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參數(shù)資料
| 型號： | AN8021NS |
| 廠商： | PANASONIC CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | External excitation flyback AC-DC switching power supply control IC |
| 中文描述： | 1 A SWITCHING CONTROLLER, 700 kHz SWITCHING FREQ-MAX, PDSO8 |
| 封裝： | 0.225 INCH, PLASTIC, SOP-8 |
| 文件頁數(shù)： | 13/16頁 |
| 文件大小： | 141K |
| 代理商： | AN8021NS |
13
Voltage Regulators
AN8021L, AN8021SB
I
Application Notes (continued)
[2] Operation descriptions (continued)
6. Timer latch
When the short-circuit or overload of the power supply output continues for a certain period, the pulse-by-pulse
overcurrent protection is not sufficient for protection of the transformer, fast recovery diode (FRD), schottky diode
in the secondary side and the power MOSFET. For this reason, the timer latch function is employed, which stops
the power supply by hitting the OVP, when the overcurrent condition continues for a certain period.
The short-circuit or overload of the power supply output is monitored as the decrease of the power supply output
(at this time the pulse-by-pulse overcurrent protector is in the operating condition). The decrease of the power
supply output is detected as the decrease of current amount from the current feedback terminal of the normal
PWM control. When the decrease amount of this current exceeds a certain value, the comparator inside the IC
reverses and the constant current flows to the TIM/OVP terminal.
The external capacitor is connected to the TIM/OVP terminal. Electric charges are accumulated in this capacitor
to rise the OVP terminal voltage. When the OVP operating threshold voltage (6 V typical) is reached, the OVP starts
operation to stop the IC and keeps this stop condition. (Refer to figure 8.)
Timer period
The period from the time when an error of the power supply output is detected to the time when the OVP starts
operation (hereinafter referred to as timer period) should be longer than the rise time of the power supply. Since
at operation start the IC is in the same condition as the overload or output short-circuit condition, if the timer
period is shorter, the power supply works latch and can not start.
Therefore, the IC is designed so that the timer period can be set to any desired value with capacitance value of
the external capacitor connected to the TIM/OVP terminal. However, particular care should be taken, because too
large value of this capacitance may cause the breakdown of the power supply.
Power supply
output voltage
0
V
O
Power supply stop
Time
Power MOSFET
current
0
I
DS
Power supply stop
Time
TIM/OVP
terminal
voltage
0
V
OVP
Power supply stop
Time
OVP
V
TH
=
6 V (typ.)
Figure 8. Timer latch basic operation
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AN8021SB | 制造商:PANASONIC 制造商全稱:Panasonic Semiconductor 功能描述:AC-DC switching power supply control IC |
| AN8022 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述: |
| AN8022L | 制造商:PANASONIC 制造商全稱:Panasonic Semiconductor 功能描述:AC-DC switching power supply control IC |
| AN8022SB | 制造商:PANASONIC 制造商全稱:Panasonic Semiconductor 功能描述:AC-DC switching power supply control IC |
| AN-8023 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Negative Voltage Management |
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