IRPLCFL4 International Rectifier, IRPLCFL4 Datasheet - Page 5

• 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
To obtain 50% output the frequency would have to be very precisely set. This is not practical since
the tolerances of the output inductor, capacitor and oscillator timing components do not allow this.
Even if each ballast was individually adjusted in production variations in lamp behavior over tempera-
ture would mean that under some conditions the lamp arc would extinguish at this setting leaving the
system in permanent preheat which would burn out the cathodes eventually.
This explains why the 150VDC bus solution has been adopted as this allows 50% output to be
achieved without this problem. However the disadvantages discussed in the previous section demon-
strate that this approach is not without some major disadvantages.
Consequently it becomes necessary to include a closed loop feedback system that controls the lamp
current by adjusting the ballast frequency from a VCO (voltage controlled oscillator) driven by the
output of an error amplifier that senses the lamp arc current directly and compares it with a refer-
ence. This same strategy has been used in the IRPLCFL3 reference design “A Ballast that can be
dimmed from a domestic (phase cut) dimmer” and has been demonstrated to be capable of control-
ling the lamp output down to levels below 10% with very good stability. This also compensates for any
tolerances in the components of the circuit or the lamp.
Regulated Lamp Current Control System
VCO
&
DRIVER
+
Lamp Arc Current
-
Reference
www.irf.com
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