Constant Current Supply

[qwertycoolguy]

I have a need to build a constant current supply that can cater upto 15A with using 50V or more if needed. notice there is no fixed value for Vin.

Provided with a set figure this CCS must push that current through the load adjusting itself to the approphiate voltage.

the accuracy can vary from 0.5A to 1A.

Can someone please tell me if the following circuit is ok?



I would so much appreciate your ideas and comments. Please show me if my method is incorrect.

 

[Audioguru]

A low voltage zener diode is not accurate. Its voltage changes with temperature changes and changes with current changes (the supply voltage to its resistor). Use a voltage reference IC instead.
If you use a 3.3V reference IC and a 0.22 ohm resistor R2 then The minimum output voltage at 15A is about 5V and if the load resistance is low or shorted then the transistor heats with 675W!

How will you cool the thing?

 

[qwertycoolguy]

well, thank you for showing me that.

i think I need to find the minimum Load resistance. Afterwards I can decide if this design is suitable or not.

I also saw this other design where a switchedm mode IC has been hacked to create a Constant current source.



May be I can use a higher power IC replacing this switched mode IC and use the same mechanism. May be that would have a less chance of setting my room in fire?

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Or may be its normal this sort of a power supply get heated up this much? May be im supposed to use a huge sink and a fan?

I could even make that resister 0.1O ohms and reduce the power dissipation upto some extent

Could you please advice me?
It would help me a lot.

 

[Audioguru]

A linear power supply heats a lot when its input voltage is high, its output voltage is low and its current is high. A switcher does not heat much.
So use a switcher if you can find one or add a power transistor to the 3A one.

If you reduce the value of the current sensing resistor then that resistor does not get as hot but the active part of the circuit actually gets hotter.

What do you have that needs a constant current of 15A and a widely varying voltage?

 

[crutschow]

What is suppling 50V @ 15A?

 

[Audioguru]

What is suppling 50V @ 15A?

An off-hook telephone line hee, hee.

 

[qwertycoolguy]

well this is for purification of water, a social project. I am an embedded systems student and have zero knowledge in P/E. this is why I am little lost.

I was assuming that 15A 50V PSU.

Dear Audioguru,

Did u mean add a power transistor to the LM2576? if so, to where can that be done?

Well, from my replies can I go ahead and assume none of these would work and I gotto create my own switched mode PSU?
I dont have a time retrain to do this project. So thats okay too. I can do it at my phase.

Thank you for all your replies.

 

[Audioguru]

You did not say how constant current will purify water. I guess you will distill the water with heat and the electricity makes the heat? Then the steam is condensed into pure water.
Constant current is not needed. Heat can be made from AC or DC electricity.

 

[FvM]

Can you provide a link or other information about the water purification method you are trying to implement?

What's the input power supply for the circuit? Expectable voltage range, current capacity etc.