SCR, TRIAC dan DIAC
Thyristor stems from the Greek word meaning 'door'. So named perhaps because of the nature of this component is similar to a door that can be opened and closed to pass electrical current. There are several components that include, among others thyristor PUT (programmable uni-junction transistor), UJT (uni-junction transistor), GTO (gate turn off switch), photo SCR and so on. But on this occasion, which will point out the components of the thyristor, known as SCR (silicon controlled rectifier), TRIAC and DIAC. Readers can listen more clearly how the working principles and their application.
Thyristor Structure
The main characteristics of a thyristor is a component made of semiconductor material silicon. Although the same material, but it has the structure of the PN junction is more complex than a bipolar or MOS transistors. Thyristor component is more used as a switch (switch) rather than as a current amplifier or voltage as the transistor.
The basic structure is the structure of the four layer thyristor PNPN as shown in Figure-1a. When sorted, these structures can be seen as two PNP and NPN junction structures are connected in the middle as in the picture-1b. This is nothing but the two PNP and NPN transistors are connected to each collector and base.
Thyristor Structure
The main characteristics of a thyristor is a component made of semiconductor material silicon. Although the same material, but it has the structure of the PN junction is more complex than a bipolar or MOS transistors. Thyristor component is more used as a switch (switch) rather than as a current amplifier or voltage as the transistor.
The basic structure is the structure of the four layer thyristor PNPN as shown in Figure-1a. When sorted, these structures can be seen as two PNP and NPN junction structures are connected in the middle as in the picture-1b. This is nothing but the two PNP and NPN transistors are connected to each collector and base.
Figure-1: Structure of Thyristor
If visualized as transistors Q1 and Q2, then the thyristor structure can be shown as in Figure-2 the following. Visualization with transistor
Figure-2: Visualization with the transistor
Seen here collector of transistor Q1 is connected to the base of transistors Q2 and vice versa collector of the transistor Q2 is connected to the base transistor Q1.
Such a transistor circuit indicate a strengthening of the current loop in the middle. Where b is known that Ic = Ib, ie the collector current from the current base is strengthened.
If for example there is a current of Ib flowing in the base of transistors Q2, then there will be current Ic flowing in the collector of Q2. This collector current is a base current Ib on the transistor Q1, so it will appear on the strengthening of the transistor Q1 collector current. Current collector of the transistor Q1 is none other than the base current for transistor Q2. So forth, so the longer the PN connection of the thyristor is in the middle will shrink and disappear. Left is a layer of P and N on the outside.
If this condition is reached, then such a structure is nothing but the structure of the PN diode (anode-cathode) is already known. At such a time, called the thyristor in the ON state and current can flow from the anode to the cathode such as a diode.
Such a transistor circuit indicate a strengthening of the current loop in the middle. Where b is known that Ic = Ib, ie the collector current from the current base is strengthened.
If for example there is a current of Ib flowing in the base of transistors Q2, then there will be current Ic flowing in the collector of Q2. This collector current is a base current Ib on the transistor Q1, so it will appear on the strengthening of the transistor Q1 collector current. Current collector of the transistor Q1 is none other than the base current for transistor Q2. So forth, so the longer the PN connection of the thyristor is in the middle will shrink and disappear. Left is a layer of P and N on the outside.
If this condition is reached, then such a structure is nothing but the structure of the PN diode (anode-cathode) is already known. At such a time, called the thyristor in the ON state and current can flow from the anode to the cathode such as a diode.
Figure-3: Thyristor rated voltage
What if we give in this thyristor dc light loads and rated supply voltage from zero to a certain voltage as shown in Figure 3. What happens to light when a voltage is increased from zero. Yes yes, of course, the lamp will remain extinguished because the middle layer of the existing NP will get a reverse-biased (diode theory). At this time called the thyristors in the OFF state because no current can flow or very small. Currents can not flow until a reverse-bias voltage that causes a particular NP is saturated and the connection is lost. This voltage is called breakdown voltage and current at that time began to flow through the thyristors as diodes generally. At this voltage thyristor breakover voltage VBO called.
SCR
It has been discussed, that to make the thyristors to be ON is to provide trigger current P layer close to the cathode. Namely by making the gate on PNPN thyristor as in the picture-4a. Because of its location close to the cathode, can also pin gate pin gate is called the cathode (cathode gate). Thus SCR SCR created and symbols depicted as a picture-4b. SCR Thyristor in a lot of literature referred to it.
SCR
It has been discussed, that to make the thyristors to be ON is to provide trigger current P layer close to the cathode. Namely by making the gate on PNPN thyristor as in the picture-4a. Because of its location close to the cathode, can also pin gate pin gate is called the cathode (cathode gate). Thus SCR SCR created and symbols depicted as a picture-4b. SCR Thyristor in a lot of literature referred to it.
Figure-4: Structure SCR
Through the leg (pin) gate allows these components in the trigger to be ON, ie by giving the gate current. It turned out that by giving the gate current Ig which can lower the greater the breakover voltage (VBO) a SCR. Where the voltage is the minimum voltage required to be ON the SCR. Until at a certain large gate currents, it would be very easy to make SCR becomes ON. Even with a small forward voltage though. For example only 1 volt or less. Voltage and current curves of an SCR is like the one in Figure-5 the following.
Figure-5: Characteristic curves I-V SCR
At the breakover voltage VBO printed image, which if the SCR forward voltage reaches this point, the SCR will be ON. More importantly, Ig currents that can cause voltage drops to a smaller VBO. In the picture shown some currents Ig and its correlation to the breakover voltage. In the datasheet SCR, gate trigger current is often written with the notation IGT (gate trigger current). In the picture there is also shown holding current Ih that flows that maintain the SCR remains ON. So in order to stay ON the SCR forward flow from the anode to the cathode must be above this parameter.
So far put forward is how to make SCR becomes ON. In fact, once the SCR reaches the ON state so forever will be ON, although the gate voltage is removed or in the short to the cathode. The only way to make SCR becomes OFF is to make the anode-cathode current falls below Ih currents (holding current). In figure-5 SCR IV curve, if the forward current under Ih point, the SCR back to the OFF state. How much of this holding current, generally in the datasheet SCR.
How to make SCR becomes OFF is tantamount to lowering the anode-cathode voltage to zero. Because this is the SCR or thyristor is generally not suitable for DC applications. This component is used more for AC voltage applications, where the SCR can be OFF when the AC voltage waveform at the zero point.
There is one other important parameters of the SCR, the VGT. This parameter is the trigger voltage on the gate leading to the SCR ON. When viewed from the thyristor model in Figure 2, this voltage is the voltage on the transistor Q2 VBE. VGT as VBE, the magnitude of approximately 0.7 volts. As an example a series of image-6 following an SCR are known to have IGT = 10 mA and VGT = 0.7 volts. Then it can be calculated voltage Vin is required for this SCR ON is equal to:
Vin = Vr + VGT
Vin = IGT (R) + VGT = 4.9 volts
So far put forward is how to make SCR becomes ON. In fact, once the SCR reaches the ON state so forever will be ON, although the gate voltage is removed or in the short to the cathode. The only way to make SCR becomes OFF is to make the anode-cathode current falls below Ih currents (holding current). In figure-5 SCR IV curve, if the forward current under Ih point, the SCR back to the OFF state. How much of this holding current, generally in the datasheet SCR.
How to make SCR becomes OFF is tantamount to lowering the anode-cathode voltage to zero. Because this is the SCR or thyristor is generally not suitable for DC applications. This component is used more for AC voltage applications, where the SCR can be OFF when the AC voltage waveform at the zero point.
There is one other important parameters of the SCR, the VGT. This parameter is the trigger voltage on the gate leading to the SCR ON. When viewed from the thyristor model in Figure 2, this voltage is the voltage on the transistor Q2 VBE. VGT as VBE, the magnitude of approximately 0.7 volts. As an example a series of image-6 following an SCR are known to have IGT = 10 mA and VGT = 0.7 volts. Then it can be calculated voltage Vin is required for this SCR ON is equal to:
Vin = Vr + VGT
Vin = IGT (R) + VGT = 4.9 volts
Figure-6: A series SCR
TRIAC
Thyristor SCR is arguably a uni-directional, because when ON can only pass current in one direction only, from anode to cathode. TRIAC structure is actually the same as the two SCR him back and forth and put together his second gate. TRIAC symbol is shown in Figure-6. TRIAC also called bi-directional thyristors.
Figure-7: Symbols TRIAC
SCR TRIAC works much like a parallel back and forth, so it can pass the two-way flow.
In the datasheet it would be given greater detail parameters such as VBO and VBO-and-IGT and IGT, and Ih-Ih and so on. Of these parameters generally symmetrical between a plus and a minus. In design calculations, this parameter can be considered symmetrical, making them easier on the count.
DIAC
When viewed structure such as a picture-8a, DIAC is not including the thyristor family, but the principle works to make it is classified as a thyristor. DIAC is made with a structure similar to the PNP transistors. N layer on the transistor is made so thin that electrons can easily cross through this layer. While at the DIAC, the N layer is made thick enough so that electrons are quite difficult to penetrate. DIAC Such structures can also be viewed as two diode PN and NP, resulting in some literature DIAC classed as a diode.
In the datasheet it would be given greater detail parameters such as VBO and VBO-and-IGT and IGT, and Ih-Ih and so on. Of these parameters generally symmetrical between a plus and a minus. In design calculations, this parameter can be considered symmetrical, making them easier on the count.
DIAC
When viewed structure such as a picture-8a, DIAC is not including the thyristor family, but the principle works to make it is classified as a thyristor. DIAC is made with a structure similar to the PNP transistors. N layer on the transistor is made so thin that electrons can easily cross through this layer. While at the DIAC, the N layer is made thick enough so that electrons are quite difficult to penetrate. DIAC Such structures can also be viewed as two diode PN and NP, resulting in some literature DIAC classed as a diode.
Figure-8: Structure and symbol DIAC
Difficult to pass by a two-way flow, DIAC was intended for this purpose. Only with a specific breakdown voltage then DIAC can conduct current. Current which of course can be delivered back and forth from the anode to cathode and vice versa. DIAC same characteristic curve as TRIAC, but that only need to know is how its breakdown voltage.
Symbols of the DIAC is as shown in Figure-8b. DIAC TRIAC is generally used as a trigger to ON at a specific input voltage is relatively high. An example is a lamp dimmer applications that can be seen in figure-9.
Symbols of the DIAC is as shown in Figure-8b. DIAC TRIAC is generally used as a trigger to ON at a specific input voltage is relatively high. An example is a lamp dimmer applications that can be seen in figure-9.
Figure 9: Series Dimmers
If known TRIAC IGT than in the above circuit VGT = 10 mA and 0.7 volts. Then known also used is a DIAC with VBO = 20 V, it can be calculated TRIAC ON voltage:
V = IGT (R) + VBO + VGT = 120.7 V
V = IGT (R) + VBO + VGT = 120.7 V
thyristor10.jpg
In the dimmer circuit, the resistor R is usually replaced with a series resistor and a potentiometer. Here the capacitor C with a series of R is used to shift the phase voltage VAC. Lights can be set up lights dim and bright, depending on the time when the TRIAC in the trigger.
source : patas121.blogspot.com
source : patas121.blogspot.com
Nice post..Please suggest a article on working flow & difference between Thyristors, triac and a diac?
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