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AC Line Powered LED
Flasher - Some of the latest LEDs are amazing. They can produce
a surprising amount of light with very little current. In the light flasher application shown below I take advantage of a
nice surface mounted LED from King Bright. This flasher circuit draws only about 3ua of average current from the AC power
line to flash this green LED. This flasher might be used as a power indicator light . . . [Hobby Circuit designed by Dave
Johnson P.E., 12/07/08]
AC Line Under/Over
Voltage Alarm - Power lines, which deviate much beyond normal
voltages can damage expensive electronic equipment. The circuit below sounds an alarm whenever the line voltage is higher or
lower than normal. I set the alarm limits at about +-15% from standard levels . . . [Hobby Circuit designed by Dave Johnson
P.E., 03/29/09]
AC Power Line High/Low
Voltage Tester - If you wish to test a line-powered device under
both a 15% high and a 15% low voltage condition, you can use the circuit below. The circuit uses an 18v transformer with a 3
amp rating. A double pole, double throw toggle switch then switches in the . . . [Circuit by David A. Johnson P.E.,
03/14/10]
AC Power Loss Alarm - I’ve been having a problem with my instant hot water system lately. This system circulates
electrically heated water throughout my house using a small pump. The pump is wired into a ground fault interrupter (GFI)
module. Every now and then, the GFI trips, leaving me without hot water . . . [Circuit by David A. Johnson P.E., 03/29/09]
Bi-Directional Charge Coupled
Powers MOSFET Relay - The circuit uses an inexpensive C-MOS
inverter package and a few small capacitors to drive two power MOS transistors from a 12v to 15v supply. Since the coupling
capacitor values used to drive the FETs are small, the leakage current from the power line . . . [Hobby Circuit designed by
Dave Johnson P.E., 06/03/00]
Charge Coupled Bi-Directional Power
MOSFET Relay - The circuit uses an inexpensive C-MOS inverter
package and a few small capacitors to drive two power MOS transistors from a 12v to 15v supply. Since the coupling capacitor
values used to drive the FETs are small, the leakage current from the power line . . . [Circuit by Dave Johnson P.E.,
06/03/00]
Detects Low
Voltage 120Vac Power Line - This hobby circuit will turn on a
beeper when the line voltage drops below 100 volt AC . . . [Hobby Circuit designed by Dave Johnson P.E., 07/09/06]
LED Strings powered by AC Line - This shows 4 different ways to string white LEDs that are powered by a 120vac or 240vac power
line. The circuit was designed by Ken Schultz . . . [Hobby Circuit designed by David A. Johnson P.E., 12/18/04]
Low
Voltage 120vac Power Line Alarm - This circuit will turn on a
beeper when the line voltage drops below 100 volt AC. . . . [Circuit by David Johnson P.E., 07/09/06]
Power Line Alarm - This circuit will activate a beeper alarm whenever the AC line voltage is less than 100vac. .
. . [Circuit by David A. Johnson P.E., 07/12/06]
Solid State Relay Requires Only
50ua Drive Current - This circuit demands a control current that
is 100 times smaller than that needed by a typical optically isolated solid state relays. It is ideal for battery-powered
systems. Using a combination of a high current TRIAC and a very sensitive low current SCR . . . [Circuit by David A. Johnson
P.E., 06/03/00]
SSR Requires Ultra Low Control Current - Most solid
state relays require at least 5ma and often more input control current, to fully turn on the device. But such current levels
often force battery powered circuits to use excessively large batteries. The relay hobby circuit shown below demands only
50uA of input current . . . [Hobby Circuit designed by David Johnson P.E., 06/03/00]
Under/Over Voltage Alarm
on AC Line - Power lines, which deviate much beyond normal
voltages can damage expensive electronic equipment. The circuit below sounds an alarm whenever the line voltage is higher or
lower than normal. I set the alarm limits at about +-15% from standard levels . . . [Circuit by David Johnson P.E.,
03/29/09]
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