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Design Idea DI-55 (R) TOPSwitch-GX
Application DVD Device TOP245P
20 W (25 W peak) DVD Supply
Power Output 20 W (25 W pk) Input Voltage 85-265 VAC Output Voltage 3.3 V / 5 V / 12 V / -24 V Topology Flyback
Design Highlights
* Simple, low cost, low part count solution * No heatsinks required * Low EMI-frequency jitter allows EN55022B/FCC B compliance with simple EMI filter * High efficiency, >75% at 90 VAC * Low zero load power consumption, <100 mW at 230 VAC * Low standby power consumption, <1 W input at 0.5 W output, 230 VAC * Excellent cross-regulation * Differential and common mode surge immunity to 3 kV (EN 61000-4-5)
The external current limit programming and remote ON/OFF (inhibit) functions of the M pin allow current mode control and reduced switching frequency at light and no-load conditions. Current mode control is implemented by R2, Q3, R3, C16, R4 and R6. Feedback current above ~2 mA (U1 supply current) forward biases Q3 and pulls up R6. This adjusts the sink current out of the M pin, thereby allowing the output voltage feedback loop to control the primary switch current. Resistor R6 sets the maximum current limit, while R2 and C16 provide slope compensation. The value of R4 is chosen to ensure that current does not flow into the M pin, enabling the line sensing features of the pin. The current out of the M pin falls as the load is reduced until the M pin inhibit threshold is reached. The supply then operates with a fixed 25% current limit, lowering the switching frequency to maintain regulation. This greatly reduces switching losses, maintaining high standby efficiency and low no-load power consumption.
L5 BEAD D7 1N5819 C15 470 F 25 V C20 180 F 25 V L3 3.3 H D11 SB540CT C12 1200 F 10 V C17 R14 470 F 1.13 k 10 V 1% L2 3.3 H
Operation
The TOP245P selected for the design in Figure 1 is ideal for DVD and set-top box applications. The P package removes the need for a heatsink while still delivering 20 W/25 W peak at an ambient temperature of 50 C.
C1 33 F 400 V VR1 C4 33 F P6KE 400 V 130 L1 C8 2.2 nFY1 T1 EE25L 8
+12 V, 500mA
F1 3.15 A J1-2 250 VAC
RT1 t
1
R1 68
LINE J1-1 NTRL
RV1 275 VAC C3 0.047 F X2 R7 1 k
1N4007 x 4
C2 0.01 F 1 kV
4
OPTIONAL
R16 2.0 k R15 1% 2.4 k Q1 2SA0885 D8 1N4005
12 13
5 mH CM Choke
+5 V, 2.5 A J2-3
Q5 2N3906
L4 3.3 H
Q4 2N3904
D5 1N4007GP
9
D10 SB540CT
D9 1N4005
+3.3 V, 2 A J2-6
C12 1200 F 10 V 10,11
R17 200
C18 470 F 10 V
RET
R13 2 k 1% R12 6.34 k 1% R11 20.0 k 1%
J2-2, 4, 5, 7
C9 150 F 35 V
TOPSwitch-GX U1 TOP245P
CONTROL
C
D
D12 UF4003 14 C13 47 F 25 V C16 0.1 F 7 5 R3 270 Q3 1N3906
C6 150 F 35 V R8 1 1/2 W
-24 V, 50 mA J2-1
U2 LTV817A C14 R10 0.1 F 10 k
S
M
R2 18 k
R4 10 k R6 5.1 k
D6 1N4148
C5 47 F 25 V
U3 TL431
R9 10.0 k 1%
PI-3648-071106
Figure 1. 20 W Multiple Output DVD Supply.
DI-55
www.powerint.com
July 2006
DI-55 Key Design Points
* For good cross-regulation, minimize transformer leakage - use foil for 3.3 V and 5 V outputs; minimize peak primary currents by designing transformer for continuous conduction mode. * Shunt regulator (temperature compensated) between 5 V and 3.3 V outputs in dotted box on schematic is optional. It is only necessary where min and max load conditions do not occur simultaneously on both outputs. * Feedback is taken from both the 3.3 V and 5 V outputs to the reference (U3) via R9, R11 and R12. The 12 V output is DC stacked on the 5 V output for enhanced regulation and voltage centering. * Primary clamp components VR1, D5, R7, R1 and C2 limit the leakage inductance induced peak drain voltage spike. * D5 is a slow recovery diode to recover some of the clamp energy. It must be a glass passivated type to guarantee a defined trr. * Use a Zener clamp for lowest zero load input power consumption.
TRANSFORMER PARAMETERS
Core Material
EEL25, N67 or equivalent, gap for ALG of 202 nH/T2 7 pin + 7 pin Shield 1: 32T, 2 x 32 AWG Primary: 63T, 2 x 32 AWG Bias: 6T, 4 x 32 AWG Shield 2: 4T, 4 x 32 AWG 3.3 V/5 V foil: 2T + 1T, 0.12 mm foil -24 V: 13T, 2 x 32 AWG +12 V: 4T, 4 x 32 AWG Shield (NC-1), tape, primary (1-4), tape, bias (5-7), tape, shield 2 (13-NC), foil (10,11-9-13), -24 V (14-10,11), 12 V (12-8). Primary: 800 H 10% Leakage: 80 H (max.) 300 kHz (minimum)
Bobbin
Winding Details
Winding Order (pin numbers)
Inductance Primary Resonant Frequency
Table 1. Transformer Design Parameters.
Voltage (V) 3.3 5 12 -24 Load Regulation Range -5 -4 -3 -2 -1 0 1 2 (A) 0.3-0.6 0.3-1.2 0.1-0.2 0.03-0.05
(%)
3 4 5 6 7
Table 2. Worst Case Output Cross-Regulation - all Outputs Taken from Minimum to Maximum Loads.
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.
Power Integrations
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B 7/06
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