REV.-A PRINCIPLES OF OPERATION
0
vb
0
VO
c
IP
d
ION
0
Figure 2-54. Waveforms
The circuit’s constant current control process is shown above.
Peak Current Detection (to -
tl)
(1) When excitation input IN goes ON, so does MOSFET Q1. The A-coil excitation current
I
ON
then flows
along the route shown by the solid line (-).
(2) As
I
ON
increases, so does the voltage at R6.
(3) When R6 voltage exceeds
V
REF
,
COMP 1 inverts, and the T
D
voltage falls to near zero.
(4) When V
TD
drops below the COMP2 threshold voltage, COMP2 inverts.
(5) COMP2 inversion causes Q1 gate voltage to go LOW, and Q1 goes OFF.
LQ-510
2-45
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