Cirrus Logic AN349 - Manual (Page 3)

AN349
AN349REV1 3
near unity power factor across the operating input voltage range. The CS1601-based solutions greatly minimizes the need for
making this trade-off. The CS1601 can provide very low distortion at near unity PF.
Figure 3. Comparison of Power Factor vs. AC Line Voltage
3.5 Lower Link Overshoot During Lamp Strike
The CS1601-based ballast demonstrates better performance during lamp strike and start-up. The scope capture of the lamp
strike with the L6562 is shown in Figure 4. The scope capture of the lamp strike with the CS1601 is shown in Figure 5. In both
the scope captures, the PFC output is presented in blue and the bridge rectifier output signal is presented in red. From Figure 4,
it can be observed that with the L6562-based ballast, during lamp start-up, the link voltage rails up to 520V before settling down
to the nominal value of 485V. In the CS1601-based ballast, the link voltage does not go above 492V, which is the voltage thresh-
old for the over voltage protection (OVP). Since the output capacitors are rated for 500 V (Two 47uF, 250V capacitors in series),
the lifetime of these capacitors are improved by keeping the voltage below 500V under all conditions. The CS1601 requires a
lower inductance for the same power level, resulting in less stored energy during startup. At the end of startup, the stored energy
is transferred to the output bulk capacitor. Less stored energy results in a smaller V
link
overshoot.
Note: Neither solution produced any flicker during lamp strike.
Figure 4. Ballast Startup with L6562
PF Vs Line @ 60Hz
0.93
0.94
0.95
0.96
0.97
0.98
0.99
1
1.01
80 100 120 140 160 180 200 220 240 260 280 300
Input Voltage (V)
PF
CS1601
ST L6562