NCL30060GEVB
http://onsemi.com
5
General Behavior/Waveforms
The evaluation board is based on a single stage flyback
converter. This topology provides isolation and high power
factor utilizing a single power magnetic and switching
device. Single stage converters require minimizing filter
capacitance after the diode bridge and loop response less
than 20 Hz to achieve high power factor and low THDi.
Shown below are waveforms of Q1 switching MOSFET
drain voltage and current as monitored across sense resistor
R12. The evaluation board is operating with 25 W LED
load. Note the scale factors were left unchanged between
photos to highlight the relationship between drain voltage,
current, and operating frequency.
Figure 5. Drain Voltage and Current at 90 V ac Input
Figure 6. Drain Voltage and Current
at 230 V ac Input
Figure 7. Drain Voltage and Current
at 305 V ac Input
The photo below is the drain voltage showing the
envelope of the rectified sine wave input. The rectified sine
shape provides high power factor performance.
Figure 8. Drain Voltage at 230 V ac
with Slower Scan
This converter operates in critical conduction mode
(CrM) where the power switch turns on as soon as the
transformer core is reset to provide maximum utilization of
the transformer. This can be seen in Figure 9 which shows
the bias winding voltage in the top trace and the switching
MOSFET gate signal in the bottom trace.
