STAR*TEcH
Journal
June 1996
... continued from page 17.
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PosrOften
switching transistors as subs here.
I find the 2SC3039 works almost
everywhere a TO220 switcher is
needed in switching power sup-
plier.
Power dissipation rating in watts
is mostly only an issue for larger
power transistors. Not all high
voltage/high current transistors
are the same. For some it is high
voltage or current at one time, for
others it is both. The difference
will show up in the power rat-
ing.
Gain is the last parameter to con-
sider here. Many transistors show
their gain rating as a range of val-
ues if you look in the manuals.
Gain is partly dependent on the
circuit the transistor is in. There
is one type transistor called the
Darlington that has substantially
high gain than conventional tran-
sistors. It is actually two transis-
tors in one package. Darlingtons
come in all case styles. Examples
are MPSA13 in a TO92, SE9302
and TIP102 m a TO220.
Darlingtons must be replaced
with same and conventionals
with conventionals. Do not cross
one with the other.
Identification note: American
transistors usually print the whole
type number on the device, e.g.
2N4401, 2N3055.Japanese tran-
sistors usually omit the first two
characters (2S) so the device only
has the remainder printed on it.
2SD870 will be labeled D870,
2SC945 will be labeled C945,
and so on. If you have had
trouble findingjapanese transis-
tors in the replacement catalogs, -
perhaps this is why.
DIODES
Diodes serve many functions . Put
four of them in one package and
you get a bridge rectifier. Again
we must consider case style, cur-
rent, voltage, speed. Bridges are
simple, apply the more is better
rule. Case style may be the
hangup here. If the 35 amp
bridge in my toolbox has differ-
ent legs than the one in my pin-
ball machine, it won't fit on the
PC board. Don't leave the game
down all weekend for this, save
it. Screw your odd bridge to the
back box metal shield for hear
sinking and run four heavy wires
to the PC board. Your game now A
works and you can come back w,
later with the original style part.
Actual diodes come in many
types. The ones used as rectifiers
and those across solenoids can
always be subbed by higher volt-
age and/ or current rated parts.
Most diode applications are
straight forward and easily
subbed.
Switching power supplies use
fast-recovery diodes due to the
high frequency operation. Some
people find they can use slow
diodes there and have it work,
buy why bother taking the
chance when fast recovery diodes
are cheap and readily available.
Who wants a glitchy power sup-
ply? I mainly stock one and three
amp types at 400 volts or more.
Try Di GiKey.
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