Forward Technique for Off-Line Voltage Mode Application
UC1825
UC2825
UC3825
Constant Volt-Second Clamp Circuit
The circuit shown here will achieve a constant
volt-second product clamp over varying input voltages.
The ramp generator components, R
T
and C
R
are cho-
sen so that the ramp at Pin 9 crosses the 1V threshold
at the same time the desired maximum volt-second
product is reached. The delay through the functional
nor block must be such that the ramp capacitor can be
completely discharged during the minimum deadtime.
Output Section
Simplified Schematic
Rise/Fall Time (C
L
=1nF)
Rise/Fall Time (C
L
=10nF)
Saturation Curves
7
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