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Technical Tidbit - September 2012
Measuring Breakdown Voltage and Charging Objects With an ESD Simulator - Part 2
(A method that works with most ESD simulators)

ESD simulator with string of resistors

Figure 1.
Series String of 1K Ohm Resistors Mountged on the Tip of a NoiseKen ESS-S3011 ESD Simulator

Abstract: Measuring breakdown voltage and charging objects using an ESD simulator are useful lab techniques for finding problems in a system design related to charging or breakdown such as those related to ESD or lightning. The July Technical Tidbit covered a simple method using a specific ESD simulator for this purpose. A general method is presented here that can be used with most ESD simulators.

Discussion: The July Technical Tidbit presented a method of measuring breakdown and charging objects that required the use of a KeyTek MiniZap ESD simulator. The method to be presented here will work with most ESD simulators. ESD simulators, other than the MiniZap, charge a capacitor and switch it to the output making it difficult to charge objects to a known voltage. Sometimes a series of contact discharges are used to accomplish the purpose, but this exposes the equipment to the substantial stress of the contact discharges which may cause problems with the operation of the system.

Figure 1 shows a series string of four 1 KOhm resistors mounted on the tip of a NoiseKen ESS-S3011 ESD Simulator. The purpose of the string of resistors is to reduce the effect of a series of contact discharges used to charge up the desired object and prevent problems caused by the contact discharges. The resistors should be two Watt 5% tolerance resistors to be able to withstand the contact discharges. Guidance on resistor selection is given in my June 2009 Technical Tidbit, Effect of High Voltage Pulses on Resistors - ESD and EFT.

Use of an air discharge tip on the ESD simulator is desirable, even though contact discharges are being used, to make connection of the resistors to the tip easier and more reliable. In Figure 1, the resistor lead is held in place against the air discharge tip using a plastic cap (a 3/8 inch vacuum port cover for automobile intake manifolds that is available in auto part stores).

Four 1K Ohm resistors allows a relatively quick charging of the object while still reducing the peak current of the contact disharges. For instance, if one has an object with a capacitance of 20 pF then the RC time constant of the resistors and object would be 4*10**3 Ohms x 20*10**-12 Farads = 80 *10**-9 or 80 nanoseconds, slow enough to even out the peak current of the contact discharges that last a only few nanoseconds for an IEC 61000-4-2 simulator. For a 20 pF object, only a few contact discharges will be necessary to charge the object to near the ESD simulator setting whereas for larger objects more discharges may be necessary. It is unlikely to need more than ten contact discharges to reach a voltage near the ESD simulator setting for most objects to be charged. It is best to check that the charge is not bleeding off too quickly, such that the desired voltage may not be reached, using a static field meter. These instruments are not usually very accurate but are adequate for this purpose.

The method used to charge an object or measure breakdown voltage is as follows:
  1. Mount the resistor string on the ESD simulator and connect the tip of the resistor string to the object.
  2. Fire the simulator in contact mode until the object is charged as confirmed by calculation or measurement. Ten discharges are usually more than enough except for the largest objects.
  3. Remove the resistors from touching the object as quickly as possible after completing the contact discharges.
  4. If it is desired to measure breakdown use either a static field meter to indicate when the charge on the object suddenly reduces or a current probe on a cable connected to the object to indicate the discharge current.
Figure 2 shows the series string of resistors covered with an insulating sleeve. Use of the sleeve may be needed when charging to high voltages, for instance 25 kV, to prevent sparking directly to the connections between the resistors.

Close-up of test setup

Figure 2. Series String of 1K Ohm Resistors with Insulating Sleeve Mounted on the Tip of a NoiseKen ESS-S3011 ESD Simulator

Using an ESD simulator this way, one can measure breakdown voltage and charge objects up to 30,000 Volts. It is important that the ESD simulator not have leakage from the tip back into the simulator to prevent bleeding off charge during the test. This can be checked with a static field meter.

Summary: Using a series string of resistors, most ESD simulators can be used to measure breakdown voltage or to charge objects without causing other problems with the equipment related to the operation of the ESD simulator. A static charge meter or current probe with an oscilloscope (preferred) is needed in most cases to determine when voltage breakdown occurs.

I want to thank RMV Technology Group for the use of their lab facilities at the NASA Ames Research Park, Moffett Field, CA to conduct experiments to try out this method.

I am writing this from my new office in Boulder City, NV!!! I am doing morning 5 to 10 minute podcasts on technical topics most mornings I am in the office. These podcasts will appear on the home page of http://CircuitAdvisor.com by late morning except for days when I am not in the office. The first one has been posted under the headings of Free Audio, General Interest.

Additional articles on this website related to this topic are:
  1. June 2009. Effect of High Voltage Pulses on Resistors - ESD and EFT
  2. July 2012, Measuring Breakdown Voltage With an ESD Simulator
    (Special simulator characteristics are needed)
Equipment referenced or used in this Technical Tidbit:
  1. NoiseKen ESS-S3011 ESD Simulator
  2. Thermo Scientific KeyTek MiniZap Electrostatic Discharge Simulator

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If you like the information in this article and others on this website, much more information is available in my courses. Click here to see a listing of upcoming courses on design, measurement, and troubleshooting of chips, circuits, and systems. Click here to see upcoming seminars in Boulder City, NV.

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Copyright 2012 Douglas C. Smith