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I am trying to design a high voltage low current power supply. My purpose is to design it without a transformer. For example circuit like this :

400V~800V

My input is 220V AC after this circuit I am going to add some current limitter and also voltage rectifier circuit to have it in DC mode. I have seen a lot of design which is with transformer. And I thought that I can have this circuit to fullfil my needs.(which is 220V AC input ~ 800 or 1000V DC output.) Am I have to use transformer or is it just enough?. Another question is: I couldn't find any step up transformer on the internet. If I step 220 AC down to 12V and after that is it posible to increase 12V to 1000V?

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    \$\begingroup\$ What in your circuit is multiplying your input voltage? \$\endgroup\$
    – Ron Beyer
    Commented Feb 18, 2020 at 15:27
  • \$\begingroup\$ You CAN build voltage multiplier stages with an AC input, or you CAN rectify your AC and build a boost converter, but there could be serious safety issues in doing that without isolation from the mains. There's a reason you've seen lots of designs with transformers. \$\endgroup\$
    – John D
    Commented Feb 18, 2020 at 15:29
  • \$\begingroup\$ @RonBeyer capacitor voltage doubler \$\endgroup\$
    – iraquois
    Commented Feb 18, 2020 at 15:32
  • \$\begingroup\$ You are paralleling 2 doublers together though (I think they also need to be polarized caps), so you are getting a 2x doubling, not a 4x like you may think because they are in parallel with each other, not series. \$\endgroup\$
    – Ron Beyer
    Commented Feb 18, 2020 at 15:37
  • \$\begingroup\$ This circuit works, but you're not really doubling voltage, you're just using all of the voltage that is already there, instead of only using half. \$\endgroup\$
    – Criticizing Israel not allowed
    Commented Feb 18, 2020 at 15:40

2 Answers 2

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Yes, with a circuit called a voltage doubler or multiplier - a circuit that uses capacitors and diodes in a ladder structure to ‘stack’ the voltage. The amount of current is limited by the capacitor sizes used, so it might be appropriate for your relatively modest current requirement. Don’t run it directly from the line - use an isolation transformer. This will reduce the chance of a HV fault path to ground.

A flyback transformer type will make HV with fewer components and deliver more power. A power supply like you’re proposing is somewhat like a CCFL type, which might be possible to repurpose for your project. They can be run off isolated DC so you have a safer option for power besides running off the line.

Before you begin however, get very familiar with the special needs of HV design - component types, layout, insulation materials and general safety. Even at ‘only’ 30mA, 1000V can kill you. Always use an isolated supply or a transformer for an extra margin of safety.

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  • \$\begingroup\$ What, if I limit the current to for example 20ma? Then it shouldn't matter what the voltage is. According to table of dc current danger level, 20 ma is not fatal. Am I wrong? \$\endgroup\$
    – iraquois
    Commented Feb 18, 2020 at 20:57
  • \$\begingroup\$ The body has an intrinsic resistance, which varies depending on the body location and resistance at the points of contact. Since current depends on voltage, it stands to reason that everything else being equal, higher voltage is more hazardous since it can deliver more energy to the victim. Devices designed to deliver a shock (like tasers, defibrillators, electric fences) have specific rules limiting the energy they can deliver. Otherwise, from a regulatory standpoint, anything above 60V is considered potentially lethal, that is, not ‘touch-safe’. \$\endgroup\$
    – hacktastical
    Commented Feb 18, 2020 at 21:27
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Yes technically this is possible ... although I would not recommend bringing this to practice without a firm understanding of the basics!

You say low current, but depending on who you ask this might be different by orders of magnitude. (ECG specialist vs welding engineer. You get the idea.) Can you elaborate on the current requirement or application?

There are a few variations on this type of circuit, generally called voltage doublers and multipliers. These are sometimes used in electric fly swatters. Please keep in mind that this is potentially deadly! Dangerous at best. A battery powered handheld device can only output so much energy at once, a wall plug has a lot more power to deliver!

Things to keep in mind:

  • Capacitance will dictate max current.
  • Components have to be rated for the required voltages.
  • Keep adequate clearance between components to prevent arcing.
  • 230V input is already a bad idea! Maybe experiment with lower voltages first to get a feel for the circuit.
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  • \$\begingroup\$ Thank you for your answer. I need 10mA-40mA so if I use a transformer to have 220V AC to 1000V AC after that I think I can reduce the current with additions. Then it shouldn't be so dangerous if I have for example 20mA and if I isolate other parts of the circuit. Am I correct ? \$\endgroup\$
    – iraquois
    Commented Feb 18, 2020 at 15:52
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    \$\begingroup\$ @iraquois 1 kV at 40 mA is incredibly dangerous - I don't think you should be doing this without some more guidance. \$\endgroup\$
    – awjlogan
    Commented Feb 18, 2020 at 17:30
  • \$\begingroup\$ Indeed 1000V at 40mA has quite some punch, 40W! Do you need this current continously? Or in pulses? If the latter you could charge a capacitor to that voltage, and then you have a known amount of energy for whatever purpose. (This principle is used in electrified cattle fences. And to get back to 40W, this kind of power without a transformer starts to be really tricky! You'll probably find yourself looking at SMPS design real soon. \$\endgroup\$
    – dex
    Commented Feb 18, 2020 at 22:00
  • \$\begingroup\$ And if you consider a lineair regulating circuit: Keep in mind that the current limitation needs to be able to sink all the power in case of failure or shorting ... thus 40W ... that is a whole lot of cooling! \$\endgroup\$
    – dex
    Commented Feb 18, 2020 at 22:01

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