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Re: NO WAY

Posted by Dave Davenport (M) on December 3, 2004 at 12:55:48

In Reply to: NO WAY posted by rickmcinnis@dogwoodfabrics.com on December 3, 2004 at 10:40:20:

Hi Rick,

Okay on the choke, just make sure that the input voltage to the CCS is high enough. It can have lots of ripple but the negative peak of the ripple should be at least 20V more positive than the voltage level at the output of the CCS. As an experiment, you might try it without the choke.

There is an interesting story with the shunt regulator. The basic design of the Minimal Reactance power supply does not have a shunt regulator on the output. The design is that the CCS sources a fixed current, say for example 35mA. The load draws a fixed current, say for example 30mA. The difference, or 5mA, flows through a resistor on the output. The size of this resistor sets the B+ voltage, say for example, 40K at 5mA sets 200V. The value of the output voltage isn't important as long as it is high enough to keep the CCSs in the load in regulation.

The adjustable factors in this are two currents and a resistance. Getting the right mix can be tricky: kind of like balancing a plate on a stick. Once everything is set the way you want it is stable and provides the needed regulation.

This is fine if you are building one but is a problem for production. The problem is that each batch of MOSFETs has slightly different characteristics. Therefore for each batch you have to empirically choose a resistor to set the source current, a resistor to set the load current and a load resistor.

So to get around having to do this I added an "automatic variable resistor" to the output in place of the fixed resistor. This is the shunt regulator. Because of its function, to keep the voltage high enough to drive the CCSs in the load, it does not need to have a precision reference.

Dave

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