power supplyvoltage-regulator
Is there a linear regulator that can follow a reference?
The broader problem I have is that I have an ADC with reference that can only source 50mA (I have no control over the ADC or reference circuit) but I have some sensors that are low impedance and measured with a Wheatstone bridge so I need the same reference voltage but more current.
I thought of doing this (below) but there must be an IC that does the job.
simulate this circuit – Schematic created using CircuitLab
Using an op-amp is probably the best way to deal with this requirement but you might be better with an emitter follower circuit: -
The op-amp will drive the NPN so that its emitter (Voltage across the load) is the same voltage as the +Vin pin on the op-amp.
I borrowed "The Photon's" drawing because although it was wrong, it was easily amended to show an emitter follower. If you did use a FET (N channel with source to load) this would work but you might find that Vin needs to be higher for it to work. BJT base drive only needs to be 0.6V above the emitter - I'd still recommend using an op-amp with rail-to-rail output capability so that Vin can be a bit lower.
I'm also assuming the op-amp is powered from Vin and GND.
If you had a short in place of the potentiometer, you should have read 1.25 volts (or so) at the output of the LM317, not 12.5 volts.
When you changed your meter to read current, presumably moving the red lead to the "10 Amp" socket, the meter would have very low resistance. When you then connected the meter between the LM317 output and ground, a very large current would flow, apparently causing the LM317 to explode.
If I recall correctly, the LM317 is spec'd to deliver 1 amp, with due regard to voltage drop, power dissipation, heatsinks and phase of the moon - that only states the current that it can safely carry under suitable conditions - it DOES NOT limit the current to that value!
The current measurement function of a multimeter should only be used with the meter connected in series with a load whose current drain you wish to measure. It must NEVER be connected directly across a power supply.
Best Answer
The requirement basically translates to the ability to source high current at a specified reference voltage.
A low component count way to implement this is to use a high power high current op-amp as a voltage follower, with the reference voltage at the non-inverting input.
For instance, the Burr Brown (now TI) OPA549 can deliver 8 Amperes continuous current with a suitable heat sink. With its 300,000 open loop gain, this should be sufficient for using the available low current reference to generate a stable high current output.
There are many other such high current op-amps, which dispense with the need for the external MOSFET.
From this page:
In other words, a voltage regulator IC is not required.