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Electronic Power supply load

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Full Member level 2
Jun 22, 2001
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I need to build an electronic power supply load for testing purpose.
Any information, link or diagram is welcome.



high power current sink

The usual method is to make a high power current sink. Start with a power transistor with its emitter or source connected to a small resistor which is connected to ground.

have an op amp -input connected to the resistor and its output connected to the base or gate. Putting a voltage on the other op amp input will control the current drawn.

This other voltage can come from a manual variable resistor voltag divider or a DAC run by a computer if you want dynamic measruements.

I wonder do those expensive electronic loads (ProDigit, Kikusui) also use the method Flatulent described? I've often wondered why they're so expensive.

Anyway, these circuit ideas are really useful. does anyone know of any online schematic respositories that have these types of circuits and explanations of how they work? All books out there deal with opamps and transistors, but in seperate chapters, never how to combine them.

Another interesting circuit is the MOSFET switch using two MOSFETs, again no books I've seen have these ready made recipes. An online collection would be a really nice thing to have reference to.

- Jayson

simple hobby circuit

What I explained is simple enough for a hobby use. The commercial devices have much more performance and exceed ordinary hobby needs.

For instance, they can draw current with 0V or so across them. They can measure the output impedance of the supply at different frequencies.

In the attached file the schematic of an electronic load for PSU testing. It's interesting the possibility to switch between fixed ampere consumption and fixed Ohm load. It's from a kit that an hobby magazine sell in Italy: "Nuova Elettronica".

Hi, needed something simular a couple of month ago and built a load with opamps and power mosfets simular to the one described in the link two posts up. Works fine, a bit unstable, but with som extra filtering It has been to great help for my SMPS project.

re Me


Check out the TI (formerly Unitrode) design note "Adjustable Electronic Load for Low Voltage DC Applications".


rgds, Al

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