Current Limiter Using Emitter Follower NPN Transistor

B

blackshadow

New Member

• Apr 28, 2011

• #1

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

 

C

carbonzit

Active Member

• Apr 28, 2011

• #2

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.)

 

B

blackshadow

New Member

• Apr 28, 2011

• #3

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?

 

B

blackshadow

New Member

• Apr 28, 2011

• #4

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

 

C

carbonzit

Active Member

• Apr 28, 2011

• #5

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

Member

• Apr 28, 2011

• #6

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

Click to expand...

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.

 

B

blackshadow

New Member

• Apr 28, 2011

• #7

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

 

B

blackshadow

New Member

• Apr 28, 2011

• #8

Brevor said:

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.

Click to expand...

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

User Extraordinaire

Forum Supporter

Most Helpful Member

• Apr 29, 2011

• #9

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