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參數(shù)資料
| 型號(hào)： | L4990A |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | PRIMARY CONTROLLER |
| 中文描述： | 主控制器 |
| 文件頁(yè)數(shù)： | 14/24頁(yè) |
| 文件大?。?/td> | 322K |
| 代理商： | L4990A |
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DEMONSTRATION BOARD
To evaluate the device performance, a demon-
stration board has been realized. Despite its sim-
plicity, it exploits most of the features of the
L4990.
The board embodies an applicationbased on the
following specification of universal mains AC-DC
adapter:
Input voltage range: 85-270 Vac (50/60 Hz)
Outputvoltage: 15 V
Outputcurrent: 0.5 to 2A
Outputvoltage ripple : 300 mV (max.)
Load regulation:
±
5%(0.5 to 2 A loadchange)
Target efficiency @ Iout = 2 A: ; 80% over the
input voltagefull range
Some preliminary decisions, concerning topology,
operating mode, switching frequency, maximum
duty cycle allowed and control technique, have
been made.
As for topology, at this power level and output
voltage, flyback is the most advantageous one,
mainly because of its simplicity, which means low
parts count,low cost and inherent high efficiency.
A peculiar design choice aiming at optimizing the
overall system concerns the operating mode: the
converter will work in continuouscurrent mode at
low input voltages, when input current is greater,
and in discontinuous mode at higher input volt-
ages.Numerous benefits originate from that.
Compared to discontinuous current mode, con-
tinuous operation involves lower peak currents
(typ. -40%) at the same throughput power. This
implies lessstress for all power components.
The transformer inductance is higher and, there-
fore, a smallerair gap is required for a given core:
this increasesprimary-to-secondary coupling and,
as a consequence, reduces leakage inductance
and improvesenergy transfer. Both efficiency and
load regulation will take advantage of that.
Another point in favor is a reduction of the mini-
mum output power that the system is able to de-
liver keepingthe output well regulated.
Few components are required in addition for
slope compensation.
Actually, continuous mode flyback suffers also
from a poor dynamic behavior during load tran-
sients because of the narrow bandwidth of the
control loop due to stability problems. However,
great dynamic performance is not required to AC-
DC adapters,so this problem is of no concern.
The boundary between the two operating modes
has been set at about 150 Vac (@ Iout=2A).
The selection of the switching frequency is a mat-
ter of trade-off between achieving a small trans-
formersize and high efficiency. 200 kHz seems to
be a good compromise.
In this application, the wide input voltage range
requires a large duty cycle sweep. The higher is
the maximum duty cycle, the larger is the operat-
V15=GND
V5=V13=GND
V15=VREF
V5=V13=GND
t
d
t
d
tc
tc
V2
V10
V2
V10
D
X
=
tc
tc+ td
D
X
=
tc
2 ·tc+ td
D97IN498
Figure 29. Half duty cycle option.
L4990 - L4990A
14/24
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PDF描述 |
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| L4990AD | PRIMARY CONTROLLER |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| L4990AD | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:PRIMARY CONTROLLER |
| L4990D | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:PRIMARY CONTROLLER |
| L4991 | 功能描述:TEST COIL FOR REED SWITCH, 1PC RoHS:是 類別:開(kāi)關(guān) >> 配件 系列:- 標(biāo)準(zhǔn)包裝:100 系列:- 其它名稱:886.0007886.0007-ND |
| L4992 | 制造商:STMicroelectronics 功能描述: 制造商:STMicroelectronics 功能描述:VOLT SUPERVISOR CNTRLR 5.1V/3.3V 32TQFP - Trays |
| L4993 | 制造商:STMICROELECTRONICS 制造商全稱:STMicroelectronics 功能描述:Low drop voltage regulator |
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