Designing an adjustable power supply - REV. 1
September & Oktober 2019
Tor K. Gjerde
Background
As my brother was in need for an adjustable power supply for a smart mirror project, a compact little unit needed to be developed. A nice little challenge and great opportunity to learn more about power supply designs!
The supply needed to be able to step down a 12 volt DC output from a conventional AC/DC converter “brick” – down to a few different voltages including an adjustable 0 – 6 volt 8 amp max output and a 5 volt 4 amp max output.
One of the key feautures needed was one of the outputs to be digitally adjustable through communication with a Rasberry Pi unit. This was solved incorporating a TPL0501 – 100k digital potentiometer used to adjust a reference voltage. The SPI protocoll was used for communication between the Raspberry Pi and the potentiometer.
Key parameters
- 1. DC-DC buck converter, input 12 volt.
- 2. Fixed 5v output using Texas instrument IC: TPS54424
- 3. Adjustable voltage output using Texas instrument IC: TPS 54824
- 4. Digitally adjustable trough SPI protocoll
- 5. Total power usage monitoring also accesible through SPI
TPS54425 datasheet: http://www.ti.com/lit/ds/symlink/tps54424.pdf
TPS54824 datasheet: http://www.ti.com/lit/ds/symlink/tps54824.pdf
Working with the Texas instrument converter ICs turned out to be a walk in the park. The datasheets clearly outlined how to calculate needed support components in order to get the desired voltage outputs and characteristics.
No problems were encountered using a digitally adjustable potentiometer in order to accomodate adjustable voltages on the go. I’ll do some more testing and hook up the output to an oscilloscope in order to validate and document possible ripple effects.
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