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AC Line Powered LED Pilot Light
This simple circuit can be used to light a LED indicator lamp, powered
from the 120vac line. I have included component values for 240vac
lines as well.
Isolated AC Current Monitor
This circuit uses a small AC current transformer from Magnetek to produce
an isolated voltage proportional to the AC current in the primary winding.
The transformer contains a single turn primary with a low 0.001-ohm
resistance. It can easily handle 30 amps of AC current and provides
at least 500vac of isolation. With the components shown, the output
AC voltage is scaled so 1 amp of current produces 100mv of AC voltage....
Line Powered
60hz Clock Generator
This circuit is connected to the 120vac power line and transfers 60Hz clock
pulses to a logic circuit. The optoisolator used provides 5000 volts of
isolation between the power line and the logic side of the circuit....
Line Powered White LED Array
There has been a lot of excitement lately in the lighting industry. Some
companies are beginning to manufacture general lighting fixtures, which replace
incandescent and fluorescent lamps, using LED lights. When proper heat
management is designed into the light fixtures, these LED lights can produce
more light with less electricity and last much longer than other devices.
They can also operate well in cold temperatures. Some of these new
lighting fixture designs use a large number of white LEDs, wired into long
series wired string arrays. The circuit below is designed to provide a
regulated DC voltage for these strings.
Line Powered
Xenon Flash Transmitter
This line powered xenon flash circuit drives a small camera type flash tube. It
has an optical isolator to allow the flash to be safely triggered from some
remote device. A flash rate of 2Hz is possible with the circuit.
Miniature
5v Line Powered Isolated Supply
Often a circuit requires a 5v DC supply to power some logic circuits. The
conventional method is to use an AC wall adapter. But, many systems, which
bring AC power onto a circuit board, need a small AC to DC power supply right on
the circuit board. The circuit below provides such a supply. It uses
a classic series capacitor charge pump which acts as a current limiting device.
Unplugged Appliance Alarm
I got a call from an administrator at a large prison. He told me that he
was having problems with inmates who keep unplugging refrigerators, vending
machines and microwave ovens in a commons area. He wanted a
battery-powered device, which could be mounted to the outside of the power cord
of an appliance. The device would produce a loud alarm whenever the power
plug of the appliance was unplugged from a power outlet.
Unplugged
Power Cord Alarm
Many medical devices, such a portable X-ray and ultrasound equipment, carry
their own batteries. However, the frantic pace of some hospital emergency rooms
might cause the device to be shoved off into a corner without being plugged back
into an AC power source to recharge their batteries. So, I designed this circuit
to emit an audible alarm whenever the device’s power cord was unplugged from the
wall for a period of time. The device was designed to snap onto the outside of a
power cord, where it senses the AC electric field emitted. No direct connection
to the internal wires of the power cord is needed. I also included a low battery
voltage monitor....
