Introduction to The Deacons

Ac Diode switch, or Diatic for short, is another solid state, three-layer, two-joint semiconductor device. Unlike the transistor, however, Diac has no base connection, making it two terminal devices labeled A1 and A2.

Diacs are an electronic component that does not offer control or amplification but acts as a bidirectional switching diode, as they can transmit current from both polarities of a suitable AC voltage source.

In our tutorial on SCRs and Triages, we found that these devices can be triggered by simple circuits that produce fixed-state gate currents, as shown in ON-OFF switching applications.

Deacon

The switch is that the door current does not flow when the S1 is on and the lamp is "OFF". When the S1 switch is turned off, the gate current flows IG and transmits in positive half-loops as the SCR only works on the Ι dial.

We also remember that once the "on" switch is turned off, the SCR will only "turn off" again when the feed voltage drops to a value that is less than the value of the holding current of the IA, which is the anode current.

If we want to control the average value of the lamp current instead of simply putting it in the "ON" or "OFF" position, we can apply a short door current pulse at a preset trigger point to allow scr to be transmitted. only for part of the half-cycle. Then the average value of the lamp current is changed by changing the latency T between the start of the cycle and the trigger point. This method is commonly known as "phase control".

But two things are needed to maintain phase control. One is a variable phase shift circuit (usually an RC passive circuit). The second is a type of trigger circuit or device that can produce the necessary door impact when the delayed waveform reaches a certain level. Such a solid state semiconductor device designed to produce these door impacts is Diac.

The deacon is structured like a transistor but does not have a base connection that allows it to be connected to a circuit in both polarities. The dialects are primarily used as trigger devices in phase trigger and variable power control applications, as they help provide a sharper and more instantaneous trigger pulse used to make the main switching device "ON" (as opposed to a continuously rising ramp voltage).

The deacon symbol and the voltage-current characteristic curves of the diac are given below.

Diac Symbol and I-V Characteristics

Deacon
Diac Symbol and I-V Characteristics

From the characteristic curves of the deacon IV above until the applied voltage is greater than VBR, we can see that the deacon prevents the flow of current in both directions. At this point, the deterioration of the device occurs, and the deacon transmits intensively, similar to zener.

In an ordinary zener diode, the voltage on it remains constant as the current increases. However, transistor action in dialogue causes the voltage to decrease as the current increases. When in a conductive state, the deacon resistance drops to a very low value, allowing a relatively large current value to flow. Fault voltages for the most commonly found deacon, such as ST2 or DB3, typically range from about ±25 to 35 volts. Higher circuit voltage values are available, for example, 40 volts for DB4 diac.

This action gives the deacon a negative resistance property, as shown above. Since the deacon is a symmetrical device, therefore it has the same property for both positive and negative voltages, and it is this negative resistance action that makes the deacon suitable as a triggering device for SCRs or triage.

Diathe-Deacon Applications

As mentioned above, the deacon is widely used as a solid state triggering device for other semiconductor switching devices, mostly SCRs and triage. Triages are widely used in applications such as lamp dimmers and engine speed controllers, and therefore are used in conformity with the triage to provide full wave control of the AC source, as shown by the deacon.

Diyak AC Phase Control

Deacon
Diyak AC Phase Control

As the AC supply voltage increases at the beginning of the cycle, the capacitor, C constant resistance, R1 and the posiometer are charged via the serial combination of VR1 and the voltage increases along the plates. When the charging voltage reaches the circuit break voltage of the dialect (about 30 V for ST2), the deacon breaks and the capacitor is discharged from the dialogue.

Discharge produces a sudden current pulse that ignites the triage into the transmission. The phase angle at which the trilata is triggered can be changed using VR1, which controls the capacitor's charging rate. Resistance limits door flow to a safe value when R1, VR1 is minimal.

After firing into the triage, it is kept in the "ON" state by the load current flowing through it, while the voltage in the resistance-capacitor combination is limited to the "ON" voltage of the triage and maintained until it continues. End of the current half-cycle of the AC resource.

At the end of the half-cycle, the supply voltage drops to zero, lowers the current in the triage below the holding current, IH puts it in the "OFF" position and stops the diak transmission. The supply voltage then enters the next half cycle, the capacitor voltage begins to rise again (this time in the opposite direction), and the triage ignition cycle is repeated again.

Triyak Transmission WaveForm

Deacon
Triyak Transmission WaveForm

Next, we found that The Deacon is a very useful device that can be used to trigger triage, allowing it to quickly become "ON" when a certain voltage level is reached due to its negative resistance feature. But this means that when we want to use a triage for AC power control, we will also need a separate realm. Fortunately for us, somewhere, a bright spark replaced the independent deacon and triage with a single switching device called Quadrac.

Quadricela

The quadrate is basically a Diyak and Triage produced together in a single semiconductor package. Therefore, it is also known as "internally triggered triage". This all-in-one duplex device is door-controlled using both polarity of the main terminal voltage. This means that it can be used in full wave phase control applications such as heater controls, lamp dimmers and AC engine speed control, etc.

Deacon
Quadrac

Quayrakes such as Triyak are a three-terminal semiconductor switching device labeled MT2 for main terminal one (usually anode), MT1 for main terminal two (usually cathode) and G for door terminal.

Depending on the requirements of quay, voltage and current switching, the TO-220 package is available in various package types, the most common. Quadrac is designed to replace most triage devices.