dc current limit without heat

[ataul]

hi friends,
I want a dc constant current limiting circuit without so much heating any components for my lead acid battery charger. have any idea to solve my problem?
please help!

 

[JimB]

Then minimise the volt drop across your current limiter.

W = V x I

Fundamental law, you have to live with it.

JimB

 

[Nigel Goodwin]

Or use a far more complicated PWM charging scheme, this will reduce the amount of heat that needs dissipating.

But essentially laws are laws and you can't get round them, just 'fudge' them a little.

 

[ataul]

Or use a far more complicated PWM charging scheme, this will reduce the amount of heat that needs dissipating.

But essentially laws are laws and you can't get round them, just 'fudge' them a little.

Thanks for reply
yes i know pwm tecnique, but i have not any practical circuit diagrams,
I work with some pwm circuit but i can't manage it. current controling is easy but keep it constant with varying load is dificult. feed back voltage manage from shunt is another problem. so i looking for practical circuit diagrams. I know fundamental low but that is important for beginners!

best regards

ataul.....

 

[Hero999]

It sounds like you require fold-back current limiting but you haven't stated the supply voltage or trip current.

 

[Styx]

Thanks for reply
yes i know pwm tecnique, but i have not any practical circuit diagrams,
I work with some pwm circuit but i can't manage it. current controling is easy but keep it constant with varying load is dificult. feed back voltage manage from shunt is another problem. so i looking for practical circuit diagrams. I know fundamental low but that is important for beginners!

best regurds

ataul.....

That is why a true current source has an effing big inductor any change in load (as long as teh resultant voltage doesn't get too close to the source voltage rail) is fine.

A simple chopper cct is all that is needed with a suitable current-sense in the coil free-wheel path

 

[Hero999]

If you want simple how about this electronic fuse circuit?

I know it's not the best solution but it's cheep and cheerful and if you're cleaver you can incorperate it into a simple voltage regulator

 

[akg]

i don't understand the connection around D1

 

[Dr.EM]

I think its actually a shunt regulator.

 

[Hero999]

No, it isn't, I'll give you a clue, D1 is a thyristor, it should be a sensitive gate type.

 

[Styx]

isn't that just a crowbar cct

 

[ataul]

If you want simple how about this electronic fuse circuit?

I know it's not the best solution but it's cheep and cheerful and if you're cleaver you can incorperate it into a simple voltage regulator

hero999
thanks for circuit diagrams.but I don't understand how it works as a constant current mode? I think in put voltage must be ac(~) ok i will test it in my lab.
I told u my own plan,at first i make a voltage controled pwm circuit and invert this pwm signal to drive npn or n chanel power mosfet in switch mode in negetive side and place a very low velue shunt resister for low heat desipation and amplify shunt voltage from respect to ground and feed this voltage as a pwm control voltage. is it ok?or not ok?

* sory for my poor gramer & speling.

best regards
ataul

 

[Hero999]

isn't that just a crowbar cct

Nope.

ataul,
This circuit acts like an electronic fuse, it's probably the easiest way to solve your problem it'll cut off the power when overloaded.

Yes you could go for a switching regulator but why do you need to, is there any particular reason you want a constant current source?

 

[Styx]

Nope.

ok, I have seen the position of the load so it cannot be a crowbar. BUT how does the thyristor stop conducting then?

 

[Hero999]

Alright I'll explain.

Tr1 carries most of the current to RL, normally R1 biases Tr1 on.

R2 is a current sensing resistor when the voltage across it exceeds about 0.6V it turns on D1 which diverts Tr1's base current through RL causing it to turn off.

D1 will remain on until the power supply is interrupted.

C1 and R3 provide a short time delay to prevent any capacitance in RL from tripping it.

 

[Styx]

you could of just said it was a non-resetable electronic fuse

 

[ataul]

Nope.

ataul,
This circuit acts like an electronic fuse, it's probably the easiest way to solve your problem it'll cut off the power when overloaded.

Yes you could go for a switching regulator but why do you need to, is there any particular reason you want a constant current source?

hero999

Again thanks for promt reply, now i understand your posted circuit. This is fine
for electronic fuse if it modify to auto reset then it will be meet my purpose.
because when i drow over current tr1 will cut off by scr and if auto reset again and again it will act as a constant current source but tr1 must be full on in every time resulting nominal heat will produce by tr1. My aim is how can
minimise power desipation as low as posible. whatever out put current be pulsed it will no problem for charging 12v lead acid battery.
My reson is charging a lead acid battery in near heat free constant current mode. linear constant current circuit prouduce much more heat in small box it is very unlike for me.

thanks again

ataul...

*friends sory for bad grammer & speling

 

[Hero999]

you could of just said it was a non-resetable electronic fuse

No it isn't, it's a resetable electronic fuse, you just disconnect and reconnect the load and it resets - D1 doesn't remain latched when the current's interrupted.

ataul,
This circuit isn't suitable for your application, you do require a proper switching power supply, which is easy to find using Googling for "constant current switching regulator".

 

[Styx]

No it isn't, it's a resetable electronic fuse, you just disconnect and reconnect the load and it resets - D1 doesn't remain latched when the current's interrupted.

disconnecting is akin to a reset

 

[Hero999]

Well how would an automatic reset work then?

It wouldn't be safe to turm it back on when it's short circuited would it?