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参数资料
| 型号： | AN-9008 |
| 厂商： | Fairchild Semiconductor Corporation |
| 元件分类： | 圆形连接器 |
| 英文描述： | Circular Connector; No. of Contacts:37; Series:MS27656; Body Material:Aluminum; Connecting Termination:Crimp; Connector Shell Size:15; Circular Contact Gender:Socket; Circular Shell Style:Wall Mount Receptacle RoHS Compliant: No |
| 中文描述： | 在一个反激变换器使用QFETs |
| 文件页数： | 3/9页 |
| 文件大小： | 124K |
| 代理商： | AN-9008 |
3
Rev D, July 2000
Performance in a Flyback Converter
Figure 3 shows the design of a commercially available 60 watt flyback converter with two outputs
(+160V, +15V), operating at a switching frequency of 80kHz and an input voltage of 220VAC. This
type of switching power supply is used for applications, such as monitors, TVs, and miscellaneous
instruments, requiring multiple output voltages . This discontinuous mode flyback converter, using
a KA3882 current mode controller, features good voltage tracking with the use of pulse by pulse
current sensing on the primary side, and an isolated secondary feedback loop. The PWM IC
KA3882 directly drives the power MOSFET.
As the power MOSFET sequentially turns on and off, energy is stored in the transformer core dur-
ing the on time, and is then transferred to the output capacitor during the off time. When the power
MOSFET turns off, the energy stored in the leakage inductance causes a voltage spike across the
drain-to-source terminal of the power MOSFET, which amounts to at least twice the input voltage
(Vin + nVo + leakage inductance voltage
1
). Most applications need clamp circuits to restrict this
voltage spike from exceeding the BVdss rating of a MOSFET. A power MOSFET must have high
voltage capability with lower on-resistance and smaller gate charge for higher efficiency.
Figure 3: Flyback Converter Circuit Diagram
1. 'n' indicates a turns ratio of the transformer windings. The voltage of Vin + nVo + leakage inductance voltage of the transformer appears at
the primary side.
7
8
6
3
5
2
1
4
K
L1
D1
T1
Fuse
U1
U2
U3
Q1
1
Vout1
160V 0.3A
Vout2
QFET(FQP7N60)
or Conventional
MOSFET
3
Vin=220VAC
1
2
3
C1
1
2
1
2
C4
1
2
1
2
1
5
4
8
C2
1
2
C3
1
2
C5
1
2
R2
1
2
1
2
1
2
1
2
R1
1
2
R3
1
2
2
R5
1
2
C6
1
2
R14
1
2
1
2
D3
1
2
C10
1
2
C9
1
2
R11
1
2
D4
1
2
R11
1
2
R13
1
2
D5
1
2
C8
1
2
R10
1
2
1
3
C7
1
2
R9
1
2
R6
1
2
1
R7
2
R8
1
2
R19
1
2
R20
1
3
2
1
2
D7
1
2
C13
1
2
R14
1
2
1
R16
1
2
1
R17
2
2
1
2
C14
1
2
D2
1
2
C11
1
2
R4
1
2
C12
1
2
R18
1
2
1
5
4
8
D6
1
2
5V 0.8A
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