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Aug 30 2019

Analysis of Silicon Controlled Rectifier Circuit Diagram

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Silicon Controlled Rectifier

ⅠIntroduction


Ⅱ Simple One-way SCR Touch Switching Circuit with 12V


 

 

 

 

 

 

Ⅲ 13 Cases of Silicon Controlled Rectifier Circuit

3.1 Socket with Adjustable Voltage

3.2 Simple Mixing Dimmer

3.3 Vacuum Cleaner with Adjustable Speed

3.4 Light Control Electronic Switch

3.5 Automatic Delay Lighting Switch

3.6 Voice Control Music Lantern

3.7 Simple Delay Lighting

3.8 One-button Self-locking Switch

3.9 Simple Power Failure Self-locking Switch

3.10 Double Color Lighting

3.11 SCR AC Voltage Regulator

3.12 Electric Blanket Thermostat

3.13 Safe and Power-saving Push-button Bedside Lamp


ⅠIntroduction

Silicon controlled rectifier, which can be referred to as SCR, is available in one-way, two-way, turn-off, and light control types. It has the advantages of small size, light weight, high efficiency, long life, convenient control, etc. It is widely used in various automatic control and high-power electric energy conversion occasions such as controlled rectification, voltage regulation, inverter and non-contact switch.

A one-way silicon controlled rectifier is a controllable rectifying electronic component that can be turned off and turned on under the action of an external control signal, but once turned on, the external signal cannot make it turned off. It can only be turned off by removing the load or lowering the voltage across it. The one-way silicon controlled rectifier is a four-layer, three-terminal semiconductor device composed of three PN junctions. Compared with a diode having one PN junction, the forward conduction of a one-way silicon controlled rectifier is controlled by the gate current; Compared with a transistor having two PN junctions, the difference between them is that the one-way silicon controlled rectifier has no amplification effect on the gate current.

 Conduction conditions of SCR: 

First, the forward voltage must be added between the anode and the cathode of the silicon controlled rectifier, and the control pole must also be added with a forward voltage. The above two conditions must be met at the same time, and the silicon controlled rectifier will be conducted. In addition, once the silicon controlled rectifier is turned on, it will still be turned on even if the gate voltage is lowered or removed.

 Shutdown conditions of SCR: reduce or remove the forward voltage applied between the anode and the cathode of the silicon controlled rectifier so that the anode current is less than the minimum holding current.

 

 Simple One-way SCR Touch Switching Circuit with 12V

Touch the metal switch, SCR1 is turned on, and the load is working. ouch the metal switch, SCR2 is turned on, relay J is energized and starts to work. K is disconnected, and the load is de-energized. After SCR2 is turned off, the capacitor discharges to relay J, and the relay is held for 4 seconds, so the circuit action is more accurate. If the load is replaced by a relay, the load at high current operation can be controlled.

Figure 1 

Figure 1.

The silicon controlled rectifier is a new type of semiconductor device, which has the advantages of small size, light weight, high efficiency, long life, fast action and convenient use. The interest of learning can be stimulated by displaying the practical application cases of the silicon controlled rectifier.

 

Ⅲ 13 Cases of Silicon Controlled Rectifier Circuit

3.1 Socket with Adjustable Voltage

Figure 2

Figure 2.

The circuit is shown in the figure 2, which can be used for temperature adjustment (for electric soldering iron), dimming (for light), speed control (for motor). It is very convenient to use because you just need to insert the plug of the electric appliance into the socket.

V1 is a bidirectional diode 2CTS, V2 is a 3CTSI two-way SCR, and adjusting the RP can change the voltage on the socket.

3.2 Simple Mixing Dimmer

 Figure 3

Figure 3.

According to the electrical principle, the capacitor is connected to the sinusoidal AC circuit, and the maximum value of the voltage and current is 90° out of phase. According to this principle, C1 and C2 are connected in series, and the difference is taken out from the middle for use, which is more stable than the series connection of the resistor and the capacitor. In the circuit, D1 and D2 rectify the positive half wave and the negative half wave of the power supply respectively, and add them to trigger A and charge C1 or C2. Next, further use W to change the trigger time for phase shifting. As long as the resistance of W is adjusted, the purpose of changing the output voltage can be achieved. D1 and D2 also function to limit the trigger voltage of the flip-flop to protect the two-way silicon controlled rectifier.

3.3 Vacuum Cleaner with Adjustable Speed

The vacuum cleaner uses a SCR element to form a speed control circuit, which can control the motor speed as needed to adjust the suction force of the pipe. The speed control circuit shown in the figure below is relatively mature and is commonly used in high grade high-power vacuum cleaners.

Figure 4 

Figure 4.

3.4 Light Control Electronic Switch

The "on" and "off" of the light control electronic switch are realized by the conduction and blocking of the SCR, and the conduction and blocking of the SCR are subject to the brightness of natural light (or artificial brightness). The device is suitable as the lighting of the street, dormitory corridor or other public places to play the role of daylighting and night lighting to save electricity.

 Figure 5

Figure 5.

 Working principle: 

As shown in the above figure, after 220V AC passes through the bulb H and rectifies the full bridge, it becomes a DC ripple voltage, which is applied as a forward bias to VS and branches R of the silicon controlled rectifier. During the daytime, when the brightness is greater than a certain degree, the photodiode D exhibits a bottom resistance state and is ≤1KΩ, so that the triode V is turned off, and its emitter has no output current. The one-way silicon controlled rectifier VS is blocked because there is no trigger current. At this time, the current flowing through the bulb H is ≤ 2.2 mA, and the bulb H cannot emit light. The resistor R1 and the zener diode DW bias the transistor V to no more than 6.8V to protect the triode. At night, when the brightness is less than a certain degree, the photodiode D exhibits a high resistance state which is ≥100KΩ, so that the transistor V is forward-conducting, and the emitter has a voltage of about 0.8V, so that the silicon controlled rectifier VS triggers conduction, and the bulb H emits light. The RP is a brightness selection element that implements switching in the morning or evening.

 Installation and commissioning: 

During installation, place the soldered printed board in a transparent plastic box and fix it in series with the controlled light H and let it face the brighter space in front of the skylight or lighting window of the house. To avoid direct illumination of night lights within 3 meters, the commissioning should be carried out at night. Adjusting the resistance of the RP so that the controlled lamp H starts to illuminate at the appropriate brightness.

3.5 Automatic Delay Lighting Switch

When you leave the room at night, you always need to turn off the lights first. But if the light switch is not at the door, it is very inconvenient to turn off the light and then walk to the door in the dark.

The switch described in this article uses only 9 components, which can be easily added to the original switch, so that your lamp can be delayed for several tens of seconds after being turned off, so that you have enough time to leave the room so that you don't need to walk in the dark.

 Working principle: 

The circuit principle is shown in the figure below. A and B are respectively connected to the two ends of the original switch. When the switch S is closed, the positive half cycle of the alternating current passes through D6, R2, R1, D1 and the control pole of the silicon controlled rectifier, triggering the conduction of the SCR; the negative half cycle of the alternating current passes through D4, R2, R1, D1 and the control pole of the SCR and triggers it to conduct. After the silicon controlled rectifier is turned on, it is equivalent to make C and D short-circuited, so that the A and B are also closed by the diode and the conductive SCR. At this time, the light is on.

Figure 6 

Figure 6.

After the switch S is turned off, since the capacitor C1 is discharged through R1, D1 and the control pole of the silicon controlled rectifier, the SCR still has a trigger current to maintain conduction. The discharge current is gradually reduced and after a while, the SCR is turned off and the lamp is off. The delay time of this circuit is about 40 to 50 seconds.

 Component selection: 

Choose the silicon controlled rectifier with maximum current of 1A and the withstand voltage of 400V, select 1N4004 for D1, D3 ~ D6 and use a color capacitor with a withstand voltage of 630V and 35μF as C1. If the switch S is closed and the light is not on, the resistance of R1 can be appropriately reduced.

3.6 Voice Control Music Lantern

The circuit of the lantern controller is as follows: R1, R2, D and C form a resistor step-down half-wave whole-wave circuit, and output DC power about 3V for the control loop of the SCR. The piezoelectric ceramic piece HTD acts as an acoustic-electric transducer, and In normal times, adjust W to make the BG collector output low level, the SCR is turned off, and the lantern does not work. When the HTD receives the acoustic signal, the BG collector level rises and the SCR is turned on. Therefore, the lantern can flash with the rhythm of the music broadcast by the indoor recorder.

 Figure 7

Figure 7.

W can be used to adjust the sensitivity of the voice control. When W is adjusted from is large to small, the sensitivity of the voice control is higher, but when the W is too small, the light is always on. At this time, the voice control function is lost. When debugging, the W is gradually reduced from a large value to a certain resistance value. At the same time, the electric light is turned on, and then slightly increase W, and the electric light is extinguished. At this time, the sensitivity of the voice control is the highest, and the ordinary talking sound two or three meters away from the HTD can make the lantern flash. If the sensitivity is too high, just adjust W to a larger value, and the light will not turn out, indicating that the β value of BG is too small, and transistor with the larger β value should be used. The resistors are all 1/8W carbon film resistors.

3.7 Simple Delay Lighting

The delay lighting described in this article is very simple and easy to install. It can be directly connected to both ends of the ordinary switch. When in use, turn on the switch and the light is on, and after the light is turned off, the light will be turned off after a few seconds due to the action of the delay circuit. This circuit is safe and reliable and is suitable for beginners to make by themselves.

 Principle of the circuit: 

The circuit of the delay lighting is shown in the figure. The delay circuit is shown in the dotted line. In the figure, K is a pull switch or a wall switch. When K is closed, the delay circuit does not work, and the electric light is in a normal light-emitting state. When K is turned off, the voltage is charged to the capacitor C via R1 on the one hand. Since no current flows through R2 during the charging of C, the transistor V is always in an off state; on the other hand, the voltage provides a trigger voltage for the silicon controlled rectifier through R3 and R4 to put SCR in conduction. Therefore, the light is on for a while after the light is turned off. When the capacitor C is fully charged, the triode V is turned from off to on, the SCR is turned off, and the lighting is extinguished.

Figure 8 

Figure 8.

During the delay period of this circuit, the delay time is determined by the values of R1 and C, and you can also determine the time according to your own needs. The silicon controlled rectifier in this circuit, you can choose the two-way SCR, and its brightness of the lighting during the turn-off delay time is about half of the brightness when the lighting is turned on. It can suit people's visual needs, and at the same time save energy.

 Production of the circuit: 

The one-way SCR in the figure is MCR100-8, and the withstand voltage must be 600V or more. The power of the bulb is better not more than 100W. The diode VD is 1N4007 and V is C1815. The resistors are all 1/8W carbon film resistors.

When making, you need to use a small circuit board to solder the components in the dotted frame. It is best to install this circuit in the bottom groove of the pull switch, glue it with glue and connect the lead to the two terminals of the switch.

3.8 One-button Self-locking Switch

Figure 9 

Figure 9.

 Description of one-button self-locking switch 

— It does not work when it is powered on only.

— After the button is pressed, it is released and the relay is closed.

— When the button is pressed for long, the relay is released, and the relay is closed after you release the button.

— When the button is pressed, the relay is released and the pull-in action is cyclic.

— You can choose the relay DC9V because the 47Ω resistor has a voltage drop

3.9 Simple Power Failure Self-locking Switch

Figure 10 

Figure 10.

When the grid is powered normally, it is used like a normal switch. Press K1then the 220V AC provides a trigger voltage to the two-way silicon controlled rectifier through the voltage division of R1 and R2, so that the SCR  is turned on. After the SCR is turned on, during the positive half cycle of the power supply voltage, a small amount of current is charged to C through R4 and D, and the SCR is triggered by the voltage division of R3 and R2; during the negative half cycle, C discharges to R3 and R2 and triggers the two-way SCR so that the silicon controlled rectifier can continue to be conducted to ensure the normal operation of the load. Once the grid suddenly loses power, the charge on C is discharged through R3 and R2. After the power supply is restored, since K1 is normally open and there is no voltage on C, the two-way SCR cannot be triggered to conduct. The circuit is in a self-locking state,so no current flows through the load. Only when K1 is pressed again, the load can work normally, thus effectively preventing waste and accidents caused by power supply recovery after power failure. The normally closed button K2 is used to turn off the circuit under normal circumstances.

3.10 Double Color Lighting

This color lighting uses a multi-vibrator as a control signal, and the lights alternately shine, which can add a lot of brilliance and cheerful atmosphere to the holiday evening (especially the dance).

The working principle is shown in the figure below. After the AC 220V power supply is stepped down, rectified and filtered by C1, VD1, VD2 and VD3, a stable voltage of 3V is obtained at both ends of VD3. The VT1 and VT2 in the multivibrator are turned on in turn, and the collector current controls the two-way silicon controlled rectifier VS1 and VS2 to work, and the color lighting will alternately flash.

Figure 11 

Figure 11.

 Selection of components: 

Capacitor C1 is 0.47μ/400V (polyester capacitor), C2 is 220μ/6V, C3 and C4 are 50μ/16V. The resistor R1 is 1 M/1 W, and R2 and R3 are 20 K/ 1/4 W. 1N4004 are selected for diodes VD1 and VD2. The zener diode VD3 is selected as 3V/1W. The light-emitting diodes VD4 and VD5 are FG114001. The two-way silicon controlled rectifier VS1 and VS2 are TLC3A/400V. Transistors VT1 and VT2 are 3CK9D(60 ≤ β ≤ 120).

 Instructions: 

— If the color lighting does not work, you need to replace the 3V regulator with a 4.5V regulator.

— In order to prevent the current flowing through the light-emitting diodes VD4 and VD5 from being excessively large, it is preferable to string a 300 Ω current limiting resistor in the circuit.

— When adjusting, you can change the value of R1, R2 or C1, C2 thus directly control the changing rhythm of the color lighting.

— If the two-way silicon controlled rectifier VS1 and VS2 are 3A/400V, the load power is preferably below 300W and should not exceed the maximum limit of 500W. If you want to increase the power, you can use a thyristor with a current greater than 3A, but the capacity of C1 needs to be increased. If the original value is 0.47μ/400V, it can be replaced by 0.68~1μ/400V.

— This device uses plastic as the outer casing to avoid electric shock to people so it is safer.

3.11 SCR AC Voltage Regulator

The AC voltage regulator uses a SCR regulator. The SCR AC voltage regulator has a simple circuit, easy installation and convenient control so it can be used as a voltage regulating device for household appliances, and can be used for lighting dimming, electric fan speed regulation, electric iron temperature adjustment and the like. The output power of this voltage regulator is up to 100W, which can be used by ordinary household appliances.

Principle of the circuit: 

The circuit diagram is as follows

Figure 12 

Figure 12.

The SCR AC voltage regulator is composed of a controllable rectifier circuit and a trigger circuit. As can be seen from the figure, the diodes D1 - D4 form a bridge rectifier circuit, and the double base diode T1 constitutes a relaxation oscillator as a synchronous trigger circuit of SCR. When the voltage regulator is connected to 220V AC, it is rectified by the diode D1—D4 through the load resistor RL, and a pulsating DC voltage is formed across the A and K of the SCR. The voltage is stepped down by the resistor R1 and used as a DC power source of the trigger circuit. At the positive half cycle of the alternating current, the rectified voltage charges the capacitor C through R4 and W1. When the charging voltage Uc reaches the peak voltage Up of the tube T1, the tube T1 is conducted, so that the capacitor C is rapidly discharged through the e, b1 junction and R2 of the tube T1. As a result, a sharp pulse is obtained at R2. This pulse is sent as a control signal to the gate of the SCR, turning the SCR on. The tube voltage drop after the SCR is turned on is very low, generally less than 1V, so the relaxation oscillator stops working. When the AC power passes through the zero point, the SCR is turned off by itself. When the alternating current is in the negative half cycle, the capacitor C is recharged again. Therefore, the power on the load RL can be adjusted.

 Selection of components: 

The adjustment potentiometer of the regulator is a WH114-1 type synthetic carbon film potentiometer with a resistance of 470KΩ. This potentiometer can be directly soldered on the circuit board. R1 uses a metal film resistor with a power of 1W, and the rest of the resistors use a carbon film resistor with a power of 1/8W. D1~D4 select silicon rectifier diodes with reverse breakdown voltage greater than 300V and maximum rectification current greater than 0.3A, such as 2CZ21B, 2CZ83E, 2DP3B, etc. SCR selects silicon controlled rectifier devices with forward and reverse voltages greater than 300V and rated average current greater than 1A, such as domestic 3CT.

3.12 Electric Blanket Thermostat

Electric blankets sold in the market generally have two temperature files, that is, high and low. When you dial in the high temperature file, you always wake up because it becomes so hot; when you dial in the low temperature file, sometimes you will feel the heat is not enough when you wake up. To this end, the author made this electric blanket thermostat, which can control the temperature of the electric blanket to a suitable range.

 Working principle: 

The circuit is shown below. In the figure, the IC is the time-base circuit of NE555; RP3 is the temperature adjustment potentiometer, and its sliding arm potential determines the trigger potential V2 and the threshold potential Vf of the IC, and V5 = Vf = 2Vz. The 220V AC voltage is stepped down by C1 and R1, D1 and D2 are rectified, C2 is filtered, and after DW is regulated, a voltage of about 9V is obtained for IC. The power is turned on at room temperature. Since V2 ≤ Vz and V6 ≤ Vf, the pin 3 of IC is at a high potential, the BCR is triggered to conduct, the heating wire is energized and heated, and the temperature is gradually increased. As the temperature of the thermal sensor BG1 increases, the penetration current Iceo increases, and V2 and V6 increase. When the BCR is cut off, the heating wire stops heating, the temperature begins to gradually decrease, and the Iceo of BG1 gradually decreases, and V2 and V6 decrease. When V6 ≤ Vf, V2 ≤ Vz, pin 3 of IC returns to high potential, BCR is triggered to conduct, and the heating wire starts to heat up again. Practice has proved that when RP2 is adjusted to make V2=1/2 of V6, the temperature difference is zero; when V2=V6, it is the largest.

Figure 13 

Figure 13.

 Selection of components: 

BG1 can choose 3AX, 3AG and other PNP-type manifolds; BCR uses small plastic-sealed two-way SCR of 400V or more , other components can be selected according to icons.

 Production points: 

The thermal sensor BG1 can be taken out with a temperature-resistant thin flexible wire, and it is placed in a capacitor aluminum case together with the pin connector, and the thermal grease is injected to form a temperature probe. When using, you just need to put the probe in the appropriate part.

3.13 Safe and Power-saving Push-button Bedside Lamp

A time-delay bedside lamp is convenient for many readers to use at night. The push-button bedside lamp described in this article can meet the requirements of safety and convenience. The circuit principle is shown in the figure below.

Figure 14 

Figure 14.

The bedside lamp is composed of a power-saving monostable circuit and a controllable lamp. The two parts are coupled by optocoupler, the electrical part is completely independent and the use is very safe. When K1 is disconnected, VT1 is cut off, its collector voltage is 0V, VT2 is cut off, and the grounding end of pin 1 of NE555 is open and does not work. At this time, the power consumption of the circuit is only the penetration current of VT1 and VT2 and it is about 3~ 5μA. Four batteries can be used for more than one and a half years. After pressing K1, VT1 is saturated and turned on. The voltage across R3 is close to the power supply voltage, VT2 is saturated, conducted and the NE555 is working. At this time, the pin 2 of NE555 changes from high level to low level, and is less than 1/3 of the power supply voltage. NE555 flips, the pin 3 outputs a high level, and one of them can pass the R7 drive photocoupler 4N25, so that the two-way silicon controlled rectifier VS is turned on and the bedside lamp H is on; the other one passes through the diode VD1 and the resistor R6 to provide VT2 with a large enough bias current to maintain the saturation and conduction of VT2. At this time, even if K1 is disconnected, the working state of VT2 is unchanged, that is, the transient state of NE555 is unchanged. During this period, the power supply charges C1 through R5, so that the voltage across C1 is continuously increased. When the voltage across C1 is greater than 2/3 of the power supply voltage, NE555 is discharged through pin 7 of its discharge end, and the transient state of NE555 is over. The pin 3 changes from high level to low level, VT2 is cut off, and it enters another stable state. Only when K1 is turned on again, NE555 enters the temporary steady state again, and the bedside lamp will light up again.

There are no special requirements for the bedside lamp and it is easy to install and easy to debug. As long as the installation is correct, it can be used normally. If the delay time is too short, you can increase the resistance of R5 or the capacity of C1, and vice versa. The button part should be externally installed during installation, and the remaining components are placed in a plastic case to ensure safe use.

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