Samsung HPR4272CX/XAC Service Manual page 98

Circuit Description
② Implementation of Sustain Voltage
As the main part of a SMPS for PDP, sustain voltage must supply a high power, 200V/1.4A.
To comply with the specification, the flyback converter method was used.
- PWM Oscillation frequency
Oscillator timing capacitor, Ct, is charged by Vref through Rt and discharged by an internal current source. During change time,
the internal clock signal blanks the output to the low state, Selection of Rt and Ct therefore determines both oscillator frequency
and maximum duty cycle. Change and discharge times are determined by the formulas;
tc = 0.55RtCt
td = RtCtln{(0.0063Rt-2.7)/(0.0063Rt-4)}
Frequency, then, is: f=1/(tc+td)
For Rt>5KΩ , f=1.8/RtCt
f=1.8/(15K§Ùx2.2nF)=48KHz
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