- Published: Sunday, 26 May 2013
- Written by Jon Chandler
- Hits: 9674
When designing a microcontroller circuit, you may need a source of higher voltage. This is particularly true when using a 3.3 volt micro such as the PIC18F25K22 on the Amicus board or when using the new Firewing board.. A circuit might operate perfectly from a pair of AA batteries except for a few milliamps needed at a higher voltage for an LCD or to power a sensor. The usual option is to use a battery pack with more cells and multiple voltage regulators, but Dave at EEVBlog shows us an easier way in a recent video:
The above illustration (courtesy Spinningspark at Wikipedia) shows how simple the circuit can be to generate a higher voltage. A couple Schottky diodes and caps and a PWM output from the micro is all that's needed. Dave explains how the circuit works and its limitations in his usual comprehensive and entertaining style in the video. This is a great way to generate a few milliamps at a higher voltage.
Dave used the example of powering a 5 volt LCD display with this voltage doubler circuit. Another approach was suggested by Burt sometime back. The same parts of the voltage doubler can be re-arranged to create a voltage inverter that operates on the same principle. After some initial confusion about the function of this inverter, it was shown that many 5-volt character LCDs will operate properly from as little as 3 volts – the problem is that when the supply voltage is reduced, the LCD Ve bias voltage for display will reach zero and then negative values as the supply voltage is decreased. This inverter circuit can be used to supply a negative bias voltage.
For a description of using this circuit with an LCD, read this post in the Microchip forums by Mbedder.
There are other applications requiring a negative voltage for which this circuit can be used. The same limitations apply.