IRPLCFL4 International Rectifier, IRPLCFL4 Datasheet - Page 6

• Manufacturer Part Number: IRPLCFL4
• Description: IC BALLAST DIMMING CFL 3-WAY
• Manufacturer: International Rectifier

Specifications of IRPLCFL4

• 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: *IRPLCFL4

IRPLCFL4
The front end of the ballast shows the neutral line input (i.e. the one that is always connected) going
to the center point of the DC bus storage capacitors C3 and C4. Live inputs 1 and 2 are connected to
two completely separate voltage doubler diode pairs which are connected to the DC bus. This allows
the use of an integrated bridge rectifier or 4 individual diodes, in spite of the fact that the circuit in this
case is not a full wave rectifier.
If live input 1 is connected to the line, an 60Hz sinusoidal AC voltage will be present at the point where
the anode of D1 joins the cathode of D2. This voltage will swing between the 300V DC bus voltage and
the 0V COM point of the circuit. If live input 1 is not connected to the line this point will be floating with
no voltage present. The same applies with live input 2 at the point where the anode of D3 meets the
cathode of D4. These two points are fed via resistors R7 and R8 to the parallel combination of R10
and C7 which are connected to 0V COM. The value of C7 is high enough to ensure that the amount of
ripple that is present at the pin 5 of ICE will be negligible so a DC voltage will effectively appear there.
This sets the reference level for the dimming feedback loop.
It follows that this reference voltage will change depending on whether live input 1 is connected only,
live input 2 is connected only or both are connected. The values of R7 and R8 will be chosen so that
this voltage is substantially different if either live input 1 of live input 2 are connected alone. When
both are connected the voltage will be the sum of the voltages produced by each single live input
being connected.
For this application in general R7 can be chosen to give the correct reference voltage to provide 50%
light output as perceived by the human eye which occurs at a point somewhat lower than 50% ballast
power and R8 can be chosen for 75% which is at about 50% of the nominal total ballast power at full
light output. The problem here is that these two voltages added together do not produce a high
enough reference voltage to give 100% light output when both live inputs are connected. To overcome
this an additional opamp has been used which has a reference voltage at pin 6 set at a point above
the voltage produced at pin 5 when a single live input is connected and below the voltage at pin 5
when both are connected. The opamp is configured as a non-inverting DC amplifier with a fixed gain
so the output will give a higher voltage when both lives are connected and a lower voltage when only
one is connected. In this way it is possible by selecting the values of R4, R5, R6 and R11, to achieve
any three light levels that may be required.
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