Protection

TVS Diodes (General)

Q: 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 but small current handling (≤10 A IPP). General TVS are tuned for high surge current (50-500 A) with higher capacitance (10-1000 pF) — better for power rails, worse for high-speed data.

Q: What surge level should my TVS survive?

Match the system test you need to pass. IEC 61000-4-5 Level 2 = 1 kV line-to-line / 2 kV line-to-earth; Level 3 = 2 kV / 4 kV; Level 4 = 4 kV / 8 kV. The 8/20 μs surge waveform sets IPP.

Q: 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.

Q: 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.

Q: 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.

Q: What's the difference between SMA, SMB, DO-214, DO-218?

Package size / current rating. SMA (DO-214AC) ~1 A continuous, SMB (DO-214AA) ~3 A, DO-214AB ~5 A, DO-218AB up to 12 A continuous with load-dump-specific 10/1000 μs ratings.

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.

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 (load dump). 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 2× cap of uni.

What Magnias offers

Magnias TVS portfolio covers VRWM from 3.3 V to 600 V, with IPP ratings from 1 A to 100+ A, in packages ranging from SOD-323 to SMA / SMB / DO-214 / DO-218AB. We offer both standard and low-capacitance variants, automotive AEC-Q101 qualified, and specialised RS-485 asymmetric TVS (e.g. PT0712JL for +12 V/−7 V RS-485 bus protection).

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 but small current handling (≤10 A IPP). General TVS are tuned for high surge current (50-500 A) with higher capacitance (10-1000 pF) — 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 Level 2 = 1 kV line-to-line / 2 kV line-to-earth; Level 3 = 2 kV / 4 kV; Level 4 = 4 kV / 8 kV. The 8/20 μs surge waveform sets IPP.

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 SMA, SMB, DO-214, DO-218?

Package size / current rating. SMA (DO-214AC) ~1 A continuous, SMB (DO-214AA) ~3 A, DO-214AB ~5 A, DO-218AB up to 12 A continuous with load-dump-specific 10/1000 μs ratings.

← Previous ESD Protection Diodes All categories Next → Load Dump TVS (DO-218)

What is it?

When do you need it?

How to pick the right one

What Magnias offers

Common questions

ESD Protection Diodes

Load Dump TVS (DO-218)

Short-to-VBUS Protection

Common-Mode Filter + ESD (CMF+ESD)