High Power Adjustable DC Supply Required

[shawnmk]

Dear All,

I am building the first demo circuit available on LT1952 datasheet. I have completed the control circuit which involves the LT1952 chip. However, to test it I require a power supply with below specifications.

Power Supply Requirements:
input DC voltage supply: 36-72V
and input DC current: 7-10A
That is about 500W DC power supply is required. (such power supplies are costly and in addition, I dont have access to a lab,)

So, in my search to build such a supply, I found a 12V/10A positive adjustable voltage regulator (LT1083) on https://www.electro-tech-online.com/custompdfs/2011/04/1083ffd.pdf
I am planning to make a series combination of a couple of LT1083 to meet my specifications of power supply voltage and current. Please advise if this is wise attempt.

Alternatively, I could also build a rectifier. Could you please suggest some reference designs for rectifiers of such high power?

Thanks,

 

[RCinFLA]

Do you realise how much heat dissipation is going to be required? Assuming you start with 75 vdc, when regulator output is set to 36 vdc the power dissipated by series pass linear regulator will be (75v-36v) * 10 amps = 390 watts. The device will shut down due to thermal overload even if you put a massive heat sink on it since the thermal resistance of the case will result in overheating of IC.

You need a switching adjustable power supply. If you need a very clean DC then a pre-switcher is used to produce a couple of volts above the linear regulator output voltage. This minimizes dissipation on linear output regulator.

 

[Reloadron]

If you can get your hands on a 10 Amp or greater variac maybe just hang a full wave bridge on it and run with it. Add some filter caps. That will give you your 36 to 72 volts @ 10 Amps. With some looking you should be able to find a variac in industrial surplus somewhere.

Ron

 

[crutschow]

If you can get your hands on a 10 Amp or greater variac maybe just hang a full wave bridge on it and run with it. Add some filter caps. That will give you your 36 to 72 volts @ 10 Amps. With some looking you should be able to find a variac in industrial surplus somewhere.

I bought a used one from fleabay.

Edit: Remember that a Variac is not isolated from the mains so for safety you should also add an isolation transformer.

 

[Reloadron]

Good point, from a safety standpoint you would not have mains isolation sans an isolation transformer.

Ron

 

[tcmtech]

I believe he said,

Power Supply Requirements:
input DC voltage supply: 36-72V
and input DC current: 7-10A

or is that a misprint and its what you want out of it?

Please be more specific as to what the actual input power source will be and the actual output being supplied will be.

 

[Reloadron]

Hi tcmtech

I believe he got it from the first typical application of this data sheet. Were you thinking a welder power supply?

Ron

 

[tcmtech]

Not really. I have no idea what he actually wants.

If its 12 volt 20+ amp output from a 36 to 72 volt input I would say that the given specs sheet would be a fair choice but if its from a 120 or 240 VAC line power source I would go with a different IC or a different circuit entirely.

 

[Reloadron]

My guess was he wants a DC power supply capable of voltages between 36 to 72 volts capable of 10 amps. However, I figure wait till he returns I guess.

Ron

 

[shawnmk]

Hey guys,

thanks for your inputs. I understand that dealing with 250W Forward Converter is really taking a huge risk. Since I am a novice and I am finding it really difficult to get a power supply of the range specified, I was asked to tone down the power to 25W. Makes things a lot easier.

Just to bring you guys up to date:

The project is building a DC-DC converter. Its is a buck converter converting DC voltages 36-72V to 12V,20A. The power output is 12x20 = 240W.
The DC-DC Forward converter is a buck converter with transformer replacing the first inductor in the circuit. So, essentially its a transformer isolated version of the buck converter.

Thanks once again.

 

[moffy]

If you have an isolating transformer, it seems strange to be using a Buck topology.

 

[shawnmk]

sorry I didnt understand ...

 

[moffy]

The DC-DC Forward converter is a buck converter with transformer replacing the first inductor in the circuit. So, essentially its a transformer isolated version of the buck converter.

A buck/step-down converter is a non isolated power supply topology. If you use an isolating transformer you would use something different.

 

[shawnmk]

which is exactly what I am trying to say:
it is not a buck transformer.
it is a transformer isolated version of the buck. Note that the forward converter can also be used in a boost configuration.

 

[moffy]

Perhaps if you provided a schematic this would clear up my confusion.

 

[moffy]

Do you mean Buck-Boost or just Buck? They are two different things.