Texas Instruments TPS92311A19230VEVM Evaluation Module TPS92311A19230VEVM TPS92311A19230VEVM Datenbogen
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Produktcode
TPS92311A19230VEVM
V
COMP
V
SW
t
ON
I
LED
t
OFF
t
DLY
V
ZCD
I
LP
I
LS
2xt
DLY
V
ZCD-OVP
V
ZCD-ARM
V
ZCD-TRIG
V
ZCD-PEAK
t
t
t
t
SNVS811B – MAY 2012 – REVISED MAY 2013
The setting of the delay time, t
DLY
will be described in a separate paragraph. During steady state operation, the
duration of the on-period t
ON
can be determined with two different modes: the Constant On-Time (COT) mode
and the Peak Current Mode (PCM), which are configured by setting the MODE1 and MODE2 pins. For the COT
mode, t
mode, t
ON
is generated by comparing an internal generated saw-tooth waveform with the voltage on the COMP
pin (V
COMP
). Since V
COMP
is slow varying, t
ON
is nearly constant within an AC line cycle. For the PCM, the on-
period is terminated when the voltage of the ISNS pin (V
ISNS
) reaches a threshold determined by V
COMP
. Since
the instantaneous input voltage (AC voltage) varies, t
ON
varies accordingly within an AC line cycle. The duration
of the off-period (t
OFF
) is determined by the rate of discharging of the secondary current through the transformer.
Also,
(1)
where n is the turn ratio of L
P
and L
S
.
shows the typical waveforms in normal operation.
Figure 15. Primary and Secondary Side Current Waveforms
Copyright © 2012–2013, Texas Instruments Incorporated
9
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