参数资料
型号: AFL2815SW
厂商: International Rectifier
英文描述: ADVANCED ANALOG HIGH RELIABILITY HYBRID DC/DC CONVERTERS
中文描述: 先进的模拟高可靠性的混合式DC / DC变换器
文件页数: 5/16页
文件大小: 445K
代理商: AFL2815SW
www.irf.com
5
AFL270XXS Series
ERROR
AMP
& REF
OUTPUT
FILTER
INPUT
FILTER
OUTPUT RETURN
DC INPUT
INPUT RETURN
CONTROL
1
2
4
3
5
6
SYNC INPUT
CURRENT
SENSE
+ SENSE
- SENSE
SENSE
AMPLIFIER
ENABLE 2
SHARE
SHARE
AMPLIFIER
7
11
10
9
12
8
+ OUTPUT
SYNC OUTPUT
ENABLE 1
CASE
PRIMARY
BIAS SUPPLY
AFL270XXS Circuit Description
Figure I. AFL Single Output Block Diagram
Connection of the
+
and
-
sense leads at a remotely locat-
led load permits compensation for resistive voltage drop
between the converter output and the load when they are
physically separated by a significant distance. This con-
nection allows regulation to the placard voltage at the point
of application. When the remote sensing features is not
Figure II. Enable Input Equivalent Circuit
Pin 4 or
Pin 12
1N4148
100K
290K
150K
2N3904
+5.6V
Disable
Pin 2 or
Pin 8
used, the sense leads should be connected to their respec-
tive output terminals at the converter. Figure III. illustrates a
typical application.
Circuit Operation and Application Information
The AFL series of converters employ a forward switched
mode converter topology. (refer to Figure I.) Operation of
the device is initiated when a DC voltage whose magnitude
is within the specified input limits is applied between pins 1
and 2. If pin 4 is enabled (at a logical 1 or open) the primary
bias supply will begin generating a regulated housekeeping
voltage bringing the circuitry on the primary side of the con-
verter to life. Two power MOSFETs used to chop the DC
input voltage into a high frequency square wave, apply this
chopped voltage to the power transformer. As this switch-
ing is initiated, a voltage is impressed on a second winding
of the power transformer which is then rectified and applied
to the primary bias supply. When this occurs, the input
voltage is shut out and the primary bias voltage becomes
exclusively internally generated.
The switched voltage impressed on the secondary output
transformer winding is rectified and filtered to provide the
converter output voltage. An error amplifier on the second-
ary side compares the output voltage to a precision refer-
ence and generates an error signal proportional to the dif-
ference. This error signal is magnetically coupled through
the feedback transformer into the controller section of the
converter varying the pulse width of the square wave sig-
nal driving the MOSFETs, narrowing the width if the output
voltage is too high and widening it if it is too low.
Remote Sensing
Inhibiting Converter Output
As an alternative to application and removal of the DC
voltage to the input, the user can control the converter
output by providing TTL compatible, positive logic signals
to either of two enable pins (pin 4 or 12). The distinction
between these two signal ports is that enable 1 (pin 4) is
referenced to the input return (pin 2) while enable 2 (pin 12)
is referenced to the output return (pin 8). Thus, the user
has access to an inhibit function on either side of the isola-
tion barrier. Each port is internally pulled “high” so that
when not used, an open connection on both enable
pins
permits normal converter operation. When their use is
desired, a logical “low” on either port will shut the
con-
verter down.
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