Cross Reference
Protection

TVS Diodes (General)

Workhorse transient voltage suppressors for power rails and lower-speed signal lines.

What is it?

A TVS (Transient Voltage Suppressor) diode is a heavy-duty avalanche diode designed to clamp voltage spikes on power rails or signal lines. When the rail voltage exceeds the TVS breakdown voltage, the diode conducts heavily and absorbs the surge energy as heat. Unlike the ultra-low-cap ESD diodes, general-purpose TVS parts are tuned for higher current handling (tens to hundreds of amps) at the cost of higher capacitance, which is fine for DC rails and slower signals.

TVS clamping a voltage spike on a power railVtVRWMVCunclamped surgeclamped by TVS
During a transient the TVS clamps the rail voltage to VC (clamping voltage) instead of letting the surge reach the downstream IC. The shaded curve shows what would happen without protection.

When do you need it?

  • DC power inputs that face cable plug-in transients (e.g., 5 V / 12 V / 24 V wall adapter jacks).
  • Industrial 24 V control rails where inductive switching causes voltage kicks.
  • RS-485 / RS-232 / CAN bus lines exposed to outdoor cabling.
  • PoE (Power over Ethernet) input clamping on the powered-device side.
  • Anywhere a higher surge rating than an ESD diode can provide is needed, typically IEC 61000-4-5 surge testing at Level 3 or 4.

How to pick the right one

VRWM (Reverse Working Voltage)
Must be at or just above the nominal rail voltage. Pick too high and clamping is sloppy; too low and the TVS conducts in normal operation.
VBR (Breakdown Voltage)
Typically 10-15% above VRWM. This is where the diode starts conducting.
VC (Clamping Voltage) at peak IPP
The voltage seen by the protected circuit during the worst-case surge. Choose so VC < absolute-max rating of the downstream IC.
IPP (Peak Pulse Current)
Surge current capability at 8/20 μs (IEC 61000-4-5) or 10/1000 μs (the waveform used for TVS power ratings). Match to the surge class your product must pass.
PPP (Peak Pulse Power)
Power dissipation during the surge. Higher PPP = larger die, larger package, more cost.
Uni- vs Bi-directional
Uni for DC rails, bi for AC signals or balanced data lines. Bi-directional has roughly half the capacitance of uni at the same voltage.

What Magnias offers

Magnias TVS diodes cover VRWM from 5.0 V to 440 V and 200 W to 5000 W peak pulse power (10/1000 μs): SMF in SOD-123FL (200 W, 400 W), SMA (400 W, 600 W), SMB (600 W, 1000 W), SMBF (1500 W, 3000 W) and SMC (1500 W, 3000 W, 5000 W). Uni- and bi-directional, with halogen-free (-H) and AEC-Q101 (-A) versions for most series (see each datasheet). The 6600 W / 8000 W DO-218 parts are on the Load Dump page, and the asymmetric RS-485 protector PT0712JL (12 V / 7 V, SOT23) is on the ESD page.

Common questions

How is a general-purpose TVS different from an ESD diode?
Same physics, different optimisation. ESD diodes are tuned for very low capacitance and fast response, with surge ratings from a few amps to a few tens of amps. General TVS are tuned for surge energy, hundreds to thousands of watts at 10/1000 μs, with much higher capacitance: better for power rails, worse for high-speed data.
What surge level should my TVS survive?
Match the system test you need to pass. IEC 61000-4-5 test levels are 0.5 kV (level 1), 1 kV (level 2), 2 kV (level 3) and 4 kV (level 4), plus a special level X. Product standards usually test line-to-line one level below line-to-earth. The test voltage divided by the source impedance (2 Ω line-to-line, 12 Ω line-to-earth on power ports) gives the peak 8/20 μs current the TVS must take.
Can a TVS replace a fuse?
No. A TVS clamps voltage; a fuse breaks current. Use them together, TVS to clamp the spike, fuse (or PTC) to interrupt sustained over-current.
Should I add a series resistor?
Sometimes. For high-energy events a small series resistor (1-10 Ω) before the TVS shares the energy burden and reduces clamping voltage at the IC. Common on RS-485 / CAN / sensor lines.
Why is bi-directional TVS asymmetric on RS-485?
RS-485 swings asymmetrically about ground (+12 V / −7 V common-mode range). A symmetric bi-dir TVS either clamps in normal range (bad) or has unnecessarily high VBR on one side. Asymmetric TVS like our PT0712JL match the bus profile exactly.
What's the difference between SMF, SMA, SMB, SMC and DO-218?
Size and peak pulse power. SMA (DO-214AC), SMB (DO-214AA) and SMC (DO-214AB) are three sizes of the DO-214 family; SMF (SOD-123FL) is smaller and DO-218 is larger. TVS packages are rated by peak pulse power, not continuous current. Magnias parts at 10/1000 μs: SMF 200-400 W, SMA 400-600 W, SMB 600-1000 W, SMBF 1500-3000 W, SMC 1500-5000 W, and DO-218 load-dump parts 6600-8000 W.
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