#611 Half-Wave Dickson Charge Pump
Zener-regulated 12V Dickson Charge Pump driven with Arduino PWM using a single pin.
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.
I’ve already covered this in LEAP#393 Dickson Charge Pump. In that case it used two PWM signals to drive each stage of the charge pump with alternative voltage.
This project demonstrates a modified version that uses only one signal to drive every other stage of the charge pump ladded, with intermediate stages coupled to ground.
NB: this was suggested by @steveschnepp on Issue#25. It is also covered in the wikipedia article.
Switching Signal
I’m using Timer2 Fast PWM to generate a square-wave on Arduino pin 11 (OCR2A) at 62kHz - OC2A to clear on Compare Match and OC2B disconnected. The duty cycle is set at 50%.
Here’s a scope trace of the waveform.
Since we’re using the chip’s native PWM capabilities, it is not possible to change the pin 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 14.5V 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 HalfWave.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
