Today’s electronic projects often require more than one supply voltage. 5V is often used to power MCUs, while sensors and peripheral interface controllers usually need 3.3V – if both types are used in your circuit, both voltages must be provided. Typically, one of the voltages is produced from the main supply (battery, wall wart, etc.) and the second voltage is then derived from the first using either linear LDO regulator if the second voltage is lower than the first or a boost converter if the second voltage is higher.
The boost converter I’ve designed uses Microchip MCP1253 charge pump controller. It doesn’t use an inductor and is capable of providing selectable 5V or 3.3V output voltage and up to 120ma of output current. The converter is half-inch long and weighs just 0.5g. All through-hole pads are placed on 0.1″ grid making it breadboard-friendly. Thanks to inductorless desgn, the converter is inexpensive, stable, and easy to use while providing automatic switching between step-down and step-up modes, and offering extra options, such as external shutdown and supply monitoring. The following picture shows board connections (click on it to make it bigger):
- Vin, Vout, GND are the only connections necessary out of the box (they are marked on the other side of the PCB). Input voltage can be 2.0-6.0V, output voltage is set to 5V. The converter automatically switches from buck to boost, therefore it is possible, for example, to have regulated 5V output in the whole discharge range of a battery of four alkaline cells (3.6-6V), or 3.3V from a single LiPo (if you switch output voltage to 3.3V, see below). The output current is 120ma, maintained down to 2.8 Vin at 5V Vout
- 3-pad Vout set jumper is set to 5V by a shorting middle pad to the right one. To switch output voltage to 3.3V remove the short using solder wick and short middle pad to the left one
- Shutdown The converter can be stopped by pulling this signal low. By default, it is hardwired to Vin, in order to use it, you need to cut a trace inside Shutdown enable jumper. The jumper can be later closed, if necessary, similarly to output voltage selector
- Power Good This signal falls low when output is out of regulation, which can indicate low battery or excessive load. In order to use this signal, a 100K 0603 resistor must be soldered on vacant pads indicated by the arrow Power Good Resistor
Design files are available for download. Fully populated and tested boards are offered for sale at the store. If there is enough interest, I can also offer blank PCBs as well as boards preconfigured for 3.3V output voltage. Please leave a comment if you’d like these options added.