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Design Idea DI-51 DPA-SwitchTM
5 W Flyback DC-DC Converter
Application DC-DC Converter Device DPA423R Power Output 5W Input Voltage 36-75 VDC Output Voltage 5V
(R)
Topology Flyback
Design Highlights
* * * * * * * Small footprint: 35 mm x 20 mm (1.4 in. x 0.8 in.) High efficiency flyback (>80% min.) 8.8 W per cu. in. Low component count Accurate line OV and UV protection Thermal, short circuit and output overload protection No current sense components
Resistor R3 programs the internal current limit of the DPA423R to 53% of nominal. This limits the overload power that can be delivered in a fault condition. Zener VR1 clamps the leakage inductance spikes to keep the DRAIN voltage at a safe level. The bias supply for U1 is provided from the auxiliary flyback transformer winding (pins 2 and 4), rectified and filtered by diode D1 and capacitor C23. A snubber for diode D2 (capacitor and resistor) can be used, but was not needed in this application. Inductor L2 and capacitor C12 form a post filter to reduce high frequency output switching ripple. A soft-finish network, C18, D3 and R7, eliminates output turn-on overshoot. The remaining components provide output voltage regulation and loop compensation.
Operation
DPA-Switch greatly simplifies the design compared to a discrete implementation. Resistor R1 sets the input under/over voltages to 33 V and 86 V, respectively. Including tolerances, these thresholds guarantee the converter is operational between 36 V and 75 V without the cost of additional line sense components.
C7 1 nF 1.5 kV + VIN 36-75 VDC L1 10 H 0.85 A
1
R14 10
T1 7,8
D2 SL23 1A/30 V
C10 C11 100 F 100 F 10 V 10 V
L2 300 nH 6A
C12 100 F 10 V
5 V, 1 A
FL
5,6
RTN D1 BAV19WS
2 4 3
C23 4.7 F 20 V U2 R7 U2 10 k R10 18 k 1%
R1 619 k 1% C1 0.22 F 100 V C2 1 F 100 V
DPA-Switch
U1 DPA423R
D L
CONTROL
D3 BAV19WS R6 150
C16 220 nF R12 5.1 C17 1 F R9 220
C
S VR1 SMBJ 150 A
X
F
R3 14.4 k C5 1% 47 nF
R4 1.0 C6 68 F 10 V
C18 10 F 10 V U3 LM431AIM3
-VIN
R11 18 k 1%
PI-3547-062403
Figure 1. DPA-Switch Flyback DC-DC Converter. .
DI-51
www.powerint.com
July 2003
DI-51 Key Design Points
* For the nominal under-voltage set point VUV: R1 = (VUV - 2.35) / 50 A VOV = (R1 x 135 A) + 2.5 V * For highest efficiency designs: use continuous conduction mode operation designed at approximately 0.4 KRP; minimize turns in the transformer while keeping AC flux density (BM) < 3000 Gauss; fully fill a single layer for each winding to minimize leakage inductance and maximize copper fill factor; use a Schottky rectifying diode (D2) with a low forward drop (in this case, the SL23 diode has a Vf = 0.320 V at 125 C/2A). * Resistor R3: the PIXls spreadsheet calculates the peak current (IP) of the power supply. Resistor R3 is chosen to set the internal current limit 10% to 15% above the calculated IP value. This limits overload power (worst case is at high input line). * Set resonant frequency of post-filter (L2, C12) beyond crossover frequency (typically 5% to 10% of switching frequency). * For main secondary current loop from transformer pin 8 to diode D2 and capacitors C10, C11 and back to pin 6 of the transformer: ensure identical path length for C10 and C11 to guarantee they equally share the ripple current. * Due to the very tight size constraints on this power supply, the drain voltage traces should be kept as short as possible and where possible, shielded by surrounding them with source potential traces. This will prevent noise coupling to the low-voltage signal pins of the DPA-Switch. TRANSFORMER PARAMETERS
Core Material EFD-10 Ferroxcube 3F3 AL of 100 nH/T2 EDF-10 8 pin (or equivalent) 1/2 Primary (1-FL), Tape, Bias (4-3), 5 V (5-8), Tape, 1/2 Primary (FL-2), Tape 174 H 10% 4.7 MHz (minimum) 1.0 H (minimum)
Bobbin
Winding Order (pin numbers) Primary Inductance Primary Resonant Frequency Leakage Inductance
Table 1. Transformer Construction Information.
85 84 83
Efficiency (%)
82 81 80 79 78 77 76 75 1 2 3 4 5
36 VDC 48 VDC 72 VDC
Pout (W)
Figure 2. Efficiency vs. Output Power. For the latest updates, visit our Web site: 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, nor does it convey any license under its patent rights or the rights of others. The products and applications illustrated herein (including circuits external to the products and transformer construction) 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. The PI Logo, TOPSwitch, TinySwitch, LinkSwitch and EcoSmart are registered trademarks of Power Integrations, Inc. PI Expert and DPA-Switch are trademarks of Power Integrations, Inc. (c)Copyright 2003, Power Integrations, Inc.
WORLD HEADQUARTERS AMERICAS Power Integrations, Inc. San Jose, CA 95138 USA Customer Service: Phone: +1 408-414-9665 Fax: +1 408-414-9765 e-mail: usasales@powerint.com CHINA Power Integrations International Holdings, Inc. China Phone: +86-755-8367-5143 Fax: +86-755-8377-9610 e-mail: chinasales@powerint.com EUROPE & AFRICA Power Integrations (Europe) Ltd. United Kingdom Phone: +44-1344-462-300 Fax: +44-1344-311-732 e-mail: eurosales@powerint.com KOREA Power Integrations International Holdings, Inc. Seoul, Korea Phone: +82-2-782-2840 Fax: +82-2-782-4427 e-mail: koreasales@powerint.com SINGAPORE Power Integrations, Singapore Republic of Singapore 308900 Phone: +65-6358-2160 Fax: +65-6358-2015 e-mail: singaporesales@powerint.com JAPAN Power Integrations, K.K. Keihin-Tatemono 1st Bldg. Japan Phone: +81-45-471-1021 Fax: +81-45-471-3717 e-mail: japansales@powerint.com APPLICATIONS HOTLINE World Wide +1-408-414-9660 TAIWAN Power Integrations International Holdings, Inc. Taipei, Taiwan Phone: +886-2-2659-4570 Fax: +886-2-2659-4550 e-mail: taiwansales@powerint.com INDIA (Technical Support) Innovatech Bangalore, India Phone: +91-80-226-6023 Fax: +91-80-228-9727 e-mail: indiasales@powerint.com APPLICATIONS FAX World Wide +1-408-414-9760
A 7/03
www.powerint.com
PI-3548-060403

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