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Stabilized Power Supply with Short-Circuit Alert

This circuit provides a stabilised power supply with short-circuit indication for testing electronic circuits. It has four regulated outputs (12V, 9V, 6V, 5V) and one unregulated 18V output selected via a rotary switch. If a short circuit occurs, LED2 will light and the piezobuzzer will sound to cut power. A fuse failure is also indicated, with the bicolour LED showing red if the fuse breaks. The circuit can be built on a PCB with heat sinks and housed in a metal box.

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Diego Manchay
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78 views1 page

Stabilized Power Supply with Short-Circuit Alert

This circuit provides a stabilised power supply with short-circuit indication for testing electronic circuits. It has four regulated outputs (12V, 9V, 6V, 5V) and one unregulated 18V output selected via a rotary switch. If a short circuit occurs, LED2 will light and the piezobuzzer will sound to cut power. A fuse failure is also indicated, with the bicolour LED showing red if the fuse breaks. The circuit can be built on a PCB with heat sinks and housed in a metal box.

Uploaded by

Diego Manchay
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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CIRCUIT IDEAS

STABILISED POWER SUPPLY WITH


SHORT-CIRCUIT INDICATION
D. MOHAN KUMAR

I
VED
DWI
S.C.

ere is an efficient 4-stage stabilised


power supply unit for testing electronic circuits. It provides well
regulated and stabilised output, which is

18V, 500mA step-down transformer to generate 18V AC. A rectifier diode comprising diodes D1 and D2 provides 18V DC,
which is smoothed by capacitor C1 and
given to the combination of regulator ICs
(IC1 through IC4). The regulator ICs pro-

negative terminal is also at full supply voltage (selected). If there is a short circuit at
the output, LED2 glows to activate the
piezobuzzer.
A fuse-failure indicator distinguishes
short circuit at the output and input fail-

essential for most electronic circuits to give


proper results. The circuit provides an audio-visual indication if there is a short circuit in the PCB under test, so the power
supply to the circuit under test can be
cut-off immediately to save the valuable
components from damage.
The circuit provides four different regulated outputs (12V, 9V, 6V and 5V) and
an unregulated 18V output, which are selectable through rotary switch S2. The selected output is indicated on the analogue
voltmeter connected to the outputs rails.
The circuit uses a standard 18V-0-

duce fixed, regulated outputs of 12V, 9V,


6V and 5V, respectively, which are connected to the rotary switch contacts. This
power supply is useful for loads requiring
up to 200mA current.
Complementary transistors T1 and T2
conduct when the power to the circuit is
switched on. Full selected supply voltage
is available at the collector of transistor
T2, which is used to power the load. LED3
indicates the presence of output voltage.
The negative terminal of piezobuzzer PZ1
is connected to the output rail via LED2,
so the piezobuzzer remains silent as its

ure. It consists of a bicolour LED (LED1)


and resistors R1 and R2. When power is
available and the fuse is intact, red and
green halves of LED1 are effectively in
parallel to output a yellowish light. When
fuse fails, green LED goes off and red LED
lights up to indicate fuse breakdown.
The circuit can be easily constructed
on a general-purpose PCB. Use small heatsinks for all ICs to dissipate heat. The output voltage can be read on a voltmeter.
Enclose the circuit in a metal box with
provisions for voltmeter, LEDs, rotary
switch, etc.

ELECTRONICS FOR YOU

JULY 2004

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