Overview

The Laboratory Power Ssupply is a power supply for electronics hobbist. The project was started during the 2006 summer although I had this idea for along time. Every electronics lab should have some power supply that you can adjust and tune according to your lab's use. I needed one. LPS has the following specifications:

0..20V/4A

Two positive variable power supplies with a full voltage scale digitally controlled. The output current is measured and is also limited. Both voltage and current are controlled by a Pulse Width Modulation system and an integrator system. The total output power of both power supplies will not exceed 80VA.

0..-20V/4A

Two negative variable power supplies. They are similar to the positive power supplies.

LPS will also feature:

• Measure of output current and voltage
• Recording of these measures over time
• An isolated serial connection for a remote control and monitoring

Architecture

In its heart, LPS has 3 Atmel ATmega16 micro-controllers that communicate with an I2C bus.

LPS Architecture

The power supply is provided by two toric transformers that deliver 80VA on 2x9V. One transformer is dedicated to the positive supply while the second one to the negative supply. A rectifier board is associated with each transformer and it delivers two outputs one around 13 volts and a second around 26 volts. Both outputs are decoupled by 22000uF capacitors. The rectifier board also contains a set of relays and current sense resistors to measure and limit the current. The board directly delivers the power to the power supply transistors which are mounted on a huge heater. To control the power supply a specific board uses an Atmel ATmega16 micro-controller to control two different power supplies. A first power supply controller is dedicated to the positive voltage, thus controlling the +0..20V outputs. A second one is dedicated to the negative supplies and controls the 0..-20V outputs. Because the ATmega16 does not have enough IO to connect the LCD, the serial line, control the power supply theoutput current, it was necessary to have a master board. The master board also contains an Atmel ATmega16 which communicates with the two power supply boards with the I2C serial bus. The LPS master directly connects to the 2x16 LCD controller.

Why so many micro-controllers? The Atmel ATmega16 is very very cheap. Instead of adding some control logic to have a single micro-controller drive the 4 power supplies, it was easier and appeared to be less expensive. It was also an interesting challenge to create such a distributed application.

Planning

The project is now planned using Planzone Online Project Management Software to better identify what must be done and have an estimate of the remaining work.

References

• LPS Documentation