The high current regulator circuit can be delivering up to 3-amp load current continuously. The output voltage can be set in the range of 4V to 22V. Fine variation in the output voltage can also be done using a potentiometer VR3. The output current, ranging from 350mA to 3000mA can be varied by potentiometer VR1.
Circuit Description of High Current Regulator Circuit
The high current regulator circuit given here utilizes all the advantages of the operational amplifier LM3140 (IC1). It has very high input impedance, high gain, high CMRR, low drift, and high stability. The high current regulator circuit uses low-cost, high-performance NPN transistors which makes it suitable for high-current applications and is protected from overloads and short circuits which is indicated by LED2.
Any variation in the output voltage is sensed by IC1 and compared with the reference voltage to produce an error signal which in turn controls the output voltage. Thus, the output voltage is kept constant across the output terminals.
The bridge rectifier made from diode D1 through D4 rectifies voltage from secondary terminals of transformer X1 and fed to filter capacitors C1 followed by C2. Zener diode ZD2 and ZD3 provide the reference voltage of 10.2V (5.1V each) which is stepped down using an attenuator made from resistors R5 and R6 and variable resistor VR4 and fed to pin 3 of IC1. The temperature coefficients of the diodes cancel each other.
Transistor T1 supplies a constant current to zener diode ZD2 and ZD3. Therefore, the current through resistor R6 is also constant. The reference input to IC1 is set by VR4. The output voltage can be varied continuously by VR2 which is used as a coarse adjustment and VR3 as a fine adjustment.
IC1 drives the transistor Darlington pair comprising T3 and T4 to increase the output current up to 3A. Whenever the output current exceeds the set value, transistor T2 limits the output current. Transistor T5 is also switched on along with T2 to indicate the overload and short-circuit.
Capacitors C4 with C5 suppress the oscillations which are generated by the feedback. The capacitors C4 and C5 are discharged through R13, VR2, and VR3 whenever the output voltage decreases. Diode D5 bypasses the negative polarity voltage.
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PARTS LIST OF HIGH CURRENT REGULATOR CIRCUIT
| Resistor (all ¼-watt, ± 5% Carbon) |
| R1 = 1.5 KΩ, 1W
R2 = 390 Ω R3 = 2.7 KΩ R4 = 150 Ω R5 = 8.2 KΩ R6 = 5.6 KΩ R7 = 1.2 KΩ R8 = 1.5 KΩ R9 = 1 KΩ, 0.5W R10, R12 = 120 Ω R11 = 0.18Ω, 5W R13 = 1.5 KΩ, 0.5W VR1 = 1.6 Ω, 6W VR2 = 10 KΩ, LIN. VR3 = 500 Ω, LIN. VR4 = 5 KΩ |
| Capacitors |
| C1 = 3300 µF, 35V (Electrolytic Capacitor)
C2 = 0.33 µF (Ceramic Disc) C3 = 0.1 µF (Ceramic Disc) C4 = 47 µF, 40V (Electrolytic Capacitor) C5 = 0.1 µF (Ceramic Disc) |
| Semiconductors |
| IC1 = LM3140 (Operational Amplifier)
T1 = BC177 (General Purpose silicon, PNP transistor) T2, T3, T5 = SL100 (Medium power silicon NPN Transistor) T4 = 2N3005 (Silicon NPN Power Transistor) D1 – D4 = 1N5404 (Rectifier Diode) D5 = 1N4003 (Rectifier Diode) ZD1 = CMZ8 (Zener Didoe) ZD2 = CAZ, 5.1V (Zener Didoe) ZD3 = CMZ 5.1V (Zener Didoe) LED1, LED2 = Any Color LED |
| Miscellaneous |
| X1 = 230V AC Primary 0-18V, 3A Secondary TransformerSW1 = DPDT Switch
F1 = 600mA Fuse |