iso 7637-2 pulse 1 vs iec 61000-4-5 waveform comparison

IEC Surge/EFT Generators for ISO 7637-2 Automotive Pre-Compliance


Like most long articles, this started off as a short one. It all stemmed from a customer question:


“We had some issues using a LED driver that could not cope with load dump and volt spikes. Do you have any provisional tests that could determine the circuit reliability? It doesn’t have to be to [ISO 7637-2]”


The ISO 7637-2 standard defines automotive conducted transient test pulses on vehicle power lines (12V or 24V). It is called up by standards including:

  • UNECE Regulation 10.06 for E-marking
  • EN 50498 (aftermarket automotive equipment)
  • ISO 13766-1 (earth-moving and building construction machinery)

I don’t have an ISO 7637-2 pulse generator. Automotive surge generators are less commonly found in many EMC test labs due to their more specialised nature.

Systems are available to hire; budget for €/£1000/week for a generator that will cover Pulses 1, 2 and 3. They are also available to buy new;  expect to pay around €/£15k. If you need to cover pulse 4 then this will increase the costs yet again, mostly for the bipolar amplifier.

But, like most EMC test labs, I do have an IEC 61000-4-4 (EFT) and IEC 61000-4-5 (Surge) generator capable of 1.2/50us and 10/700us pulses.


Question: Could I use the IEC generator to simulate the surge pulses from the ISO generator?


This question comes with caveats:

  1. The aim here is pre-compliance / confidence testing with the tools available. Not to replace the ISO 7637-2 tests entirely.
  2. We are only looking at the potentially destructive Pulses 1, 2a, 3a and 3b.


Unit 3 Compliance can perform pre-compliance and full CE Marking testing to EN 50498. We can also perform pre-compliance testing for many of the R10 tests for E marked products.

Please get in touch for a chat if this is of interest.


Conclusions (TLDR)

ISO Pulse 1

  • IEC 10/700 pulse generator can be used as a close substitution for a 12V system
  • For a 24V system the 10/700 pulse is not as good a match. Follow the flowchart to select the test compromise and set the surge voltage based on the values in the tables.

iec 10-700 for pulse 1 24V surge voltage selection flowchart

iso pulse 1 24V vs iec 10-700 Best Compromise

iso pulse 1 24V vs iec 10-700 Best Compromise actual voltages and currents

ISO Pulse 2a

  • Not a good match, recommend a compromise between current and energy as shown in these tables

iso pulse 2a vs iec 1.2-50 Best Compromise

iso pulse 2a vs iec 1.2-50 Best Compromise actual voltages and currents

ISO Pulse 3a, 3b

  • IEC EFT generator is a good match and can be substituted for ISO pulse 3a and 3b


Pulse Parameter Comparison

Comparing the pulse widths and impedances against each other gives a mixed picture.

For Pulse 1, neither waveform is a great match with both of the ISO pulses having a longer pulse width than the 10/700 generator. Whilst the 24V bus pulse has a much higher impedance, this could be corrected with an additional series resistor in the IEC  generator output.

comparison table - iso 7637-2 pulse 1 to IEC 61000-4-5 10-700

For Pulse 2a, the 1.2/50us IEC generator appears to be an excellent match.

comparison table - iso 7637-2 pulse 2a to IEC 61000-4-5 1.2-50

For Pulse 3a and 3b, the 5/50ns EFT generator is pretty close but the width of the ISO pulse is three times bigger.

comparison table - iso 7637-2 pulse 3a 3b to IEC 61000-4-4 eft 5-50n


However, as we shall see below, this approach is incorrect as it does not tell the whole story.


Pulse Width Definition

The problem comes from how the pulse widths are defined in the standards. Let’s take the comparison between ISO Pulse 1 to IEC 10/700 comparison as an example.

e can see that the ISO pulse width is defined at the 10% crossing point, whereas the IEC pulse width is defined at the 50% crossing point.

iso 7637-2 pulse 1 vs iec 61000-4-5 waveform comparison

This is not helpful.

How do we compare a ISO 1000us @ 10% with a IEC 700us @ 50% waveform?


Open Circuit Ideal Waveform Comparison

I found some information over on the PSCAD website that showed the equation for the waveshape (from IEC 61000-4-5)…

exponential surge waveform formula…along with some Matlab optimised coefficients for alpha, beta and k.

From the PSCAD website “Standard Surge Waveforms”


ISO 7637-2:2011 gives the equation for the falling edge only of the pulse waveform. It also states that “The influence of the rise time is not taken into account (tr << td), which is allowed for all pulses specified in this part of ISO 7637

iso 7637-2 pulse shape equation


Modelling Notes

After watching a Numberphile video on coronavirus infection curve modelling I decided to give Geogebra a try for modelling these waveforms. It’s quite a useful graphing calculator package, much more powerful than I’ll ever need to use.

I also modified the equation for the IEC waveshape equation to take into account the generator and load impedances by taking the first term of the ISO equation and adding it to the start of the IEC equation.

A required surge voltage of 1V was used for simple direct comparison.


Pulse 1 (12V) vs IEC 10/700us

Geogebra Link

ISO 7637-2 (Pulse 1, 12V) vs IEC 61000-4-5 (10_700) geogebra

Pulse 1 (24V) vs IEC 10/700us

Geogebra Link

ISO 7637-2 (Pulse 1, 24V) vs IEC 61000-4-5 (10_700) geogebra

Pulse 2a vs IEC 1.2/50us

Geogebra Link

ISO 7637-2 (Pulse 2a) vs IEC 61000-4-5 (1.2_50) geogebra

Pulse 3a/3b vs IEC 5/50ns

Geogebra Link

ISO 7637-2 (Pulse 3a_b) vs IEC 61000-4-4 (5_50ns) geogebra


Review of Waveform Comparisons

For Pulse 1 we can see that the 10/700 IEC waveform is actually a really good match for Pulse 1 for a 12V bus.

The same cannot be said for the 24V bus requirement. Some further thinking is required here.

The 55 ohm impedance for the 24V version of the pulse is the 15 ohm 10/700 generator natural impedance with a series 40R resistor in addition.

comparison table - iso 7637-2 pulse 1 to IEC 61000-4-5 10-700 - GEOGEBRA RESULTS

Despite Pulse 2 looking like a good comparison initially, the modelling shows that it is actually a very poor match.

comparison table - iso 7637-2 pulse 2a to IEC 61000-4-5 1.2-50 - GEOGEBRA RESULTS

For Pulse 3, the IEC EFT generator is a very good match and should be able to be used without any issue

comparison table - iso 7637-2 pulse 3a 3b to IEC 61000-4-4 eft 5-50n GEOGEBRA RESULTS


Dealing With Pulse 1 (24V) and Pulse 2a

How could we go about compensating for the poor match between Pulse 1 (24V) and 10/700 IEC and between Pulse 2a and 1.2/50 IEC?

We need to ask ourselves: are we more interested in the peak voltage & current or pulse energy?

To answer this, first we need to understand the power input design of the Equipment Under Test (EUT)


EUT Design Assessment

It is useful to establish the following EUT design parameters:

  • Is there a discrete reverse protection diode? What is the Vrrm and Trr rating (reverse recovery time) of this part?
  • What is the maximum clamping voltage of the TVS diode and can the downstream circuitry survive this voltage?

vehicle power input protection circuit

It is important to remember that Pulse 1 is a negative going pulse caused by the disconnection of a large inductive load in parallel on the vehicle power bus. If the EUT has a reverse protection diode fitted then it’s Vrrm and Trr will change the effect of the test on the EUT.

W2AEW has a good video on diode reverse recovery time over on YouTube.

It is also important to test at full current consumption if a reverse recovery diode is present as this will affect recovery time and therefore surge performance.


EUT Surge Suppression

The assumption is that we are testing an EUT that contains some basic low voltage electronics of some kind. The extension of this assumption is that it has some kind of surge suppression component connected across the power inputs.

This could be a Metal Oxide Varistor (MOV) or a Transient Voltage Suppression Device (TVS). These have a non-linear impedance with voltage and will restrict or “clamp” the input voltage to a defined level. Perhaps a component like a SMBJ26CA-TR.

This clamping voltage is dictated by the impedance of the part when conducting. This would be a diode-like VI curve for a TVS or the current-dependant resistor of a MOV.

Peak current is dictated by available peak voltage and generator impedance. So we need to be interested in the peak current to ensure that the correct clamping voltage is met.

Also, because the MOV or TVS absorbs some of the pulse energy internally, these components will have a datasheet rating for pulse energy. Exceeding this could cause significant damage to the part and affect its capability to handle future surges.


Pulse 1 Peak Voltage & Current or Pulse Energy?

Our main tools for adjusting an IEC pulse to suit an ISO pulse are:

  • Peak voltage
  • Series impedance

The surge generator has an easily adjustable peak voltage through the control panel or software so this is the main method that will be used.

The Peak voltage is a significant consideration if the system has the reverse protection diode but the compromise test will depend on it’s voltage rating.

I’ve produced a flowchart to help selection of the right test level for using IEC 10/700 instead of ISO Pulse 1

iec 10-700 for pulse 1 24V surge voltage selection flowchart



Pulse 1 Best Compromise Voltage

I ran some more simulations in Geogebra adjusting the ratio between the IEC and ISO peak voltages and tabulated the results.

ISO 7637-2 (Pulse 1, 24V) vs IEC 61000-4-5 (10_700) Matched Pulse Energy

iso pulse 1 24V vs iec 10-700 Best Compromise

The best compromise is to minimise the total difference between current and voltage when expressed as ratios. This works out at a V_iec or around 0.6 * V_iso.

This yields the following test voltages, peak currents and pulse energies for the different severity levels.

iso pulse 1 24V vs iec 10-700 Best Compromise actual voltages and currents



It is interesting that the series impedance for the 24V version of ISO Pulse 1 is up at 50 ohms. This higher impedance implies that the surge expected in such a system would be induced from a parallel adjacent cable in a wiring loom rather than something directly connected to the ignition switch / inductive load circuit directly.


Pulse 2a Best Compromise Voltage

Same approach as for Pulse 1

iso pulse 2a vs iec 1.2-50 Best Compromise

iso pulse 2a vs iec 1.2-50 Best Compromise actual voltages and currents



Test Practicalities & Further Compromises

Pulse 1 Power Disconnection

The waveform for Pulse 1 shows a synchronised disconnection from the DC supply and application of the surge voltage. Since this is not easily done without

It is the surge pulse that will cause the damage rather than the momentary disconnection of voltage therefore, for these compromise tests, this is being ignored.


Coupling/Decoupling Network Requirements

The CDN inside the IEC test generator for mains coupling is adequate for the task of decoupling but the options inside my KeyTek ECAT test generator preclude the coupling of the 10/700 waveform. Instead, some creative front panel wiring with banana plugs will be required.

Since this CDN is designed for decoupling of surge and EFT impulses from the mains, I’m sure it will adequately protect the 12V linear power supply being used and also prevent the power connection from unduly affecting the test.

In may case, input is through a 16A IEC mains plug/socket but it is easy to make an adaptor. Output is via a BS1363 socket or, more convieniently, 4mm banana plugs.



The End.

This took way longer to research and write that I was hoping. Something in the order of three days of work was spent going backwards and forwards, thinking about it whilst doing DIY at home (nearly painting the cat as a result) and half listening to Tiger King on the TV.

I’m quite pleased with the result and I hope this eventually proves useful to someone.




By James Heilman, MD - Own work, CC BY-SA 4.0,

Ventilator Projects and EMC Testing (EN 60601-1-2:2014)


If you haven’t already, check out part 1 of this blog Part 1: Rapidly Manufactured Ventilator (RMV) Projects and EMC Regulations

We’re going to take a look at the EMC requirements for RMVs, consider some of the risks posed by EMC and propose some methods of mitigating them.

Probably the biggest EMC risks are Radiated RF Immunity and ESD due to their higher than normal test levels.

If you need any fast turnaround design support and testing services for your Rapidly Manufactured Ventilator project then get in touch.


As noted in the MHRA RMVS specification on page 24:

“EMC Testing (TBC): Must comply with IEC 60601-1-2:2014, Medical electrical equipment — Part 1-2: General requirements for basic safety and essential performance — Collateral Standard: Electromagnetic disturbances — Requirements and tests”

So lets take a look at a the EMC tests that might be required for a typical Rapidly Manufactured Ventilator project.

This is with the view of meeting the Essential Performance / Basic Safety requirements of EN 60601 whilst addressing the highest risk items first. This is prioritising speed of testing instead of performing a belt and braces, test everything approach that would be the common approach for Medical Devices.


These ventilators are going to be used in a hospital / clinical care environment under medical supervised use and not in a home environment.

60601-1-2 classifies a hospital as a Class A emissions environment for Radiated and Conducted emissions. This means that less time needs to be spent fighting to get the emissions below Class B.

Risk items to radiated emissions could include any brushed DC pump motors as these are notoriously noisy. Ferrite cores may be required around motor cables to mitigate this noise.

Following the design guidelines further down this article for any PCBs is recommended and will greatly assist with reducing EMC radiated emissions.

Most RMVs will be using an off the shelf power supply already approved to EN 60601 for Safety and EMC. AC Power conducted emissions should therefore look after itself and won’t be a significant worry for testing.

For Harmonic Distortion and Flicker, there is an interesting note in EN 60601-1-2 in Annex A

“It is assumed that ME EQUIPMENT and ME SYSTEMS used in hospitals (and large clinics) are not connected to the PUBLIC MAINS NETWORK.”

If this is the case, then Harmonics and Flicker requirements and tests need not apply as these only relate to the public mains network.



Most ventilator systems have no external electrical ports apart from the power supply. They are mostly self contained units. This greatly speeds up and simplifies the testing, and reduces the risk of problems with Signal Input / Signal Output Ports (SIP/SOP Ports in the standard, analogous to a Signal Port from other EMC standards).

Mains borne interference (EFT, Surge, Conducted RF) should be handled by the EN 60601 pre-approved power supply without issue. It will still need checking but ultimately the risk is low.

Dips and Interrupts and the hold up time of the power supply is something that would need considering at the Risk Analysis level to derive the correct immunity criteria for each of the individual tests.

If this needs improving then selecting a slightly larger power supply than nominally required could help. More likely, additional bulk decoupling on the main power rail (e.g. 1000uF) will help maintain the system DC voltage under these conditions.

Immunity Performance Criteria

Caveat: This section is me thinking aloud as I have no domain specific knowledge for Risk Management and Medical Devices. I’m trying to approach this from a common sense perspective to aid anyone working on a RMV.

The function of the EMC Immunity tests for Medical Devices is to ensure that the Essential Functions continue to operate and that Basic Safety condition is maintained.

Normally the immunity performance criteria would be based on the type of EM phenomena being simulated in the test. This is normally Criteria A for continuous phenomena (radiated or conducted RF immunity) or Criteria B for momentary phenomena (ESD, EFT, Surge, Dips/Interrupts). Criteria C only tends to crop up for longer duration power interruptions.

In the case of a Medical Device, maintaining the Essential Performance is the key parameter. If a momentary EM phenomena causes this to happen then this is a major problem.

Therefore immunity performance criteria must be considered for the key function of the device as well as the duration of the EM phenomena.

Based on this thought process, a sensible starting point for the immunity criteria is:

Assume criteria A (unaffected performance) for:

  • Key function of assisting patient breathing for all tests. This includes momentary EM phenomena tests = ESD, EFT, Surge, Dips/Interrupts.
  • Non-critical functions under continuous EM phenomena tests = Radiated and Conducted RF Immunity

Assume Criteria B for:

  • Key function performance for this means that there should be a function in the RVM firmware that remembers its last current operating state and settings and that it starts up in that state from a power cycle. This creates a requirement for programmable non-volatile memory (some kind of EEPROM) in the RVM.
  • All momentary EM phenomena tests for non-critical functions e.g. display readout may temporarily distort or flicker so long as it recovers

Assume Criteria C for:

  • Non-critical functions from momentary power loss e.g. screen/display readout or setting

Immunity Risks

There are two big risks to the immunity performance: Radiated RF Immunity and ESD.

Radiated RF Immunity

Test Requirements

The basic requirement for radiated RF immunity is a flat 3V/m from 80MHz to 2.7GHz. So far so good, this is a fairly easy test to meet.

Now the bad news. Table 9 gives a list of spot frequencies to be tested to simulate close range exposure to common wireless technology standards. The table is summarised here:

Frequency (MHz)ModulationTest Level (V/m)
38518 Hz pulse, 50%27
450FM +/- 5kHz dev.
1kHz sine
710, 745, 780217 Hz pulse, 50%9
810, 870, 930 18 Hz pulse, 50% 28
1720, 1845, 1970 217 Hz pulse, 50% 28
2450 217 Hz pulse, 50% 28
5240, 5500, 5785 217 Hz pulse, 50% 9

As you can see, this has testing up to 28V/m, a significantly higher field strength than 3V/m!

Risks to the EUT

This test loves to mess with analogue sensors. In the case of ventilators, the pressure sensors used frequently have an analogue output to a DAC on the CPU. This presents two risk areas:

  1. Demodulation of noise inside the pressure sensor amplifier. This takes the small transducer signals and amplifies it up to the output voltage. Noise demodulated here would cause the carrier to be superimposed on the pressure readings.
  2. The input of the ADC could be susceptible to noise picked up on the analogue voltage from the pressure sensor, even if the pressure sensor itself is unaffected. This will affect the readings.

Since the airflow and pressure sensors are a key component to the operation of the ventilator, these must be protected at all cost.

Design Recommendations

Design ideas to mitigate this interference include

  1. Keep traces/connection as short as possible between sensors and ADC
  2. If you can mount them all on the same circuit board then do so
  3. This circuit board will have one layer dedicated to a solid ground plane fill over the entire plane. All ground pins

    Check out my video presentation on PCB grounding and HF current flow.
  4. Cables = antennas that are good at receiving the interference. Minimise use of cables where possible.
  5. Figure out what your minimum bandwith requirements for airflow are and filter the signal appropriately. You probably won’t need to sample the airflow faster than 10kHz so put a low pass filter right next to the ADC input. Something like a 4k7 and a 1nF will give you a 3dB of 34kHz. This will reduce the risk of RF noise being demodulated by the ADC input.
  6. Decouple the supply lines to the pressure sensor well
  7. Add a small filter to the pressure sensor input, perhaps another RC filter as shown above. This will help prevent the pressure sensor from being affected by the test.
  8. It is possible that the pressure sensor will be directly affected by the radiated noise picked up by the sensor body itself and not by the traces. It would be prudent to provide a PCB footprint for a shielding can near the sensor. I have seen this effect on gas sensors in the past.

Risk Analysis

Assuming that the advice above is followed, the risk to the EUT is manageable.

One of the interesting features of Radiated RF Immunity testing is that of the Problem Band where most issues occur.

radiated rf immunity susceptibility characteristics

Most of the time, the problem band is in the 100MHz to 300MHz area (I’ll cover this in more detail in a future article). Cables tend to be the best antennae at these frequencies and, hopefully, our ventilator only has one cable of interest – the AC power cable. This has plenty of filtering for conducted emissions reduction which should handle this noise.

Probably the two biggest problem frequencies from the spot frequencies above are going to be 385 MHz and 450 MHz.

Then we are into the realms of direct pickup on internal signal cables and PCB traces at higher frequencies. If we’ve laid out our PCB well as highlighted above (short analogue traces, filtering, good ground plane, shielding provision) then this will help mitigate our risks.



The levels of ESD testing are almost twice that of the regular EMC standards with a requirement for 8kV contact and 15kV air discharges.

ESD is very good at upsetting digital systems and it has a particular fondness for edge triggered pins e.g. reset lines and interrupts.

Design Recommendations

If the reset line for the CPU controlling the RVM is shared with other digital circuit blocks or supervisory controllers then an RC low pass filter at the input to the CPU is highly recommended. This helps prevents unwanted resets.

Checking can be implemented in the Interrupt Service Routine to ensure that an interrupt condition actually exists, effectively de-bouncing the input.

Thankfully the Ingress Protection requirements for the RVM of IP22 and the requirement to provide flat, easily cleanable surfaces will probably dictate the use of some kind sealed membrane keyswitch panel. These have good ESD immunity as no direct contact discharge can take place on an switch where the plastic covering remains in place.

Whatever user interface technology the RVM employs, this will be a key risk area for ESD. If this is on a separate PCB to the main controller, all interfaces will need some kind of filtering. A small capacitor to ground on each of the lines that goes to the keypad would be a good idea. 0603, 100pF usually works well here.

Lastly on the mechanical design, keeping the electronics well away from the enclosure seams will also reduce the risks of creepage of any discharge into the circuit board.

Summary Test Plan


  • Radiated Emissions, Class A, 30MHz to 1GHz (EN 55011)
  • Mains Conducted Emissions, Class A, 150kHz to 30MHz (EN 55011)


Text in bold is highlighted as a risk item.

  • ESD, (EN 61000-4-2), 8kV contact, 2/4/8/15kV air. Test to connectors as well.
  • Radiated RF Immunity (EN 61000-4-3)
    • 80MHz to 2.7GHz @ 3V/m
    • Various spot frequencies at up to 27V/m
  • EFT (EN 61000-4-4), AC Mains Port, 2kV
  • Surge (EN 61000-4-5), AC Mains Port, 1kV line-to-line, 2kV line-to-ground
  • Conducted RF Immunity (EN 61000-4-6), AC Mains Port, 3V/m (6V/m in ISM bands)
  • Dips and Interrupts (EN 61000-4-11), AC Mains Port, various


Not only has this article identified key EMC risks to Rapidly Manufactured Ventilators but also provided some design guidelines to dealing with the problems that might arise.

Some of the guidelines within might be useful to anyone designing a Medical Device. We haven’t covered the requirements for Patient Coupled Ports or SIP/SOP ports from an EMC perspective as they aren’t of too critical a concern for an RVM.

We can see how looking at the standard and pulling out the required tests can help us understand the risks involved in the design.

Experience of knowing how the tests will typically affect the EUT is the key to unlocking good design practices. In my case, this comes from having worked on many designs with problems and the learning that comes from fixing the issues that crop up.

Remember EMC test success comes from good EMC design. For a time critical RVM there is one chance to get it right – no do-overs!

I hope you found this article useful. See you when all this has calmed down.
All the best,

By James Heilman, MD - Own work, CC BY-SA 4.0,

Ventilator Projects and EMC Regulations (UK)


1. CE marking probably won’t be necessary for UK for temporary ventilators
2. Still need to apply to MHRA for permission to use in clinical setting
3. This will likely involve the supply of test data to MHRA
4. The requirement for EMC testing is currently To Be Confirmed
5. U3C will give any ventilator design a pro bono EMC design review

In the current Covid-19 pandemic there are many project teams around the world coming up with designs for ventilators. The potential is for many such devices to be required.

The problem that this article identifies is that for normal medical devices, the length of time taken to get products approved is defined in terms of months. This is especially true for ventilators which are, according to several sources, a Class IIb device requiring a robust quality system and Notified Body approval.

The current requirement is for devices to be delivered within weeks.

Recognising this, the MHRA in the UK have published a “Specification for ventilators to be used in UK hospitals during the coronavirus (COVID-19) outbreak.”

Interesting points from this document in relation to the Electromagnetic Compatibility (EMC) characteristics are:

Page 10: “2. It is not anticipated that devices will be CE marked and approval by the MHRA will be through the “Exceptional use of non-CE marked medical devices” route (”

The procedure covered under the “Exceptional use of non-CE marked medical devices” involves applying to the MHRA directly for a pass to supply this product for use without CE marking. This request will have to include data that shows compliance with the test criteria in Appendix B of the MHRA specification.

Page 11:3. When the current emergency has passed these devices will NOT be usable for routine care unless they have been CE marked through the Medical Device Regulations. The device must display a prominent indelible label to this effect.

Page 24: “EMC Testing (TBC): Must comply with IEC 60601-1-2:2014, Medical electrical equipment — Part 1-2: General requirements for basic safety and essential performance — Collateral Standard: Electromagnetic disturbances — Requirements and tests”

Note that the requirement for EMC testing remains TBC = To Be Confirmed. I strongly feel that at least some testing should take place, but functionality of the ventilator has to come first.

Next article will be a breakdown of the EMC test requirements called up in EN 60601-1-2:2014. I’ll also highlight some risk areas that designers of these ventilators will need to to bear in mind.

If anyone has any need for pro bono EMC design review services for ventilator projects or needs some EMC testing turning around quickly then get in touch.

I hope you are all keeping well during these interesting times.