參數(shù)資料
型號： 88EM8081XX-SAG2C000-T
廠商： MARVELL SEMICONDUCTOR INC
元件分類： 穩(wěn)壓器
英文描述： 2 A POWER FACTOR CONTROLLER, 120 kHz SWITCHING FREQ-MAX, PDSO8
封裝： GREEN, SOIC-8
文件頁數(shù)： 37/64頁
文件大小： 667K
代理商： 88EM8081XX-SAG2C000-T
88EM8080/88EM8081
Datasheet
Doc. No. MV-S106340-01 Rev. B
Copyright 2010 Marvell
Page 42
Document Classification: Proprietary
August 6, 2010, Preliminary Information
5.3.5
NTC Compensation Circuit Design
The secondary side error amplifier output voltage VC varies between the maximum value VZD6 and
the minimum value 2.5V (U1 (TL431) minimum supply voltage). From equation (13) it can been seen
that the variation of VC depends on the tolerance of R11 and R23 value, VFB reference voltage and
CTR value of optocoupler.
But the CTR value of optocoupler has a wide variation from unit to unit and also with temperature.
For example, the relative CTR of FOD817 form Fairchild changes from 105% to 55% with ambient
temperature from 0C to 110C. If ambient temperature increases, the CTR of optocoupler
decreases, which results in a lower value for VC. When ambient temperature is over 110C, the VC
voltage could reach the minimum limit value of 2.5V. Then the power system will be out of regulation.
It is pointed out that 0C and 110C are selected for illustration only.
At 0C VC would increase from the value at room temperature. If it is high enough zener D6 would
conduct and the power system is out of regulation.
In order to keep VC at a reasonable range (below zener D6 Voltage and above 2.5V with a margin) a
NTC compensation circuit, shown in Figure 22, is introduced. An actual reference design is shown
for illustration of NTC compensation. This compensation circuit is composed of a NTC resistor
NTC1, resistor R10 and R23 instead of resistor R23 only.
Figure 22: Isolated LED Current Control with NTC Compensation
VIN
C14
0.1
μF
FB
IS
N
S
OC
P
SGND
PGND
VD
D
4
U3
SW
5
7
8
1
2
6
3
88E
M
8
08
1
C9
0.1
μF
R19
20.5
1/8W
3
4
R11
1.24k
1
2
D1
4.7V
500mW
VDD
C4
22
μF
25V
HVDC
R5
1.0
1/4W
C6
100pF
Q1
650V
4.5A
D9
STPS3150RL
C11
330
μF
35V
C13
330
μF
35V
NTC1
33k
R23
3.01k
R10
4.02k
LED +
LED -
C2
1.0
μF
35V
R4
4.99k
R8
0.1
R3
4.99k
R1
4.99k
R2
243k
U2
TS321LT
1
2
PC1A
FOD817A
D6
15V
500mW
1
2
R22
10k
R21
4.99k
C1
1.0
μF
50V
12
3
VR
E
F
1
5
3
4
2
U1
TL431
+25.0 VDC, 500mA (nominal)
Input Voltage from
Rectifier Bridge
IEOPTO
T1
C8
0.047
μF
50V
R7
187
R12
200
P/O PC1A
VC
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