The post explains a simple automatic mains lamp reverse dimmer circuit which can be used to imitate a sunrise effect.
A sunrise simulator lamp is a modified version of a dimmer circuit. 120V AC lamp is connected to a bridge rectifier that supplies DC though there is no functional difference as the lamp is passive and being resistive in nature there is no operational problem.
The circuit is made such that the lamp illuminates over a period of 20 minutes. The lamp is connected in series with a N channel MOSFET.
Here in this case IRF 640 having a V -DS of 200V and I of 11Amp at 100oC or an IRF 740 having V-DS of 400V and Id of 6.3Amp at 100oC is recommended.
However, for a 120V supply IRF 740 is a better choice. A current limiting resistance is employed in series with the lamp. The lamp has a drawing current of 500mA that determines the wattage of the current limiting resistance.
LM324 a quad OP-Amp is employed for the multiple stages required to build the circuit. A triangular wave form of around 700Hz is produced at pin number 1 and a slow variable DC voltage is generated at pin number 8.
These two voltages are compared in the last stage of the op-Amp. This stage is acting as a comparator.
Quite naturally the comparator generates varying duty cycle. This is the parent methodology of generating PWM wave form. This PWM signal shall trigger the MOSFET and start illuminating the bulb within sixty seconds of powering up. And the full illumination is reached over a period of 1/3 of an hour.
This period can be adjusted by varying the resistance connected to pin number 9. The current limiting resistance of 2.2 ohms along with the capacitor of 0.015microFarrad connected across it also acts as a RFI suppressor.
Before each operation, there should be a minimum interval of 5 to 10 minutes. During this time the 3300microFarrad capacitor gets discharged through the 10K resistor and the diode connected with it. As the circuit is connected to main supply, caution should be taken while in use.
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