ICL7660 Charge-Pump Negative-Rail Generator

Turn a single positive supply into a clean +/- pair with one chip and two capacitors — the trick analog circuits use to skip the second power supply.

Difficulty: Breadboard. Estimated build time: about 20 minutes. Estimated parts cost: about US$3.80. 4-line bill of materials. Compare supplier offers when available. A single-chip negative-voltage generator that turns +5 V into -5 V (or +9 V into about -9 V) so you can power an op-amp or rail-to-rail audio circuit from a single positive supply.

Wire the pump capacitor

Connect VCC (pin 8) to +5 V and GND (pin 3) to ground. Wire a 10 uF electrolytic capacitor between CAP+ (pin 2) and CAP- (pin 4). This is the 'pump' capacitor — every cycle the chip charges it from VCC through one pair of MOSFETs, then disconnects it and re-routes it to dump the charge into the output capacitor through the other pair.

Wire the output reservoir

Connect a 10 uF electrolytic capacitor between VOUT (pin 5) and GND. The negative terminal of this capacitor goes to ground; the positive terminal goes to VOUT. (Yes, the 'positive' terminal of the cap is at the negative voltage — counter-intuitive at first, but the cap doesn't care which rail is higher.) Leave LV (pin 6) and OSC (pin 7) floating for now; the default 10 kHz internal oscillator is fine for this build.

Measure the output

Power up and probe VOUT with a multimeter — you should see about -4.5 V (a few hundred millivolts of internal drop is normal). Connect a 1 kOhm load between VOUT and ground; voltage will sag a little because the chip has roughly 50-100 Ohms of effective output impedance. To check ripple, look at VOUT on an oscilloscope set to AC coupling, 50 mV/div — you should see ~30 mV pp of switching ripple at ~10 kHz. Now you can use this rail to power the negative supply of a TL072, NE5532, or any other dual-supply op-amp from a single 5 V wall wart.