ESD Air & Contact Discharge Calculator
Look up common ESD test-voltage pairs and calculate the charge and stored energy of a nominal 150 pF source. Keep air discharge, contact discharge, and protection-device requirements clearly separated.
Compare a test-voltage pair
Choose a reference level or enter the two voltage magnitudes separately. A shared level number does not mean that the two methods create equivalent stress.
Your discharge comparison
Waiting for the calculator.
Contact discharge
Voltage reference
- Charge magnitude |Q|
- —
- Stored energy E
- —
Air discharge
Voltage reference
- Charge magnitude |Q|
- —
- Stored energy E
- —
Energy stored in the nominal capacitor
Shared relative scale. Stored source energy is not the energy absorbed by a TVS or an IC.
Contact-current reference
- First peak
- — nominal magnitude
- At 30 ns
- — nominal magnitude
- At 60 ns
- — nominal magnitude
- Rise time
- — 10–90% reference
Lookup only at contact settings of 2, 4, 6, or 8 kV. Source: TI SLVUAC7, Table 3. Values describe a nominal generator reference, not current through your protected IC. Calibration tolerances and the complete waveform are not evaluated.
Includes inputs, calculated values, lookup references, and limitations.
Contact and air voltages stay separate
These familiar level pairs help record a requirement. They are not a conversion rule, a test sequence, or evidence that a product passed.
| Reference level | Contact discharge | Air discharge |
|---|---|---|
| Level 1 | ±2 kV | ±2 kV |
| Level 2 | ±4 kV | ±4 kV |
| Level 3 | ±6 kV | ±8 kV |
| Level 4 | ±8 kV | ±15 kV |
| Special / open level | Specified in the test plan | Specified in the test plan |
The table is a reference; calculated inputs do not establish an immunity rating.
Reference values: Texas Instruments SLVUAC7, Tables 2–3 (2014 application guide). The table and current lookup are not a complete calibration specification for a particular standard edition.
Check the edition in your test plan
IEC 61000-4-2:2025, Edition 3 revised the basic equipment-immunity test standard. The revision includes additional air-tip calibration requirements; AMETEK CTS’s technical overview also explains the added second-peak parameter, Ip2. This calculator does not assess those requirements. Use the edition, test points, sequence, and acceptance criteria specified for your product.
Three distinctions that matter
Voltage is not equivalent stress
The air-discharge arc depends on approach and environmental conditions. A nominal 15 kV air setting cannot be converted into an equivalent contact voltage by a fixed multiplier.
Method context: STMicroelectronics AN3353.
Source energy is not IC energy
The capacitor calculation describes energy available before the event. Its distribution depends on the generator, arc, discharge path, enclosure, PCB, and protection circuit. Do not compare it directly with a diode rating to declare a pass.
Component ratings are not system results
An IC’s HBM or CDM handling rating is not an IEC equipment-immunity rating. Likewise, selecting an ESD-rated protection device does not validate every enclosure, interface, or PCB implementation.
Model context: TI’s overview of transient test models.
What is calculated—and what is looked up
Nominal charge and stored energy
|Q| = C × |V|
E = ½ × C × V²
C = 150 × 10⁻¹² F
V = entered kV × 1,000Results use microcoulombs (µC) and millijoules (mJ). At 8 kV, the nominal capacitor holds 1.200 µC and 4.800 mJ. Reversing polarity changes the charge sign, not its magnitude or the stored energy.
The 150 pF / 330 Ω reference network is documented in TI’s BQ76942 IEC ESD test report, Section 4.3. It is not a universal model for every ESD standard.
Contact-current reference lookup
The tool returns the tabulated nominal contact values only at 2, 4, 6, or 8 kV. Other inputs still produce capacitor charge and energy, but no extrapolated current waveform.
At a contact setting of 8 kV:
First peak: 30 A nominal
Current at 30 ns: 16 A nominal
Current at 60 ns: 8 A nominal
Rise time: 0.8 ns nominalV / 330 Ω is not used as the first-peak current. A single RC exponential cannot reproduce the calibrated ESD waveform. No corresponding air-current waveform is inferred.
Input range: 0.1–30 kV for each method. This is a software input limit, not a prescribed test range or generator capability. Values above the displayed reference levels require a separately specified test plan. The model does not include capacitance tolerance, stray capacitance, arc physics, coupling, residual charge, current-path impedance, or DUT response.
Review more than the kV headline
- Normal operating voltage: confirm working standoff voltage and leakage across the application’s operating range.
- Signal integrity: check capacitance, channel count, package parasitics, and bandwidth for the protected interface.
- Residual voltage: review clamping and dynamic behavior under relevant pulse conditions, including the PCB return path.
- Board implementation: examine placement at the entry point, routing, grounding, and the path around—not through—the sensitive circuit.
Protection design context: ST: TVS clamping protection mode.
Keep the test conditions attached
- Requirement: applicable product standard, edition, contact and air levels, polarities, and required operating behavior.
- Exposure: connector pins, accessible conductive points, insulating surfaces, and indirect coupling tests where applicable.
- Configuration: enclosure, cables, power state, firmware, operating mode, and external equipment.
- Evidence: generator calibration, setup record, specified repetitions, observations during and after testing, and agreed acceptance criteria.
ESD calculator questions
Is 15 kV air discharge equivalent to 8 kV contact discharge?
No. They appear together in the common Level 4 reference pair, but that pairing does not establish equal stress. The discharge mechanism and waveform at the equipment differ. Record and evaluate the two requirements separately.
Can this calculator tell me the safe air gap?
No. Spark behavior depends on electrode geometry, surfaces, environment, approach, and other conditions. A simple kV-per-millimetre rule is not a safe-clearance or insulation-coordination calculation.
Why is no peak current shown for my custom voltage?
The contact-current lookup is limited to the published 2, 4, 6, and 8 kV reference points. The tool deliberately does not interpolate or extrapolate those values into a calibration claim. Air peak current is not inferred at any voltage.
Does 4.8 mJ at 8 kV tell me which TVS diode will survive?
Not by itself. That is the energy initially stored in the nominal 150 pF capacitor, not a measurement of the energy dissipated in the diode. Compare protection-device data under relevant pulse conditions and validate the complete interface.
Can I use HBM, CDM, or automotive ESD ratings here?
Not as equivalent ratings. The tool uses a fixed 150 pF reference capacitor and the stated contact-current lookup. Device-handling models and automotive test configurations can have different networks, waveforms, and procedures.
Does selecting “both polarities” double the energy?
No. Each result is the stored energy for one charged-source event at the indicated voltage magnitude. The polarity selector records the sign or signs to review; it does not add pulses, calculate cumulative energy, or define a complete test sequence.
Does the result confirm IEC 61000-4-2 compliance?
No. Matching a voltage setting is not a compliance result. Equipment performance must be assessed using the applicable standard edition, product-specific requirements, setup, calibration, test sequence, and acceptance criteria.
Protection tools and component sourcing
Need to source the selected components?
Share the exact ESD-protection or TVS part number, package, quantity, and required date. YURUNOX can review sourcing options and order-specific evidence while your engineering team retains design and validation approval.