5pcs DB3 Diac Thyristor Diode

🔹 5PCS DB3 – Bidirectional Trigger Diode (DIAC)

A bidirectional, breakover-triggered diode designed to act as a voltage-triggered switch primarily for AC circuits. The DB3 is most commonly used to provide the triggering pulse for TRIACs in light dimmers, motor speed controls, and other phase-control circuits. It is a key component for building simple, reliable AC power control.

✅ Specifications:

• Part Number: DB3 (Common standard)

• Type: DIAC (Bidirectional Trigger Diode)

• Breakover Voltage (VBO): 28V to 36V (Symmetrical, both directions)

• Breakover Voltage Symmetry (ΔVBO): Max 4V (Difference between positive and negative breakover)

• Peak Current (Ipk): 5mA (Typical pulse current during triggering)

• On-State Voltage: ~3V (Typical when conducting)

• Package: DO-35 (Small glass axial package, similar to 1N4148)

• Lead Material: Tinned Copper

• Operating Temperature: -40°C to +110°C

• Quantity: 5 pieces

⚙️ Key Features:

• Bidirectional Operation: Conducts in both directions once the breakover voltage is exceeded.

• Sharp Switching: Provides a crisp, snap-action triggering pulse to a TRIAC gate, ensuring reliable turn-on.

• Symmetrical Triggering: Ensures similar timing for both the positive and negative half-cycles of an AC waveform, leading to symmetrical control.

• No Polarity: Can be installed in either direction in a circuit.

• Industry Standard: The most common and inexpensive DIAC for hobbyist and consumer applications.

📦 Typical Applications:

• TRIAC Triggering: The primary use – in the gate circuit of a TRIAC for AC phase control (e.g., in dimmer switches for lights and fans).

• Relaxation Oscillators: Used in simple sawtooth or pulse generator circuits.

• Surge Protection: Can be used in some simple voltage-clamping circuits.

• Ignition Circuits: For small gas discharge lamps or ignition systems.

• DIY & Hobbyist Projects: Building your own AC light dimmer or motor speed controller.

🔧 Basic Operation in a TRIAC Dimmer Circuit:

1. Circuit Role: The DB3 is placed in series with a resistor and capacitor (RC timing network) across the AC line.

2. Charging Phase: The capacitor charges through a variable resistor (potentiometer).

3. Triggering: When the capacitor voltage reaches the DB3’s breakover voltage (~32V), the DB3 “fires” (switches on rapidly), discharging the capacitor through the gate of the TRIAC.

4. TRIAC Turn-On: This pulse turns the TRIAC on for the remainder of that AC half-cycle.

5. Reset: At the AC zero-crossing, the TRIAC turns off, and the process repeats for the next half-cycle. Adjusting the potentiometer changes the charging time, thus controlling the phase angle and power delivered to the load.

⚠️ Important Design Notes & Limitations:

• Not a Regular Diode: It is a trigger device, not a rectifier. It remains off until its specific breakover voltage is reached.

• Low Current Device: Can only handle brief trigger pulses (mA range). It cannot be used to switch load current directly.

• Breakover Voltage Variation: The actual VBO can vary between 28V and 36V. Circuits must be designed to work within this range.

• Not for DC: Its primary application is in AC phase-control circuits. Its symmetrical breakdown characteristic is designed around an AC waveform crossing zero.

• Replacement: A common direct replacement for other ~32V DIACs like the ST2, HT-32, or BR100/3.