The MAX1044 is a charge pump converter - it uses a capacitor as a “bucket” to pump charge from one place to another. In this case, the 1044 connects the + terminal of C1 to +9V from the battery and its negative terminal to ground. C1 charges up to 9V from the battery. The 1044 then connects the + terminal of C1 to ground, and the - terminal to pin 5. This lets C1 dump the charge into C2. The - terminal of C2 is tied to pin 5, so it gets a negative voltage equal to the voltage across C1.

power supply battery 9V to output +9V Gnd -9V - [Link]

For you high-voltage minibooster fans out there, here’s the one-chip, one battery way to do it.

The MAX1044 is a charge pump converter - it uses a capacitor as a “bucket” to pump charge from one place to another. Normally, there is a capacitor connected from pin 2 of the 1044 to pin 4. This capacitor is charged between +9V and ground, and then switched in parallel with a capacitor from pin 5 to ground in a way that makes a negative voltage on the second cap.

One 9V battery gives +18, +25, +33V - [Link]

All diode-based rectifier circuits suffer from a signal-level-dependent frequency response. This response occurs because the dynamic impedance of the diodes varies as the signal level changes. The result is a slower frequency response and distorted rectified outputs at low signal levels compared with high levels.

Fast rectifier circumvents input-level effects - [Link]

There are many circuits available for charging batteries, but many are for NiCd or NiMH batteries. They will not work for lead/acide batteries, so don’t use these!!! The best way to charge a battery is with a current limited voltage regulator. This sets a maximum current (say 1A) that will flow to charge the battery. If the current rises over this set current, the regulator will be forced to put out a lower voltage. Since voltage drops, so will the current; hence current limited. While the battery is charging, the current should decrease slowly while voltage starts to increase. In the end the current will be next to zero and the voltage will be equal to the set voltage.

Lead-acid battery charger By LM317, LM350 - [Link]

This is an advanced battery charger design based on Maxim’s battery charger IC MAX712. This device can, using a minimal set of external components, fast-charge an NiCd/NiMH rechargeable battery. Fast charge is terminated using several detection methods, including dV/dt, dT/dt and a time-based cutout. Full details can be obtained from the MAX712 datasheet, available at the Maxim Inc.

NiCd Battery Fast Charger by MAX712 - [Link]

I use the circuit above to monitor the voltage level of my Li-Poly battery packs during flight. The two Super Bright LEDs light up when the voltage level of the pack gets below 10 volts.

Lithium Polymer Voltage Monitor Circuit by LM10 - [Link]

20 Watt Simple Switcher Forward Converter (pdf) - [Link]

This circuit will allow you to operate small devices like laptop computers inside your automobile without an expensive automobile power supply. The circuit takes advantage of the fact that power transformers are linear devices and can be used to step up as well as step down. This is evident by the fact that the supply drives the secondary and the output is on the primary.

12 Volt Automotive Inverter - [Link]

LM3914 Voltage Monitor - [Link]

Power supply regulator LM2941 fanregulator - [Link]