555 alternative / need 500V DC square wave 1mAmp

Hi, are there alternatives for the 555? I need 500VCD at 1milliAmp (square wave 150kHz)

thanks for any suggestions!

• Hmm, how "square" is "square?"
• Is 500vDC being driven into a Z=500k load (1mA actual peak current?) At this V and F, stray capacitance and inductance may distort the waveform, depending on the source impedance.
• Also, what is the limit on supply current? Higher allowances can yield better performances.

Pick any two: High Speed, High Voltage, High Resolution...

and also

Hah! So you imagine the required switching current is 1mA because you envision a 500k load resistor to +500V? Sorry, Erwin, whenever you talk fast risetimes, you MUST consider the capacitance that's present. For example, let's say you can do a very good job and keep the total node capacitance, including the switch, to just 20pF. To get a 10ns falltime you'll need a switch current to ground of i = C dV/dt = 20pF 500V / 10ns = 1A, which is much more than 1mA!

I mention falltime, because this is something you can achieve with a n-channel MOSFET pulling to ground. However, risetime is another matter, because when you turn off the MOSFET, you'll get a slow risetime of 10us from your 500k pullup resistor with our postulated 20pF of node capacitance. Of course you can use a smaller pullup resistor, but you can see that a 10ns risetime isn't very practical that way. Consider, for a 10ns time constant you'd need a 500-ohm pullup resistor, dissipating 250W, and now you'd be switching 2A to ground. What's more, a 10ns RC time constant is slower than your desired 10ns risetime. :>)

I've made several 500V pulse generators with 10ns rise and falltime, but they required considerable knowledge and effort to design. One used a transformer-coupled n-type pullup FET, with 0.5A gate drive. It had 5ns 500mA gate drive for both ON and OFF, which required some interesting circuitry. Dissipation is another issue; in the particle accelerator where my design is used as an on-demand beam switch, it generates up to 30k pulses/sec, and 150kHz cycling might be too much.

No, it has rise and fall times of 100nSec. I need 10nSec....

It's fead by 230VAC, so plenty of that I suppose ;.)

What are you trying to make? You can use 600V half-bridge FET drivers to get a 40ns rise-fall performance with a 500V swing.

Winfield,

thanks for the update and info! I'll check out the design and see if I can first make a scaled down version that only needs about 24V at 100nsec rise and fall times.

W>