Figure 5.7, Voltage Regulator Circuit with Current Fold Back. A transformer is shown on the left. The top of the secondary goes to the top AC connection on the bridge. The bottom of the secondary goes to the bottom AC connection. The negative output goes to common. The positive connects to the positive of C1. The negative of C1 goes to common. The positive of C1 goes to the collector of an N P N transistor, Q1. The emitter of Q1 goes to one end of a resistor, R5. The other end of R5 goes to the positive output terminal of the power supply. The positive output terminal connects through R2 to the top of a pot, R3. The bottom of R3 connects through R4 to common. Common is the negative output terminal. The positive of C1 connects to the collector of Q2, another N P N transistor. The emitter of Q2 connects to the base of Q1. The base of Q2 connects to a resistor, R7. The other end of R7 connects to the output of an operational amplifier. The inverting input goes to the wiper of R2. The positive voltage supply for the op amp goes to the positive of C1. The negative voltage supply goes to common. The positive of C1 goes to the drain of an F E T, Q3. The source of the fet goes to one end of R1. The other end of R1 goes to the cathode of zener diode D5. The junction of R1 and D5 connects to the gate of the fet. The junction of R1 and D5 also connects to the noninverting input of the op amp. The junction of R5 and the positive output of the supply connects to the emitter of an N P N transistor, Q4. The base of Q4 connects to one end of R6. The other end of R6 connects to the junction of R5 and the emitter of Q1. Q4 is the current limiting transistor. The base of Q4 also connects to the cathode of D6. The positive end of C1 connects to one end of R8. The other end of R8 connects to R9 and the other end of R9 connects to common. There is a capacitor C2 in parallel with R9. The anode of D6 connects to the junction of R8, R9, and C2. R8, R9, and D6 are the fold back circuitry. The collector of Q4 connects to the base of Q2. End verbal description.
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