document updated 18 years ago, on Apr 5, 2006
Specifications:
- Input voltage: 3.0, 5.0, or 8.5v
- Max current: 50mA (maybe even less, the PSG-Max supposedly only goes up to 8mA)
- Output voltage: Given that human resistance can be as low as 2kΩ (lower maybe inside), that's 100v for 2kohm 50mA. So 90v seems right. Though it could easily be far far too high.
Inductor-based (via flyback)
- PIC controlled
- are used in CRT power supplies (yikes!)
- Even a flyback converter would work...
- low parts count
- high efficiency at very light load
- standby function
- calculations
- What I want is very close to a "discontinuous flyback boost converter", eg. in between each cycle, the current through the inductor drops to zero (but the voltage doesn't necessarily... hrm)
- Look at the equation(#4) for Vout here. "DT" is reall just how long the voltage is applied before turning off. Notice that DL (the load) features prominently.
- Since the Load matters quite a bit... may have to measure the resistance of the load with a low-voltage test before sending out a pulse (or is it possible that the load factors out completely? since what we're really going for is a fixed current across the skin?)
Capacitor -n- Diode
- simple, just lots of components
- Technically I need only a half-wave multiplier since I only want DC-in and DC-out
- Use ceramic capacitors
- notes
- more notes
Charge-pumps are nicht so gut because 1) the diode voltage-drop makes them much less efficient for low-voltages, and 2) they're damn complicated and make multiple outputs a huge PITA, especially compared to transformers.
Transformers need to be run continuously (making circuitry and software a fair bit more complicated), and dissipate a lot of power when using square-wave inputs
Inductors NEED a square wave input. But I need to find one of the following:
- How to calculate the max voltage output based on n ms on-time
- (better yet) how to measure peak voltage output based on n ms on-time
- sounds like a peak detector which uses a unity-amplifier as an analog buffer to remember the peak voltage would be PRIME