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N3856V Schematic ( PDF Datasheet ) - NIKO-SEM

Teilenummer N3856V
Beschreibung Synchronous Rectification Controller
Hersteller NIKO-SEM
Logo NIKO-SEM Logo 




Gesamt 13 Seiten
N3856V Datasheet, Funktion
NIKO-SEM Synchronous Rectification Controller N3856V
N3856P
GENERAL DESCRIPTION
The N3856 is a low cost , high efficiency, full
featured ,synchronous re ctification control ler
that specifically des igned for the synchronous
rectification applications of the Flyback AC/DC
PWM mode switching power supply .
The N3856 is included a totem pole output
ideally suited for driving a synchronous rectifi-
cation power MOSFET . 2 way of the current
detect provided for wide applications by any
continuous or disco tinuous mode operating
(patent pending).In cont inuous mode operatin-
g, it included a timi ng control to adjust
maximum turn-on duty to allow the designer to
determine the optimal condition for the best
efficiency by the external resistor and
capacitor. In disconti nuous mode operating, it
included a very sensitive current
detector
(about 20mV) to cont rol the synchronous
rectification MOSFET, avoid happening a large
reverse current via the synchronous
rectification MOSFET to damage the device.
FEATURES
High efficiency operating.
Adjustable Max. duty cycle designed.
Decrease areas of heatsink or PCB.
Solved heat dissipation.
Sensitive current detecter(about 20mV)
Suited for continuous and discontinuous
mode operation.
Auto frequency tracking with PWM
frequency.
Suited for fixed or variable frequency
SOIC-8 and DIP-8 package.
APPLICATION
Flyback AC/DC power supply
DEVICE SELECTION GUIDE
DIP- 8
N3856PG
SOIC- 8
N3856VG
ABSOLUTE MAXIMUM RATING
PARAMETERS SYMBOL
Vcc to GND
Surge Voltage of VCC(below 200nS)
Drain to Other Pin
Power Dissipation at Ta = 25 ,Derate 8mW/ for Ta
Operating Junction Temperature Range
Storage Temperature Range
Lead Temperature (Soldering) 10 sec
25
VCC
VCC(surge)
PD
Tj
TSTG
TLEAD
REV : 1.1
1
LIMITS
-0.3 to 30
45
180
725
-40 to +150
-65 to +150
300
UNITS
V
Vp-p
V
mW
DEC-14-2004
http://www.Datasheet4U.com






N3856V Datasheet, Funktion
NIKO-SEM Synchronous Rectification Controller N3856V
N3856P
b. Synchronous signal from primary side
The structure is designed for a high power , high performerce flyback power supply ,
the synchronous signal is provided before the MOSFET Q2 turn on from the triangle
wave of the PWM controller , it need to use a isolation transformer between the
primary and the secondary for safety request .when the circuit is designed in
continuous mode , the MOSFET of the
secondary side to be turned off by a
synchronous signal from the primary side , if works in discontinuous mode that turned
off by the current detect pin 5 to sence the voltage drop between the source and drain
of the MOSFET .
VCC
+
C5
R10
D4
+
C4
T1
1
4
D1
1N4148
5
6
8
SYNC X'FRM
*
T2A
PWM
CONTROLER
VREF
C6
0.1U
Q3 CT
2SC945
Q4
2SA733
Q2
R9
D2 SB3100
SD
Q1
G
C2
470P
R1
16K
U1
1 GATE VCC 8
2 PGND RT/CT 7
3 GND AOUT 6
4 BIAS DRAIN 5
N3856V
+ C3
Vo
Q5
2SC945
R3
1K
D3
1N4148
T2B
*
R7
4
U3
PC817
1
32
R6
U2
TL431
R8
R4
C3
R5
Schematic 2 synchronous signal type with AUX winding application
Schematic 2 is a synchronous signal type with AUX winding application ,in this
application , the pin 7 is connected to pin 3 of this IC to cancel maximum turn
on duty function because the MOSFET can get best control from the synchronous
signal .
REV : 1.1
6 DEC-14-2004

6 Page









N3856V pdf, datenblatt
NIKO-SEM Synchronous Rectification Controller N3856V
N3856P
DEMO BOARD DESCRIPTION
The Schematic 3 presents a demo board for the N3856V , This board replaces the output
rectifier diode with synchronous rectification MOSFET in flyback power supply and includes
all the components needs by the N3856V to operate, R3 and C1 can be adjusted for diffferent
switching frequency and turn-on duty demand
GND GATE
DRAIN VCC
D1
1N4148
C2
470P
U1
1 GATE VCC 8
R3
2 PGND RT/CT 7 51K
3 GND AOUT 6
4 BIAS DRAIN 5
N3856V
R1
16K
C1
470P
.
pic.4 demo board layout----componects
REV : 1.1
12 DEC-14-2004

12 Page





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