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Lamp / Light Control Circuits
Switch Circuits Control Circuits Pushbutton Controlled Up/Down
Ramping Light (March 15, 2009)
There are times when you want a lamp to gradually change from dark to light and from
light to dark, with each push of a pushbutton switch. The circuit below performs
this control function using a flip/flop and a classic pulse width modulation or PWM
method. The circuit uses a common flip/flop IC to control the on and off logic
states. A simple pushbutton switch toggles between the two states with each press of
the button. A 555 timer is used to generate a triangle waveform clock while a
common voltage comparator produces the PWM signal. An n-channel FET switches power to
the lamp with up to 3.5 Amps of current. This power switching device can be
sized as needed, so it could control much higher current if needed. The circuit will
operate from 6v to 15v. With the component values shown, the lamp will slew from dark
to light in about two seconds. This time can be lengthened or shortened by
changing the value of the 1uF capacitor.
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