current Driver

[Pao]

hi guys,

need help finding a variable current driver circuit.
thanks in advance

Pao

 

[Nigel Goodwin]

Again, give more information - such as what range of current, and to do what!.

 

[Pao]

i need a 0-20mA variable current driver that a sawtooth waveform of 250hz and 1hz and a squarewave of 1-100hz can pass. Ranging from 1-10V. I need it cause i have a project or should i say for extra credit to make a dead frog leg kick using the schematic below but apparently it lacks current seeing that it only powered by a LM324.

I know what you guys are thinking why not change the whole circuit instead of putting a current driver right? Well one reason is that the hint/ requirement my teacher gave is that we cannot change the said circuit. And 2nd I have no background or idea on how a current driver works, its a good opportunity to learn. Although Im currently researching for it. so thankz

 

[Nigel Goodwin]

What's the reason for IC10?, presumably it's supposed to be a constant current source?, but isn't your whole objective to provide a varying current?.

However, a simple NPN transistor, base to the three diodes, collector to +12V, will provide a higher current drive from it's emitter.

 

[Pao]

IC 10 was supposedly a current limiter of 20mA but it doesn't work.

 

[Nigel Goodwin]

IC 10 was supposedly a current limiter of 20mA but it doesn't work.

I wouldn't expect it to!.

 

[Pao]

I wouldn't expect it to!.

LoL well i did and got burned with it. My friend that gave that circuit now has the nickname LMspecialist LoL
got any suggestion on NPN X'sistor i could use i found this NZT651 but Im not too sure.

 

[Nigel Goodwin]

Any small signal NPN should do, and use a resistor for a current limiter!