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| 型号： | NCP1028LEDGEVB |
| 厂商： | ON Semiconductor |
| 文件页数： | 19/29页 |
| 文件大小： | 0K |
| 描述： | EVAL BOARD FOR NCP1028LEDG |
| 设计资源： | NCP1028LEDGEVB BOM CP1028LEDGEVB Gerber Files NCP1028LED EVB Schematic |
| 标准包装： | 1 |
| 电流 - 输出 / 通道： | 720mA |
| 输出及类型： | 1，隔离 |
| 输出电压： | 18V |
| 输入电压： | 90 ~ 265VAC |
| 已供物品： | 板 |
| 已用 IC / 零件： | NCP1028 |
| 其它名称： | NCP1028LEDGEVBOS |
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NCP1028
Designing the Auxiliary Winding
A NCP1028 internal arrangement clamps the voltage
applied on the V CC pin. It uses an active shunt circuitry as
shown on Figure 33. Care must be taken to avoid injecting
too much current when the clamp is activated. The
insertion of a resistor ( R limit ) between the auxiliary dc level
calculating R limit not to drop too much voltage over it when
entering standby. Otherwise, the converter will enter burst
mode as it will sense an UVLO condition. Based on these
recommendations, we are able to bound R limit between two
equations:
and the V CC pin is thus mandatory not to damage the
internal 8.7 V zener diode during an overshoot for instance
(absolute maximum current is 15 mA. Please note that
Vnom-Vclamp
ICCmax
v Rlimit v
Vstby-VCCON
ICC1
(eq. 3)
there cannot be bad interaction between the clamping
voltage of the internal zener and VCC ON since this
clamping voltage is actually built on top of VCC ON with a
fixed amount of offset (200 mV typical). R limit should be
carefully selected to avoid disturbing the V CC in low / light
load conditions. The below lines detail how to evaluate the
R limit value.
Self-supplying controllers in extremely low standby
applications often puzzles the designer. Actually, if a
SMPS operated at nominal load can deliver an auxiliary
voltage of an arbitrary 16 V (V nom ), this voltage can drop
below 10 V (V stby ) when entering standby. This is because
the recurrence of the switching pulses expands so much that
the low frequency re-fueling rate of the V CC capacitor is
not enough to keep a proper auxiliary voltage. Figure 34
portrays a typical scope shot of a SMPS entering deep
Where:
V nom is the auxiliary voltage at nominal load.
V stdby is the auxiliary voltage when standby is entered.
ICC max is the maximum current you can inject in the pin
without damaging the controller (15 mA).
ICC1 is the controller consumption. This number slightly
decreases compared to ICC1 from the spec since the part
in standby does almost not switch. It is around 1.0 mA for
the 65 kHz version and 1.4 mA for the 100 kHz one.
VCC (min) is the level above which the auxiliary voltage
must be maintained to keep the controller away from the
UVLO trip point. It is good to obtain around 8.0 V in order
to offer an adequate design margin, e.g. to not reactivate the
startup source (which is not a problem in itself if low
standby power does not matter).
standby (output un-loaded). Thus, care must be taken when
Drain
V CCON = 8.5 V
V CC(min) = 7.5 V
+
-
+
Startup
Source
+
V CC
R limit
D1
-
+
V clamp = 8.7 V Typ.
+
C VCC
+
C AUX
L aux
I > 6 mA
Ground
Figure 33. A more detailed view of the NCP1028 offers better
insight on how to properly wire an auxiliary winding.
20-8.7 v R
limit v 1 m , that is to say : 1.3 k W t Rlimit
t 4 k W .
Since R limit shall not bother the controller in standby, e.g.
keep V auxiliary to around 8.0 V (as selected above), we
purposely select a V nom well above this value. As explained
before, experience shows that a 40% decrease can be seen
on auxiliary windings from nominal operation down to
standby mode. Let's select a nominal auxiliary winding of
20 V to offer sufficient margin regarding 8.0 V when in
Plugging the values in Equation 3 gives the limits within
which R limit shall be selected:
12-8
10 m
We purposely limited the injected current to 10 mA in
order to include a safety margin.
standby ( R limit also drops voltage in standby … ).
http://onsemi.com
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| NCP1028P065G | 功能描述:电流型 PWM 控制器 NCP1028 65 KHZ RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| NCP1028P100G | 功能描述:电流型 PWM 控制器 NCP1028 100 KHZ RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
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| NCP102SNT1G | 功能描述:低压差稳压器 - LDO LDO LINR REG CONTRL RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
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