Current source is needed

[solomhamada]

Hello .. I'm new here guys

I'm in a serious big problem

I need a constant current source. And thought they say it's easy .. I don’t know how !

The load is varying .. so plz help me .. any circuit I have found varied the output current with the load!!!!!!

SO, I'm in deep big shity problem

So .. help me , cuz I'm sinking here!!!!

Solom hamada

 

[Styx]

wow

All I see now is read!!!!!!111!!!!one!!!

seriously annoying!!!

need a bit more infomation.
You can get extreamly good current-source diodes for upto 5mA
Current mirrors handle cunstant current upto 100mA

then you start getting into control.

 

[audioguru]

Your font size and colour are blowing everyone away!
A current source circuit is simple and millions of them and descriptions about how to make them are on Google.
Nobody can help you since you don't specify the most important requirements such as voltage and current, nor how much they vary.
An ordinary 1M resistor can supply a constant current of 100uA to a load at 1V, from a 101V supply.
Is that what you want?

 

[solomhamada]

sorry for the !s

hi

sorry , i dont get what you want to say in ur reply


can u tell me more?

 

[solomhamada]

specifications!

hi again,

sorry for the annoying font guys

but as i said .. I"m new

well, you asked for the specifications ,

i need a max 10 volts voltage and a constant 10 mA current in a PT100 tempreature sensor that vary starting from 100 ohms at room tempreature.

Honestly, i dont know many details, but .. any one who needs info to help me .. plz ask me !

thx for the advice and for the efforts

solom hamada

 

[JimB]

A PT100 temperature sensor has a resistance of 100 ohm at 0 degC, and 138 ohm at 100 degC.

Putting a current of 10mA through 100ohm will dissipate 1watt, resulting in the sensor heating up and not reading the correct temperature.

I think you need to re-evaluate your current requirements.

JimB

 

[audioguru]

The temp sensor will send out smoke signals with such a high current.
Didn't you look on its datasheet?

Edit: Wait a minute! 10mA through 100 ohms is only 10mW, not 1W.

 

[mstechca]

Hello .. I'm new here guys

I'm in a serious big problem

I need a constant current source. And thought they say it's easy .. I don’t know how !

The load is varying .. so plz help me .. any circuit I have found varied the output current with the load!!!!!!

SO, I'm in deep big -BEEP-y problem

So .. help me , cuz I'm sinking here!!!!

Solom hamada

First of all, I dont appreciate people that use swear words, especially when it is in a post. Secondly, Black is the colour to be used, not green, blue, or red. Black is the easiest colour to read. Thirdly, you need to specify your input voltage range, and what current is required.

 

[Russlk]

This is a constant current 10 mA source. R3 is the load. If the load has a positive temperature coefficient, the power in the load will cause the resistance to increase which causes the power to increase- etc. - etc.

 

[audioguru]

the power in the load will cause the resistance to increase which causes the power to increase- etc. - etc.

Huge sketch with weird values for resistors (400, 4k).
Do you think that only 10mW will cause its resistance to runaway?
I couldn't find its datasheet, but if it is anything like a 2N3904 transistor with a thermal resistance from junction to ambient of 200 degrees C/W, then with 10mW it will increase its resistance with a 2 degrees C error.

 

[Styx]

just buy a current mirror

 

[JimB]

Edit: Wait a minute! 10mA through 100 ohms is only 10mW, not 1W.

Doh!

P = I ^2 x R

JimB