Help with building a current supply
Help with building a current supply
(OP)
I'm looking to build an adjustable current power supply for anodizing. I've got everything to make a 12V, 10A, unregulated power supply (Transformer, Bridge Rectifier, 27,000 uF Capacitor to smooth out ripple).
I now need some help with the closed loop current control. Basically I'm wanting to use a pot to set a desired current (somewhere between 0-9A). Anyone know how to do this?
I now need some help with the closed loop current control. Basically I'm wanting to use a pot to set a desired current (somewhere between 0-9A). Anyone know how to do this?
Bryan





RE: Help with building a current supply
http://www.inventgineering.com/current_s...
The page is meant only as a guide. For your application, you will need a current source with some high power output transistor such as a darlington since a typical op amp does not have the power to drive the base of a single PNP for 9 amps. You can create a PNP darlington by cascading two PNP transistors. The reference resistor should be about 0.1 ohm for the current levels you are wanting. The zener voltage reference and potnetiometer establishes a voltage across the reference resistor. With 0.1 ohm, 1 volt will source 10 amps. The output transistor will need a heat sink!
RE: Help with building a current supply
Be sure to put the mosfet on a large heatsink and plan on using a fan. Keep in mind that the bridge rectifier will be dissipating at least 10amps at .8 volts for each half cycle. Also note that the voltage droop from the 27000 uF cap being discharged at 10 amps for a half cycle is only 3 mV or 6mV based on your configuration.
This means that the capacitor must be recharged for a very short interval near the peak of the rectified sine wave and this current will be far greater than 10 amps, even though it is only for a 3-5 milliseconds. The current is limited only by the transformer winding resistance. The bridge must be able to handle this repetitive surge current, and also the power of more than 10amps times .8 volts.
RE: Help with building a current supply
RE: Help with building a current supply
RE: Help with building a current supply