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Design Idea DI-130
TinySwitch-III
Application LED Lighting Device TNY279P
(R)
Passive PFC LED Lighting Supply
Power Output 18 W Input Voltage 185-265 VAC Output Voltage 10 V Topology Flyback
Design Highlights
* * * * * Very high efficiency: 82% Low component count: only 40 parts No common-mode choke required to meet EN55022B conducted EMI requirements Valley Fill circuit allows supply to meet IEC61000-3-2 THD limits ON/OFF control rejects the high line ripple voltage caused by the Valley Fill (THD correction) circuit
switching cycles. As the load current reaches the current limit set-point threshold, U1 drives U3 on. The photo-transistor in U3 pulls current out of the EN/UV pin of U2, causing it to skip switching cycles. Once the output current drops below the current limit set-point threshold, U1 stops driving U3, which stops pulling current out of the EN/UV pin of U2, and switching cycles are enabled again. The TL431 (U4) provides a reference for U1 to compare against the voltage drop across R11. The output diode (D9) is located in the lower leg of the transformer (T1) secondary winding to reduce EMI noise generation. An RCD clamp (R16, C4 and D13) protects the drain node of the MOSFET from the flyback voltage spike. The Valley Fill circuit (D5, D6, D7, C15, C16 and R15) limits the values of the third and fifth harmonics of the line frequency current, which enables this supply to meet the requirements for Total Harmonic Distortion (THD) specified in IEC61000-3-2. The frequency jittering function in U2, a shield winding in T1 and a Y class capacitor (C8) across T1 reduce the generation of conducted EMI so that a simple pi filter (C13, L1, L2 and C14) allows the supply to meet EN55022B limits.
C8 2.2 nF 250 VAC C6 C7 680 F 680 F 35 V 35 V D9 SB580 C9 100 nF 50 V R5 1 k 1/8 W U1
1 8 4
+
Operation
The flyback converter shown in Figure 1 uses a member of the TinySwitch-III family (U2, a TNY279P) to provide up to 1.8 A of load current to six, high-intensity, Luxeon LEDs (the LXHL series). The output voltage is slightly below the forward voltage drop of the LEDs. Therefore, when the LEDs are connected to the supply, it operates in constant current (CC) mode. If the LEDs are disconnected from the supply, Zener diode VR1 provides voltage feedback, which regulates the output voltage at about 13.5 VDC. A 100 m resistor (R11) senses the output current and an Opamp (U1) drives the optocoupler (U3), which provides feedback to U2. The TinySwitch-III family of devices regulate by disabling or skipping MOSFET
1
10
10 V, 1.8 A R11 100 m 1W RTN
D1, D2 1N4007 R14 5.1 k F1 3.15 A L1 2200 H L2 2200 H C16 6.8 F 400 V
R16 100 k 1/2 W D6 1N4007
2
C4 1 nF 1 kV
3
6
C13 185-265 47 nF VAC 275 VAC
C14 220 nF 275 VAC
D5 1N4007 R15 10 1/2 W
D13 UF4005 TinySwitch-III U2 TNY279P EN/UV
BP/M
R12 C12 220 pF 47 1 kV 1/2 W
R17 5.1 k 1/8 W
2 3 R11 2 k 1/8 W
D11 1N4148 R10 51 VR1 12 V
LM358
D
R13 5.1 k
D3, D4 1N4007
D7 1N4007
C15 6.8 F 400 V
S
C16 1 F 50 V
U3 PC817A
C10 100 nF 50 V
C17 100 F 16 V
R6 68 k 1/8 W U4 TL431 2%
PI-4520-110606
Figure 1. Circuit Diagram of a Passive PFC Power Supply for Driving Lighting LEDs.
DI-130 November 2006
DI-89 DI-130 Key Design Points
* * * Take the value of input capacitance calculated by PI Expert or the PI Xls spreadsheet, divide it by two, and round up to the next standard value to select the values of C15 and C16. Using PI Expert or the PI Xls spreadsheet, design the supply for the maximum output power at the maximum VF of the LEDs. The LM358 (U1) contains two operational amplifiers. Ensure that the inputs to the second amplifier (pins 5 and 6) are connected to secondary ground.
PI-4525-110606
86 84 82
Efficiency (%)
80 78 76 74 72 70
100% 75% 50% 25%
Figure 3. Input Voltage (100 V /div) and Current (100 mA/div), Showing the Effect of the Valley Fill Circuit.
TRANSFORMER PARAMETERS Core Material PC40EF25-Z
185 195 205 215 225 235 245 255 265
Bobbin
EF25 Horizontal bobbin
Input Voltage (VAC)
Figure 2. Efficiency vs. Input Voltage at Different Load Levels, Room Temperature, 50 Hz Line.
Primary: 92T, 0.3 mm heavy nyleze magnet wire Winding Details Secondary: 14T 2 x 0.4 mm Triple Insulated Wire (TIW) Winding Order (pin numbers) Inductance Primary (2-4), Secondary (6-10) 1.6 mH
Table 1. Transformer Design Parameters.
TIW = Triple Insulated Wire, NC = No Connect, FL = Flying Lead
For the latest updates, visit www.powerint.com Power Integrations reserves the right to make changes to its products at any time to improve reliability or manufacturability. Power Integrations does not assume any liability arising from the use of any device or circuit described herein. POWER INTEGRATIONS MAKES NO WARRANTY HEREIN AND SPECIFICALLY DISCLAIMS ALL WARRANTIES INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS. The products and applications illustrated herein (transformer construction and circuits external to the products) may be covered by one or more U.S. and foreign patents or potentially by pending U.S. and foreign patent applications assigned to Power Integrations. A complete list of Power Integrations' patents may be found at www.powerint.com. Power Integrations grants its customers a license under certain patent rights as set forth at http://www.powerint.com/ip.htm. The PI logo, TOPSwitch, TinySwitch, LinkSwitch, DPA-Switch, PeakSwitch, EcoSmart, Clampless, E-Shield, Filterfuse, StackFET, PI Expert and PI FACTS are trademarks of Power Integrations, Inc. Other trademarks are property of their respective companies. (c)Copyright 2006, Power Integrations, Inc.
Rev. A 11/06
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