2nd meeting: Determination about the circuit

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.

1st meeting: brief idea

Today my partner and I went to meet our supervisor for the first time in order to get a better understanding of the puepose and check some details of the project. The supervisor introduced the main functions of the project and the basic structure of the circuit to us. He also made it clear to us about what to do to prepare for the project which will come in the first 5 weeks of next semester. He suggested us to search google for some circuits, and simulate them on computer to see whether it can meet the requirements of the project. After the determination of the circuit, we should come up with an electronic component list of what we may need to build out circuit, ad hand it in to the technicians in the lab.

An ideal constant voltage power supply would have zero output noise at all frequencies. Thus, as shown in the figure below, the output would remain perfectly constant in spite of any changes in the output current demanded by the load.

A simple unregulated power supply consisting of only a rectifier and a filter is not capable of providing a ripple free DC output voltage whose value remains reasonably constant. In this project,to obtain such a approximation of the ideal output with characteristic of the figure, some type of control element (regulator) must be included in the supply.

In practical, a transformer can drop a high user-voltage to a low AC signal, and then a bridge circuit can rectify such a small AC signal to a DC input, but there is still some rest AC wave cannot be rectifies to affect the output. Thus now, through discussion and analysis, our supervisor suggested us ignore the transformer and bridge circuit. What we need to design is a regulator circuit works with a DC input provided by the power supply on lab bench along with a small AC signal as the input noise, so that we can check whether the output voltage can be regulated to a constant DC voltage regardless of the AC ripple in the input. For the sake of offsetting the noise (the small AC signal in the figure), we can invert the AC signal to a completed opposite direction AC signal. And then the original and inverting AC noise are able to counterbalance each other, so that only the constant DC voltage can be left and output.

What is regulated linear DC power supply?

When we received this project, firstly we should know the definition and functions of the regulated DC power supply.

A regulated DC power supply can be also named a (voltage) regulator. It consists of a embedded circuit which may be a simple "feed-forward" design or may include negative feedback control loops. The circuit should use some electronic components, like resistors, capacitors, zener diodes, diodes, transistors, operational amplifier and so on.

Depending upon the designing of the circuit, a regulated power supply can be used to regulate one or more AC or DC voltages. However, this project only focuses on the regulated linear DC power supply. The designed circuit of this project should be able to power the load which must be operated within certain power supply limits. The output from the regulated linear DC power supply should be able to be adjusted linearly within a certain range and nearly always DC voltage regardless of the AC ripple from the input.

Actually, voltage regulators have been widely applied in variety of fields, from electronic products to electrical systems. For instance, if without voltage regulators in the computer power supplies to stabilize the DC voltages, the processors of the computers will make bugs and generate error and irregular signals to the following system units, then the system of the computer will be in disorder and the whole computer cannot work normally.