Charge Pump DC to DC Power Converters

Vee (negative supply) from PIC PWM by David Covick

Wagner Lipnharski says:

                                 Diode
                            .------>|------------o---o  High V
                            |                    |
                            3| <- point A        |
                            3|                  --- HV C
                            3|                  ---
                            3|                   |
+1.5V----o------------------3| <- point B        |
         |                  3|                  GND
         R                  3|
         |      Nc----------3| <- point C
         o------P           3|
         |      Ne--.       3|
         |          |       3| <- point D
         |         GND       |
         |                   |
         '---------||--------'
                   C

This circuit use a "one coil" transformer with two taps. At power on, all points have the same +1.5V.

1. Resistor R makes the NPN transistor conducts
2. Current Flows from ground to point C, via coil to B to +1.5Vdc.
3. Point C is grounded
4. Point D will develop a voltage below ground
5. Point A will develop a voltage higher than +1.5V.
6. Voltages goes increasing
7. Voltage at point D is enough negative to cut off transistor via capacitor C.
8. Transistor opens, Point C goes floating.
9. High + Voltage at Point A is rectified and stored at HV C.
10. Capacitor C (blocking the transistor) starts to discharge via R and coil taps D-B.
11. Upon C discharged, R is enough to turn on transistor again.

Cycle repeats in a frequency determined by R, C, and the transformer itself.

This kind of configuration was widely used, using a cheap small transistor audio output transformer (transistor radio), connecting the secondary in series with the primary.

See also:

• http://romanblack.com/smps/conv.htm A cheap circuit to make +13v from a +5v supply. Useful for some types of FLASH memory which require a higher programming voltage.

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