Basic: Rectifier and Voltage

1 - Rectifier AC

1.1 - Power in electric circuits.

In the electronic circuits of devices such as Radio-Cassette, Amlpy, color TV, VCD, etc. ... we use a DC power at different voltage levels, but outside of the devices plugged Zac is back plugs directly into 220V 50Hz AC power, so the electronics needed to convert a part from AC to DC voltage supply for the circuit on, converters include:

• Power transformer: low voltage from 220V down to the lower voltage such as 6V, 9V, 12V, 24V, etc. ...
• Rectifier: Changing the AC into DC electricity.
• Ripple filter circuit filters the rectified AC to DC power flatter.
• Circuit Voltage: Keep a constant supply voltage for the load consumption

General diagram of the power circuit.

1.2 - Rectifier sales cycle.

Rectifier sales cycle using a diode in series with the load consumption, the positive cycle => Diode polarized so that upon passing an electric current passes through diode and the load, the negative cycle, diode is broken opposite poles so there is no flow through the load.

Type the output voltage of rectifier sales cycle.

1.3 Rectifier whole cycle

The cycle Rectifier Diode used four questions in the sphere (also called the rectifier bridge) as shown below.

Rectifier whole cycle.

• In the positive cycle (of strings above the ocean, the bottom negative) current through diode D1 => through Rtai => end of the rope through the diode D4 of sound
• In the negative cycle, the voltage across the secondary coil reversal (first string on the negative, bottom positive) electric current through D2 => through Rtai => the sound of strings on the D3.
• Thus the two cycles are current through load.

2 - filter and rectifier circuit pressure deficit

2.1 - Circuit filtering capacitor.

After we obtained the rectifier DC voltage ripple, without the filter capacitor voltage ripple is not usable in the circuit, so in the power circuit, we have to mount the filter capacitor is value from several hundred to several thousand μF μF to the diode bridge rectifier.

Type of voltage DC rectifier in the two cases together and there is no convergence

• The above diagram illustrates the case of a power circuit and no capacitor filter capacitor filter.
• When the switch K open rectifier filter capacitor can not participate, so the voltage gain is undulating form.
• When the switch K is closed, rectifier with filter capacitor C1 participating sources, resulting in filter output voltage is relatively flat, if the capacitor C1 is the capacitance the larger the voltage at the output as flat, capacitor C1 in power often have several thousand μF value.

Illustrates: Power of the larger filter capacitor, the voltage output as flat.

• In the rectifier, filter capacitor if there is no load or a load of produce consumption is insignificant compared with the output of the transformer, the DC voltage gain is DC = 1.4. AC

2.2 - Rectifier's 2.

Rectifier circuit diagram of two sources

• To become a rectifier of 2 we must use the same values ​​of two capacitors connected in series, then play one of the voltage xoau way point between two capacitors => we will get 2 times the voltage increases.
• In the circuit when the switch K open rectifier circuit back to normal form.
• When the switch K is closed, the circuit becomes of second rectifier, and the resulting output voltage is obtained 2-fold increase.

3 - fixed voltage regulator circuit

3.1 - fixed voltage regulator circuit using Zener Diode.

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33V voltage regulator circuit to create a fixed voltage supply circuit in Televisions mystery tune

• Since no fixed source of 110V through a resistor R1 and reduce the limit on the DZ 33V for a fixed supply voltage detection circuit for channel
• When designing a voltage regulator circuit as we need to calculate the resistor that limits the maximum reverse current through the line that is less than DZ DZ tolerance, maximum flow through dz is the current through R2 = 0
• As the diagram above, the maximum line voltage drop on R1 DZ by dividing the value of R1, this is called electric current I1 have

I1 = (110-33) / 7500 = 77/7500 ~ 10mA

Normally it should flow back through DZ ≤ 25 mA

3.2 - fixed voltage regulator circuit using transistors, IC voltage regulator.

Zener diode voltage regulator circuit as used above have the advantage of simplicity but the disadvantage is the small amount of current (≤ 20mA). To 
be able to create a fixed voltage but the current was stronger than many people get more transistors to amplify the line as shown below.

Transistor circuit voltage is amplified

• In the circuit on the voltage at point A can be changed and also the AC ripple voltage at point B, but no change and relatively flat.
• Principle of voltage: through resistors R1 and DZ reduce fixed voltage of the transistor Q1 B foot, assuming the voltage vacuum 
  tube E = Q1 down> when the voltage U BE increases => the current through Q1 lights up = > do leg E of the lamp voltage increases, and vice versa ...
• Circuit voltage on the simple and effective should be used very widely and it was their production of IC LA78 ..to replace the voltage regulator circuit, IC LA78 .. as part of a schematic circuit diagram of the blue.

IC voltage they LA78 .. Voltage IC LA7805

• 5V voltage regulator IC LA7805
• 8V voltage regulator IC LA7808
• 9V voltage regulator IC LA7809
• LA7812 IC voltage regulator 12V

Note : 
They IC78 .. only for the consumption of about 1A or less, when assembled in the circuit IC in the U> Uout from 3 to 5V while the new IC to take effect.

3.3 - Application of their IC voltage 78 ..

Their voltage IC 78 .. widely used in the source, as the source of the VCD, the color TV, computer ...

Application of the voltage regulator IC LA7805 and LA7808 in the VCD source

4 - linear voltage regulator circuit (with feedback)

4.1 - Block diagram of the voltage regulator circuit with feedback.

The block diagram of a feedback voltage regulator circuit.

* Some characteristics of the voltage regulator circuit with feedback:

• Provides DC voltage at the output constant in both cases the input voltage changes or current consumption of the load changes, but this change must be limited.
• For DC voltage output quality, reduce AC ripple phenomenon.

* Principle of operation of the circuit.

• Sampling circuit monitors the output voltage through a distributed application needs to create (Ulm: voltage sampling)
• Create a standard circuit voltage => reduce retrieve a fixed voltage (Uc: standard pressure)
• Comparator circuit compares two voltage sampling Ulm and Australian standard pressure to form the control voltage.
• Correction amplifier will amplify the control voltage, then brought to adjust the operation of the production tube in the opposite direction, if the output voltage increases => feedback circuits through adjustment => work of leading lights down => the output voltage drops. Conversely, if the output voltage reduction => feedback circuits through adjustment => work of the leading lights up => and the output voltage increases =>> resulting output voltage does not change.

4.2 - Analysis of the circuit operation is the source of feedback in black and white TV Samsung

Input voltage is AC ripple voltage output flat

Linear voltage regulator circuit in Televisions Samsung Mono.

* The meaning of components in the diagram.

• Capacitor 2200μF filter capacitors are the main source, filter the rectifier voltage 18V, this is an input voltage of the voltage regulator circuit, the voltage may increase or decrease of about 15%.
• Q1 is the lamp of the main power supply line to the load, the output voltage of the voltage taken from the leg opening C Q1 lights and 12V fixed value.
• R1 is to be the engine capacity of less ghanh a large electric current through the lamp out.
• Pressure Components R5, R6 VR1 and sampling to create pressure on the leg lamp B Q2.
• Zener diode DZ and R4 create a voltage compared to standard fixed output voltage.
• Q2 is light compared and amplified voltage error => taken to control the operation of the lights of Q1.
• R3 contacts between Q1 and Q2, R2 distribution voltage for Q1

* Principle of operation.

• Output voltage will tend to change when the input voltage changes, or changes in current consumption.
• Suppose that : When the voltage on the increase => the output voltage increases => voltage vacuum tube E Q2 increased more than leg B (DZ reduce due to 
  Foot-E lights up Ura Q2, but only took part Ura Ulm) so U BE reduction => Q2 leading lights down => Q1 leading lights down => the output voltage drops. Similarly, when Uvao reduced through adjustment circuit => I re obtained Ura up. Time adjustment of the feedback loop is very fast for a few seconds and μ is the output filter capacitor to remove, without affecting the quality of the DC voltage => resulting output voltage is relatively flat.
• When adjusting the variable resistor VR1, the voltage sampling changes, leading to changes in Q2, leading to Q1 change => the result is the output voltage changes, VR1 to adjust the desired voltage.

4.3 - Circuit-date source of local television.

Schematic linear voltage source in the Japanese domestic color TV.

• Filter capacitor C1 is the main source of the diode bridge rectifier.
• Output filter capacitor C2 is the source of the linear circuit.
• Pressure components R4, VR1, R5 generated voltage samples U LM
• R2 and create pressure DZ Australian Standard
• R3 contacts between Q3 and Q2, R1 the bias for the light of Q1
• Resistor R6 is a division line, is of great public resistance.
• Q3 is the comparison lamp voltage detector and error amplifier
• Voltage error amplifier probe
• The source of light Q1
• => Source to work in the voltage range can be changed to 10%, the output voltage is always fixed.

Exercise: Do you read your analysis of the principle of operation of the power circuit.