The features will be:
- Voltage: 0 .. 400V
- Current: 0 .. 0,5A
- Short circuit proof
- Interlock relay and switchable outputs for safety
- Circuit diagram, PCB and optional software under GPL
- Serial and/or USB interface for easy lab automation.
- Display showing mode of operation and actual values
Part 1 - Preliminary Thoughts
My development goal is to have a power supply for the development of tube equipped high end audio circuits. It should be possible to connect 2 units in series or parallel, depending on the needs of the circuit under development. Output voltages up to 800V and output currents up to 1A could be obtained from such a setup.
The purpose sets some tough goals: high precission regulated outputs, quickly reacting on changes. Extraordinary low noise. Easy yet safe handling.
These goals are contradictionary to some degree. A very fast reacting device has often a poor DC precission. Offsets and drifts are typical. This could lead us to a compound arrangement. A fast amplifier ensures quick reaction and a second precise amplifier corrects DC issues. We will see later how this problem has been solved.
Extraordinary low noise is difficult to achieve with switching power supplies. This points us to a linear regulator. On the other hand a SPS has a far better efficiency but is much more complicated in design. I will use a technique to reduce the heat dissipation of the power supply but the regulator itself is a linear scheme.
Filtering of inputs and outputs is an important part when you want to get a high quality power supply. I will set some spot lights on techniques how to get the currents 'clean'.
The last chapters are dealing with the microcontroller who enables us to program and remotely control the power supply. Integration into automatic test equipment or a programmable tube tester are now in reach.
Part 2 - The Mains Input Section
Lets face it: the mains input is a dirty place to live for sensitive electronic equipment. The AC voltage is not suitable to supply semiconductors and all the noise and disturbances are presenting high demands for filters and regulators.
A power supply capable of delivering 200W (400V x 0,5A = 200W) can waste a lot of energy by heating the environment - your lab. Effective means to control the heat are required.
Power lines are contaminated with noise of many different sources. From very low frequencies up to the GHz range all kinds of signals can be found.The energy contained within these signals varies also from hardly to detect up to destructive levels.
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