Characteristics and Application of High Voltage Bidirectional Trigger Device SIDAC

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Characteristics and Application of High Voltage Bidirectional Trigger Device SIDAC

1 Features

The bidirectional trigger device widely used in electronic ballasts is DB3, which has a triggering voltage of about 30V, a small triggering current (mA level), and a residual voltage of about 20V after conduction. These characteristics determine that it can only be used in small current trigger circuits. Here we introduce a high-current, high-voltage bidirectional trigger device SIDAC (Silicon Diode for Alternating Current), which has a larger power capacity than ordinary DIAC (DB3 series) and can provide a larger start-up current.

2 Basic working principle of SIDAC

SIDAC is a two-terminal negative resistance device based on the principle and structure of thyristor. Since the voltage drop across the two ends is only about 1.5V when it is triggered to turn on, the working state of this device is similar to a switch, so SIDAC is also called a bidirectional trigger switch. The volt-ampere characteristics of SIDAC are shown in Figure 1. Once the voltage applied to the two ends of SIDAC exceeds its breakdown voltage UBO, it will immediately turn to the on state through a negative resistance area. The low on-state voltage drop makes it have very low power loss and can provide a large current in an instant. Only when the current flowing through SIDAC is interrupted or lower than its holding current IH, SIDAC will automatically turn from the on state to the off state.

Figure 1 SIDAC volt-ampere characteristic curve

In the figure, UBO-break voltage, IBO-break current, UDRM-off-state repetitive peak voltage, IDRM-off-state repetitive peak current, IH-holding current, US-turn-on voltage, IS-turn-on current, UT-on-state voltage

The circuit symbol of SIDAC is shown in Figure 2.

Figure 2 SIDAC circuit symbol

3. Characteristics of SIDAC

(1) SIDAC has a high trigger voltage and a wide range, currently ranging from 90V to 330V.

(2) SIDAC has negative resistance characteristics, and the on-state voltage UT is very low, only about 1.5V, so a large current can pass through it instantly.

(3) SIDAC is a non-polarity bidirectional trigger device. The surge current ITSM in one cycle can reach 20A. It discharges the fully charged capacitor through the inductor to generate high-energy high-voltage pulses.

(4) Once the SIDAC is turned on, it is in a self-locking state and will not turn off until the current flowing through it is interrupted or is less than the holding current IH.

(5) Fast response speed (ns level).

(6) The packaging form is flexible and diverse. It can be packaged in DO-41, DO-201AD, TO-92, TO-220 plastic resin. It can be packaged in single chip or multiple chips together.

(7) Adopting glass passivation technology, it has good high temperature resistance and high reliability.

4 Typical Applications

SIDAC is widely used and has been widely used in high-energy ignition circuits, high-voltage generators, overvoltage protection, oscillators, and thyristor circuits.

(1) High voltage generator circuit, see Figure 3. This circuit can be used in air conditioners and refrigerators for electronic sterilization and deodorization.

(2) Electronic ignition circuit with low voltage input, see Figure 4.

Figure 3 High voltage generator circuit

Figure 4 Electronic ignition circuit

(3) High-voltage halogen lamp ignition circuit, see Figure 5.

(4) Thyristor replacement circuit, see Figure 6.

(5) Relaxation oscillator circuit, see Figure 7. Selection of current limiting resistor R:

Figure 5 Halogen lamp ignition circuit

Figure 6 Thyristor replacement circuit

(a) Circuit

(b) Waveform

Figure 7 Relaxation oscillator circuit

Rmax≤(Ui-UBO)/IBO

Rmin≥(Ui-UTM)/IH(min)

(6) Transistor protection circuit, see Figure 8. When a transistor is used to disconnect an inductive load, a transient overvoltage will occur at the CE junction, and SIDAC can be used to protect the safety of the transistor.

(a) Circuit

(b) Waveform

Figure 8 Transistor protection circuit

Note: (1) Adjust the input pulse width tW to make IC = 0.63A