12v to 200v Converter
The completed unit
This mini-project is the main power-supply for the Valve Crunch/Tremelo floor pedal presented elsewhere on this site. Since the PSU is a separate unit, and may be of use elsewhere I decided to document it apart from the pedal. The unit expects a 12v input at X1 – this was a cheap wall-wart in the original, make sure you get the polarity right!
No claims to originality are made, and most of the circuit is lifted from the Linear Technology Data/Application sheet for the device, with the addition of the voltage-multiplier (known with affection by TV engineers as a ‘Cockroft-Walton Multiplier’) which takes the output voltage to around 200 volts. If you intend building/using this item, the usual caveats regarding high voltages apply – this unit will BITE you if you aren’t careful – BEWARE of charges remaining on capacitors long after the unit has been removed from the 12 volt source – even the 470nF capacitors will give you a nasty shock. Keep your fingers away from anything East of the LT1073!
A word about the components:
- For the 3 X 470nF capacitors I used 400v metallised polyester which are then covered with an epoxy resin and have a pleasant orange-brown
- D1, D2 & D3 are 400v 1A fast-recovery diodes (I used UF4004) – don’t be tempted to use ordinary rectifier diodes here – they aren’t up to the job.
- L1 is a 470μH axial inductor with a reasonably low DC resistance – the one I used was rated at IDCMax of 90mA and had a DC resistance of 13Ω.
- C4 is 22μF 63v aluminium electrolytic, C6 is 100nF 50v ceramic disc, and C5 is a 100μF 400v snap-in high-ripple aluminium electrolytic.
- The resistors are all 1/2 watt 5% types
- You may have to adjust the value of R3 to achieve the desired voltage, I installed a 10-turn 100K preset on mine and adjusted this to exactly 200v
All the above should be freely available. I purchased mine at ESR.
The LT1073 I obtained as a free sample from Linear Technology, but these are available from both RS Components and Farnell in the UK.
The PCB is an Eagle project and can be downloaded (as a WINRAR archive) here.
12v to 200v Converter
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