The circuit shown in figure 1 serves to control a servo motor with a current of up to 200 mA. The output transistors can be BD135 and BD135 that allow controlling currents up to 500 mA without problems. The power supply must be symmetrical and the resistor R3 is calculated to obtain the desired feedback for the control. Darlington transistors can be used at the output as the TIP115 and 110 pairs, in which case larger currents can be controlled, reaching 1.5 A. Other operational ones can be used.
