0B2WA — Reliable Miniature Cold-Cathode Voltage Regulator
The 0B2WA (also designated as 6627/0B2WA) is a high-reliability, miniature, cold-cathode, gas-filled diode designed for voltage regulation. It maintains a substantially constant operating voltage of approximately 108 V over a wide current range of 5 to 30 mA.
The tube is engineered for critical industrial and military applications where severe environmental conditions, such as high temperatures, high altitude, and extreme mechanical shock and vibration, are encountered. It features controlled manufacturing processes to ensure extremely small voltage drift and excellent repeatability throughout its operating life.
Mechanical Design and Pin Configuration
The 0B2WA is housed in a T-5 1/2 glass envelope with a small-button miniature 7-pin base (JEDEC E7-1 or 7C10). It can be mounted in any position.
Physical Dimensions
- Maximum Overall Length: 2 5/8 inches (66.7 mm)
- Maximum Seated Length: 2 3/8 inches (60.3 mm)
- Maximum Diameter: 3/4 inch (19 mm)
- Approximate Weight: 0.3 ounces (11 g)
Basing and Terminal Connections
The tube utilizes the 5BO (or 7C10) basing arrangement. The pin connections, viewed from the bottom of the base, are as follows:
The redundant anode (Pins 1 and 5) and cathode (Pins 2, 4, and 7) connections are designed to provide a safety feature: the load circuit can be wired through the socket terminals such that removing the tube from its socket automatically opens the load circuit, preventing unregulated high voltage from damaging downstream components.
Electrical Characteristics and Operating Parameters
The 0B2WA operates by establishing a stable glow discharge (cold cathode) in an inert gas atmosphere.
Key Electrical Specifications
- Nominal Tube Voltage Drop: 108 V (typically ranging from 105 V to 111 V over the full current range).
- Operating Current Range: 5 to 30 mA DC.
- Regulation (5 to 30 mA): Typically 1.0 V to 1.1 V, with a maximum limit of 2.5 V (or 3.0 V at end of life).
- Anode Breakdown Voltage (Ignition Voltage):
- In ambient light (5 to 50 foot-candles / 50 to 500 lux): Typically 118 V to 123 V, maximum 130 V.
- In total darkness: Maximum 130 V to 210 V depending on the specific test standard.
- Voltage Jump (6 to 10 mA): Typically less than 10 mV, maximum 100 mV.
- Voltage Repeatability (10 mA): Typically 0.1 V to 0.3 V, maximum 0.4 V to 0.6 V.
- Noise Output (30 mA): Typically less than 1 mV, maximum 5 mV.
- Leakage Current (at 50 V DC): Typically less than 1 µA, maximum 5 µA.
Reference Tube Characteristics
When operated in the narrow current range of 6 to 10 mA, the 0B2WA exhibits highly stable characteristics comparable to a dedicated voltage reference tube, with minimal voltage drift.
Absolute Maximum Ratings
To ensure reliable operation and prevent premature failure, the following absolute maximum limits must be respected:
Circuit Design and Application Guidelines
Series Resistor Calculation
A series current-limiting resistor (R1) must always be connected in series with the 0B2WA to prevent the current from exceeding the maximum rating of 30 mA and to ensure it does not drop below the minimum rating of 5 mA.
The value of R1 is calculated based on the unregulated supply voltage (V1) and the load current (IL):
- To limit maximum current:
R1 > (V1_max - V2_min) / (IT_max + IL_min)
where V2 is the tube voltage drop (minimum 105 V) and IT_max is 30 mA.
- To maintain minimum current:
R1 < (V1_min - V2_max) / (IT_min + IL_max)
where V2 is the tube voltage drop (maximum 111 V) and IT_min is 5 mA.
Additionally, the designer must verify that the minimum supply voltage (V1_min) is sufficient to initiate ionization (start the tube) under the worst-case load condition:
V1_min * [R2 / (R1 + R2)] > V_starting
where R2 is the load resistance and V_starting is the anode breakdown voltage (typically 130 V).
Shunt Capacitance and Oscillation
If a shunt capacitor is placed in parallel with the 0B2WA, its value must be strictly limited to 0.1 µF. Capacitance values larger than 0.1 µF can form a relaxation oscillator with the tube's negative resistance characteristic, causing unstable voltage regulation and severe oscillation.
Parallel and Series Operation
- Parallel Operation: Operating multiple 0B2WA tubes in parallel to handle higher load currents is generally not recommended. If parallel operation is necessary, a small equalizing resistor of approximately 100 Ω must be placed in series with each tube to ensure equal current distribution. However, this significantly degrades the overall voltage regulation.
- Series Operation: Multiple tubes can be connected in series to obtain higher regulated voltages (e.g., two 0B2WA tubes in series provide approximately 216 V). When operating in series, care must be taken to ensure that the unregulated supply voltage is high enough to start both tubes.
Warm-Up and Drift
To achieve minimum voltage drift, a warm-up period of at least 3 minutes should be allowed after turning on the equipment. This allows the bulb temperature to reach thermal equilibrium. If the tube is subjected to high starting currents during turn-on, it may take up to 20 minutes for the regulated voltage to stabilize to its normal operating value.
Reliability and Environmental Testing
The "WA" suffix denotes a premium, ruggedized construction designed to meet strict military specifications (such as MIL-E-1). Randomly selected samples are subjected to rigorous quality control tests:
- Shock Resistance: Designed to withstand impact accelerations of 450 G (Navy flyweight high-impact machine, 30° hammer angle) or up to 900 G (60° hammer angle) for 5 impact accelerations in each of four different positions.
- Vibration Fatigue: Subjected to sinusoidal vibrational acceleration of 2.5 G at a fixed frequency (typically 25 to 60 Hz) for 32 hours minimum in each of three mutually perpendicular planes.
- Glass Strain: Immersed in boiling water (97–100°C) for 15 seconds and immediately plunged into cold water (not more than 5°C) to test envelope integrity.
- Life Testing: Evaluated over 100-hour (survival rate), 500-hour (intermittent), and 1000-hour life tests at a bulb temperature of 150°C. At the 1000-hour end point, the maximum allowable change in tube voltage drop is 4%, and the regulation must remain within 3.0 V to 4.0 V.
Technical Summary
The 0B2WA is a ruggedized, cold-cathode, gas-filled miniature voltage regulator featuring a 7-pin base and a T-5 1/2 envelope. It provides a highly stable 108 V output over an operating current range of 5 to 30 mA. With its robust mechanical design, it is capable of reliable operation under extreme conditions of shock (up to 900 G), vibration (2.5 G), high altitude (120,000 feet), and high temperature (150°C). The tube's multiple internal connections allow for a load-disconnect safety configuration, making it an excellent choice for high-reliability military and industrial power supplies.
