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Design Idea DI-118
TinySwitch-III
Application Charger Device TNY276P
(R)
4.5 W CV/CC Charger with <260 mW No-Load Consumption
Power Output 4.5 W Input Voltage 90-265 VAC Output Voltage 5.7 V, 800 mA Topology Flyback
Design Highlights
* * * * * * * Simple, low cost, low parts count CV/CC solution Low input power at no-load: <260 mW at 265 VAC Efficiency >65% at 90 VAC Meets CEC / ENERGY STAR requirements for active mode efficiency (66.8 % vs 62.6 % requirement) Compact design using small, low cost EE16 core size >15 dBV margin to EN55022B conducted EMI limits No Y-capacitor: <10 A line frequency leakage current
When the primary current reaches the MOSFET current limit, the controller turns it off, and the energy in T1 is transferred to the output. Schottky diode D6 and capacitor C5 rectify and filter the output. Inductor L3 and capacitor C7 attenuate the switching ripple on the output. The primary clamp (D5, R2, C4 and R1) limits the maximum peak drain voltage to less than the 700 V BVDSS rating of the internal MOSFET. Resistor R2 reduces high-frequency leakage inductance ringing and thereby EMI. The tightly controlled tolerances of U1 allow this configuration to still meet low no-load input power levels. The pi filter formed by C1, L1, L2 and C2 attenuates conducted EMI while C8 and R8 on the secondary side reduce high frequency ringing. The integrated frequency jitter feature of U1 along with E-ShieldTM techniques allow such simple EMI filtering to ensure compliance with EN55022B, even without a Y capacitor across the primary to secondary isolation barrier. The output is regulated using optocoupler feedback. During CV operation, reference IC U3 senses the output
C8 1 nF R8 50 V 10 1 NC NC 10 D6 SB260 R4 100
Operation
The CV/CC charger circuit shown in Figure 1 was designed as a Flyback converter, using TNY276P (U1). The device has its four SOURCE pins on one side of its 8-pin package, which simplifies the layout of the PCB copper for heatsinking. Additionally, the value of C3 selects the reduced current limit of U1. Both factors allow U1 to deliver full power from within a sealed enclosure, at an external ambient temperature of 40 C. In less thermally challenging applications, a TNY275P operating at its standard current limit (C3 = 0.1 F) could be used to reduce cost, without any other changes. The internal MOSFET within U1 conducts current through the primary winding of T1 during each enabled switching cycle.
L1 1 mH D1 1N4005 RF1 8.2 2.5 W 90-265 VAC D3 1N4005 D2 1N4005 C4 1 nF 1 kV C2 4.7 F 400 V R2 100 D5 1N4007GP D4 1N4005
L2 Ferrite Bead
D S S
C5 470 F 10 V
R3 1.2 2W
L3 Ferrite Bead 3.5 x 7.6 mm
C7 100 F 10 V
5.7 V, 800 mA
R1 200 k
2 3,4 T1 EE16
7
C1 4.7 F 400 V
RTN
U2-B
TinySwitch-III U1 TNY276P
EN/UV
BP/M
R7 13.7 k 1% C6 100 nF 50 V R5 1 k
C3 1 F 50 V
U2-A PC817A
U3 TL431
R6 10 k 1%
PI-4422-051006
Figure 1. 4.5 W, 5.7 V CV/CC Charger Using TNY276P.
DI-118
September 2006
DI-89 DI-118
voltage via R6 and R7 and drives the optocoupler. However, the control shifts to CC mode of operation when the voltage across R3 exceeds the forward drop of the photo-diode in U2. TinySwitch-III allows this simple CC sensing scheme to be used, while still meeting active mode efficiency requirements. * For consistent EMI performance in production, manufacturing variations in transformer T1 must be minimized from unit to unit. This is especially important in designs that do not use a Y-capacitor. Place tape between the primary winding layers to reduce intra-winding capacitance. This will help reduce the no-load consumption.
EN55022B Limits
QP AV
PI-4421-050906
*
Key Design Points
* Verify that the maximum drain voltage is <650 V at high line and maximum overload condition. Adjust the values of R1 and C4 as necessary. However, avoid making the clamp circuit too large (ie. low value of R1 and high value of C4), as this will increase the no-load power consumption. Selecting a fast diode vs. an ultra-fast diode for D5 will improve efficiency by recovering leakage energy. If glass passivated (1N4007GP) is unavailable a FR107 may be used. TRANSFORMER PARAMETERS Core Material Bobbin Winding Details Winding Order (pin numbers) EE16, NC-2H material or equivalent, gap for ALG of 156 nH/T2 5+5 pin horizontal Shield: 28T, 2 x 33 AWG Primary: 120T, 33 AWG Shield: 8T, 2 x 27 AWG 5.7 V: 10T, 25 AWG T.I.W. Shield (3-NC), tape, primary (2-1), tape, shield (NC-3), tape, 5.7 V (10-7), tape Primary: 2.25 mH 12% Leakage: 45 H (max)
80 70 60 50 40
*
dBV
30 20 10 0 -10 -20 0.15
1.0
10.0
100.0
MHz
Figure 2. Worst-Case Conducted EMI (Output RTN Connected to Artificial Hand Input of LISN).
6.5 6 5.5 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 0
PI-4423-050906
Output Voltage (VDC)
Inductance
Primary Resonant 850 kHz (min) Frequency
Table 1. Transformer Design Parameters.
T.I.W.: Triple Insulated Wire, NC: No Connection
115 VDC 230 VDC Low Limit High Limit
0
100
200
300
400
500
600
700
800
900
Output Current (mA)
Figure 3. Typical Output Characteristics.
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, 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 09/06
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