Fremont Micro Devices
FT825
FT825-12S480mA Design Report
Title
18 Watts Isolated PSR LED Driver with High PF
Input Voltage: 90~264Vac; 50/60Hz
Output Voltage: 40V_dc
Output Current: 480mA_dc
Power Driver for LED T8 Tube
Specification
Application
Author
FMD Application Engineering Department
Date
2012-10-22
Reversion
2.0
FEATURES
Ultra-thin (less than 10mm) design;
The LED driver can be assembled at the back side of LED Display Boards, to get well-distributed
LED light.
Highly energy efficient
>87%@115Vac input; >88%@230Vac input
High PF value
>0.93, 90~264Vac input
Minimum BOM, PCB Size minimized, highly cost-competitive
Length of Printed Circuit Board is 216mm
Integrated protection and reliability features
LED Open / Short-circuited Protection with auto recovery
Cycle by Cycle Current Limiting Protection
No over-shoot for LED output current during start-up, high reliability and long lifetime.
ON/OFF test passed ( Input 264Vac, 4S ON/ 4S OFF, endured 10000 times)
Meets IEC 61000-4-5 Surge, IEC 61000-3-2 Class C harmonics requirements
Meet EMI EN55015 B & FCC Part 18 Class B standard
© 2012 Fremont Micro Devices Inc.
Confidential Rev. 0.8
DR825-A-page1
Fremont Micro Devices
FT825
Contents
1
2
3
4
5
6
7
7.1
7.2
7.3
Brief Introduction................................................................................................................. 3
Power Supply Specification................................................................................................ 4
Circuit Diagram..................................................................................................................... 5
PCB Layout ...........................................................................................................................6
Bill of Materials...................................................................................................................7-8
Transformer Specification....................................................................................................9
Performance Test Data........................................................................................................10
Input Voltage vs Output Current/ Power Factor/ THD/ Efficiency……………...…………..…10-12
Output Voltage vs Output Current ………………………………………………..…………………...13
TemperatureRise……………………………………………………………………...…..………………14
8
8.1
8.2
8.3
8.4
8.5
8.6
8.7
8.8
Key Waveforms …………………………………………………………………..……………….15
Line Voltage and Current…………………………………………………………….…..………………15
Power MOSFET Vds(p-p) and Ids(p-p) Under Working……..……........……………..…...…….…15
Power MOSFET Vds(p-p) and Ids(p-p) At Start-up..…………………………………….....……..…15
Power MOSFET Vds(p-p) and Ids(p-p) While Output is Short-circuited……….……………..…16
Output Voltage and Current with Full-load…………………….………………………...……….…..16
Output Voltage and Current While Output is Short-circuited……………………………………..16
Output Voltage with No-Load (LED Open)..………………………………………………………......17
Output Voltage and Current At Start-up…………………………………………...……………….....17
9
9.1
9.2
EMI…………………………………………………………………………………………………...18
Conducted EMI Measurement…………………………………………………….………………...18-21
Radiated EMI measurement………………………...………….…………………………………...22-25
© 2012 Fremont Micro Devices Inc.
Confidential Rev. 0.8
DR825-A-page2
Fremont Micro Devices
FT825
1
Brief Introduction
The FT825-12S480mA LED driver is an isolated PSR solution, utilizing Fly back topology that works in
Boundary Conduction Mode (BCM) with Power Factor Correction (PFC) function. It works under universal
AC voltage from 90V to 264V and provides output voltage 25~44Vdc & output current 0.48A for LED strings.
Few components are used in the FT825-12S480mA LED driver; it increases the power density and reduces
the total material cost, in contrast to conventional single stage PFC solution with opto-coupler and
secondary CC/CV circuit. Meanwhile, the PSR controller IC FT825 is combined with optimized system
design, which guarantees the LED driver system working in BCM to enhance efficiency for the LED driver.
The design target is to keep the LED driver ultra-thin and highly energy efficient. It facilitates the assembly
of the end products LED T8 Tubes while keeping the temperature rise of all components within an
acceptable range.
Figure 1. PCB Assembly（Top View）
Figure 2. PCBA Assembly（Bottom View）
Figure 3. PCBA Height（<10mm）
© 2012 Fremont Micro Devices Inc.
Confidential Rev. 0.8
DR825-A-page3
Fremont Micro Devices
FT825
2
Power Supply Specification
The table below represents the minimum acceptable performance of the design.
Actual performance is listed in the results section.
Description
Input
Voltage
Frequency
Output
Output Voltage Output
Current Continuous
Output Power
Vout
Iout
Pout
25
40
0.48
19.2
42
V
A
W
Vin
f
LINE
90
47
115/230
50/60
264
64
Vac
Hz
2
Wires, no P.E.
Class II Equipment
Symbol
Min.
Typical
Max.
Unit
Remark
Efficiency
Full Load
Environmental
Conducted EMI
Radiated EMI
Safety
Meet CISPR 15B/EN55015B
FCC Part 15 Class B / EN55015
Meet IEC60950
87
%
Measured at
115/230Vac input
Measured at 12S
Power Factor
0.93
480mA rating and
90~264Vac input
Measured at 12S
Total Harmonic Distortion
THD
20
%
480mA rating and
90~264Vac input
PCBA Dimension
Ambient Temperature
T
AMB
216X17.5X10
60
mm
℃
Natural Ventilation
Sea Level
© 2012 Fremont Micro Devices Inc.
Confidential Rev. 0.8
DR825-A-page4
Fremont Micro Devices
FT825
3
Circuit Diagram
Figure 4. Circuit Diagram
© 2012 Fremont Micro Devices Inc.
Confidential Rev. 0.8
DR825-A-page5
