How to Read TVS Diode Reverse Leakage Current (IR): Temperature, VRWM, and Standby Power

Reverse leakage current, or IR, is the small current that flows through a TVS diode while the device is reverse-biased and still below breakdown. The number only makes sense when the test voltage and temperature are stated. As the operating voltage approaches VRWM or the junction temperature rises, actual leakage can increase significantly.

For a high-current power input, a few microamps may be unimportant. In a battery-powered product, a high-impedance sensor input, or a precision divider, the same current can change standby life or measurement accuracy. IR therefore belongs in the selection table alongside VRWM, VBR, VC, and pulse capability.

What does the IR value actually describe?

IR is measured at a specified reverse voltage. Many TVS diode tables use VRWM as the test point, but the exact condition must be checked for the individual part. Temperature matters just as much. A value measured at 25 °C should not be treated as the guaranteed leakage at the hottest operating condition.

VRWM is the maximum reverse working voltage at which the TVS is intended to remain off under specified conditions. If the normal rail repeatedly reaches this value because of tolerance, charging voltage, ripple, or regeneration, the margin is already thin. Leakage can rise, and the device may begin to dissipate noticeable power even when no surge is present.

Moving to a higher VRWM may reduce the risk of normal-state conduction, but it also shifts the breakdown and clamping window upward. The downstream MOSFET, capacitor, or power IC must still survive the resulting clamp voltage. A higher voltage rating is not a free fix.

Why does leakage rise with temperature?

A TVS diode is a semiconductor junction, and reverse leakage is temperature-sensitive. Inside a sealed enclosure, the local board temperature can be much higher than ambient. A TVS placed beside a hot MOSFET, inductor, or resistor may start a surge event with considerably less thermal margin than the room-temperature design suggests.

Microamp-level measurements also pick up board contamination, humidity, fixture leakage, and parallel circuit paths. When leakage matters, measure the complete board at the maximum continuous voltage and target temperature, then repeat the test with the TVS removed or isolated. That separates device leakage from the rest of the assembly.

For long-life products, allow the board to reach thermal equilibrium before recording the current. A quick measurement immediately after power-up can make a marginal design look cleaner than it is.

A 24 V model comparison

The ASIM SODA24V-SH is a unidirectional 24 V TVS diode in an SOD-123FL package. Its breakdown voltage range is 26.7 to 29.5 V, and its listed reverse leakage current is 1 µA. The device has a 200 W peak pulse power rating; at 5.14 A, its maximum clamping voltage is 38.9 V.

The ASIM SMA04J24V is also a unidirectional 24 V device with the same 26.7 to 29.5 V breakdown range and a listed IR of 1 µA. It is a 400 W SMA device, with a maximum clamping voltage of 38.9 V at 10.3 A.

The comparison makes one point clear: equal leakage does not mean equal surge capability. The reverse is also true. A larger power rating does not automatically produce lower leakage. IR, pulse current, clamp voltage, and package size answer different design questions.

These values apply under the stated product conditions. A high-temperature design still needs the relevant leakage and derating information plus a board-level measurement.

Where can TVS leakage cause a real problem?

Battery-powered equipment

In a product designed for single-digit microamp sleep current, each protected port can consume a meaningful share of the power budget. Several TVS devices across multiple connectors add together. Use the worst credible operating voltage and temperature for the calculation rather than relying on the typical room-temperature figure.

High-impedance measurement nodes

Leakage through a TVS can interact with pull-ups, dividers, sensor outputs, or bias networks. The result may be an offset that changes with temperature. If a measurement node allows only a small error current, convert that error budget into a maximum permitted protection-device leakage before selecting a part.

Communication lines

On communication interfaces, asymmetric leakage can shift the bias point or increase imbalance. Board contamination can make the symptom humidity-dependent, which often leads engineers to suspect firmware or the transceiver first. Removing the protection device for a controlled A/B comparison is a useful diagnostic step.

Does higher leakage mean the TVS has failed?

A permanent increase in leakage after a surge can indicate junction damage, but the test must control voltage and temperature. Clean the board, allow it to cool to the same starting condition, and compare the stressed device with a new device and an unpopulated board.

Do not continue powering a device that shows rising leakage or localized heating at normal voltage. Replace it, then investigate the event that caused the damage. Check pulse width, source impedance, repetition rate, and the length of the TVS return path. A damaged part is evidence; it is not the root-cause report.

Common questions about TVS reverse leakage

Does lower IR always mean better protection?

No. IR describes the off-state behavior. Protection also depends on VRWM, breakdown voltage, clamping voltage at the relevant current, pulse capability, and PCB current path.

Can a 12 V rail use a TVS with a 12 V VRWM?

Only after the maximum continuous rail voltage is known. Charger tolerance, ripple, and regeneration may push the real voltage above 12 V. If the rail operates close to VRWM, leakage and unwanted conduction become more likely.

Can a standard multimeter measure TVS leakage accurately?

An ohmmeter rarely reproduces the specified reverse voltage, and board-level parallel paths can dominate the reading. Use a stable voltage source and suitable current measurement equipment under controlled temperature conditions.

Do bidirectional TVS diodes always leak less than unidirectional parts?

No. Leakage depends on junction structure, voltage rating, die area, and test conditions. Compare actual part data rather than assuming one polarity configuration is inherently lower leakage.

Before approving a TVS diode, place maximum continuous voltage, maximum temperature, standby-current budget, and downstream voltage tolerance in the same review. If one of those values is missing, the leakage assessment is not finished.