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SLUS557B − MARCH 2003 − REVISED APRIL 2004
APPLICATION INFORMATION
FEEDFORWARD CIRCUIT
VIN
UC2802x
RFF
7
4
RAMP
CFF
CLOCK
6
5
CT
RT
UDG−03050
Figure 13. Feedforward Technique for Off-Line Voltage-Mode Applications
CONSTANT VOLT-SECOND CLAMP CIRCUIT
The circuit for the UC28023 shown in Figure 14 describes achievement a constant volt-second product clamp
over varying input voltages. The ramp generator components, R and C are chosen so that the ramp at Pin
T
R
9 (ILIM/SD) crosses the 1-V threshold at the same time the desired maximum volt-second product is reached.
The delay through the functional inverter block must be such that the ramp capacitor can be completely
discharged during the minimum deadtime.
UC28023
VIN
OUT
RT
14
ILIM/SD
9
CR
UDG−03050
Figure 14. Achieving Constant Volt-Second Product Clamp with the UC28023
12
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