MAX16841_13 Datasheet, PDF (9/18 Pages) Maxim Integrated Products – Controller IC for Dimmable Offline LED Lamps

MAX16841
Controller IC for Dimmable Offline LED Lamps
Circuit components R11, R12, C15, Q6, Q7, R13, and
R14 are used to control the input current. Q6 and Q7
are matched transistors. The voltage on C15 represents
the average input voltage. The average voltage is then
used to control the current in the current-mirror circuit
formed by R12, R13, R14, Q6, and Q7. The current
flowing into R12 is approximately proportional to the
voltage across C15 and is now reflected on the collector
of Q6, and sinks the same amount of current from the
collector of Q7 that flows into R12. Inside the device is
a 50FA current source. The current flowing into R16 sets
the input current, or the average current flowing into R20.
The circuit tries to keep the input power over the line volt-
age almost constant.
F1
L1
AC1
R1
R26
R2
L2
AC2
DB+
R4
D3
18V
Q5
R6
G
DB-
DB+
R11
C15
R12
REFI
Q6
Q7
R13 R14
DB+
L3
D2
3
D1
1
2
C9
R22
R23
C14
R24
LED+
C10
C11
C12
LED-
4
DB-
C2
G
Q2
D10
D6
C13
L5
R5
15V
C1
R3
Q1
R34
D4
C8
DB+
R7
U1
IN
R8
Q3
4 _DIMOUT
IN ⁸
C5
MAX16841
D12
R9
3 _TH
NDRV ⁷
R21
Q4
REFI
R10
1 _REFI
CS ⁶
C16
R16
R18
R20
C3
C4
R17
2 _COMP
GND ⁵
Figure 1. Nonisolated (Buck) Topology
Maxim Integrated
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