I want a 100 Joule pulse in 350 micro seconds. I have 1000V nbu 1012 capacitor discharge circuit . In datasheet, Max. average power is 3000 W(page 8), however I need 100/350us= 285kW instantaneous power when pulse is activated. Does the nbu circuit can handle 100Joule discharge at 350us, (with any capacitor with maximum voltage is 1000) or should I seach for other pulse discharge circuits?

Additional info: The resistor value is about 20ohms (but I'm not sure, I will check this within 1-2 days). I calculated that 200uF (1000Volts) capacitor can store 100 J. Time constant of RC circuit is 4ms.

Do these calculations say that it is not realizable to discharge 100 Joule in 350us with 1000V capacitor? So should I increase the voltage of capacitor and discharge circuit?

  • 1
    \$\begingroup\$ If your time constant is 4ms then you won't discharge the energy in 350us. What are you attempting to design? What is your 20 ohm load - might it be a coil? \$\endgroup\$
    – Andy aka
    Commented Dec 1, 2014 at 8:32
  • \$\begingroup\$ I want to give pulse to flashlamp which will be about 20 ohm. I do not have capacitor yet, but lowering capacitance might lowers the time constant but a higher voltage is needed. \$\endgroup\$
    – electro103
    Commented Dec 1, 2014 at 8:49
  • \$\begingroup\$ Resistor needs to be under 3 ohms (1kV, 330A). Reducing capacitance would imply higher voltage, but that exceeds the discharge circuit rating. Can you parallel load resistors? \$\endgroup\$
    – user16324
    Commented Dec 1, 2014 at 11:01

1 Answer 1


If the flash lamp will handle the power, your unit should do the job. However, you need a much bigger capacitor.

As you've calculated, 100 joules in 350 usec is 285 kW, assuming constant current and voltage. At 1 kV, this is a current of 285 amps. the nbu max is 1000 amps for pulses less than 1 msec, so you're fine there.

However, if you've sized the cap so that its energy is 100 joules at 1000 v, it will be completely discharged at the end of the pulse, and so the current cannot be constant.

Let's say you want the capacitor voltage to be 1000 volts at the beginning of the pulse, and 900 volts at the end. That says that your capacitance needs to be about 1000 uF.

Also, as you know you need to find the flash equivalent resistance. In order to get 285 amps at 1000 v, you need an equivalent resistance of less than 1000 / 285 ohms, or 3.5 ohms. Allowing for stray resistances in the wiring and the nbu, you'll need a maximum flash resistance on the order of 2.5 ohms. Any more and you'll need a higher voltage on the cap, and the nbu won't work.


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