Help Needed... Light dimmer

[seranko]

Hey guys,

I want to simulate the sunset and sunrise in my aquarium tank using 2 60 Watts incandescents lights... In order to do that I need help with the circuit design.

I have a Koyo 05 PLC, which can control the start and stop the process. In the morning when the PLC closes a contact, the circuit start to increase the brightness in the bulbs progressively, this last aprox. 10 minutes... In the evening, the PLC will open the same contact and the bulbs goes progressively off...

Would you guys PLEASE help me with this design ???

Thanks in advice,

Seranko

 

[IanP]

Here is a concept of one of several options:

A ramp generator build of costant current source (one FET transistor+R) and a capacitor followed by a buffer generates a ramp over 600s (adjustable).
This voltage is fed to a PWM (0%-100% duty cycle) that controls a MOSFET (trough optocoupler). This mosfet controls 2 x 60W lamps fed of >300dc. 300+ Vdc is produced by rectifying the mains and using a smoothing capacitor.
So this is the circuit.

Your PLC contact is applied between 12V supply and the current source. When it is closed the current source charges a capacitor; voltage rises, so is the PWM duty cycle ratio, and the intensity of the light.

To make the process reversable you will need to connect a resistor to discharge the capacitor; the discharge current will be lower the the charging current so both ways are covered. Maybe the rising and falling times will not be equal, but I think this is only minor deficiency of this concept.

Added after 5 minutes:

Why wouldn't you emply the PLC to generate to 0% to 100% PWM?