Datasheet

UC28023
UC28025
SLUS557F -- MARCH 2003 -- REVISED AUGUST 2010
13
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APPLICATION INFORMATION
FEEDFORWARD CIRCUIT
7
6
5
RAMP
CT
RT
UC2802x
4CLOCK
CFF
RFF
VIN
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
T
and C
R
are chosen so that the ramp at Pin
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.
14
9
OUT
ILIM/SD
UC28023
CR
RT
VIN
UDG--03050
Figure 14. Achieving Constant Volt-Second Product Clamp with the UC28023