Circuit Diagram
Description
Description
In this circuit, a 120VAC lamp is slowly illuminated over a
approximate 20 minute period. The bridge rectifier supplies 120 DC to
the MOSFET and 60 watt lamp. A 6.2K, 5 watt resistor and zener diode is
used to drop the voltage to 12 volts DC for the circuit power. The
bridge rectifier should be rated at 200 volts and 5 amps or more. In
operation, a 700 Hz triangle waveform is generated at pin 1 of the LM324
and a slow rising voltage is obtained at pin 8. These two signals are
compared at pins 12 and 13 to produce a varying duty cycle rectangular
waveform at pin 14, which controls the MOSFET and brightness of the 60
watt lamp. When power is applied, the lamp will start to illuminate
within a minute or so, and will slowly brighten to full intensity in
about 20 minutes. You can make that longer or shorter with adjustments
to the 270K resistor at pin 9. The 2.2 ohm resistor and .015uF cap
connected to the lamp serve to supress RFI. The diode at pin 9 and 10K
resistor on pin 8 are used to discharge the 3300uF cap when power is
removed. Power should be off for a few minutes before re-starting.
Caution: This circuit is connected directly to the AC line and
presents a hazard if any part is touched while connected to the line.
Use caution and do not touch any parts while the circuit is connected to
the AC line. You may want to use a 9 volt battery connected across the
12 volt zener to check the basic operation. The DC voltage at pins
1,2,3,5,6,7 will all be around 4.3 volts if the circuit is working
correctly. If the DC voltages are all correct, you can use a variac to
slowly apply the full line voltage and check for proper operation.
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