Current Limiter Using Emitter Follower NPN Transistor

[blackshadow]

Hi,

i would like to implement a current limiter using transistors particularly emitter follower. is there a way i can saturate the transistor such that the voltage source is readily avaialble in the load?

in some design, there is a reference diode at the base of the transistor

thanks

 

[carbonzit]

Try the circuit shown here. I just built this, for use as a LED tester, and it works well. Keep in mind it's limited to the power dissipation of the transistor. (This circuit was suggested by another member here.)

 

[blackshadow]

thanks carbonzit. however, in my design, my load is located at the emitter side. my problem is that the voltage is limited to the voltage input at the base minus the Vbe. this is because i could not saturate the transistor at this state. do you have any idea?

 

[blackshadow]

i posted another thread which include the circuit. kindly refer to it. thanks

 

[carbonzit]

Just curious: why is it so important that your load be on the emitter side? All the current is going to go through the transistor and the load, regardless of which side it's on.

 

[Brevor]

my problem is that the voltage is limited to the voltage input at the base minus the Vbe.

Thats about as good as you can get. If you can redesign your circuit maybe you could use a P channel mosfet instead of a transistor.

 

[blackshadow]

i needed my load to be grounded on the other side.

 

[blackshadow]

Thats about as good as you can get. If you can redesign your circuit maybe you could use a P channel mosfet instead of a transistor.

thanks for the input brevor.

i was just thinking how would i deal with the negative feeback mechanism to limit further increase in the current flowing.
do you have ideas?

 

[Ian Rogers]

Why not use a PNP current mirror AFTER the NPN to give you these levels?

or try this type of current limiter **broken link removed**

Ian