I will be ordering components as I live in a little rural town half way between Cape Town and Port Elizabeth in South Africa. Here, you cannot even buy a resistor.
Herman, I have been there, had to do that. I got started in electronics in Morristown, Tennessee, about 1953 or thereabouts. This wasn't exactly a rural town, but it was close. I walked to school, and sometimes helped feed a pig after school. The pig was being raised by a school chum for profit. Fortunately, there was a TV repair shop near where I was living with my grandparents that year, and I made friends with the owner, a young man in his twenties. He was able to "scrounge" parts for me from broken TVs and radios that he serviced, but were abandoned by owners who couldn't afford to pay for the repairs. As I grew older, I learned to buy parts by mail order from Allied and Lafayette Electronics using money earned by mowing grass in the summer, shoveling snow in the winter, and delivering newspapers year round. By the time I graduated high school and went off to serve in the Air Force I had acquired a nice array of test equipment and (mostly) salvaged electronics parts.
I built my first vacuum tube plate power supply in the 1960s for my Novice amateur radio rig. It used a series regulator (a TV horizontal-sweep power pentode,
6BQ6GTB IIRC) to obtain a variable, voltage-regulated, output voltage at the cathode of the pass tube. Good for several hundred milliamperes at four or five hundred volts if you pushed it hard enough. The negative feedback was provided by, again IIRC, a high-mu duo-triode,
12AX7. Reference voltage for feedback was provided by a gas regulator tube, an
OA2 perhaps. I used whatever I happened to have in my "junque box" at the time. Almost all the parts I used were salvaged from discarded TV sets. The schematic below is not exactly what I used, but it is close enough to give you the general idea, Today this would be constructed entirely with solid-state components, but the vacuum tubes are still available if you search for them.
Since the cathode of the pass tube is at B+ potential (200 V in the example above), its filament heater should be driven from a separate, isolated, center-tapped, filament transformer with sufficient insulation in the secondary winding to hold off the output voltage. The center-tap of the filament transformer secondary winding is connected to the cathode of the pass tube, so the heater element and the cathode are at the same potential.
I haven't tried it, but you should be able to parallel two or more pass tubes to increase the output current capability. It would be interesting to see a build using a chassis full of 6BQ6s operating in parallel to deliver one amp at 220 V DC to your LED strip lights. Whoops! Times three, since you need separate power supplies for red, green, and blue LEDs. Probably need forced air to keep the pass tubes cool, but you might need that anyway to cool the heat sinks in a solid-state version. There is something about the gentle glow of the tube filaments, and the soft red glow of their anode plates, that makes vacuum tubes still attractive to me.
Well, to look at and admire, not so much to actually build.
You still haven't told us what the "control signal" from the high-end PLC is providing. I am guessing a 0 to 10(?) V DC analog signal from a DAC module. This will be important in deciding how to control a solid-state power supply using op-amps. Some hands-on trial-and-error will be required if I were to build this.
Can you make a simple wiring sketch on how to use the op amp?
The data sheet for the
Texas Instruments LM317HV never refers to voltages this high. Can it in fact be used at this kind of input voltage? While I have frequently used the LM series in the order of 5,9,12v and ones like lm350 for adjustable use, I do not know too much about series regulators theory and properties. Can you help some more?
Quote from the first page of the LM317HV datasheet:
"Since the regulator is floating and sees only the input-to-output differential voltage, supplies of several hundred volts can be regulated as long as the maximum input to output differential is not exceeded, or in other words, do not short the output to ground." There is essentially no limit on how high the output voltage can be, but the LM317HV must be well-insulated from power supply common, and the voltage drop across it from IN to OUT must always be less than 60 V DC. In other words, it floats on the high voltage power supply output. The trick is to control the ADJ terminal (which is always maintained by the LM317HV to be 1.25 V less positive than the OUT terminal by controlling current through a resistor connected between OUT and ADJ) by using an op-amp capable of driving ADJ toward the desired output potential, but with a much lower control voltage (that's what op-amps do: amplify small voltage differences). The op-amp is nested inside a negative feedback loop that samples the output voltage and compares it with a stable reference voltage, the difference driving the op-amp output. There are some pesky details regarding open-loop gain, stability, and response time that must be considered, as well as some means to avoid disaster if the output were shorted, but its almost that simple. Perhaps you should try breadboarding a three-terminal regulator with an op-amp controlling the ADJ voltage to get a "feel" for how this all works without vacuum tubes. I think you will be pleasantly surprised at how simple it is.
