- Published: Sunday, 27 March 2011
- Written by Jon Chandler
- Hits: 3368
Here's a great writeup on a lab power supply with fixed positive and negative 5 volt outputs and an adjustable output. A nice feature of this setup is the use of a PIC-based circuit to read supply voltage and current.
"One important parameter in embedded system designing is power consumption. This parameter is directly related to the battery lifetime, if the system is to be powered from a battery. In order to determine the power rating of your designed system, you need to know how much current the system draws from the source at a given voltage. While working on my projects, I usually measure current by placing an external ammeter in series with the current’s return path. This is not always convenient to do, and so I thought of making a special power supply unit for my lab that would display both voltage and current information on a LCD screen while prototyping my circuit. This way I can continuously monitor how much power my test circuit is drawing at a specific operating voltage. This power supply unit provides fixed ±5 V as well as a variable dc voltage ranging from 1.25 V to 9 V. A PIC16F689 microcontroller is embedded into the power supply unit to measure the adjustable output voltage along with the load current. Besides, this unit also has a built-in frequency counter to measure the frequency of an external signal. The range is over 50 MHz. However, it has been tested up to 20.0 MHz, and works fine. There are still few I/O ports of PIC16F689 that are not used. So I am thinking about adding one or more features (like capacitance meter) to it. But that would be on my second version..."