LT3799I(RevA) 查看數據表（PDF） - Linear Technology
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LT3799I Datasheet PDF : 20 Pages
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LT3799
Block Diagram
D2
R4
C1
•
L1C
R5
R10
R3
C3
R1
R2
VIN
D1
T1
C2
L1A
L1B
N:1
6 CT
FAULT
DETECTION
C4
FAULT
5
COMP+
7
9
FB
S&H
A3
+
+ –A2
600mV
–
C6
1M
COMP–
SW1
8
CTRL1
1
CTRL2
2
+++– A5
A6
CTRL3
3
10
DCM
16
VIN_SENSE
1.22V +
–A8
ONE
SHOT
A7
CURRENT
COMPARATOR
–
+A1
SR
Q
S
MASTER
LATCH
A4
MULTIPLIER
LOW OUTPUT
CURRENT
OSCILLATOR
4 VREF
11
VIN
R7
R8
DRIVER
INTVCC 13
GATE 14
SENSE
15
GND
17
3799 BD
C5
M1
R6
VOUT +
C7
VOUT –
Operation
The LT3799 is a current mode switching controller IC
designed specifically for generating an average current
output in an isolated flyback topology. The special problem
normally encountered in such circuits is that information
relating to the output voltage and current on the isolated
secondary side of the transformer must be communicated
to the primary side in order to maintain regulation. Histori-
cally, this has been done with an opto-isolator. The LT3799
uses a novel method of using the external MOSFETs peak
current information from the sense resistor to calculate
the output current of a flyback converter without the need
of an opto-coupler. In addition, it also detects open LED
conditions by examining the third winding voltage when
the main power switch is off.
Power factor has become an important specification for
lighting. A power factor of one is achieved if the current
drawn is proportional to the input voltage. The LT3799
modulates the peak current limit with a scaled version of
the input voltage. This technique provides power factors
of 0.97 or greater.
The Block Diagram shows an overall view of the system.
The external components are in a flyback topology con-
figuration. The third winding senses the output voltage
and also supplies power to the part in steady-state opera-
tion. The VIN pin supplies power to an internal LDO that
generates 10V at the INTVCC pin. The novel control circuitry
consists of an error amplifier, a multiplier, a transmission
3799fa
8
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