getting a constant a current

[Rin]

how to get a constant current like 200mA if the input ranges from 6v-9v..

is this possible?

 

[dougy83]

A current source provides a constant current. Choose a topology that suits your current and voltage overhead requirements. Some examples are shown on https://en.wikipedia.org/wiki/Current_source

 

[Rin]

should i tap my current out in the emmitter side same as voltage out?

or in the collector side ?

 

[dougy83]

Please provide a schematic to explain what you are referring to.

 

[Rin]

here sir

View attachment 67174

 

[dougy83]

For that circuit your load is connected between the supply voltage and the collector of the transistor as shown in the attached circuit (copied from the wikipedia page linked above).

 

[Rin]

what if i tap my load in the emitter side that can be my Vout and Iout?..ive checked in the multisim and it gives me sufficient output

 

[dougy83]

what if i tap my load in the emitter side that can be my Vout and Iout?..ive checked in the multisim and it gives me sufficient output

If you connect a load of the emitter side (in series with emitter resistor) the load will affect the current drawn. The only case this is acceptable is if the load has a constant resistance, or is much smaller than the emitter resistor: in the former case the current will remain constant, in the latter, it will not change much.

 

[kinarfi]

My favorite constant current device (CRD) is a jfet

 

[kinarfi]

My favorite constant current device (CRD) is a jfet

 

[Rin]

thanks guys

how can i maintain a current if no R2 in the circiut or no load?

i tested it on multisim i remove the R2 in the circiut and it gives me 0A

how can i make a same current like 200mA with R2 and 200mA with NO R2 in the circuit?

**broken link removed**

 

[ericgibbs]

thanks guys

how can i maintain a current if no R2 in the circiut or no load?
You cannot with that circuit

i tested it on multisim i remove the R2 in the circiut and it gives me 0A
It would the transistor is OFF

how can i make a same current like 200mA with R2 and 200mA with NO R2 in the circuit?
You cannot , R2 sets the 200mA

**broken link removed**

What is the 200mA going to be used for,?

 

[Rin]

200mA a sample current rating from the circuit

is there any adjustments in the circiut that i can make to make it possible?

 

[ericgibbs]

200mA a sample current rating from the circuit

is there any adjustments in the circiut that i can make to make it possible?

I know it may sound as though I am being difficult..

Whats the sample current for? give more details of the application.

 

[Rin]

i am making a simple supply with no use of regulators that can be inputed by 6v-9v and will regulate a 5.1v w/ a current of 200mA ..and there are two conditions
a)w/ load-R2 is not remove
b)no load-R2 is remove or short circiut

 

[ericgibbs]

i am making a simple supply with no use of regulators that can be inputed by 6v-9v and will regulate a 5.1v w/ a current of 200mA ..and there are two conditions
a)w/ load-R2 is not remove
b)no load-R2 is remove or short circiut

With those conditions its never going to happen with that circuit

 

[Roff]

My favorite constant current device (CRD) is a jfet

Errmm...
That is a 200uA current sink, not 200mA.

 

[dougy83]

You really should try to understand how the constant current source circuit works.

 

[ChrisP58]

Do you really need a constant current?

Or do you really only need a constant voltage of 5.1 with a current capacity of up to 200mA? If so, then all you need is a simple LDO voltage regulator.

 

[Rin]

@chris
i need a constant voltage of 5.1 with a current capacity of up to 200mA ...no regulators

@doug
i guess the circiut is only applicable when there is load