THYRISTOR

The thyristor is a four layer P-N-P-N device with different levels of doping for each layer. The cathode is the most heavily doped and the gate and anode are less heavily doped . The central N type layer is only slightly doped and is also thicker than the other layers enabling it to support a high blocking voltage

In operation the thyristor may be considered as an NPN and a PNP transistor connected back to back, forming a positive feedback loop within the device. The output of one transistor is fed to the input of the second and the output of the second transistor is in turn fed back to the input of the first. A small trigger pulse on the gate will turn the thyristor on and once a current starts to flow, it quickly builds up until both transistors are fully turned on or saturated and the only way it can be turned off is by removing the supply voltage

The device is designed to act as a switch and can carry very high currents

TRIAC

A TRIAC is used in AC power control applications in order to switch high voltages and high levels of current over both parts of the AC waveform. As a result, triac circuits are used in a number of applications that require power switching. The triac was developed after the creation of the thyristor which is able to control AC current over one half of the cycle. The triac circuit can be visualized as two thyristors that are opposite, parallel, and have the two gates connected together with the anode of one device connected to the cathode of the other. A common household device which uses the triac circuit are light dimmers found in domestic houses

TRIAC Composition

The basic Triac circuit has bi-directional properties. Similar to a thyristor, it has three terminals with a gate acting as a trigger to turn the device on. The other two terminals are then referred to as Main Terminal 1 (MT1) and Main Terminal 2 which have similar properites due to the bi-directional nature of the circuit

How Does a TRIAC Work

A TRIAC is triggered by a positive or negative voltage being applied to its gate electrode. Once the circuit is triggered, it will conduct elecgtricity until the current drops below the designed threshold value. As a result, they permit the control of large power flows with very small control currents. TRIACs also let the percentage of current that flows through the circuit to the load to be controlled which is also referrred to as phase control. TRIACs will normally have a DIAC included in the circuit when used as a control for electrical equipment in order to dampen the level of harmonics produced by the circuit

What are the Uses for a TRIAC

There are a number of uses for TRIACs in industry in small AC power applications. Examples of uses of TRIACs include dimmer switches, speed controls for electric fans, in computerized control circuits of household appliances, and in electric motor controls

TRANSFORMATEURS

One has generally only the tension of the sector, of which the most current values lie between 110 and 240 V, but for the electronic instruments, the tensions necessary often have a different value. The mains transformer precisely ensures the transformation of the tension of the sector, while increasing or by decreasing its value in order to obtain the supply voltages of the various circuits

 

 

CONSTITUTION OF THE TRANSFORMER

 

On the figure 1-a, the essential elements of a transformer are represented, i.e. the closed ferromagnetic core and the rollings up laid out around the central part of the core

 

On this figure only two rollings up are represented ; it is the minimal number which a transformer can present: indeed, one of rollings up is connected to the sector while the other, at the ends of which one obtains a tension of value different from that of the sector, is connected to the circuits to feed
When one needs several tensions of different values, one uses an additional rolling up for each tension ; the transformers can thus comprise three rollings up or more  one of them is always connected to the sector and it is called primary winding or more simply primary, while the other rollings up connected to the circuits to feed are called secondary windings or more simply secondary
Since all the secondaries behave in the same way, it is enough, to analyze the operation of a transformer, to examine only one secondary, as one did on the figure 1-a
On this figure, the primary education was drawn a little above it secondary to clearly distinguish two rollings up which, actually, are superimposed: the primary education is rolled up initially, then, the secondary
On the figure 1-b, one drew the graphic symbol representing the transformer on the electric diagrams: the same graphic symbol as that used in the preceding lessons to represent rollings up of windings is used here for rollings up, while the core is represented by a segment of right-hand side traced between the primary education and the secondary. When there are several secondaries, one generally draws them all on the same side of the segment, so that other side, it has only the primary education there
We will see now how a transformer functions, i.e. how its secondary can provide a power of a value different from that which is applied to its primary education

  

DIAC

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A diac is a full-wave or bi-directional semiconductor switch that can be turned on in both forward and reverse polarities. Indeed the name diac means diode AC switch

The diac is widely used to assist even triggering of a triac when used in AC switches. Diacs are mainly used in dimmer applications and also in starter circuits for florescent lamps

Circuit symbol for the diac

 

Typically the diac is placed in series with the gate of a triac. Diacs are often used in conjunction with triacs because these devices do not fire symmetrically as a result of slight differences between the two halves of the device. This results in harmonics being generated, and the less symmetrical the device fires, the greater the level of harmonics produced. It is generally undesirable to have high levels of harmonics in a power system

To help in overcoming this problem, a diac is often placed in series with the gate. This device helps make the switching more even for both halves of the cycle. This results from the fact that the diac switching characteristic is far more even than that of the triac. Since the diac prevents any gate current flowing until the trigger voltage has reached a certain voltage in either direction, this makes the firing point of the triac more even in both directions

Diac structure

The diac can be fabricated as either a two layer or a five layer structure. In the three layer structure the switching occurs when the junction that is reverse biased experiences reverse breakdown. A five layer diac structure is also available. This does not act in quite the same manner, although it produces an I-V curve that is very similar to the three layer diac. It can be considered as two break-over diodes connected back to back

fuses

ANL Fuse

These large fuses are used mainly in higher power systems and in the main fuse at the battery. ANL fuses range in size from 60A 300A

 

AGU Fuse

Used in most fuse distribution blocks the AGU fuse is one of the more commonly used fuses in mobile audio systems. Our AGU fuses range from 30 80A

ATC Fuse

Often found in amplifiers, the ATC Fuse is also very common in automotive fuse panels. Fuse ratings range from as little as 5A up to 40A

Mini ATC Fuse

Just as the name indicates, the Mini ATC is a smaller version of the ATC Fuse. These are used in newer model automobile fuse panels, offered in 5A-40A

 

MAXI Fuse

The Maxi fuse is the larger version of the ATC fuse. These are used in amplifiers and in automotive fuse panels. Size range from 20A 100A

Mini-ANL Fuse

Also called MIDI or AFC Fuse; are smaller versions of the ANL Fuse. They are similar in shape and are very versatile. Compact in design, yet available up to 150A make the Mini-ANL Fuse very popular