NCP1219PRINTGEVB
http://onsemi.com
26
Most of the losses on the board are on the main switch,
transformer, secondary rectifier (D12) and secondary
snubber resistor (R18). The main switch losses are
dominated by on state conduction losses, but the aluminum
heat sink reduces the power dissipation in the device. High
peak currents during the load step create heating in the
transformer, as seen in Figures 40 and 42. The losses in D12
during load step conditions are shown in the lower
right
−
hand corner of the board in Figures 40 and 42. The
heat spreading from D12 can also be seen on the bottom side
of the board. The secondary snubber is designed to prevent
overvoltage stress on the secondary rectifier. The power
dissipation in R18 occurs at high line conditions when the
snubber acts to clamp the voltage on the diode, as seen in the
upper right hand corner of the board. At low line, DSS mode
is active and the power dissipation in the controller and the
series HV resistors (R41 and R42) can be seen in Figure 41.
Summary
A 30 W (48 W) converter is designed and built using the
flyback topology. The converter is implemented using the
NCP1219. The average load efficiency is measured above
83.5% over the complete operating range.
The standby input power is measured below 1 W under
universal mains operating ranges. The low standby power is
achieved using a forward auxiliary winding with DSS
operating at low line conditions only. The converter
complies with Energy Star 2.0 EPS requirements.
The converter provides excellent transient response by
minimizing overshoot, undershoot, and recovery time.
Output voltage ripple is measured at 16 mV. Phase margin
and crossover frequency are measured at 60
°
and 1.3 kHz,
respectively.
This evaluation board is designed to demonstrate the
features and flexibility of the NCP1219. This design is a
guideline only and does not guarantee performance for any
manufacturing or production purposes.
References
1. Basso, Christophe P. Switch
−
Mode Power
Supplies SPICE Simulations and Practical
Designs. 1st ed. New York, NY: MacGraw Hill.
2. Pressman, Abraham I. Switching Power Supply
Design. 1st ed. New York, NY: MacGraw Hill.
3. PWM Controller with Adjustable Skip Level and
External Latch Input Datasheet NCP1219,
www.onsemi.com.
