Current Limiter Testing of Zener Diodes.3 Amp LM741 Op-Amp Constant Current Source.
How to Test Silicon Controlled Rectifiers, Triacs.LM317 High Power Constant Current Source Circuit.LM334 Constant Current Source with Resistive Sensors.LM317 Adjustable Voltage, Current Boost Power Supply.Arduino Controlled Power Constant Current Source.Arduino Measures Current from Constant Current Source.This completes our introduction to the LM317 constant current source. 5 shows the LM317 trickle charging a 5-volt NiCd battery pack. Remember this analog current regulator is in series with the load and power will divide.įig. Don't go wild with a large Vcc powering a small voltage load. Note the LM317 will get hot - power not consumed by the load will be dropped by the pass transistor, LM317 etc. The load doesn't change the current from a constant current source in fact I could short out the output and maintain 120mA. 5 we have only a single LED yet the current remains 120mA. VOUT the load has no effect on the current. In Fig 4 we removed a LED for a voltage drop on the load at 6.4V restoring current regulation. This makes LM317 useless as a constant current source below 5-volts.
1 shows the LM317 used as a series pass constant current source with a single resistor. With only three pins as shown above, one can produce a current of about 1-amp max. While designed as a variable voltage regulator, it will double as a stable constant current source. The next series of circuits will use the LM317. See Constant Current Circuits with the LM334. The downside is the LM334 can only source 10mA. A constant current circuit can also be used as a current limiter.Įarlier we discussed various constant current circuits using a PNP transistor, a LM741 OP-AMP and settled for a LM344 constant current source as the most stable. A constant current source (CCS) in electronics is a device/circuit that produces a constant value of current regardless of source voltage or load resistance.