TVS Diode Clamping Voltage Selector
Check whether a TVS candidate fits between your maximum operating voltage and the protected circuit’s voltage limit. Keep the clamping current, pulse waveform, and temperature attached to the comparison.
Check a TVS candidate
This tool screens conventional avalanche TVS devices for a positive surge on a positive DC line. It does not certify protection, select a device from a live catalog, or assess negative pulses.
Voltage & pulse screening
Waiting for the calculator.
What needs attention?
Voltage reference map
Optional: clamping trend at the entered current
The straight line connects the entered maximum breakdown point and maximum clamping point. These limits may not describe one physical device curve. This is an illustrative estimate, not a guaranteed maximum, and it never changes the screening verdict.
Rsec = (VC,max − VBR,max) / (IPP − IT)
VC,trend = VBR,max + Rsec × (Iapplication − IT)The text report includes inputs, checks, reference conditions, and limitations.
Do not select by the voltage name alone
A “15 V TVS” is not a 15 V surge clamp. Read the rating, its test current, and the conditions together.
Normal operating window
Use the maximum normal voltage, including tolerances, to establish the stand-off requirement. Review leakage at the actual operating temperature.
A test-current point
Breakdown is specified at IT. It is not the clamp voltage reached while a large surge current flows.
The surge-voltage check
Pair the maximum clamp rating with its IPP and waveform, then include additional pin overshoot and your reserved voltage headroom.
Parameter and waveform guidance: Texas Instruments — How to Select a Surge Diode.
Keep the manufacturer with the part number
These three presets are reference examples, not a recommended replacement list or a statement of availability. Values from another manufacturer may differ even when the basic part name looks similar.
| Part number | VRWM | VBR min–max | VC,max | IPP | IT |
|---|---|---|---|---|---|
| SMBJ15A | 15 V | 16.7–18.5 V | 24.4 V | 24.6 A | 1 mA |
| SMBJ24A | 24 V | 26.7–29.5 V | 38.9 V | 15.5 A | 1 mA |
| SMBJ33A | 33 V | 36.7–40.6 V | 53.3 V | 11.3 A | 1 mA |
Source: Littelfuse SMBJ datasheet, electrical characteristics and pulse-rating notes. The tool does not model self-heating or apply automatic temperature derating. Package, pad area, repetition, and rating conditions still require review.
Screen the limits before refining the estimate
Voltage-window calculation
Minimum VRWM target = Vnormal,max
Maximum VC target = Vdevice limit − Vreserve − Vovershoot
Reference headroom = VC target − VC,maxThe check retains the datasheet maximum clamp value even below its rated current. For a conventional monotonic avalanche device, this is a first-pass endpoint screen under matching conditions, not a calculated pin-voltage waveform.
If the endpoint screen misses your voltage window, it does not automatically prove that the part fails at your lower current. Obtain applicable maximum clamping data or testing; do not use the optional linear trend as proof.
Condition matching comes first
The application and rating waveform must match, the entered initial and reference temperatures must match, and the event must be an isolated pulse. Different conditions produce a review flag, not an automatic conversion.
Current above the entered IPP blocks use of the endpoint as an application clamp. Equality leaves no current reserve. Equal clamp headroom or equal stand-off voltage is also flagged for review.
Clamping and temperature context: STMicroelectronics — AN316 TVS Clamping Protection Mode.
Input ranges are software limits, not device ratings: 0.1–1,000 V normal line; 0.1–2,000 V device limit; 0.0001–10,000 A pulse current; −65 to 175°C temperature. Only conventional positive-avalanche behavior is screened. Snapback devices, active clamps, sustained overvoltage, automotive load dump, and IEC ESD behavior require dedicated analysis.
Change the protection approach
- Stand-off is too low: choose a candidate that accommodates the true normal line maximum, then recheck its clamp rating.
- Clamp is too high: investigate applicable lower-clamp data, a lower-dynamic-resistance device, or a coordinated protection stage.
- Surge current is too high: review source impedance, coupling, and a higher-capability TVS at the required pulse duration.
- Overshoot consumes the margin: inspect routing, return paths, package parasitics, and measurement technique.
Complete the board-level review
- Thermal stress: evaluate the actual pulse shape, energy, mounting, temperature derating, and recovery between events.
- Signal loading: check leakage and capacitance on precision, RF, and high-speed data lines.
- Polarity: evaluate the negative transient separately, including forward conduction for unidirectional devices.
- Fault behavior: consider sustained faults, upstream current limiting, and appropriate fuse or disconnect coordination.
Further selection questions: STMicroelectronics TVS FAQ.
TVS selection questions
Why does the result still use VC,max at a lower current?
The main result is a datasheet-endpoint screen. It does not assume that clamping voltage scales directly with current. A lower clamp value needs applicable characterization or a validated device model. The optional line estimate is kept separate from the screening decision.
Can I use a 10/1000 μs rating for an 8/20 μs event?
Not directly in this tool. Choose ratings specified for the required current waveform, or obtain suitable data from the manufacturer. Changing the waveform selection does not convert a datasheet rating.
Is the surge current the same as the load current?
No. Enter the current diverted through the TVS during the transient. It depends on the source, coupling, source impedance, clamp behavior, and circuit paths. The tool does not calculate it from a surge generator’s open-circuit voltage or short-circuit current.
Does “within the entered limits” mean the design is protected?
No. It means only that the numeric endpoint checks have positive headroom under the entered reference conditions. Dynamic overshoot, self-heating, component tolerances, negative pulses, and the actual circuit still need validation.
Can I use this for AC, ESD, or automotive load dump?
This page screens positive surges on positive DC lines using conventional avalanche TVS ratings. It does not analyze the negative half-cycle of AC, fast ESD waveforms, or a load-dump pulse and its energy. Use the relevant manufacturer model and application test conditions.
What should I include when asking for a TVS quote?
Provide the exact manufacturer and full part number, unidirectional or bidirectional version, package, qualification needs, quantity, target date, and any approved alternatives. Keep the engineering selection and required evidence attached to the request.
Continue the protection review
Have a TVS part number or protection BOM?
Send the exact device, manufacturer, package, and quantities. YURUNOX can review sourcing options, available documentation, and delivery requirements.