Coin Slot

Coin Slot Magazine - #V8N7 - 1983 - March [International Arcade Museum]
game
repair
ELECTRONIC
GAME
POWER SUPPLIES
by Jay Hanna,
Steve Lawless,
Alan Preis
In the last issue of The Coin Slot
diode in this circuit is positioned
Ea = Ep x 0.32
we discussed AC line power,
with its anode attached to an AC
Ea = Epp x0.16
sinusoidal wave forms, trans
generator(transformer or line cord),
These equations will be useful to
former types and basic diode action.
Before we begin to discuss the var
ious types of rectification, I would
like to mention the different values
of AC voltage waveforms: RMS (ef
fective), Average, Peak, and Peak to
it will only pass the positive half
determine what the final output volt
cycle of the AC waveform. The re
sultant Ea (average voltage) for half
wave rectification is 52 volts.
The following equations show the
age of a given power supply should
relationships between these voltage
serious problem. The resultant wave
form from this type of rectifier is
Peak
waveforms. They are applicable to
very difficult to smooth out (filter)
any value of effective AC voltage
(not necessarily 115 volts AC). It is
neither necessary, nor relevant from
a repair standpoint, to know how
these equations are derived.
into a steady, clean (non-rippling)
As shown in Figure 1, a 115 volt
AC power line has an actual peak
voltage (as measured from a zero
voltage reference) of approximately
163 volts. The peak to peak voltage
would therefore be 326 volts. Think
of this voltage as the useful amount
be.
The half wave rectifier has one
DC voltage, which is required for
most electronic devices. One type
of circuit that can solve this problem
is the full wave rectifier (Figure 4A).
Erms = Ep x 0.707
Epp = Ep x 2
of AC, or what value your voltmeter,
Figure 4A
Ep = Erms x 1.414
5:1
would indicate if the voltage were
measured.
Referring to Figure 2, we see a
Figure 3
Load
Diode
pulsating DC voltage, which is the
result of half wave rectification. This
waveform can be obtained by using
the circuit shown in Figure 3. Re
member, a diode can only pass cur
rent in one direction, and since the
Load
80VAC
:
A full wave rectifier circuit makes
use of a center tapped transformer.
In this type of transformer an extra
lead or tap is provided at the exact
Erms
electrical center of the transformer's
secondary. If this center tap is
grounded, the voltages at each end
of the secondary will be 180 degrees
out of phase with each other.
Figure 1
end of the secondary is at its most
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Figure 2
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positive peak in the sine wave, the
voltage at the other end of the
secondary will be at its most nega
tive peak (see Figure 4B). The volt
Ep163V
„ — /_ _ ™. \
12 International Arcade Museum
© The
In
other words, if the voltage at one
age at point A of the transformer's
secondary is shown as a solid line
52V
in this figure, while the voltage at
point B is depicted as a dotted line.
To understand how a full wave
rectifier circuit works refer to both
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