Elenco Electronics EP-130, Manual, Page: 28 / 160

This circuit shows how single pulses of high voltage
electric energy are generated when a charged
capacitor is suddenly discharged through a
transformer. (Capacitor-discharge automobile
ignition systems use this same type of reaction.)
The operation of this circuit is simple, but the
concepts involved are important to understanding
more complicated circuits. If you have a
Voltage/Ohm meter, you can scientifically measure
the energy that is discharged through the
transformer.
The 470
μ
F capacitor stores up energy when the
batteries supply millions of electrons to the
capacitor’s negative electrode. At the same time, the
batteries draw the same number of electrons from
the capacitor’s positive electrode so that the positive
electrode is deficient in electrons. Since the current
must pass through the 4.7k
Ω
resistor, it requires at
least 12 seconds for the capacitor to receive the 9V
charge from the batteries.
The amount of charge in a capacitor can be
indicated by the “voltage across” the capacitor (the
voltage supplied by a battery or other power source)
or, more accurately, by the quantity of electrons
displaced in one of the capacitor’s electrodes.
The quantity of electrons in an electrode of a
capacitor is measured in coulombs. One coulomb is
a quantity of 6,280,000,000,000,000,000 electrons
(6.25 x 10
18 ).
To determine the charge in either electrode of the
capacitor (Q), multiply the capacitance (C) by the
voltage across the capacitor (E). (Q = C x E). For the
470
μ
F (470 x 10 -6 F) capacitor at 9V, this is
calculated as follows:
Q = C x E = 470 x 10 -6 x 9 = 4.23 x 10 -3 coulombs
or:
470 x 0.000001 x 9 = 4.23 x 10 -3 coulombs
(265,564,400,000,000 electrons)
When you press the key, the above number of
electrons pass through the transformer winding a
very short time and induce a high voltage in the
secondary winding. This causes the LED to flash.
If you have a VOM, connect it as directed to terminal
3 and terminal 5 of the transformer to indicate the
presence of 90V or more. The indicated voltage is
held by the capacitor and is released when the
transformer is brought into the circuit.
Notes:
-28-
EXPERIMENT #15: CAPACITOR DISCHARGE / HIGH VOLTAGE GENERATOR
Wiring Sequence:
o
1-138
o
2-118-124
o
3-PROBES
o
5-PROBES
o
79-119
o
80-117-137
o
121-122
Schematic