VACS:Projects:Hardware:LPS:ControllerBoard

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Power Supply Controller

Overview

The power supply controller board controls two positive or negative power supplies. It is built arround an Atmel ATmega8 that measures and drives the power supply outputs.

PWM Digital to Analog Conversion

To control the output voltage and limit the output current a variable voltage must be generated by the micro-controller. Using a DAC would be possible but it requires several IOs and the DAC also increases the cost of the power supply controller. Instead, we use a simple PWM signal that is integrated with a low pass filter. The output voltage of the low pass filter is proportional to the PWM duty cycle. The low pass filter is created with a Sallen and Key filter which gives a 2 order low pass filter (12db/octave).

The filter frequency

Fc = 0.8Hz

0.25 at 2F 0.0625 at 4F 0.015625 at 8F 0.0039 at 16F (20mV)

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