anyone just tampering with an idea. It can hurt - usually high frequency burning is the main worry rather than electrocution because of the operating frequency needed (circa 50 kHz). I know; I've built one for an X-ray power supply.

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