LM324 PWM Control Motor Speed
This uses the LM324, a 14-pin DIL IC containing four individual op-amps and running off a single-rail power supply. The sawtooth is generated with two of them (U1A and U1B), configured as a Schmitt Trigger and Miller Integrator, and a third (U1C) is used as a comparator to compare the sawtooth with the reference voltage and switch the power transistor.
Rather than have the fourth op-amp sat there doing nothing, it’s used as a voltage follower to buffer the reference potential divider. The high input and low output impedance of this draws very little current from the PD, so high value thermistors can be used in the thermal version of this controller.
Other Link
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