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Design Idea DI-84 (R) TinySwitch-II 3 W Charger:
<30 mW No-load Consumption
Application Charger Device TNY264P Power Output 3W Input Voltage 85-265 VAC Output Voltage 5 V, 600 mA Topology Flyback
Design Highlights
* Less than 30 mW no-load power consumption (for 115/230 VAC input) * Meets CISPR-22 Class B without Y capacitor * Low cost, low component count solution * Meets CEC active mode efficiency with good margin
The bias winding should provide enough current to fully disable the internal current source at no-load. Other load conditions are not important, as the device will be powered from the DRAIN pin if bias is lost. This allows a simple flyback winding to be used. Figure 2 shows that the bias winding and choice of R2 should provide approximately 600 A at no-load to minimize consumption. The circuit meets CISPR-22 Class B conducted EMI limits without a Y capacitor, and therefore has very low AC leakage current. Superior EMI performance is achieved via the TinySwitch-II frequency jitter, an output RC snubber, use of the bias winding as a shield, and careful selection of clamp Zener voltage.
Operation
The TinySwitch-II flyback converter in Figure 1 generates a constant voltage, constant current (CV/CC) 5 V, 600 mA output. Typical applications include wall-mounted chargers for cell phones, PDAs and other battery powered portable equipment. The key performance characteristic of the circuit shown is the extremely low no-load consumption of <30 mW. A linear transformer charger of similar rating will typically consume 1 W to 4 W at no-load. At $0.12/kWh, the TinySwitch-II can therefore reduce energy costs by $1 to $4 per year. This no-load performance is achieved by using a transformer bias winding as a low voltage source for TinySwitch-II operating current. Even without this winding, a TinySwitch-II circuit will consume <300 mW at no-load. The bias winding disables the internal high voltage current source, which normally powers the IC from the DRAIN pin, thereby further reducing power consumption.
T1
Key Design Points
* Design bias winding circuit to provide approximately 600 A at no-load. Figure 2 shows the details. * Minimize secondary circuit bias currents. Use low current feedback Zeners for best tolerance. The very low Zener bias current in this design will provide better than 10% output voltage tolerance. * Design transformer with low reflected voltage to minimize clamp losses. A larger device (TNY266) may enable further reduction in VOR. * Wind transformer for lowest leakage inductance. Choose wire gauges to completely fill winding layers.
R6 33 C3 470 pF 100V L3 Ferrite Bead C6 470 F 10 V R3 1.5 k R2 9.2 k Q1 2N3906 C7 100 F 10V VR2 BZX79B5V1
L1 1.0 mH
T1 EE13 LP = 1.9 mH 1 VR1 BZY97C130 102T 32 AWG R1 200 1/2 W 2
8
D7 11DQ06 8T 24 AWG T.I.
5 V, 0.6 A
7 3 4
L
RF1 8.2 1.0 W
D1 1N4005
D2 1N4005
D5 1N4007G
15T 32 AWG
C5 47 F 16 V
Fusible
85 - 265 VAC C1 4.7 F 400V C2 4.7 F 400V
D6 1N4148
EN/UV BP
N
D U1 TNY264P TinySwitch-II S
D3 1N4005
D4 1N4005
L2 Ferrite Bead
C4 0.1 F 50 V
U2 PC817A
R4 820 R5 2.4 2W
RTN
PI-3659-060205
Figure 1. TinySwitch-II 3.0 W Cell Phone Charger.
DI-84
www.powerint.com
June 2005
DI-84
* Winding transformer with tape between primary layers further reduces intra-winding capacitance and no-load consumption.
PI-3298-091402 PI-4013-060205
80 70
35
No Load Consumption (mW)
33 31 29 27 25 23 21 19 17 15
No Load Consumption
60 50 40 30 20 10 0 300 400 500 600 700 800
115 VAC 230 VAC
900
85 105 125 145 165 185 205 225 245 265
BYPASS Pin Current (A)
Figure 2. No-load Input Power vs. BYPASS Pin Current.
PI-3684-082603
Input Voltage (VAC)
Figure 3. No-load Input Power vs. Line Voltage.
6 5 4 3 2 1 0 0
TRANSFORMER PARAMETERS
Core Material Bobbin Winding Order (pin numbers) Primary Inductance EE13 TDK PC40, or equivalent AL of 128 nH/T2 EE13, 8 pin Primary: 1-2, tape, Bias: 3-4, tape, Secondary: 7-8, 5 V, tape 1.9 mH 10%
Output Voltage (VDC)
115 VAC 230 VAC
Limits for Output Voltage and Current
100 200 300 400 500 600 700
Primary Resonant 500 kHz (min) Frequency Leakage Inductance 50 H (max)
Output Current (mA)
Figure 4. 5.0 VDC, 600 mA CV/CC Curve.
Table 1. Transformer Construction Information.
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 LIMITATIONS, 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, EcoSmart, PI Expert and PI FACTS are trademarks of Power Integrations. Copyright 2005, Power Integrations
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