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參數(shù)資料
| 型號： | NCP1014ST65T3 |
| 廠商： | ON SEMICONDUCTOR |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Self-Supplied Monolithic Switcher for Low Standby- Power Offline SMPS |
| 中文描述： | 1 A SWITCHING REGULATOR, 71 kHz SWITCHING FREQ-MAX, PSSO4 |
| 封裝： | PLASTIC, SOT-223, 4 PIN |
| 文件頁數(shù)： | 12/24頁 |
| 文件大?。?/td> | 324K |
| 代理商： | NCP1014ST65T3 |
NCP1010, NCP1011, NCP1012, NCP1013, NCP1014
http://onsemi.com
12
Plugging Equations 7 and 8 into Equation 6 leads to
Vds(t)
Vin
and thus,
PDSS
The worse case occurs at high line, when Vin equals
370 Vdc. With ICC1 = 1.1 mA (65 kHz version), we can
expect a DSS dissipation around 407 mW. If you select a
higher switching frequency version, the ICC1 increases and
it is likely that the DSS consumption exceeds that number.
In that case, we recommend to add an auxiliary winding in
order to offer more dissipation room to the power MOSFET.
Please read application note AND8125/D, “Evaluating
the Power Capability of the NCP101X Members” to help in
selecting the right part/configuration for your application.
Vin
ICC1
(eq. 9)
.
Lowering the Standby Power with an Auxiliary Winding
The DSS operation can bother the designer when its
dissipation is too high and extremely low standby power is
a must. In both cases, one can connect an auxiliary winding
to disable the selfsupply. The current source then ensures
the startup sequence only and stays in the off state as long as
V
CC
does not drop below VCC
ON
or 7.5 V. Figure 18 shows
that the insertion of a resistor (Rlimit) between the auxiliary
DC level and the V
CC
pin is mandatory to not damage the
internal 8.7 V active Zener diode during an overshoot for
instance (absolute maximum current is 15 mA) and to
implement the failsafe optocoupler protection as offered by
the active clamp. Please note that there cannot be bad
interaction between the clamping voltage of the internal
Zener and VCC
OFF
since this clamping voltage is actually
built on top of VCC
OFF
with a fixed amount of offset
(200 mV typical).
Selfsupplying 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 (Vnom), this voltage can drop to below
10 V (Vstby) when entering standby. This is because the
recurrence of the switching pulses expands so much that the
low frequency refueling rate of the V
CC
capacitor is not
enough to keep a constant auxiliary voltage. Figure 19
portrays a typical scope shot of a SMPS entering deep
standby (output unloaded). So care must be taken when
calculating Rlimit 1) to not trigger the V
CC
over current
latch [by injecting 6.3 mA (min. value) into the active
clamp] in normal operation but 2) not to drop too much
voltage over Rlimit when entering standby. Otherwise the
DSS could reactivate and the standby performance would
degrade. We are thus able to bound Rlimit between two
equations:
Vnom
Vclamp
Itrip
Where:
Vnom
is the auxiliary voltage at nominal load.
Vstdby
is the auxiliary voltage when standby is entered.
Rlimit
Vstby
VCCON
ICC1
(eq. 10)
Itrip
is the current corresponding to the nominal operation.
It must be selected to avoid false tripping in overshoot
conditions.
ICC1
is the controller consumption. This number slightly
decreases compared to ICC1 from the spec since the part in
standby almost does not switch.
VCC
ON
is the level above which Vaux must be maintained
to keep the DSS in the OFF mode. It is good to shoot 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).
Since Rlimit shall not bother the controller in standby, e.g.
keep Vaux to around 8.0 V (as selected above), we purposely
select a Vnom 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 standby
(Rlimit also drops voltage in standby
…
). Plugging the
values in Equation 10 gives the limits within which Rlimit
shall be selected:
20
8.7
6.3 m
1.1 m
1.8 k
Rlimit
3.6 k
If we design a power supply delivering 12 V, then the ratio
between auxiliary and power must be: 12/20 = 0.6. The OVP
latch will activate when the clamp current exceeds 6.3 mA.
This will occur when Vaux increases to: 8.7 V + 1.8 k x
(6.4m + 1.1m) = 22.2 V for the first boundary or 8.7 V +
3.6 k x (6.4m +1.1m) = 35.7 V for second boundary. On the
power output, it will respectively give 22.2 x 0.6 = 13.3 V
and 35.7 x 0.6 = 21.4 V. As one can see, tweaking the Rlimit
value will allow the selection of a given overvoltage output
level. Theoretically predicting the auxiliary drop from
nominal to standby is an almost impossible exercise since
many parameters are involved, including the converter time
constants. Fine tuning of Rlimit thus requires a few
iterations and experiments on a breadboard to check Vaux
variations but also output voltage excursion in fault. Once
properly adjusted, the failsafe protection will preclude any
lethal voltage runaways in case a problem would occur in the
feedback loop.
When an OVP occurs, all switching pulses are
permanently disabled, the output voltage thus drops to zero.
The V
CC
cycles up and down between 8.5–4.7 V and stays
in this state until the user unplugs the power supply and
forces V
CC
to drop below 3.0 V (VCC
reset
). Below this
value, the internal OVP latch is reset and when the high
voltage is reapplied, a new startup sequence can take place
in an attempt to restart the converter.
Rlimit
12
8
(eq. 11)
, that is to say:
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| NCP1014ST65T3G | 功能描述:電流型 PWM 控制器 Low Standby Power Monolithic Switcher RoHS:否 制造商:Texas Instruments 開關(guān)頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| NCP1014STBUCGEVB | 功能描述:電源管理IC開發(fā)工具 POSITIVE OUTPUT BUCK EVB RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
| NCP1015 | 制造商:ONSEMI 制造商全稱:ON Semiconductor 功能描述:Self-Supplied Monolithic Switcher for Low Standby- Power Offline SMPS |
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