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參數(shù)資料
| 型號： | SG5842A |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Highly Integrated Green-Mode PWM Controller |
| 中文描述： | 高度集成的綠色模式PWM控制器 |
| 文件頁數(shù)： | 10/14頁 |
| 文件大?。?/td> | 481K |
| 代理商： | SG5842A |
Product Specification
Highly Integrated Green-Mode PWM Controller
Constant Output Power Limit
SG5842A/JA
System General Corp.
Version 1.4.2 (IAO33.0026.B6)
- 10 -
www.sg.com.tw www.fairchildsemi.com
October 30, 2007
When the SENSE voltage, across the sense resistor R
S
,
reaches the threshold voltage, around 0.85V, the output
GATE drive is turned off after a small delay t
PD
. This delay
introduces additional current, proportional to t
PD
V
IN
/ L
P
.
Since the delay is nearly constant regardless of the input
voltage V
IN.
Higher input voltage results in a larger
additional current and the output power limit is also higher
than under low input line voltage. To compensate this
variation for a wide AC input range, a sawtooth
power-limiter (saw limiter) is designed to solve the unequal
power-limit problem. The saw limiter is designed as a
positive ramp signal (V
LIMIT_RAMP
) and is fed to the inverting
input of the OCP comparator. This results in a lower current
limit at high-line inputs than at low-line inputs.
V
DD
Over-Voltage Protection
V
DD
over-voltage protection has been built in to prevent
damage due to abnormal conditions. Once the V
DD
voltage is over than the V
DD
over-voltage protection
voltage (V
DD-OVP
) and lasts for t
D-OVP
, the PWM pulses is
latched off. The PWM pulses stay latched off until the
user unplugs the power supply from the mains outlet.
Limited Power Control
The FB voltage increases every time the output of the
power supply is shorted or over loaded. If the FB voltage
remains higher than a built-in threshold longer than t
D-OLP
,
PWM output is turned off. As PWM output is turned off,
the supply voltage V
DD
begins decreasing.
)
(K
I
R
154
.
2
OLP
-
D
(ms)
t
Ω
×
=
-----------------
(2)
When V
DD
goes below the turn-off threshold (eg, 10.5V)
the controller is totally shut down. V
DD
is charged up to
the turn-on threshold voltage of 16.5V through the
start-up resistor until PWM output is restarted. This
protection feature remains activated as long as the
over-loading condition persists. This prevents the power
supply from overheating due to over loading conditions.
Protection Latch Circuit
For the SG5842A/JA family, the built-in latch function
provides a versatile protection feature that does not
require external components
(see ordering information
for a detailed description)
. To reset the latch circuit,
disconnect the AC line voltage of the power supply.
Thermal Protection
An external NTC thermistor can be connected from the
RT pin to ground. A fixed current, I
RT
, is sourced from the
RT pin. Because the impedance of the NTC decreases at
high temperatures, when the voltage of the RT pin drops
below 1.05V, PWM output is latched off. The RT pin
output current is related to the PWM frequency
programming resistor R
I
.
Noise Immunity
Noise from the current sense or the control signal may
cause significant pulse width jitter, particularly in
continuous-conduction mode. Slope compensation helps
alleviate this problem. Good placement and layout
practices should be followed. Avoid long PCB traces and
component leads. Compensation and filter components
should be located near the SG5842A/JA. Finally,
increasing the power-MOS gate resistance is advised.
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| SG5842ADZ | Highly Integrated Green-Mode PWM Controller |
| SG5842JA | Highly Integrated Green-Mode PWM Controller |
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相關代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SG5842A_09 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Highly Integrated Green-Mode PWM Controller |
| SG5842ADZ | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Highly Integrated Green-Mode PWM Controller |
| SG5842ASY | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Highly Integrated Green-Mode PWM Controller |
| SG5842ASZ | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Highly Integrated Green-Mode PWM Controller |
| SG5842BSZ | 制造商:Fairchild Semiconductor Corporation 功能描述: |
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