Short circuit protect power supply

can anyone help me simply explain how the transistor 9013 work....
i have try b4... this circuit can work properly....
when short circuit occur the led wll turn on....
tq....

Hello COG,

good to see you back again !

first tell me what is the output voltage you have set from the LM317,

the 1 ohm resistor is a current sense resistor and it triggers the transistor (9013) when the out current is more than or equal to 1 amp, in other words the transistor is off when the O/P current is below 1 amp.

the 1 ohm current sense resistor will develop 1volt when 1 amp current flows thru it and this 1 volt turns on the transistor ( normally transi requires 0.65 volt to turn on)


hope you have understood


Arun

the input voltage(-) ,1ohm and output voltage(-) are connected at the same line right then where is the current came from...?
isnt when short between the output voltage(+) and output voltage (-) the current flow form output voltage(+) to base of 9013...?
if i change the 1ohm (1watt) resistor to 1ohm(1/4watt)...?any different between this two...?
thanks a lot yr reply...Arun

difference is heat dissipation, 1/4Watt resistor wont be able to handle 1Amp of current and ultimately it will burn.

I would suggest u use a current limiting resistor between the base of the transistor and the ground. This is because as arun suggested, the base emmiter junction would break down when the voltage across the 1 ohm resistor crosses ~0.65V and in the case of ur present circuit, it would try to maintain the voltage across the 1 ohm resistor to that voltage by sinking excess current through itself. So if ur Vin can source even 1A current, the rest of the 0.35A will flow through the base of the transistor damaging it .

i have some quenstions need to ask....
1. the input voltage(-) ,1ohm and output voltage(-) are connected at the same line right then where is the current came from...?
2. isnt when short between the output voltage(+) and output voltage (-) the current flow form output voltage(+) to base of 9013...?

Mr pdi33...
u suggest me use a current limiting resistor between the base of the transistor and the ground is lik this correct or not...?

the circuit

COG,
well, the current limit resistor in the circuit i proposed is as below,

thank Mr Ajay, Mr Pdi33 and Mr Arun a lot...

em... i hav another questions about this circuit...
i use lm317 to make 5V fix supply but the current is 2A...
will 2A too big...?
have any connection to reduce the current...?
the input voltage is 36V...
hope anyone can give me solution...
thx...