TVS / Transient Suppressor
Diode
A diode built to die for your circuit: normally invisible, it clamps voltage spikes (ESD, inductive kicks, surges) by avalanching in nanoseconds and dumping the energy as heat.
Schematic symbol
Diode
How tvs / transient suppressor appears in a circuit diagram.
Types & variants
Key specs
Standoff voltage (Vrwm)
VMaximum normal operating voltage — pick above your rail.
Clamping voltage (Vc)
VWhat the protected circuit actually sees during a strike.
Peak pulse power
We.g. 400 W / 600 W / 1.5 kW for a standard 8/20 µs pulse.
Capacitance
pFMust be low (<3 pF) on USB/HDMI or it distorts the signal.
Markings
Part code on the body (e.g. SMBJ5.0A = 5 V unidirectional, 600 W). 'CA' suffix usually means bidirectional.
Standard values
SMAJ/SMBJ/SMCJ series in 5, 12, 24, 33 V standoffs; PESD/USBLC6 arrays for data lines.
How to choose
Standoff ≥ your working voltage, clamping ≤ what your ICs survive, pulse rating ≥ the threat (ESD vs lightning surge are very different energies). Bidirectional for AC or signals that swing negative.
Pinout & package
2-lead SMA/SMB/SMC for power rails; SOT-23/DFN arrays for data lines. Unidirectional types have a cathode band toward the protected rail.
Example circuits
- TVS across a 12 V automotive input
- USB data-line ESD array
- Clamp across a relay coil driver
Common failures
Fails SHORT after absorbing too much (rail goes down — that's it doing its job), or degrades leaky after repeated strikes.
How to test
Diode mode: unidirectional reads like a diode one way, open the other; bidirectional reads open both ways. A short both ways = sacrificed, replace it.
Substitutes
A Zener handles small/slow transients; an MOV handles big mains surges but degrades with each hit. For fast ESD, only a TVS is really right.