IRPLCFL5U

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(ZVS) and non-ZVS protection, as well as integrated bootstrap diode. The IC protects against non-

ZVS by automatically setting the frequency to ensure ZVS. The IC will eventually shut-down if the

non-ZVS condition cannot be achieved.

One of the biggest advantages of the IR2520D is that it incorporates an internal current crest factor

driven shutdown function and it eliminates the need for a high-precision current sensing resistor

that is typically used to detect over current. The IC uses the VS pin and the RDSon of the low-side

half-bridge MOSFET for over-current protection and to detect non-ZVS conditions. An internal 600V

FET connects the VS pin to the VS sensing circuitry and allows for the VS pin to be accurately

measured during the time when pin LO is high, while withstanding the high DC bus voltage during

the other portion of the switching cycle when the high-side FET is turned on and VS is at the DC bus

potential. Please refer to the IR2520D data sheet for further information on the IR2520D including

electrical parameters, state diagram and complete functional description. As a result of the IR2520D

features, the IRPLCFL5U circuit using the IR2520D is a complete CFL solution that offers better

reliability and longer lamp life than self oscillating solutions while reducing component count and

ballast size.

5. Circuit Description

The schematic for IRPLCFL5U is shown in figure 5.1. The BOM with the components values is

shown in table 5.2.

The ballast incorporates a fuse, EMI filter, input rectifier, bus capacitor, half-bridge, control and

output stage. The output stage is the classical resonant circuit consisting of an inductor, LRES, and

a capacitor, CRES. The circuit is built around the IR2520D Ballast Control IC. The IR2520D pro-

vides adjustable preheat time, adjustable run frequency to set the lamp power, high starting fre-

quency (about 2.5 times fmin) to avoid lamp flash, capacitive mode protection for open filament

condition and current crest factor protection for failure to strike or no lamp conditions.

The AC line input voltage is rectified to provide a bus voltage of approximately 300 volts. The start

up resistors, Rsupply1 and Rsupply2, are sized such that they can supply the micro-power current

during under-voltage lockout (UVLO). When VCC exceeds the UVLO+ threshold, the IR2520D

begins to oscillate and the charge pump circuit (CSNUB, DCP1 and DCP2) supplies the current to

VCC that causes the internal 15.6V zener clamp to regulate.

The IR2520D Ballast Control IC controls the frequency of the half-bridge as well as the ballast

states and protection modes such as lamp preheat, lamp ignition, running mode, low AC line

protection and lamp/ballast fault protection.