參數(shù)資料
型號(hào): L6566ATR
廠商: 意法半導(dǎo)體
元件分類: 基準(zhǔn)電壓源/電流源
英文描述: Multi-mode controller for SMPS with PFC front-end
中文描述: 多模式開關(guān)電源控制器,PFC前端
文件頁(yè)數(shù): 39/51頁(yè)
文件大?。?/td> 410K
代理商: L6566ATR
L6566A
Application information
39/51
While the brownout protection is active the start-up generator keeps on working but, being
there no PWM activity, the Vcc voltage continuously oscillates between the start-up and the
HV generator restart thresholds, as shown in the timing diagram of
Figure 25 on page 38
.
The brownout comparator is provided with current hysteresis in addition to voltage
hysteresis: an internal 15 μA current sink is ON as long as the voltage applied on the
AC_OK pin is such that the AC_FAIL signal is high. This approach provides an additional
degree of freedom: it is possible to set the ON threshold and the OFF threshold separately
by properly choosing the resistors of the external divider (see below). With just voltage
hysteresis, instead, fixing one threshold automatically fixes the other one depending on the
built-in hysteresis of the comparator.
With reference to
Figure 25 on page 38
, the following relationships can be established for
the ON (Vsen
ON
) and OFF (Vsen
OFF
) thresholds of the sensed voltage:
Equation 13
which, solved for R
H
and R
L
, yield:
Equation 14
Figure 26. Ac voltage sensing with the L6566A
It is typically convenient not to use additional dividers connected to high-voltage rails
because this could make it difficult to meet no-load consumption targets envisaged by
energy-saving regulations.
Figure 26
shows a simple voltage sensing technique that makes
use of the divider already used by the PFC control chip to sense the ac mains voltage with
just the addition of an extra tap.
The small-signal NPN Q and the capacitor C
F
make a peak detector, so that the information
of the rms mains voltage can be found across C
F
. Tap’s position determines the dc voltage
to be sensed by the AC_OK pin. It is convenient to use a level as high as possible to
minimize the effect of V
BE
changes with temperature. However, it could be necessary to limit
the maximum sensed voltage below 7V to prevent Q’s emitter reverse breakdown; it would
not be destructive because the reverse current would be quite small (the resistors seen by
L
H
OFF
R
L
6
H
ON
R
R
45
.
45
.
Vsen
R
485
.
10
15
485
.
Vsen
=
+
=
45
.
Vsen
45
.
R
R
;
10
15
Vsen
078
.
Vsen
R
OFF
H
L
6
OFF
ON
H
=
=
L6566A
Rectified
input voltage
R
H
Sensed
voltage:
Vsen < 7V
R
L
C
F
3
MULT
L6561
L6562/A
L6563
Vcc
5
AC_OK
16
Q
Q
For minimum
temperature drift
相關(guān)PDF資料
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