MAX5021EPA 查看數據表（PDF） - Maxim Integrated
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MAX5021EPA Datasheet PDF : 11 Pages
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Current-Mode PWM Controllers for Isolated
Power Supplies
L
85VAC TO
265VAC IN
N
G
CENTRAL SEMICONDUCTOR
CBR1-D100S
AC
L2
470µH
AC C1
10µF
400V
R8
1.2kΩ
D1
250mA, 75V
CENTRAL SEMICONDUCTOR
CMPD914
C3
VCC
0.22µF
C9
10µF
400V
U1
CTX03-15256 D2
T1
3A, 40V
ON SEMICONDUCTOR
R1
360kΩ
480µH, 60T
RS = R1 + R2 D1
R2
360kΩ
R11
10Ω
8T
MBRS340T3
3T
C4
150µF
6.3V
R3
1kΩ
1%
C2
0.22µF
C7
1000pF
OPTO
TEXAS
INSTRUMENTS
VIN
TLV431AIDBV
OPTO
FAIRCHILD
CNY17-3
MAX5022
OPTO
NDRV
N1
INTERNATIONAL RECTIFIER
IRFRC20
+5V OUT
R4
24.9kΩ
1%
R10
10Ω
C6
0.1µF
C5
0.01µF
R5
8.06kΩ
1%
R9
240kΩ
NOTE: ALL RESISTORS ARE 5% UNLESS OTHERWISE SPECIFIED.
GND CS
R6
C8
10Ω
RCS
8200pF
1.78Ω
1%
Figure 1. Universal 5W Off-Line Standby Power Supply
NDRV did not switch enough times to build up sufficient
voltage across the tertiary output to power the device.
The device will go back into UVLO and will not start. Use
a low-leakage ceramic or film capacitor for C2 and C3.
As a rule of thumb, off-line power supplies keep typical
startup times to less than 500ms even in low-line condi-
tions (85VAC input). Size the startup resistor, RS, to sup-
ply the maximum startup bias of the IC (85µA) plus the
additional current required for charging the capacitors
C2 and C3 in less than 500ms. This resistor dissipates
continuous power in normal operation, despite the fact
that it is only used during the startup sequence.
Therefore it must be chosen to provide enough current
for the low-line condition as well as have an appropriate
power rating for the high-line condition (265VAC). In
most cases, split the value into two resistors connected
in series for the required voltage of approximately
400VDC.
The typical value for C2 and C3 is 220nF. The startup
resistor, RS, provides both the maximum quiescent cur-
rent of 85µA and the charging current for C2 and C3.
Bypass capacitor C3 charges to 9.5V and C2 charges
25
IC COMES OUT OF UVLO
(WAKEUP)
20
15
VIN SUPPLIED BY C2
VIN
VIN SUPPLIED BY TERTIARY
10
WINDING (NORMAL OPERATION)
VCC BYPASS CAPACITOR
FULLY CHARGED
5
VCC
VCC DROPS SLIGHTLY WHEN
NDRV BEGINS SWITCHING
0
0
50
100
150
200
TIME (ms)
Figure 2. VIN and VCC During Startup
to 24V all within the desired time period of 500ms, for
an overall average charging current of 15µA. Hence,
the startup resistor must provide a total of at least
100µA. Developing 100µA from an input voltage of
6 _______________________________________________________________________________________
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