[Moved] Constant Current Source

[Ishaan Karnik]

I am supposed to develop constant current source.
The catch is that the current source is to be of 100 Amps., 5-15 Volt Output with analog current control scheme.
Input can be 12-36VDC or 240VAC(Wall Supply).
I have found out that such power supply exist but we not to buy them.
Any ideas fellow.
Regards,
Ishaan Karnik.

 

[chuckey]

Re: Constant Current Source

You must go down the inverter route, as your input could be 12V and your output 15V. Also your power requirements are very high which means a linear regulator is out of the question.
The best way to go would be to use one transformer with a 230V rated inverter on it with a second set of primary windings to carry the 12-> 36 V inverter windings. You would have one set of output windings/diodes/capacitor. You would need some sort of feed back which is switched in some way to hand control of the output current to the correct input inverter.
It would be simpler to design just one inverter, say 12V -> 100 A, and feed it from a 230V -> 12V power supply, but it would have a lower efficiency and use more components.
Try the power forum.
Frank

 

[Ishaan Karnik]

Re: Constant Current Source

You must go down the inverter route, as your input could be 12V and your output 15V. Also your power requirements are very high which means a linear regulator is out of the question.
The best way to go would be to use one transformer with a 230V rated inverter on it with a second set of primary windings to carry the 12-> 36 V inverter windings. You would have one set of output windings/diodes/capacitor. You would need some sort of feed back which is switched in some way to hand control of the output current to the correct input inverter.
It would be simpler to design just one inverter, say 12V -> 100 A, and feed it from a 230V -> 12V power supply, but it would have a lower efficiency and use more components.
Try the power forum.
Frank

Thank You for the response. The current source will always work in buck configuration. The 5-15 Volt output means that the load is recommended to be operated between 5-15VDC (lower the better as power losses will be less, only current stabilization matters), with minimum of 12 V input.

 

[ZekeR]

Re: Constant Current Source

Probably the easiest thing to do is to buy a buck converter which is already built to output this much current (this one, for example). You can place a low-valued current sense resistor (for example, 1mOhm) in series with your load, and use an op-amp to compare the voltage across this sense resistor with a reference. The op-amp's output would feed into the Vc pin (or in this case, they call it the "Ith" pin) to adjust the buck converter so it behaves as a current source. The op-amp would overpower the buck regulator's internal feedback, so it would no longer behave as a constant voltage regulator.

You have to be very careful to ensure nothing blows up! At these power levels, there are many things that can go wrong. You should probably build up a prototype using a lower-power buck regulator first just to try the idea and ensure everything works as expected (stability, etc), before building the full-blown device. Additionally, rather than building the circuit from scratch your first time, I'd recommend ordering an evaluation board. You can also call up the company that supplies the chip; you can probably get additional tech support if need be. Circuits with these power levels are prone to over-heating, so make sure each component can take the power.

One of the nicer things about the part I recommended is that the company provides a full-blown test bench in their free simulator software, which already has the part configured and ready to simulate. You can proceed to add a sense resistor and an op-amp, and see if your circuit works correctly in simulation.

 

[Ishaan Karnik]

Re: Constant Current Source

I have created 20-25 Amps. constant current source.
Will it work if I connect 4-5 such supplies in parallel.

 

[mtwieg]

Re: Constant Current Source

I have created 20-25 Amps. constant current source.
Will it work if I connect 4-5 such supplies in parallel.

Possibly, if you can merge their control loops together to enforce equal current sharing. Making a buck converter for 100A isn't terribly hard, so long as you can get your hands on high power inductors and good current shunt resistors. But apparently you'll need some kind of preregulator to go from your 12-36VDC or 240Vac to an intermediate DC voltage, like 20VDC, and that's complex in itself. For 12-36VDC in, you'd need a buckboost-type DC-DC converter, which is sort of difficult at these power levels. For 240Vac, you'll likely want PFC, but you also want to regulate down to a low DC voltage, which makes PFC difficult. Neither are great options...

For your 12-36VDC input condition, where does that actually come from? Because drawing >100A from 12VDC is usually a bad idea, regardless of topology. Couldn't you just change that range to 15-36VDC or something? Then you could get away with just not using a preregulator stage at all, which has huge benefits.

 

[Ishaan Karnik]

Re: Constant Current Source

Possibly, if you can merge their control loops together to enforce equal current sharing. Making a buck converter for 100A isn't terribly hard, so long as you can get your hands on high power inductors and good current shunt resistors. But apparently you'll need some kind of preregulator to go from your 12-36VDC or 240Vac to an intermediate DC voltage, like 20VDC, and that's complex in itself. For 12-36VDC in, you'd need a buckboost-type DC-DC converter, which is sort of difficult at these power levels. For 240Vac, you'll likely want PFC, but you also want to regulate down to a low DC voltage, which makes PFC difficult. Neither are great options...

For your 12-36VDC input condition, where does that actually come from? Because drawing >100A from 12VDC is usually a bad idea, regardless of topology. Couldn't you just change that range to 15-36VDC or something? Then you could get away with just not using a preregulator stage at all, which has huge benefits.

Input voltage is pre-regulated. It comes from main power supply that supports other devices. It is not my headache.
I am told that I can get 5V/9V/12V/15V/24V/36V and few other values, with each capable to supply about 250 Amps (constant voltage and not constant current). I choose 12V because the load on that supply is hardly few Milli-Amps.
Output volt required is about 5VDC.
Can some one comment on current regulation for DC-DC Poly-Phase Buck convertor like LTC3829.
Are there any other such Poly-Phase Buck Controller with similar capabilities.
Regards.