#393 Dickson Charge Pump

Zener-regulated 12V Dickson Charge Pump driven with Arduino PWM.

Build

Notes

The Dickson Charge Pump is a very neat trick for multiplying an input voltage.

It is basically a capacitor bucket-brigade, with diodes for flow control, and a switching signal to make it go.

It is not the most efficient voltage booster, and cannot drive very high currents, but may be a convenient solution depending on the application.

Switching Signal

I’m using Timer2 Fast PWM to generate a pair of square-waves on Arduino pins 3 and 11 (OCR2B, OCR2A) at 62kHz. The duty cycle is set at 50%, and the waves are an inverted pair by setting OC2A to clear on Compare Match and OC2B to set on Compare Match.

Here’s a scope trace of the two waveforms (CH2 is offset -6V for clarity).

pwm_pump_control

Since we’re using the chip’s native PWM capabilities, it is not possible to change the pins that the PWM signals appear on.

Note: it is possible to use other pins by using one of the other timers. This sketch uses Timer2 as it is generally available and is not used by other standard libraries.

See LEAP#254 AvrHardwarePWM for more details on hardware PWM.

Zener Regulation

Without the zener diode in place, this 4-stage charge pump delivers about 16V at the output tap.

The 1N4742 has a nominal zener voltage of 12V. An (optional) 2.2kΩ resistor is in series to soak up some of the voltage drop.

I’ve included a 10kΩ resistor to simulate a load on the 12V supply.

Performance

Works great:

very little ripple, < 20mV
charge pump and load drawing under 2mA
Arduino, which is also powering the charge pump, is drawing around 20mA total

Code

The DicksonChargePump.ino sketch is about as simple as it gets:

sets up PWM
in the main loop, demonstrates how to turn on and off the PWM outputs by changing the pin mode (5 seconds on, 5 seconds off)

Construction

The capacitors used here are monolithic ceramics, 220nF for the pump stages and 1µF for the final. The ones I have are rated for at least 25V.

Breadboard

Schematic