IRPLCFL3 International Rectifier, IRPLCFL3 Datasheet - Page 2

• Manufacturer Part Number: IRPLCFL3
• Description: KIT DESIGN CFL TRIAC DIMMING
• Manufacturer: International Rectifier

Specifications of IRPLCFL3

• Main Purpose: Lighting, Ballast Control
• Utilized Ic / Part: IR2156
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Secondary Attributes: -
• Embedded: -
• Primary Attributes: -
• Other names: *IRPLCFL3

IRPLCFL3
A BASIC 120VAC DIMMER CIRCUIT
AC INPUT
16uH
100nF
15K
TRIAC
500K
47nF
33nF
AC OUTPUT
When a compact ballast is connected to a circuit containing such a dimmer, the triac will
only conduct if it is fired at a point during the mains half-cycle where the rectified mains
voltage is greater that the storage capacitor voltage. In this instance the capacitor will
be charged to the same voltage and the triac will then switch off. In this way it would be
possible to adjust the DC bus voltage of the ballast to some extent by adjusting the triac
firing point from 90º to 180º however this will not provide a satisfactory means of
controlling the light output.
There is also an additional problem encountered due to the fact that a dimmer of this
kind requires an inductor in series with the triac to limit the rise time of the current when
the device is fired. Without this inductor, mains current harmonics would be produced at
frequencies high enough to cause considerable radiated and conducted interference
problems. Since the load presented by a ballast circuit is effectively capacitive, when
the triac is fired there will be ringing caused by the resonance of the suppression
inductor of the dimmer and the capacitive load. This can cause the triac to fire and then
switch off as the ringing output voltage swings above and then below the input voltage
causing the current to fall below the holding current. This can occur several times during
each half cycle, resulting in severe lamp flicker and loss of control of the output.
PROPOSED SOLUTION
A system has now been developed, based around the IR2156, where the ballast is able
to operate with minimal flicker over a considerable portion of the adjustment range of a
dimmer and the light output may be controlled over this range from maximum output
down to around 10%.
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