Does anyone know of a Voltage Controlled Current Source IC? Or do you know how I can build one with as few other components as possible taking up a minimal amount of space?
current range needed is from 0mA to 350mA
Electronic – Voltage Controlled Current Source integrated circuit? Exists
constant-currentcurrent-sourcedriveroperational-amplifier
Related Solutions
This circuit uses a FET to drive a transistor, but you can replace the transistor with a darlington, so that you get kind of an hybrid superdarlington.
This should solve the opamp output current limitation.
For an "all-in-one" option, the ADB8810 looks pretty close to the kind of thing you want. If you search for "programmable current" on e.g. Analog Devices, Nat Semi, Linear Tech, TI, Maxim, etc you will probably find quite a few options like this.
Another option would be to use a DAC (or indeed a potentiometer if no uC involved) to control an opamp with transistor set up as a current source.
For ~1000 levels you would need 10 or more bits, so this would be pretty cheaply done.
Something like this circuit might do:
The transistor could be any NPN or MOSFET (with appropriate Vth) or darlington capable of sinking the necessary current (EDIT - as Wouter mentions the 2N2222 is not a good choice, something in a package rated for higher power e.g. a TO-220 package would be better)
Opamp should be rail to rail in/out if possible to make things easier.
The 1 ohm sense resistor can be changed to suit the current required. This was set up to output 1mA per 10mV in, so 3.5V produces 350mA (at the opamp input it is actually 1mA per 1mV, the resistor divider divides the DAC input by 10)
Best Answer
Since you haven't specified output impedance, accuracy, or much anything else except as few components as possible, this is what you want:
This makes use of the propoerties of a bipolar transistor where its collector current is largely not dependent on collector voltage, and the B-E drop is reasonably fixed. The voltage on the emitter will be close to Vin + 700 mV. The power voltage minus that will be across the resistor. That voltage divided by the resistor value will be the current thru the resistor, which is close to the collector current.
Let's say you want the 0-350 mA output current range controlled by a 3.5 V range of voltage. In that case, R1 would be 100 Ω, and the control voltage range would be PWR - 700 mV to PWR - 4.2 V.
This isn't what I would call a "precision" current source, but it is actually good enough for many real applications. It can be made more precise by putting a opamp around it to more accurately control the voltage across the resistor. Once you have that, you can use a PFET instead of a bipolar transistor because the feedback will compensate for the G-S voltage not being as fixed as the B-E voltage of a bipolar transistor. The advantage of a FET is that the drain current equals the source current (and therefore the resistor current), whereas with a bipolar the collector current is the emitter current minus the small base current. However, since your primary goal is simplicity without mention of other parameters, such more complicated topologies would just be overkill.