# Need a technique to rectify high voltage high frequency

I recently made a high frequency transformer which I will be using to drive a large spark gap tesla coil. I machined the bobbin at work from nylon and bought the 60x55x15 cores on Mouser to form a 120x55x15 core which I will expect to handle at least 1kw input and has already been tested to over 4kw input and is holding up very well with no signs of failing. I have also made taps on the primary coil (5,10,15turns) to vary output voltage and power respectively. Now I need an efficient technique to rectify this transformer.

I understand I need avalanche rated diodes. My question is, are ultra fast diodes such as a recovery time of <75ns for example automatically rated as avalanche. I do not fully understand what makes a diode avalanche so I'm struggling to find some from RS Components although I do know they are designed to break down to handle reverse voltages in a controlled fashion.

Switching frequency is 45khz on a full bridge, output voltage on the primary tap of 15turns is roughly 20kv on the secondary

Thanks

• expected current? – Sunnyskyguy EE75 Jan 4 at 17:13
• A maximum of 250ma – walshy155 Jan 4 at 17:15
• I was intending to buy several single diodes from RS Components UK and making a series string, then they will be housed in the oil with the transformer. – walshy155 Jan 4 at 17:24

Or use 40 per string for margin. 1N4007 8pF each But verify L and SRF freq.

Insert diode PCB in oil.

BEWARE that forward capacitance increases with current and Ri decreases and trr recovery time increases. So if your average current is 250mA yet peak current 10x this you will have a trr problem so use faster diodes such as RS1MWF ( Diodes inc.) SMD.

• 1N4007 have perhaps 5-30$\mu$s trr, not at all suitable for 45kHz. They're okay at 60Hz or 400Hz. – Spehro Pefhany Jan 4 at 18:19