1500 W TVS Ratings: Pulse Energy and Protection Coordination

Understand 1500 W TVS ratings, calculate pulse energy from voltage and current, and check clamping, temperature, repetition and protection coordination.

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1500 W TVS Ratings: Pulse Energy and Protection Coordination

A 1500 W TVS rating describes peak power on a specified pulse, not a guaranteed 1.5 J energy capacity. Select the device by the surge waveform, clamping voltage, starting temperature and repetition, then check how it coordinates with upstream protection and the downstream circuit.

Last updated: October 23, 2026

What the Class Actually Specifies

Read the class as a set of conditions, because the same nominal rating hides quite different test bases.

Bourns’ SMCJ series puts it at a minimum 1500 W peak pulse power dissipation on the non-repetitive 10/1000 µs waveform (the 1 ms width is the decay-to-half-current point), derated above a 25 °C ambient, in a DO-214AB (SMC) package covering 5.0 V to 495 V of standoff with breakdown to 550 V. STMicroelectronics’ SM15T series quotes 1500 W for a 10/1000 µs waveform and up to 10 kW for an 8/20 µs waveform, with 5.8 V to 188 V standoff entries in Table 2. Leakage is ordering-code-specific: SM15T12A/CA has a 0.2 µA maximum at its rated standoff and 25 °C, while SM15T6V8A/CA allows 500 µA under the corresponding condition. The family advertises up to 1250 W at maximum junction temperature; apply the exact test conditions and derating curves.

Parameter	Bourns SMCJ	ST SM15T
Peak pulse power	1500 W minimum on the specified 10/1000 µs non-repetitive waveform; 1 ms is its decay-to-half-current width	1500 W at 10/1000 µs; up to 10 kW at 8/20 µs
Capability at maximum junction temperature	Derate above 25 °C ambient	Up to 1250 W at 150 °C
Standoff range	5.0 V to 495 V	5.8 V to 188 V in Table 2
Forward surge current, distinct from avalanche clamp current	200 A at 8.3 ms single half sine (unidirectional)	The cited table lists reverse-avalanche I_PP for clamping; this is a different parameter from forward I_FSM
Steady-state dissipation	5.0 W at a 75 °C lead temperature	The 1500 W pulse rating is not a continuous-power rating
Leakage	Per part number at rated standoff	At rated standoff and 25 °C: SM15T12A/CA, 0.2 µA max; SM15T6V8A/CA, 500 µA max
Standards coverage stated	IEC 61000-4-2 (min level 4), IEC 61000-4-4, IEC 61000-4-5	IEC 61000-4-2 above level 4 at 30 kV air and contact, IEC 61000-4-4 level 4

The Energy Arithmetic

Calculate energy from the device voltage and current over time: E = ∫v_TVS(t)i_TVS(t)dt. Peak power alone does not supply that integral.

A constant 1500 W rectangular pulse lasting exactly 1 ms would dissipate 1.5 J. This is a mathematical example, not an SMCJ energy rating.
The Bourns SMCJ pulse graph on page 4 defines its 1 ms width at half peak current, with a continuing tail. Use that waveform and the pulse-rating and temperature curves; do not replace it with a rectangular pulse.
For load dump, TI SNOAAA1 explains that TVS energy depends on source voltage, clamp voltage, duration and source impedance. Its example 12 V Test A ranges are 79–101 V, 0.5–4 Ω and 40–400 ms. The absorbed energy is not a fixed value determined by those ranges alone.

For a simple resistive-source model, i_TVS(t) ≈ max[(v_source(t) − v_TVS(t))/R_source, 0], assuming negligible load current and wiring inductance. This is an estimate, not a device guarantee. Include the real clamp characteristic, circuit dynamics and pulse train when validating a design. A 1500 W 10/1000 µs label alone establishes neither a pass nor a failure for a much longer load-dump event.

Coordination: the Part Nobody Reviews

A suppressor is one element of a chain, and the chain is what either survives or fails.

Work backwards from the protected node. The downstream circuit sets the maximum voltage it can tolerate; the suppressor’s clamping voltage at the actual surge current has to sit below that. The source impedance and the event duration set the current the suppressor must carry; the pulse power and derating curves decide whether it can. For a sustained fault, coordinate the fuse time-current curve and clearing I²t with the available fault current and the TVS failure behavior. A pulse-power rating is not a standalone fuse-clearing energy limit. Verify that normal transients do not cause nuisance opening. Where a central clamp already exists — an alternator-mounted suppressor in a vehicle, for example — the local device is sized for the residual, not for the full event.

That coordination is why industrial designs often look conservative on paper: the part is chosen for the residual energy after the upstream stage, not for the raw event. Where a supplier can provide derating curves, pulse definitions and qualification documents, that calculation can be checked rather than assumed.

Move from a pulse budget to a specific component

A pulse-power class does not identify a complete ordering code or guarantee that a given load-dump waveform is covered. After checking waveform, repetition, temperature, and protected-circuit limits, use the SMCJ device-selection guide to review a specific package and datasheet entry.

FAQ

What does the 1500 W rating mean?

It is peak pulse power under defined test conditions. Bourns ties its 1 ms width to the 10/1000 µs waveform graph and requires derating above 25 °C. ST SM15T lists 1500 W at 10/1000 µs and up to 10 kW at 8/20 µs. Consult the exact series curves and conditions for temperature and repetition; these figures are not continuous-power or fixed-energy ratings.

Can a 1500 W TVS absorb an automotive load dump?

The wattage label alone cannot answer that. Determine the required source waveform, impedance, duration, repetition and starting temperature, then check the exact device clamp characteristic and long-pulse capability. If an upstream suppressor is present, evaluate the residual at the local TVS. Use a device with relevant characterization and verify the assembled protection circuit.

What is the difference between the 600 W and 1500 W classes?

Under matching waveform and temperature conditions, 1500 W is a higher peak pulse power rating. The cited SMBJ and SMCJ examples use SMB and larger SMC packages respectively. A higher power rating does not by itself establish lower clamping voltage, a fixed increase in joules, or drop-in interchangeability. Compare the full electrical and mounting conditions.

Why does clamping voltage have to be quoted at a current?

Because clamping is not a fixed value. The device holds a higher voltage at a higher current, so a clamping figure without its peak pulse current says nothing about behaviour at your event.

What should be requested before approving one?

The pulse definition behind the power rating, the derating curves with temperature, the clamping voltage at the expected surge current, the leakage at the hot end of the range, and the qualification evidence for the target market.

Official Resources

References

Bourns, SMCJ Transient Voltage Suppressor Diode Series — source of the 1500 W minimum peak pulse power at T_P = 1 ms, the derating condition above 25 °C, the 5.0 V to 495 V standoff range with breakdown to 550 V, the 200 A 8.3 ms surge current, 5.0 W steady-state dissipation at a 75 °C lead temperature, and the IEC 61000-4-2, 4-4 and 4-5 coverage in the DO-214AB package. bourns.com — SMCJ series datasheet (PDF)
STMicroelectronics, SM15TxxA, SM15TxxCA — 1500 W TVS in SMC — source of the 1500 W (10/1000 µs) and up to 10 kW (8/20 µs) ratings, the 1250 W figure at maximum junction temperature, the Table 2 standoff entries and part-specific leakage limits, and the IEC 61000-4-2 and 4-4 coverage. st.com — SM15T series datasheet (PDF)
Texas Instruments, Protection against Unsuppressed Load Dump in Automotive Systems, SNOAAA1 — source of the ISO 16750-2 test A pulse parameters used in the energy comparison. ti.com — unsuppressed load dump application brief (PDF)
Vishay, SMBJ5.0A thru SMBJ188A, document 88392 — the 600 W class and its DO-214AA package used for the class comparison. vishay.com — SMBJ datasheet (PDF)

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