UCC28610
www.ti.com ......................................................................................................................................... SLUS888C–JANUARY 2009–REVISED SEPTEMBER 2009
Primary Current Sense
The UCC28610 uses a current mirror technique to sense primary current in the Current Modulator. See Figure 27
for details. All of the primary current passes into the DRV pin, through the Driver MOSFET and out of the GND
pin. The Driver MOSFET current is scaled and reflected to the PWM Comparator where it is compared with the
CL current. At the beginning of each switching cycle a blanking pulse, tBLANK,(Ilim), of approximately 220 ns is
applied to the internal current limiter to allow the driver to turn on without false limiting on the leading edge
capacitive discharge currents normally present in the circuit.
Current Modulator
Peak
Current
IFB
Control
IFB
ICL
CL
From Emitter
of Opto-
Coupler
FB
1
3
IFB
RCL
IDRV
IDRV
ICL
From Source
of
HVMOSFET
DRV
100000
6
7
PWM
Comparator
PWM Flip-
Flop CLR
Driver
GND
tBLANK,(Ilim)
Figure 27. CL pin and DRV Current Sense
Copyright © 2009, Texas Instruments Incorporated
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