Is anyone here familiar with any circuit's for voltage and/or current sources programmatically controllable? Voltage ranges max or fixed of around 500-750VDC with a power rating from 5W to 200W. Regulation and repeatability of about 1% would be needed.
My initial approach was to use motorized potentiometer with a fixed voltage source with feedback as this seems relatively straight forward. This is not the approach I want to take for various reasons.
I've looked at some of the basic current source circuits but all tend to be low power and low current. I believe it is possible to design a larger version by using higher capacity components and/or paralleling or serializing several smaller circuits.
Essentially it is just resistive but of course a little capacitive and inductive. The power needs to be applied continuously. Actually in one case it would need to supply power to a transformer for voltage translation into a highly inductive load.
In this case something like PWM would not work or at least I believe it would not be a good option because of certain complicating factors.
I need to emulate a *real* voltage/current source as closely as possible that can supply continuous current to the load. By continuous current I mean as if the supply was ideal.
The supplies will mainly power passive components but some power may need to siphoned off to power some integrated circuitry.
A similar application which a variable source is needed is in computing IV characteristic curves. This is almost what I am doing but not quite. In my case the device is actually being used in real time and not being sampled at discrete voltage or current points. Here using something like PWM to control the current or voltage might introduce artifacts in the operation of the devices. This is not to say that one might still be able to use PWM and regulate the output.
What it all boils down to is that I need a simple programmable voltage and, separately, current source that while operating at it's programmed state acts closely, as close as any basic power source, to an ideal source.
yes, but I need a circuit so I can use it in my for my own application. It most likely won't go into production but that isn't the point.
I could use a triac to cut down the power but I'd need separate filter caps for each "sub-supply". It would also have very low regulation and high inrush currents when in low power mode.
AFAIK there are many ways to do "it" but I can't seem to find a way to do it decently. Maybe some switched mode power design would work?
No, it was only to compare the requirements for something that is easily conceivable without me having to explain all the details of what I'm trying to do. i.e., if I had a somewhat simple circuit that solved the problem I mentioned about the IV characteristics then it would also solve my real problem except for the caveat I mentioned.
All I need is a voltage controlled voltage source and a voltage controlled current source for the voltage range.
e.g.,
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Those circuits may or may not work for my application. I suppose I have to do some experimentation. Unfortunately I haven't seen many mosfets with a very large DS breakdown(about 1k).
I was hoping for a bit more circuits to look at besides using a fet in linear mode. I guess I should try it out though as it does seem the simplest I have found. Ultimately I need to use feedback so I can set the voltage digitally. Maybe I can do that with a simple microprocessor feedback loop but maybe there is some package that can take care of all that for me? i.e., buffer's the fet input for drive and has an input for selecting output voltage to be proportional to supply voltage?
I think I still have some 4CX250's around here somewhere.
...Jim Thompson
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Winfield Hill and Paul Horowitz are authors of a book called "The Art of Electronics." If you look in the 2nd edition (I think that's 1989, or so), there is a nice section on "Special-Purpose Power Supply Circuits," starting on page 368 in chapter 6. First thing talked about is high voltage regulators and in figure 6.48 they talk about regulating the ground return as one example in the ballpark of the voltage you are looking at. Another is optoisolation, examples shown in figure 6.50. Some of the basic ideas are in there, but a complete circuit for your needs probably isn't.
j>It most likely won't go into production but that isn't the point.
It sounds like you are making the classic mistake (read: time=money) of building (a one-of) something you can buy.
If this is a short term need, it's even crazier. Buying a programmable power supply (perhaps used) then reselling it when your need has passed would likely be essentially zero cost.
I'll take a look at it. I have designed a simple feedback loop using opamps that compares the voltage scaled down with a reference voltage and attempts to match it by using feedback and a mosfet. I'll have to play around with it some more and look at more examples to see if it's a good idea. The difficult part is controlling the high side mosfet of several hundred volts from a low side driver. I'll have to dust off AOE and read it. Wasn't a new edition suppose to come out shortly?
Let me decide that. It's my time and money so I should be the one who makes that choice.
Trust me that a programmable supply, which I assume you mean some thing like a large bulky bench supply and not some IC, is out of the question. It totally defeats the purpose of what I'm trying to do. This is a side project with part learning and part utility. If it performs extremely well then it could be marketed so I don't want to limit it's capabilities just to save a few bucks and hours in the short term.
Now if there are small modules/IC's that do exactly that then it definitely would be something to look into. In fact this would be preferred rather than implementing it discretely assuming it isn't too costly.
I think if it were me i would start with a 24 to 36 V feed that into a two transistor inverter then to a transformer followed by a voltage multiplier; finally a skimming regulator and current limiter. Best efficiency, all reasonable parts, add fast shutdown for load faults and all that is good.
Actually, we do have several examples of exactly what Jon is talking about. A voltage-controlled voltage-source, VCVS, is simple enough: Use an amplifier. Voltage-controlled current sources, or VCCS, as spice calls them, or transconductance amps, come in several forms. The Howland circuit (AoE 2nd pg 182) is often mentioned in textbooks. It's not one of my favorites, but just yesterday I came across one in Keithley's 642 electrometer, where it does a great job of adding an input offset voltage to a discrete MOSFET follower opamp stage.
I'm more fond of circuits like AoE fig 4.11, page 181, where an intrinsically high-impedance device configuration (BJT collector or MOSFET drain) is used for the output. These are easy to setup in a bipolar form, if needed.
You can find many different forms of these circuits discussed in detail on s.e.d in the Google archives, if you look.
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I'm especially fond of a circuit that I developed in collaboration with Tony Williams, an old s.e.d. regular, R.I.P., such as here,
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You can download my RIS-496 programmable CS circuit, see, ftp://ftp.rowland.org/pub/hill/RIS-496-1.pdf This circuit has been discussed several times on s.e.d, like
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I recently upgraded the circuit to use power MOSFETs instead of Darlington transistors (they have serious second-breakdown problems, severely limiting their high-voltage power capability). The new circuit is called an AMP-671, and its output features a pair of opamp-controlled MOSFET current sources. These circuits can have a voltage-control stage added, so they're a programmed current source until a voltage limit is reached.
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