Star Tech Journal
Issue: 1986-December - Vol 8 Issue 10 - Page 13
STAR*TECH Journal
December 1986
This supply has two more sections that are
not used on every supply. SCR, Rl7, Rl8,
and Dl2 make up an overvoltage Crowbar
circuit. If the output voltage rises above
5 volts, Dl2 starts to breakdown. The
current through Rl8 causes a voltage drop
across it. This voltage is applied to the
gate of the SCR through Rl7. When the
potential exceeds the trigger voltage, the
SCR conducts, shorts the voltage to
ground, and hopefully saves the boards.
Power Supplies: Theory Of Operation
Jajy
W
Janes Beck
Greater Southern Distributing Co.
Atlanta, Georgia
Over the past few rronths I've been
atterrpting to show you how to modify power
supplies to get better performance or to
obtain voltages that they didn't normally
have. This leaves one problem. What do you
do when the supply breaks down? Needless
to say proper logic board operation
requires proper power supply operation.
'!he last thing to look at is Rll and Dll.
Rll is a current limiting resistor for the
LED Dll. This is used to visually check
that there is an output. It doesn't rrean
the output is correct, just that there is
sorrething there.
Figure 1 shows a basic +5 volt regulator
taken from a Mylstar MA.CH III nanual.
+ 11, 5V
DC
Q11
2N58'79
H.S. 31
+5V DC
+
R13
12
2W
•
(13)
-
-
012
1N4734
5V
SCR
MCR 68-1
C12
C13
100UFI 0.1UFl
16V _l 50V_L
-=- C14
0.22UF
35V
TANT.
U11 K
TL431 &-:.:..R ----e----+----r----.
T0-92 A
-=-
-=-
I +
f66
110,1
1/4W
MV5752
-=-
Next rronth we'll "power up" our supply and
look at each section in operation. '!hat
way we can see how the failure of a
specific section will affect the overall
operation.
Let's break it down and look at the
separate sections.
First is the reference voltage section.
This is the actual regulator of the whole
system. It supplies the "rock steady"
voltage that determines the output
voltage. It is made up of Ull (an
adjustable Zener), Rl2, R15, R16, and VRl
(the +5 adjust).
(Ull functions just like a fixed Zener,
but by varying the voltage on the R
terminal, you change the breakdown
voltage.) This section gives us a nicely
regulated voltage, but the current it
supplies is very small compared to what
the boards need.
That takes us to the next section. Qll and
Ql2 make up the current arrplifier. 'Ibey
&ake the low level current supplied by the
• eference section and bring it up to a
useable level. Qll is the transistor
referred to as the Series-Pass since, as
you can see, it is in series with the
unregulated voltage and the load.
R11
180
1/4W
Conversion Kits
Lowest prices in America!
For Sale:
Kit Price:
CHOPLIFTER
MAT MANIA
LEGEND OF KAGE
GHOSTS' N GOBLINS
10 YARD FIGHT
JAILBREAK
TIGER HELi
1942
VIE AR KUNG FU
SUPER BASKETBALL
BIG BUCKS TRIVIA
GALAGAIII
RUSH ' N ATTACK
MANY MORE
S595
$Call
$Call
$595
$299
$425
$Call
S575
S399
S299
$375
S375
$475
Cheap!
COIN DATA, INC~
PO Box 1209, 107-E Dick
Buchanon St, Lavergne, TN 37086
615/793-9142
December 1986
This supply has two more sections that are
not used on every supply. SCR, Rl7, Rl8,
and Dl2 make up an overvoltage Crowbar
circuit. If the output voltage rises above
5 volts, Dl2 starts to breakdown. The
current through Rl8 causes a voltage drop
across it. This voltage is applied to the
gate of the SCR through Rl7. When the
potential exceeds the trigger voltage, the
SCR conducts, shorts the voltage to
ground, and hopefully saves the boards.
Power Supplies: Theory Of Operation
Jajy
W
Janes Beck
Greater Southern Distributing Co.
Atlanta, Georgia
Over the past few rronths I've been
atterrpting to show you how to modify power
supplies to get better performance or to
obtain voltages that they didn't normally
have. This leaves one problem. What do you
do when the supply breaks down? Needless
to say proper logic board operation
requires proper power supply operation.
'!he last thing to look at is Rll and Dll.
Rll is a current limiting resistor for the
LED Dll. This is used to visually check
that there is an output. It doesn't rrean
the output is correct, just that there is
sorrething there.
Figure 1 shows a basic +5 volt regulator
taken from a Mylstar MA.CH III nanual.
+ 11, 5V
DC
Q11
2N58'79
H.S. 31
+5V DC
+
R13
12
2W
•
(13)
-
-
012
1N4734
5V
SCR
MCR 68-1
C12
C13
100UFI 0.1UFl
16V _l 50V_L
-=- C14
0.22UF
35V
TANT.
U11 K
TL431 &-:.:..R ----e----+----r----.
T0-92 A
-=-
-=-
I +
f66
110,1
1/4W
MV5752
-=-
Next rronth we'll "power up" our supply and
look at each section in operation. '!hat
way we can see how the failure of a
specific section will affect the overall
operation.
Let's break it down and look at the
separate sections.
First is the reference voltage section.
This is the actual regulator of the whole
system. It supplies the "rock steady"
voltage that determines the output
voltage. It is made up of Ull (an
adjustable Zener), Rl2, R15, R16, and VRl
(the +5 adjust).
(Ull functions just like a fixed Zener,
but by varying the voltage on the R
terminal, you change the breakdown
voltage.) This section gives us a nicely
regulated voltage, but the current it
supplies is very small compared to what
the boards need.
That takes us to the next section. Qll and
Ql2 make up the current arrplifier. 'Ibey
&ake the low level current supplied by the
• eference section and bring it up to a
useable level. Qll is the transistor
referred to as the Series-Pass since, as
you can see, it is in series with the
unregulated voltage and the load.
R11
180
1/4W
Conversion Kits
Lowest prices in America!
For Sale:
Kit Price:
CHOPLIFTER
MAT MANIA
LEGEND OF KAGE
GHOSTS' N GOBLINS
10 YARD FIGHT
JAILBREAK
TIGER HELi
1942
VIE AR KUNG FU
SUPER BASKETBALL
BIG BUCKS TRIVIA
GALAGAIII
RUSH ' N ATTACK
MANY MORE
S595
$Call
$Call
$595
$299
$425
$Call
S575
S399
S299
$375
S375
$475
Cheap!
COIN DATA, INC~
PO Box 1209, 107-E Dick
Buchanon St, Lavergne, TN 37086
615/793-9142
Future scanning projects are planned by the International Arcade Museum Library (IAML).