參數(shù)資料
型號(hào)： LT4430
廠商： Linear Technology Corporation
英文描述： Secondary-Side Optocoupler Driver
中文描述： 二次側(cè)驅(qū)動(dòng)光電耦合器
文件頁(yè)數(shù)： 12/20頁(yè)
文件大?。?/td> 2118K
代理商： LT4430
LT4430
12
4430f
S U
APPLICATIO
Setting Output Voltage
Figure 5 shows how to program the power supply output
voltage with a resistor divider feedback network. Connect
the top of R1 to V
OUT
, the tap point of R1/R2 to FB and
the bottom of R2 directly to GND of the LT4430. The FB
pin regulates to 600mV and has a typical input pin bias
current of 75nA flowing out of the pin.
The output voltage is set by the formula:
V
OUT
= 0.6V (1 + R1/R2) – (75nA) R1
W
U
U
Most optocoupler datasheets loosely specify the gain,
or current transfer ratio (CTR), between the input diode
and the output transistor. CTR is a strong function of the
input diode current, temperature and time (aging). Ag-
ing degrades the LED’s brightness and accelerates with
higher operating current. CTR variation directly affects the
overall system loop gain and the design must account for
total variation. To make an effective optical detector, the
output transistor design maximizes the base area to col-
lect light energy. This constraint yields a transistor with a
large collector-to-base capacitance. This capacitance can
influence the circuit’s performance based on the output
transistor’s hookup.
The two most common topologies for the output tran-
sistor of the optocoupler are the common-emitter and
common-collector configurations. Figure 6a illustrates
the common-emitter design with the output transistor’s
collector connected to the output of the primary-side
controller’s error amplifier.
In this example, the error amplifier is typically a trans-
conductance amplifier with high output impedance and
R
C
dominates the impedance at the V
C
node. Frequency
compensation for this feedback loop is directly affected by
the output transistor’s collector-to-base capacitance as it
introduces a pole into the feedback loop. This pole varies
considerably with the transistor’s operating conditions. In
many cases, this pole limits the achievable loop bandwidth.
Cascoding the output transistor significantly reduces the
effects of this capacitance and increases achievable loop
bandwidth. However, not all designs have the voltage
headroom required for the cascode connection or can
tolerate the additional circuit complexity. The open loop
transfer function from the output voltage to the primary-
Figure 6a. Frequency Compensation with Optocoupler Common-Emitter Configuration
–
+
V
CC
V
REF
V
C
R
C
C
C
PRIMARY-SIDE
ERROR AMP
FB
ISOLATION
BARRIER
–
+
OPTO
OPTO
LT4430
COMP
1.1V
0.6V
–
+
ERROR
AMP
R3
R4
15k
R5
90k
4430 F06a
V
OUT
FB
C3
R1
R2
C1
C2
R
K
OPTO
C
K
Figure 5. Setting Output Voltage
4430 F05
V
OUT
75nA
FB
R2
R1
OptoCoupler Feedback and Frequency Compensation
An isolated power supply with good line and load regula-
tion generally employs the following strategy. Sense and
compare the output voltage with an accurate reference
potential. Amplify and feed back the error signal to the
supply’s control circuitry to correct the sensed error. Have
the error signal cross the isolation barrier if the control
circuitry resides on the primary-side. Coupling this signal
requires an element that withstands the isolation potentials
and still transfers the loop error signal.
Optocouplers remain in prevalent use because of their
ability to couple DC signals. Optocouplers typically con-
sist of an input infrared light emitting diode (LED) and an
output phototransistor separated by an insulating gap.
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LT4430_1 制造商:LINER 制造商全稱:Linear Technology 功能描述:Secondary-Side Opto-Coupler Driver Ground-Referenced Opto-Coupler Drive
LT4430ES6 制造商:Linear Technology 功能描述:
LT4430ES6#PBF 制造商:Linear Technology 功能描述:Secondary Side Optocoupler Driver 6-Pin TSOT-23 制造商:Linear Technology 功能描述:OPTO-COUPLER DRIVER 20V TSOT 制造商:Linear Technology 功能描述:OPTO-COUPLER DRIVER, 20V, TSOT-23-6; IC Function:Optocoupler Driver; Supply Voltage Min:3V; Supply Voltage Max:20V; Operating Temperature Min:-40C; Operating Temperature Max:125C; Digital IC Case Style:TSOT-23; No. of Pins:6 ;RoHS Compliant: Yes
LT4430ES6#TR 制造商:Linear Technology 功能描述:Secondary Side Optocoupler Driver 6-Pin TSOT-23 T/R
LT4430ES6#TRM 制造商:Linear Technology 功能描述:Secondary Side Optocoupler Driver 6-Pin TSOT-23 T/R
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