|
|
PDF AN-6747B Data sheet ( Hoja de datos )
| Número de pieza | AN-6747B | |
| Descripción | Flyback Power Supply | |
| Fabricantes | Fairchild Semiconductor | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de AN-6747B (archivo pdf) en la parte inferior de esta página. Total 12 Páginas | ||
|
No Preview Available !
www.fairchildsemi.com
AN-6747
Applying FAN6747 to Control a Flyback Power Supply with
Peak Current Output
1. Introduction
Highly integrated PWM controller, FAN6747, is optimized
for applications with motor load, such as printers and
scanners, that inherently impose some kind of overload
condition on the power supply during acceleration mode.
FAN6747 provides a two-level OCP function that allows the
SMPS to stably deliver peak power during the motor
acceleration without causing premature shutdown, while
protecting the SMPS from overload condition.
Green-mode and burst-mode functions with a low operating
current maximize the light-load efficiency so that the power
supply can meet stringent standby power regulations.
The frequency-hopping function reduces electro-magnetic
interference (EMI) of a power supply by spreading the
energy over a wider frequency range. The constant power
limit function minimizes the component stress in abnormal
condition and helps optimize the power stage. Protection
functions such as OCP, OLP, OVP, and OTP are fully
integrated into FAN6747, which improves the SMPS
reliability without increasing system cost.
This application note presents design considerations to
apply FAN6747 to a flyback power supply with peak load
current profile. It covers designing the transformer, selecting
the components, and closing the feedback loop. Figure 1
shows a typical application circuit using FAN6747.
Figure 1. Typical Application
© 2010 Fairchild Semiconductor Corporation
Rev. 1.0.1 • 9/16/10
www.fairchildsemi.com
Free Datasheet http://www.Datasheet-PDF.com/
1 page  
AN-6747
APPLICATION NOTE
[STEP-6] Determine the Minimum Primary Turns
With a given core, the minimum number of turns for the
transformer primary side to avoid the core saturation is
given by:
N P MIN
= L MILIM
B SAT A e
× 10 6
= L M • 0 .825 / R CS
B SAT A e
× 10 6
(19)
where Ae is the cross-sectional area of the core in mm2, ILIM
is the pulse-by-pulse current limit level determined by
0.825V threshold, RCS is current sensing resistor, and BSAT
is the saturation flux density in Tesla.
The pulse-by-pulse current limit level is included in
Equation (19) because the inductor current reaches the
pulse-by-pulse current limit level during the load transient
or overload condition. Figure 6 shows the typical
characteristics of ferrite core from TDK (PC40). Since the
saturation flux density (BSAT) decreases as the temperature
rises, the high-temperature characteristics should be
considered. If there is no reference data, use BMAX =0.3T.
n = NP = VRO
NS VO + VF
(20)
where NP and NS are the number of turns for primary side
and secondary side, respectively, VO is the output voltage;
and VF is the diode (DO) forward-voltage drop.
Determine the proper integer for NS such that the resulting
NP is larger than NPmin obtained from Equation (19).
The number of turns for the auxiliary winding for VDD
supply is determined as:
NA
=
VDD * +VFA
VO + VF
• NS
(21)
where VDD is the nominal value of the supply voltage and
VFA is the forward-voltage drop of DDD as defined in Figure
7. Since VDD increases as the output load increases, it is
proper to set VDD at 3~5V higher than VDD UVLO level (9V)
to avoid the over-voltage protection condition during the
peak load operation.
Figure 6. Typical B-H Characteristics of Ferrite Core
(TDK/PC40)
(Design Example) An EF25/13/11 core is selected
with effective cross-sectional area of 78mm2. Choosing
the saturation flux density as 0.27T, the minimum
number of turns for the primary side is obtained as:
NPMIN
=
LM
• 0.825 / RCS
BSAT A e
× 10 6
=
508 × 10 −6 • 0.825 / 0.33
0.27 • 78
× 10 6
=
60
Figure 7. Simplified Transformer Diagram
(Design Example) Assuming the diode forward-
voltage drop is 1V, the turn ratio is obtained as:
n = NP = VRO = 100 = 3.03
NS VO + VF 32 + 1
Then, determine the proper integer for NS such that the
resulting NP is larger than NPmin as:
NS = 20,NP = n • NS = 61 > NPMIN
[STEP-7] Determine the Number of Turns for Each
Winding
Figure 7 shows a simplified diagram of the transformer.
First, calculate the turn ratio (n) between the primary side
and the secondary side from the reflected output voltage
determined in step 3 as:
© 2010 Fairchild Semiconductor Corporation
Rev. 1.0.1 • 9/16/10
5
Setting VDD* as 13V, the number of turns for the
auxiliary winding is obtained as:
NA
=
VDD * +VFA
VO + VF
• NS
=
13 + 1 • 20 = 9
32 + 1
www.fairchildsemi.com
Free Datasheet http://www.Datasheet-PDF.com/
5 Page 
AN-6747
Transformer Specification
4
N3
3
N1
N2
5
1
N4
2
JP3(fly line)
1
APPLICATION NOTE
5
10 6
9
Bottom View
Winding Specification
Pin
N1 5 Æ 3
Insulation Tape
Shielding Lead to Pin 4
Insulation Tape
N2 JP3 Æ 9
Insulation Tape
Shielding Lead to Pin 4
Insulation Tape
N3 3 Æ 4
Insulation Tape
N4 1 Æ 2
Insulation Tape
Core: EF25/13/11 (Ae=78 mm2)
Bobbin: EF25/13/11
Inductance: 508μH
© 2010 Fairchild Semiconductor Corporation
Rev. 1.0.1 • 9/16/10
Figure 15. Transformer Specification
Diameter / Thickness
0.45mm
0.55mm
0.45mm
0.2mm
11
Turns
30
3
65
3
20
3
65
3
30
6
9
3
www.fairchildsemi.com
Free Datasheet http://www.Datasheet-PDF.com/
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet AN-6747B.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| AN-6747B | Flyback Power Supply | Fairchild Semiconductor |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |