Today, I finished testing new lightweight boost converter. It is intended as a replacement for my ever-popular 3.3V to 5V converter. The new one is built around Texas Instruments’ TPS61240. It has slightly less output current (rated at 400ma) but is much simpler ( uses just 3 external components ), has several protections built-in, as well as undervoltage lockout (UVLO), which makes this power supply suitable for portable DIY devices.
Take a look at the title picture as well as the datasheet. Here is why I like this controller. First, it has been designed for battery-operated applications – thanks to built-in 2.1V undervoltage lockout it is safe to run this converter from 3 NiMH cells or one LiPo; when battery voltage drops down to UVLO threshold, the converter automatically shuts down. Second, the working frequency of the converter is 3.5MHz, which means that small and inexpensive MLCC inductor can be used. The converter also works well with ceramic capacitors. The total part count is 4 including the IC, and all components are cheap. Lastly, over-temperature and over-voltage protections make this simple supply quite robust.
The following picture shows the test setup. A pair of 10 Ohm 10W sand resistors make a 250ma load. Oscilloscope probe inserted into BNC connector directly soldered to the output and ground. Blue cylinder on the right is a magnetic probe used (after amplification, peak detecting and pulse forming) to trigger the oscilloscope from the inductor current pulse. While running with this load, converter IC and inductor are cooler than load resistors. When loaded to the maximum, converter gets quite warm but still runs stable.
The power supply can be used as ordinary 3.3V to 5V converter. It also has an ENABLE pin, which can be used to turn the IC on and off. By default, ENABLE pin is tied to VOUT. In order to use it, it is necessary to cut a trace inside a solder jumper.
I’m planning to start producing this converter and offer it for sale in about a month. In the meantime, I have about 10 blank PCBs left from prototyping run. If anyone is interested, drop me a line – the PCB is free, you’ll only pay shipping.
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