Star Tech Journal
Issue: 1986-August - Vol 8 Issue 6 - Page 8
STAA*TECH Journal
Getting Negative Voltages
From switching Regulators
By James Beck
Greater Southern Dist. Co.
Atlanta, GA
Hello again, didn't quite make it in last
nonth' s issue, but I'm back again. As
pranised, we will cover methods of getting
negative voltages from switching
regulators that only offer positive
outputs.
August 1986 (8)
F,~.i.
~/c.
V+
~~T
()~
e."
1.-V
Vcu'T
c.-t--
The main problem that is encountered with
attenpting to accooplish this, is the fact
that switchers use high-frequency pulses
to operate. Standard techniques, like we
covered in the previous nonths, won't work
all that well. M:>st rectifiers work OK at
60 Hz, but at 15 KHz and up, they tend to
·leak backwards across the junction.
V+
Fortunately in this age of the
semiconductors ;mere there is a problem,
someone has come up with a solution.
In steps the ICL7660. This wonderful
little chip takes a positive input and
converts it to an equal voltage of
opposite polarity. Fig. 1 shows the pin
out of the chip. All that is needed to
make it function are 2 capacitors and a
diode.
The typical efficiency of the device is
well above 95%. The value of the
capacitors is not critical; I have had
great results using lOuf caps. '!be output
current is low, but -can easily power
dynamic RAMs and OPanps. It may not work
with some of the newer games that use
hybrid custom chips for the RGB
generation. These hybrids suck up a lot of
current.
Fig. 2 shows the configuration for
converting voltages under 3.SV and Fig. 3
shows the configuration for converting
voltages g~eater than 3.SV. The whole unit
can be asseubled on a Perf Boa.rd in under
15 minutes and the chip can be purchased
for less than $4.
well, I haven't come up with a topic for
next DDnth as of yet, so if anyone has any
suggestions -give me a call at
. 404/352-3040.
V+
1--..::::..t__t--M----,--• -YoJt
:f'\~~
"'
COIN-OP NAIL LISTI
USAr Over 11,000 names of coin-operated
equipment owners, operators, technicians,
suppliers, Jobbers and distributors.
Newly updated. 8575.
EUROPE& Over 2,500 large operators and
distributors of coin-op equipment. 8300.
Lists era supplied
labels in zip-coda
deliverable. Order
JOURNAL, PDB 1065,
on praaaura-sanaitiva
order. Guaranteed 931
from1 STAR*TECH •
Merchantville NJ 08109.
Getting Negative Voltages
From switching Regulators
By James Beck
Greater Southern Dist. Co.
Atlanta, GA
Hello again, didn't quite make it in last
nonth' s issue, but I'm back again. As
pranised, we will cover methods of getting
negative voltages from switching
regulators that only offer positive
outputs.
August 1986 (8)
F,~.i.
~/c.
V+
~~T
()~
e."
1.-V
Vcu'T
c.-t--
The main problem that is encountered with
attenpting to accooplish this, is the fact
that switchers use high-frequency pulses
to operate. Standard techniques, like we
covered in the previous nonths, won't work
all that well. M:>st rectifiers work OK at
60 Hz, but at 15 KHz and up, they tend to
·leak backwards across the junction.
V+
Fortunately in this age of the
semiconductors ;mere there is a problem,
someone has come up with a solution.
In steps the ICL7660. This wonderful
little chip takes a positive input and
converts it to an equal voltage of
opposite polarity. Fig. 1 shows the pin
out of the chip. All that is needed to
make it function are 2 capacitors and a
diode.
The typical efficiency of the device is
well above 95%. The value of the
capacitors is not critical; I have had
great results using lOuf caps. '!be output
current is low, but -can easily power
dynamic RAMs and OPanps. It may not work
with some of the newer games that use
hybrid custom chips for the RGB
generation. These hybrids suck up a lot of
current.
Fig. 2 shows the configuration for
converting voltages under 3.SV and Fig. 3
shows the configuration for converting
voltages g~eater than 3.SV. The whole unit
can be asseubled on a Perf Boa.rd in under
15 minutes and the chip can be purchased
for less than $4.
well, I haven't come up with a topic for
next DDnth as of yet, so if anyone has any
suggestions -give me a call at
. 404/352-3040.
V+
1--..::::..t__t--M----,--• -YoJt
:f'\~~
"'
COIN-OP NAIL LISTI
USAr Over 11,000 names of coin-operated
equipment owners, operators, technicians,
suppliers, Jobbers and distributors.
Newly updated. 8575.
EUROPE& Over 2,500 large operators and
distributors of coin-op equipment. 8300.
Lists era supplied
labels in zip-coda
deliverable. Order
JOURNAL, PDB 1065,
on praaaura-sanaitiva
order. Guaranteed 931
from1 STAR*TECH •
Merchantville NJ 08109.
Future scanning projects are planned by the International Arcade Museum Library (IAML).