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getting a constant a current

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no regulators
:confused: Do you mean no integrated circuit regulator? If you are trying to get a constant 5.1V from a 6-9V supply then, by definition, you are creating a voltage regulator.
 
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@doug
i guess the circiut is only applicable when there is load :(
I'm not sure what you mean. It works with or without a load.

A better circuit is attached, which adjusts the voltage depending on the current through the load so that the load always gets the same voltage.

That said, you won't get 5V1/200mA output from 6V using the topologies shown - there simply is not enough voltage headroom. You'll have to use a more intelligent approach than the emitter follower and current sense as each of those drop at least 0.6V.

What has you learnt in class? Perhaps you have learnt about operational amplifiers? You can design one using transistors and this can be used to regulate the current without such a large voltage drop.
 
@alec
i cant use IC or OP amps as a condition

@ doug
**broken link removed** can limit the current in my circiut.. even i increase and increase the voltage?
 
@ doug
**broken link removed** can limit the current in my circiut.. even i increase and increase the voltage?
That's what the lower transistor is doing. As the current increases, that transistor starts to turn on which will reduce the drive to the upper transistor, thereby limiting the current. Feel free to simulate it.
 
Make R2 3.9 ohms. The emitter goes to the top of the load. Make it 100 ohms. The bottom of the load resistor goes to the top of R2.
 
here is a new circuit View attachment 67217

i get a constant Vout and Iout but the output current is too small and i need at least 200mA .how can i amplify it ?

if i change the value of the resistor in R1 to 10Ω but it gives me a high Vout

:confused:

thanks
 
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You really should learn how to use an ammeter. Here's a start:
And **broken link removed**
 
why i get a mV as output?
Because you're connecting your voltmeter across the current sense resistor and not the points marked 'LOAD'
 
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**broken link removed**


if i series an ammeter in the emitter
the current in the emitter side of the transistor is the same as the current in my load?

is this right? :confused:
 
here's another favorite of mine and very stable, down fall is that the LM317 seems to have a high overhead, that is it needs about 6 volts to work
 
the LM317 seems to have a high overhead, that is it needs about 6 volts to work
According to my LTSpice sim it's just under 3V. Perhaps there are different Spice models out there?
 
According to my LTSpice sim it's just under 3V. Perhaps there are different Spice models out there?
I got 3.3V across the lm317 and 1.24V across R1 at the knee of IR2 for an overhead of 4.5596V for the current limiter set up, add to that 2V across R2 and you get the 6.5 volts I incorrectly referred to as overhead, good catch.
If you are getting under 3 across the LM317 and I'm getting 3.31516V, it's probably the LM317 model, I use the LM317psp from regulator.lib.
Kinarfi
 
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