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Registered Member #1143
Joined: Sun Nov 25 2007, 04:55PM
Location: Vilnius, Lithuania
Posts: 721
Hello. I am trying to make 100kv voltage multiplier for x ray tube. I made one with 20kv 20mA diodes, but output is just 50kv (n=8) with 10kv input. I started to think that diodes are too weak for 1kw operation. So i get 200 UF4007. So now i need formula for output power calculation to get 100kv 10mA. (power calculation is to determinate capacitors for this multiplier)
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
The most important question is, what is your operating frequency?
Also, the output current depends on how much voltage drop you can tolerate, there are formulas for calculating the voltage drop with a given input voltage and output current and number of stages
It is often more practical to simulate the multiplier, for example in LTSpice. It's especially important if the input waveform is not a sine wave, because the above formula assumes that the input is a sine wave.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Output Voltage: Eout = Ein * √2 * n
Eout is the output voltage Ein is the RMS input voltage n is the number of stages in the multiplier
Sag under load: Edrop = I / ( f * C ) * (2/3 * n ³ + n ²/2 - n /6)
Edrop is the voltage drop I is the current drawn in amperes f is the frequency in hertz n is the number of stages C is the size of the capacitors used in farads
Ripple under load: Eripple = I / ( f * C ) * n * (n +1)/2
Eripple is the voltage ripple I is the current drawn in amperes f is the frequency in hertz n is the number of stages C is the size of the capacitors used in farads
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
I've seen multipliers used in high frequency dental xray heads. The output sags greatly under load, so closed loop control is needed. The anode voltage is sampled via a 200M resistor and fed back to the controller which drives the transformer harder as load (and sag) increases. Sag is reduced as frequency and stage capacitance is increased, but it will always be there. Your numbers sound pretty close to what I'd expect, crank up the drive.
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CW multiplier output power
