Figure 5.8, Voltage Regulator Circuit with Floating Error Amplifier. This circuit has two transformers although in an actual manufactured unit they likely would be two secondary windings on one transformer. T1 provides power for the regulator circuit. The secondary has a center tap. The top goes to the anode of D1. The bottom of the secondary goes to the anode of D2. The cathodes of D1 and D2 connect together and connect to the positive side of a capacitor, C1. The negative end of C1 goes to the center tap. The center tap connects to the negative output terminal. The positive of C1 connects to the collectors of both Q2 and Q3. The emitter of Q3 connects to the base of Q2. The emitter of Q2 goes to one end of R3 which is the over current sensing resistor. The other end of R3 goes to the positive output terminal. The base of Q4 goes to the junction of Q2 emitter and R3. The emitter of Q4 goes to the junction of R3 and the positive output terminal. The collector of Q4 goes to the base of Q3. We will come back to the base of Q3 after we describe the error amplifier (op amp) power supply. The secondary of T2 has a center tap. The upper end of the secondary goes to the upper AC input of a bridge rectifier. The lower end of the secondary goes to the lower AC input of the bridge. The positive output of the bridge goes to the positive end of C2. The negative of C2 goes to the transformer center tap. The negative output of the bridge goes to the negative end of C3. The positive of C3 goes to the center tap. The center tap connects to the positive output terminal of the supply. The junction of the positive bridge output and the positive end of C2 is marked plus twelve volts. The junction of the negative bridge output and the negative end of C3 is marked minus twelve volts. The plus 12 volt point goes to the drain of a f e t, Q1. The source of Q1 goes to R1 and the other end of R1 goes to the cathode of a zener diode. The gate of Q1 goes to the junction of R1 and the zener diode. The anode of the zener goes to the center tap of T2, also the positive output. The plus 12 volt point goes to the positive power supply pin of the op amp. The minus 12 volt point goes to the negative power supply pin of the op amp. The inverting input goes through R4 to the center tap. The noninverting input goes through R5 to the cathode of the zener. The noninverting input also goes through a pot connected as a rheostat to the negative output terminal. The output of the op amp goes to one end of R2. The other end of R2 connects to the base of Q3. End verbal description.
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