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I'm currently looking for transformers to generate high voltage spikes (several kV) on the secondary by suddenly changing the voltage (and therefore the current) on the primary. Ideally, I'd have a transformer with a turns ratio of 1:100 or more so that the voltage induced on the primary coil doesn't damage any low voltage components.

My issue is that I have no idea of how to find an appropriate transformer for this. Specifically, most of the filter options on sites like Mouser and Digikey do not allow you to select the turns ratio. The only transformer that seems to provide the turns ratio are current sense transformers, but I don't that those are appropriate for generating high voltage spikes.
Some datasheets, such as this one*, don't even list it either.

My question is: is there another way to determine the turns ratio from the datasheet? For instance, in the datasheet above, is the turns ratio 6.3:230 (because those are the voltages given in the Electrical Specifications section)? Or, is there a different type of transformer that I should be using?

I should mention that I'm aware of this question, however, I'm not even looking for a specific turns ratio (the only requirement is that it's greater than 1:100). My design will be built around whichever transformer I get.

*I have no opinions on this product. This is just one I found while looking for transformers.

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    \$\begingroup\$ You need more than just turns ratio. The high voltage winding insulation needs to be rated for the voltage you're trying to generate. That's why transformers are rated by coil voltage and VA. Nobody cares about the turns ratio. \$\endgroup\$
    – Transistor
    Commented Nov 17, 2020 at 22:09
  • \$\begingroup\$ @Transistor Why would nobody care about the turns ratio? Doesn't that determine the voltage/current you get on the output? It seems important if you want to supply the correct voltage to something \$\endgroup\$
    – JolonB
    Commented Nov 17, 2020 at 22:19
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    \$\begingroup\$ @JolonB: For power transformers we usually think about the desired primary and secondary voltages and desired output current (or maybe VA), and let the manufacturer determine the turns ratio and number of primary turns. Pulse transformers and high frequency transformers may have different required specs. \$\endgroup\$
    – Peter Bennett
    Commented Nov 17, 2020 at 22:35
  • \$\begingroup\$ @PeterBennett The issue I'm finding with power transformers is that they all seem to be stuck around 230 V. I can't imagine these would work at higher voltages (and even if they did, would the ratio between input and output voltage remain the same?). Is there a more suitable transformer for generating very short pulses (microseconds) at high voltage (~10 kV)? Ignition coils in cars do this exact thing, but they have a rather annoying form-factor. I'd prefer something that can be soldered to a PCB \$\endgroup\$
    – JolonB
    Commented Nov 17, 2020 at 22:51
  • \$\begingroup\$ The great majority of transformers you will find at distributors are AC power transformers intended to be operated at 50 or 60 Hz, with 120 V or 240 V primary voltage. You probably need a pulse or high frequency transformer. \$\endgroup\$
    – Peter Bennett
    Commented Nov 17, 2020 at 23:16

3 Answers 3

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You need to consider more than just turns ratio. The high voltage winding insulation needs to be rated for the voltage you're trying to generate. That's why transformers are rated by coil voltage and VA.

Most designers will be looking at input and output voltage rather than turns ratio. The turns ratio may be slightly higher than the voltage ratio to ensure that rated output voltage is achieved at rated load due to internal resistance and other losses. Note that transformers will usually give a higher output voltage when unloaded for this reason.

The transformer selection process will generally be:

  • Specify the supply voltage(s).
  • Specify the output voltage(s).
  • Specify the minimum VA.
  • Search the catalogues and find one that meets or exceeds the specifications. Alternatively have them wound to specification.
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Search for a flash lamp trigger transformer. Output voltages around 10 to 25 kV. Some datasheets have 'scope traces.

enter image description here

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  • \$\begingroup\$ That could be useful. Thanks. For the benefit of anyone stumbling across this, a trigger transformer could also be called a trigger coil. I found far more on Digikey under that name \$\endgroup\$
    – JolonB
    Commented Nov 18, 2020 at 21:40
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Try a neon sign transformer. Don't know what the turns ratio is, but it steps up 110 VAC high enough to ionize the gas in those signs.

Or an old tube-type TV flyback transformer.

Or, an automotive ignition coil. They step up 12V to 10,000V or more to fire spark plugs.

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  • \$\begingroup\$ "They step up 12V to 10,000KV or more to fire spark plugs". That's exactly what I want to do, however, I need something more suitable for mounting to a PCB (ideally it would be through-hole). I understand that the turns ratio of those are normally 1:100, so I was looking for something similar (but PCB-mountable) \$\endgroup\$
    – JolonB
    Commented Nov 17, 2020 at 22:52
  • \$\begingroup\$ 10000 kV = 10 MV. Are we sure of our multipliers here? Or is that really kelvin-volts (KV)? \$\endgroup\$
    – Transistor
    Commented Nov 17, 2020 at 23:29
  • \$\begingroup\$ Ooops, right. Too many zeros. Will correct, \$\endgroup\$
    – SteveSh
    Commented Nov 18, 2020 at 0:14

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