Description:

This TVS surge clamping voltage model calculates the theroretical surge clamping voltages and peak power level for a range of common TVS types ranging from the smallest 150W types up to the beefier 5kW and 8kW types.

The surge waveform determines the pulse duration, which scales the allowed power level for a given TVS model. Then there are test voltage, generator impedance and optional circuit resistance. These determine the approximate surge current that is to be clamped by the TVS.

For each TVS, it's internal resistance is calculated from nominal (1000µs) power level and the input figures Vbr_MAX and Vclamp → Zi = (Vclamp - Vbr_MAX) / (P₁₀₀₀ / Vclamp). Then the Vbr_MIN figure, internal resistance and external resistances are used to calculate the surge current → Isurge = (Vsurge - Vbr_MIN) / (Zi + Rsrc + Rext). From that current, the clamping voltages for each device are determined → Vbr + Isurge × Zi. With minimum voltage based on Vbr_MIN at minimum temperature and maximum voltage based on Vbr_MAX at maximum temperature.

I suggest to compare the Vnom, Vbr_MIN, Vbr_MAX and Vclamp from your candidate TVS diode with the values from our table below. When those don't match, then all bets are off.

DISCLAIMER: THIS MODEL IS BASED ON GENERAL ASSUMPTIONS OF INDUSTRY-STANDARD TVS SPECIFICATIONS. ZERO GUARANTEES GIVEN, USE AT YOUR OWN RISK!

Contact us if you need lab testing of specific parts & conditions.

Surges:

• 8/20µs → the standard surge waveform as required by IEC 61000-4-5 and similar tests. Typically uses 2Ω source impedance for line-to-line injection (which includes line to neutral), and 12Ω for line-to-earth injection.
• 5/320µs → the telecom surge wave, required by IEC 61000-4-5 for networking lines longer than 300m. Uses 'differential' injection with 25Ω source impedance.
• 10/1000µs → the reference surge that is used to specifiy the nominal power handling capability of TVS diodes.
• pulse 1 → the negative going automotive surge, typically with 10Ω impedance down to -100V open circuit voltage for 12V systems and 50Ω impedance down to -600V for 24V systems.
• pulse 2a → another automotive surge, typically with 2Ω impedance and 50V open circuit.
• pulse 5 → the infamous loaddump, typically with 2Ω impedance and 100V for 12V systems and 200V for 24V systems.

Be aware that surge voltages typically are added to the line voltage!

Settings:

Select surge type, source impedance, test voltage and optional value for additonal series resistance (in your circuit):
Surge waveform:	8/20μs5/320μs10/1000μspulse 1pulse 2apulse 5DC	Surge impedance:	2Ω10Ω12Ω25Ω40Ω0Ω
Test voltage:		Extra series resistance:
Select the temperature extremes for the application. Vmin and Vmax will be adjusted with 0.1%/°C accordingly:
Minimum temperature:		Maximum temperature:

Results:

Below are the minimum and maximum values for the resulting clamping voltage for each (common) model of TVS. Also the peak power level, marked red or green depening on whether or not it stays below the power rating of the TVS for the given pulse type.

The power level between braces is the estimated power level as it pertains to the effective duration of selected surge waveform. Highly recommended to verify this figure with the ratings from your actual TVS of choice!

Click column heading to hide a power level for ease of viewing and/or printing. Double-click a value to copy an individual assessment to clipboard.