After the Christmas holiday and the examination week, we have searched some infomation about the project circuit. We enhanced out understanding of the basic structure of the circuit design. We brought our own circuit to the meeting. Here as follows is the circuit we brout to the meeting.
But this circuit contains a 3-Terminal Adjustable Negative Regulator LM337, which has beyonds our study area at this level. The supervisor suggest us to find another circuit which can perform the similiar function but with an operational amplifier.
We search the Internet again and finally come up with a circuit meets all the requirements, which is shown as follows. The circuit is from http://www.electronicecircuits.com/electronic-circuits/regulated-power-supply-using-741-and-2n3055.
| PARTS LIST | |
| R1 | 6.8kΩ |
| R2 | 1kΩ |
| R3 | 10kΩ Potentiometer |
| R4 | 22kΩ |
| R5 | 10kΩ |
| R6 | 0.6Ω 1W |
| R7 | 330Ω |
| R8 | 2.2kΩ 1W |
| C1 | 2200µF 50v |
| C2 | 100µF 50v |
| C3 | 22µF 16v |
| C4 | o.1µF 50V |
| D1 | 3 Amp Diode |
| D2 | 3 Amp Diode |
| D3 | 1 Amp Diode |
| D4 | 6.8V 500mA Zener Diode |
| D5 | 6.8V 500mA Zener Diode |
| T1 | 2N1481 or D313 or 2SC1061 |
| T2 | 2N3055 |
| T3 | BC107 |
| IC1 | LM741 |
| TR1 | SEC 15V, 2AMP |
Brief understanding of the circuit:
- Rectifier diodes D1 and D2 along with capacitor C1 provide the main unregulated supply.
- D3, C2, R8 and zener diode provide a negative voltage supply for the operational amplifier.
- The non-inverting input terminal of LM741 is given a stable voltage by R3 which is the control to set the output.
- R4 and R5 form a voltage divider. A fraction of the regulated output is fed back via R4 and R5 to the inverting input terminal.
- The operational amplifier adjusts its output voltage so as to keep the voltage at the input terminals equal. Thus the output gets regulated.
- The output of 741 is amplified by a compound emitter follower T1 and T2.
- All the current flows through R6. If the load current exceeds 1A, the voltage drop across R6 exceeds 0.6 volts and T3 starts conducting. This bypasses the supply to T1 and T2 and the regulating action stops. The output voltage therefore starts falling when the load current exceeds 1A. Any of the output terminals can be grounded to get a positive or a negative voltage with respect to the ground.
