Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Request DIY Constant Current Circuit

Status
Not open for further replies.

svarbanu

New Member
Hi
Could any one post a circuit where the user feeds the required ampere of constant current? output range is 1 microA to 15 microA and 10 to 30 Vdc.
 
You can have one or the other but not both at the same time.

A simle LM317 can be configured as a constant current device but probably not at uA levels. What are you trying to do ?
 
Sorry the range is 1 to 15 milliamps.

I have made a circuit with lm317 and variable resistor to achieve the output range but i need some kind of input mechanism and feedback circuit to maintain the constant amperes for automating this. I am trying to do anelectrolysis which needs constant current.
 
If you use the LM317 in constant current mode, it will automatically maintain a constant current. There is a schematic and calculation in the datasheet which shows this.

I've used them before without a problem to maintain a constant current into a string of series LED's
 
Ok. but during electrolysis the conductivity of electrolyte increases due to more ions in solutions after lapse of some time. i need to avoid this. so i am guessing some kind of digital rheostat with feedback? also how do i input the required amount of milliamps into the rheostat?
 
I think you might be getting your amps and volts mixed up.

If you set the LM317 to say 10mA, it may start off with an output of 30v @ 10mA when the conductivity of the solution is low but reduce to 10 volts at 10mA when the conductivity of the solution is high. It will always try and maintain the 10mA.
 
you mean once i set the amperes by variable resistor at the beginning, the LM317 will automatically maintain this amperes irrespective of the voltage change?
 
Yes - obviously up to the circuit limits.

Without going through the datasheet I'll give you some theoretical values. Lets assume the dropout of the LM317 is 3 volts (it may be different)

With an input voltage of 30V, the output voltage will be 27 volts maximum.

Now set the current to 10mA with the external resistors, put a 1 ohm load on it, it will limit the current to 10mA
Put a 10 ohm load on it, it will still limit the current to 10mA
Put a 1000 ohm load on it, still 10mA limit
Put a 10000 ohm load on it, you'll now only have 2.7mA going through (27 volts into 10,000 ohms)

You may also want to heatsink the LM317 dependant on the input/output voltages and current required.
 
Ok. By limit i presume that you mean that it wont exceed the 10mA ? How do i keep it from dropping below 10mA ?
 
Ok. By limit i presume that you mean that it wont exceed the 10mA ? How do i keep it from dropping below 10mA ?

As already mentioned it will try and keep the current 'constant' - that's what 'constant current' means. The only limitation is the supply voltage, as it can't get above that (or indeed more than a few volts below that).
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top