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| 型号： | SG6846CLDZ |
| 厂商： | Fairchild Semiconductor |
| 文件页数： | 10/15页 |
| 文件大小： | 0K |
| 描述： | IC CTRLR PWM PROG GREEN OTP 8DIP |
| 产品变化通告： | Product Discontinuation 03/Dec/2009 |
| 标准包装： | 59 |
| 输出隔离： | 隔离 |
| 频率范围： | 44.8 ~ 136kHz |
| 输入电压： | 10.5 V ~ 25 V |
| 输出电压： | 18V |
| 功率（瓦特）： | 800mW |
| 工作温度： | -40°C ~ 150°C |
| 封装/外壳： | 8-DIP（0.300"，7.62mm） |
| 供应商设备封装： | 8-DIP |
| 包装： | 管件 |
Operation Description
Start-up Operation
The turn-on/turn-off thresholds are fixed internally at
16.5V/10.5V. To enable the SG6846C during start-up,
the hold-up capacitor must first be charged to 16.5V
through the start-up resistor.
The hold-up capacitor continues to supply V DD before
energy can be delivered from the auxiliary winding of
the main transformer. The V DD must not drop below
10.5V during this start-up process. This UVLO
hysteresis window ensures that the hold-up capacitor
can adequately supply V DD during start-up.
The typical start-up current is only 8μA, which allows a
high-resistance, low-wattage start-up resistor to be used
to minimize power loss. A 1.5M Ω /0.25W start-up
resistor and a 10μF/25V V DD hold-up capacitor are
sufficient for a universal input range.
The required operating current has been reduced to
3.7mA, which enables higher efficiency and reduces the
V DD hold-up capacitance requirement.
Green-Mode Operation
The proprietary green-mode function provides off-time
modulation to continuously decrease the switching
frequency under light-load conditions. Maximum on-time
is limited to provide protection against abnormal
conditions. To further reduce power consumption under
zero-load condition, the PWM oscillator is completely
turned off and the power supply enters burst-mode. This
green-mode function dramatically reduces power
consumption under light-load and zero-load conditions.
Power supplies using the SG6846C can meet even the
most restrictive international regulations regarding
standby power consumption.
Oscillator Operation
A resistor connected from the RI pin to GND generates
a reference current source, inside the SG6846C, used
to determine the PWM frequency. Increasing the
resistance decreases the amplitude of the current
source and reduces the PWM frequency. Using a 26k Ω
resistor results in a corresponding 65kHz switching
frequency. The relationship between R I and the
switching frequency is:
Two-level Over-current Protection (OCP)
The cycle-by-cycle current limiting shuts down the PWM
immediately when the switching current is over the
peak-current threshold. Additionally, when the switching
current is higher than half of the peak-current threshold,
the internal counter counts down. When the total
accumulated counting time is more than ~110ms
(R I = 26k Ω ), the controller is latched off and the internal
counter counts up. When the switching current is lower
than half of the peak current threshold, the internal
counter will count down. When the total accumulated
counting time is more than ~110ms (R I = 26k Ω ), the
controller is latched off.
This two-level OCP protection and up/down counter are
especially designed for SMPS with surge current output,
such as those for printers, scanners, and motor drivers.
Constant Output Power Limit
For constant output power limit over a universal input-
voltage range, the peak-current threshold is adjusted by
the voltage of the VIN pin. Since the VIN pin is
connected to the rectified AC input line voltage through
the resistive divider, a higher line voltage generates a
higher V IN voltage. The threshold voltage decreases as
the V IN increases, making the maximum output power at
high line input voltage equal to that at low line input.
The value of R-C network should not be so large it
affects the power limit (shown in Figure 18). R and C
should put on less than 300 Ω and 1000pF respectively.
Brownout Protection
Since the VIN pin is connected through a resistive
divider to the rectified AC input line voltage, it can also
be used for brownout protection. If the V IN voltage is
less than 0.7V, the PWM output is shut off. As the V IN
over 0.9V, the PWM output is turned on again. The
hysteresis window for ON/OFF is ~0.2V.
V DD Over-voltage Protection (OVP)
V DD over-voltage protection is built in to prevent
damage. When V DD is over 23.6V, the SG6846C is
latched off.
f PWM (kHz) =
1690
R I (k Ω )
(2)
Over-temperature Protection (OTP)
An external NTC thermistor can be connected from the
RT pin to GND. The impedance of the NTC decreases
If an open-circuit or short-circuit to ground occurs at the
RI pin, the internal protection circuit immediately shuts
down the controller.
? 2007 Fairchild Semiconductor Corporation
SG6846C ? Rev. 1.1.2
10
at high temperatures. When the voltage of the RT pin
drops below 1.05V, the SG6846C is turned off. For
protection-mode options, see Ordering Information.
www.fairchildsemi.com
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相关代理商/技术参数 |
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|---|---|
| SG6846CLSZ | 功能描述:软开关 PWM 控制器 Highly-Integrated Grn Mode PWM Cntrl RoHS:否 制造商:Fairchild Semiconductor 输出端数量: 输出电流: 开关频率: 工作电源电压:30 V 电源电流: 最大工作温度:+ 105 C 最小工作温度:- 40 C 安装风格:SMD/SMT 封装 / 箱体:SOIC-8 封装:Reel |
| SG6846CS | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Highly-Integrated Green-Mode PWM Controller |
| SG6846CSZ | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Highly-Integrated Green-Mode PWM Controller |
| SG6846G | 制造商:FAIRCHILD 制造商全称:Fairchild Semiconductor 功能描述:Highly Integrated Green-Mode PWM Controller |
| SG6846G_09 | 制造商:FAIRCHILD 制造商全称:Fairchild Semiconductor 功能描述:Highly Integrated Green-Mode PWM Controller |
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