 High Voltage with PWM?

Hello everyone,

I'm tying to build a geiger counter with arduino and for the geiger tube to work it needs 400 volts. I found this project on hackaday and in this post 400 Volts is generated using a PWM signal of 10kHz. I'm wondering how does that work? how is a ESP8266 able to generate 400 Volts without a transformer or some other external power source?

If someone could explain it to me it would be much apreciated!

An inductor will generate a high voltage pulse, if the current flowing is suddenly switched off.

Inductance "L" is defined by the following voltage/current relationship:

V = L (rate of change of current)/(time to change)

The circuit in that tutorial probably won't work long, if at all, because the MPSA44 transistor is rated for absolute maximum 400V from collector to emitter.

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You can get high voltage from an inductor, from the "kickback voltage".

...Those prank devices that give a shock from a small battery use an inductor.

i got it now, thank you

Here's an example of something similar using a circuit from Nerdkits

You could use a UIS rated MOSFET that will work at those voltages, preferably 600V or greater. You may even get more voltage as it will switch off faster.

To be absolutely clear, that should be
V = L (rate of change of current)
or
V = L (change of current)/(time to change)

A rate of change is already dividing by time.

In mathematical notation that would be written V = L dI/dt.

This relationship is in units of volts, henries, amps & seconds. In fact it is the definition of the henry as a unit (1 H is equivalent to 1 Vs/A)

The fact the inductor voltage depends on a rate of change is why it can be arbitrarily large even if the circuit its connected too looks to be low voltage.

Large inductors can deliver dangerous electric shocks - something you need to be aware of if experimenting with them (as in this circuit of course).

Yes, working with inductors can be exciting. (maybe more excitement than you wanted)