LM741 op amp as 3 amp current source.
Fig. 1

3 Amp LM741 Op-Amp Constant Current Source

by Lewis Loflin

LM741 op amp circuit uses two PNP transistors in Darlington configuration for 3 amp constant current supply or limiter.

The circuit is Fig. 1 we have seen before. See Constant Current Circuits with the LM334.

Here is an improvement over the design. The circuit is solid with Ic set only by the value of RE. The shortfall is the drive current from the LM741 is limited.

LM741 op amp as 3 amp current source.
Fig. 2

Fig.2 uses an additional power PNP transistor in a Darlington configuration. With a Rset value of 0.25 (two 0.5 resistors in parallel) I got almost 3.8 amps.

Note that Rset and Q2 can get hot depending on the load voltage.

Note once again: this is not a voltage regulator! Voltage is set by load resistance R. the resistance of R times Ic should be less than 10-volts if using a 12-volt supply. This circuit can handle 30-volt power supplies.

Be realistic - don't use a 30-volts input to operate a 5-volt load at 3 amps. While 15 watts are used by the load 75 watts are wasted as heat in Rset and Q2.

Keep the supply voltage about 5-volts above the desired load voltage.



Photo LM741 op amp as 3 amp current source.
Fig. 3 Test circuit.

Photo LM741 op amp as 3 amp current source.
Fig. 3 Test circuit.



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