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Can someone help me?

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semiconductor

New Member
I'm working on a project. It's basic one: POWER SUPPLY
It can provide output voltage: 24VDC, output current: 4A.
I use LM317 regulator, in association with op-amp LM301. This circuit diagram is included in LM117 datasheet, with a pass transistor (I use 2N2955)
(I downloaded it from somewhere by searching in www.google.com)
But now, I have some problems:
- When the load is decreased immediately. It would cause increase in supply current. The output current can gets over 4A (unwanted case). So I want to protect my power supply from overcurrent. I think that I can use a current limiter. But I don't know how to use it and now, I do not have a current limiter circuit diagram. Can someone help me? can you recommend me a current limiter circuit diagram!
- The second problem is: Can a current limiter protect power supply from short-circuit (R out is approximately zero ?)

Thank in advance!
Peter,
 

stevez

Active Member
You might try an LM723 which has a currrent limiting feature. Pass transistors are a must since this regulator is low power.
 

bogdanfirst

New Member
ok, i know most people use current limiting circuits, wich also protect from a short-circuit. but i also recommend putting a fuse at the output...calculate the fuse value so that it will be bigger then the output current you need, but to be small enough so that when a current that blows the fuses passes trough the circuit for a short time will not damedge the electronics. also the fuse value must be bigge then the current that the current limiter is set to, so that the fuse will not burn before the current limiter will do his job. the fuse is just as an extra safety meure in case something goes wrong .......
normally if you have a current limiting circuit you will not need a short-circuit protection circuit. but in some cases the current limiters are not fast enough most work by descreasing the voltage of the output, so if your suply has the minimum voltage value bigger them 0, you still can have a high current that will destroy your devices and power suply.
 

kinjalgp

Active Member
Current limiter is better than using fuse. With current limiter you are saved from replacing the fuse every time you cross the limit.
 

bogdanfirst

New Member
i didnt say that you need to replace the current limiter with a fuse. i just said to add a fuse, along with the current limiter circuit. it is safer this way.
 
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