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document updated 18 years ago, on Apr 5, 2006

Requirements

Low power consumption if possible
Current-limited output if possible
Electronic control of voltage output
Electronic control of frequency / pulse width

Output

To get actual pain, there are posts on the internet that suggest you need to go as high as 90v... that normal TENS units are ~40v. Fortunately there are step-up switching voltage regulators that can go this high.

Some are:

LT1082
LM78S40, universal, only use if I'm smart (and/or want to underestimate the complexity of such a beast) (and you study this long and hard, among many other things)
MAX668

The output of the voltage regulator is set via a resistor, we can used a digital resistor if necessary. The output is modulated via a high-voltage transistor connected via the PWM output.