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)： 9/20頁(yè)
文件大?。?/td> 2118K
代理商： LT4430
LT4430
9
4430f
S U
APPLICATIO
Figures 1a to 1e illustrate bias supply circuits for the
flyback converter. Figure 1a shows the typical flyback
output connection. Figures 1b and 1c exhibit equivalent
circuit performance but rotate the rectifier connection to
the ground-referred side. This connection permits the user
to take advantage of the transformer secondary’s forward
behavior when the primary-side switch is on.
Figures 1d to 1e illustrate the bias generator circuit.
V
IN
N volts appear across the secondary winding when
the primary-side switch is on. D2 forward biases and C1
charges. During this time, the secondary-voltage is in
series with V
OUT
and C1 ultimately charges to (V
IN
N +
V
OUT
– V
F
). V
F
is the forward voltage of D2. When V
OUT
is zero at startup, V
IN
N volts exists to charge C1. C1 is
generally much smaller in value than C
OUT
and the bias
supply starts up ahead of V
OUT
. R1 in Figures 1d and
1e limits peak charging currents, lowering D2’s current
rating. R1 also filters C1 from peak-charging to the volt-
age spikes induced by the secondary winding’s leakage
inductance. Between 1
Ω
to 10
Ω
is generally sufficient. R1
is usually necessary if C1 is a low ESR ceramic capacitor
or if the transformer has high leakage inductance. It may
be possible to eliminate R1 if C1 is a low cost, high ESR,
surface-mount tantalum.
W
U
U
V
IN
variation changes the bias supply in Figure 1d. Depend-
ing on V
OUT
, the transformer turns ratio N and V
IN
range,
the bias supply may exceed the LT4430’s 20V V
IN
absolute
maximum rating. If this occurs, two solutions exist. One
is to tap the secondary-side inductor to create a lower
voltage from which to rectify as illustrated in Figure 2a.
The bias voltage decreases to (V
IN
N1/N + V
OUT
– V
F
).
This solution relies on secondary-side pins being available
for the tap point.
The second solution is to make a preregulator as shown
in Figure 2b. In this example, the bias supply equals (V
Z1
– V
BE
). Select R2 to bias zener diode Z1 and to supply
base current to QBS. Resistor R3 (on the order of a few
hundred ohms), in series with Q5’s base, suppresses
possible high frequency oscillations depending on QBS’s
selection. The preregulator circuit has additional value for
fully synchronous converters. Fully synchronous convert-
ers require gate drivers to control the secondary-side
MOSFETs turn on and turnoff. The gate driver circuitry
requires supply current in the range of 10mA to 100mA
depending on the gate driver supply voltage, MOSFET size
and switching frequency. The preregulator bias supply is
ideal for powering both the LT4430 and the gate driver
V
IN
4430 F01a
T1
1:N
V
OUT
C
OUT
D1
V
IN
4430 F01b
T1
1:N
V
OUT
C
OUT
D1
V
IN
4430 F01c
T1
1:N
V
OUT
C
OUT
SYNC
Q1
V
IN
4430 F01d
T1
1:N
V
OUT
C
OUT
*OPTIONAL SEE TEXT
LT4430
V
BIAS
C1
R1*
D2
D1
V
IN
4430 F01e
T1
1:N
V
OUT
C
OUT
*OPTIONAL SEE TEXT
SYNC
LT4430
V
BIAS
C1
Q1
R1*
D2
Figure 1a. Typical Flyback
Converter Connection
Figure 1b. Equivalent Flyback
Converter Connection
Figure 1c. Synchronous Flyback
Converter Connection
Figure 1d. Flyback Converter with
Bias Generator
Figure 1e. Synchronous Flyback with
Bias Generator
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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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