ELECTROMAGNETIC COMPATIBILITY AND MEDICAL DEVICES - Design and Development of Medical Electronic Instrumentation - page 175

Gas delivery tube replaced
by # 10 insulated wire

GAS RESERVOIR
REMOVED

50 Ohm

To earth ground

Discharge return electrode
connected to 2 meter
insulated wire

To fast oscilloscope

Figure 4.19 A piezoelectric-ignition gas lighter can be modified to generate ESD-like events. The modification involves removing the gas
reservoir and replacing the gas feed line by a pin that extends beyond the gas lighter's tip. Typical ignition piezoelectric crystals can gener-
ate discharges conveying approximately 0.2 µC within a total pulse of 100 ns to 1 µs. To assess the current and waveform delivered by the
discharge, use a 50-Ω resistor in series with the ESD gun's ground terminal as a current shunt.

approximately 0.2 µ C within a total ESD pulse of 100 ns to 1 µ s. To assess the current and

waveform delivered by the discharge, use a 50- Ω resistor in series with the ESD gun's

ground terminal as a current shunt.
A simulator which produces waveforms that are closer to a professional unit compliant
with IEC-801-2 [1991] can be built for under $100 using surplus high-voltage components.
In the circuit of Figure 4.20, a TDK model PCU-554 dc-to-ac inverter is used to drive a
Cockroft-Walton quintupler. The dc-to-ac inverter is originally sold as a cold-cathode u-

orescent lamp driver for LCD screen backlighting and may be substituted by any similar part
capable of delivering at least 1.2 kV RMS at 10 mA. The module produces a high-voltage out-
put that is proportional to its dc input. Dc power for the module is supplied by a variable power
supply built around IC1, a LM317 adjustable voltage regulator. The PCU-544 operates well
for input voltages in the range 1.5 to 5 V.
The output polarity of the Cockroft-Walton multiplier depends on the way in which its
diodes are oriented. Since ESD standards call for testing with discharges of both polarities,
the multiplier was designed to yield either positive or negative output. If the high-voltage
ac output of the dc-to-ac inverter is connected to point A of the voltage multiplier and point
B is connected to ground, the output at point D will be positive. If, however, point C
receives the high-voltage ac and point D is connected to ground, point B will be negative.
The multiplier can be built on a piece of perfboard, with square-pin connectors at points
A, B, C, and D. Ideally, the multiplier assembly should be potted in RTV silicone rubber.
This board can then be disconnected from the main circuit and turned around to change
polarity.
Switching C5, the ESD model capacitor, between the output of the voltage quintupler and
the output is accomplished by K1, a vacuum relay. Vacuum relays are much better at gener-
ating fast-rise-time waveforms than most other switches (e.g.,

fl

firing thyratrons) and yield
more reproducible waveforms than those of spark gaps. Vacuum relays can be expensive (a
few hundred dollars), and it is better to search the inventory of electronic surplus stores such

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