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"universal" P-P driver board

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Back to topic.

I posted this scheme over on the "Diff Drive" thread, since Rich Walters got me started thinking about it. (derived from DePalma's splitter there) But it may be of interest here for a P-P driver. It should be able to drive decent loads.

Explanation:
The P-channel Mosfets are set up so as to operate in "near CCS" mode. The drives (Ra, Rd pots) to the Mosfets are adjusted so that the driver tubes (V1, V2) continue to operate with constant current WITH their actual loads attached (which would presumeably be some output tube grids and their biasing resistors).

This is slightly different than a CCS load, since the P-chans are adjusted to actually provide the output current so that the drivers still operate at constant current despite the load. The drivers (V1, V2) are low impedance outputs though, so they still maintain control of the output voltages.

This allows the driver tubes to operate in CCS constant Mu mode, even with load currents present. So this is an improvement over ordinary CCS loading.

I have drawn triode drivers for V1, V2 in the diagram for simplicity, but these could just as well be pentodes with screen feedbacks from the output plates (crossed feedbacks).

The interesting unknown here is what happens if the P-chans are adjusted for a little more current drive than the output requires. Then the V1,V2 drivers would begin to operate with a little less current when pulling down the load.

Since tube distortion increases with more loading generally, this would now provide anti-loading (or neg. resistance loading) for the driver tubes. Maybe one could adjust out some residual distortion from the V1,V2 tubes that way (providing they don't oscillate).

Don

PS: could use the same scheme for a P-P output stage too.
 

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My beef with PIC is "W"..... And banked memory and I/O
mapping of the most absurdly inconvenient sort. Absolutely
wasteful of code space, cycles, and ultimately my patience...Some of the new dsPIC I hear this is fixed. As PIC seems to change their instruction set every year or two...

Yes, the newer chips have 16 or more registers. I don't think that they change the instruction set, but definitely add to it.

As I only know oldskool Basic, Assembler, and now Labview. C might as well be ancient Sumerian as far as I can read it. Assembler I just don't have the patience anymore.

The last time I used basic, it was on a TRS-80. Assembler IS too cumbersome today for anything complex.

I was a bit unconventional in my formal education since I didn't go to college until I was 37 years old. It was a computer engineering degree, so we had classes in "C" advanced "C" and C++. Some of it actually sunk in.

Many of my collegues at work use Labview, but I never have. I think I have a set of disks for an old version (5.1 maybe) around here somewhere.

I have 5 power supplies already controlled by GPIB.

All of my power supplies here are strictly manual. All but one of the HV supplies have tubes in them. I think that some GPIB power supplies and Labview would be all that is needed for a curve tracer.

By the way, although the switching type supplies generally have a current limit control knob (and remote too if optioned), it only controls average current into the big output capacitor. So dead shorting one of these ( the XHR is a switcher for example) will blow the current sense resistor instantly unless its a huge thing.

The only semi modern power supply I have is an HP6448B, an old style switcher. These power supplies are often called switchers, but the switching frequency is 60Hz, and the control loop is very slow. It takes about 2 seconds for the current limiting to kick in. I have shorted the 600 volt 1.5 amp output. It makes a very big bang. Big enough to vaporize a #20 wire, and as I have shown in the past the support rods for a screen grid. Constant current mode is virtually useless.
 
We have an old scary phase controlled Sorenson 600V supply that has all the endearing characteristics you mentioned. It also sounds scary, like it's about to shoot out a jet of flame (though it never does). Our HV supplies of choice these days are the Xantrex switchers, that are much smaller, responsive and forgiving, though not necessarily more reliable ( I have one on my bench that's reluctant to start).
 
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