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Optocoupler breaks
down in welder
If possible, could you please help
me with the following problem?
We have an inverter welder that
has been imported from Europe.
The machine has an input rating
of 230VAC and the manufacturer
has stated that running the welder
at 240VAC would pose no problem.
The problem is that a MOC3023
optocoupler is breaking down and
letting AC flow back through the
circuit and cause the solenoid to
chatter. The optocoupler drives
a gas solenoid rated at 230VAC
13.5VA and incorporates an RC
circuit which consists of a .022µF
capacitor and a 22Ω watt resistor
connected in parallel.
My question is, would the 10V
Question on modifying
PC power supply
With respect to the article entitled
“Use your old PC power supply for
high current outputs” in December
1998, how high is the “high current”.
Also, have you ever described the
theory behind high power Mosfet auto
amplifiers?
Can the output current of the Power
Supply for Amateur Transceivers described in May/June 1991 be increased
to around 30A relatively easily? (T. C.,
via email).
• The December 1998 article dealt
with modifying a standard PC power
supply to deliver slightly higher voltage; eg, 13.8V instead of 12V. Typically,
you can get 8A from the 12V rail and
20A from the 5V rail.
We have not published any theory
behind Mosfet car amplifi
ers. They
increase in the primary generate
a sufficient increase in the breakdown voltage to cross the protection
threshold and blow the optocoupler? And is there any formula to
work out what the break-down
voltage would be? (P. D., via email).
• The MOC3023 only has a 400V
blocking rating so depending on
what it is driving, it could easily be
fragile, especially in a welder. Given
that its load is only a low current,
the designers probably thought that
it would easily handle the job.
Our approach would be to use
the MOC3023 to drive a 600V Triac
but one with a low holding current
or alternatively, shunt the solenoid
with an incandescent lamp to ensure reliable operation. You may
also need Varistor protection in
the circuit.
are just standard Mosfet amplifiers
powered by a DC-DC inverter. The
output of the 13.5V 25A supply cannot
be increased without substantially
upgrading the major components.
How to connect a subwoofer amplifier
I’d be the first to admit that I am a
novice in the field of electronics. With
perseverance and a lot of reading I had
thought that I had developed a basic
understanding of audio amplifiers,
until now.
I have built a couple of amplifier
modules supplied by Dick Smith
Electronics, namely the 100W module
(Cat. K3442) and the more powerful
300W beast, primarily to power subwoofers for my home-theatre system.
Each amplifier module has the Sub
Bass Processor preamp module (DSE
Cat. K5403). My dilemma is this: if
I use the subwoofer out jack on my
surround receiver I get virtually no
signal through either amp module. If I
connect the same subwoofer output to
my small 30W bookshelf stereo and get
this to power my subs, I get thumping
bass but only 30 watts worth.
Obviously there is signal coming
out of the sub out jack, so why is it
lost between here and my speakers?
(S. F., via email).
• The sub-bass processor should not
be connected to the subwoofer output of your surround sound receiver.
The sub-bass processor is intended
for those people who do not have a
subwoofer output from their receiver.
Try connecting the subwoofer signal
directly to your 100W amplifier. You
should get heaps of bass.
Bridging audio amplifier modules
I’ve bought two power amplifiers
from Dick Smith Electron
ics (Cat
K3442) and I would like to bridge
them. What do I need and can it be
done? (E. P., Vermont, Vic).
• There is a problem in bridging these
amplifier modules. As they stand, they
will deliver 100W into 4Ω or 50W into
8Ω. If they are bridged, they will only
deliver 100W into an 8-ohm load. They
cannot drive a 4-ohm load in bridge
mode, since each module cannot drive
a 2-ohm impedance.
Notes & Errata
Touch/Infrared Light Dimmer, January & February 2002: the circuit
diagram (Fig.3) should show the .01µF
capacitor and 1MΩ resistor connected
to pin 6 (RB0 input) of IC1 and not to
the A2 terminal of TRIAC1. The PC
board pattern and overlay diagram
SC
are correct.
WARNING!
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90 Silicon Chip
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