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Design Idea DI-124
LinkSwitch-TN
Application Metering / Industrial Device LNK304
(R)
Ultra-wide Input Range (57-580 VAC) Flyback Power Supply
Power Output 3W Input Voltage 57-580 VAC Output Voltage 12 V, 250 mA Topology StackFET Flyback
Design Highlights
* * * * * * StackFET flyback topology delivers full load over extremely wide input voltage range E-ShieldTM transformer construction for reduced common-mode EMI (>10 dBV margin) 66 kHz switching frequency with jitter reduces conducted EMI Simple ON/OFF controller - no feedback compensation required Auto-restart function for automatic and self-resetting open-loop, overload and short circuit protection Built-in hysteretic thermal shutdown at 135 C
TM
A 600 V MOSFET, Q1, and U1 are arranged in the StackFET configuration (cascode). The drain of U1 drives the source of Q1 while the drain of Q1 drives the transformer primary. The drain voltage of U1 is limited to 450 V by VR1-3. This extends the maximum peak composite drain voltage of U1 and Q1 to 1050 V. The resistor chain R6-R8 provides startup charge for the gate of Q1 and R9 dampens high-frequency ringing. Once the converter is operating, the gate is largely driven by the charge stored in the capacitance of VR1-3. Zener VR4 limits the gate to source voltage of Q1. Leakage inductance energy is clamped by VR5 and D9 with R10 added to reduce ringing and thereby, EMI. The operation of U1 is unaffected by the StackFET configuration. When the internal MOSFET turns on, Q1 is also turned on, applying the input voltage across the transformer primary. Once the primary current reaches the internal current limit of U1, the MOSFET is turned off and the energy stored is delivered to the output. Regulation is maintained using ON/OFF control. Switching cycles are enabled/disabled based on current into the FEEDBACK pin of U1. This is ideal as it results in a lowering of the effective switching frequency
C1 2.2 nF 250 VAC
Operation
The AC input is rectified and filtered and the resultant DC applied to one end of the transformer primary winding. The 450 V input capacitors are stacked with parallel balancing resistors to meet the required voltage rating. Resistors R1 to R4 provide fusing in case of a catastrophic failure. Inductor L1, C1 and transformer E-Shield windings allow the design to meet EN55022 B conducted limits with good margin.
D1 1N4007
D2 1N4007
D3 1N4007
D4 1N4007 C5 15 F 450 V
J1 J2 J3 J4
R1 10 1 W R2 10 1 W R3 10 1 W R4 10 1 W D5 1N4007 D6 1N4007 D7 1N4007 D8 1N4007
R13 475 k 1% 0.5 W
C6 15 F 450 V C9 5.6 nF 1 kV C8 15 F 450 V
R14 475 k 1% 0.5 W
R6 680 k 0.5 W R7 680 k 0.5 W
VR5 P6KE150A D9 UF4007
EEL16 NC 4 5 7 9 10 T1 1
D10 UF4004
L2 Ferrite Bead
J5
C7 15 F 450 V
R15 475 k 1% 0.5 W
R16 475 k 1% 0.5 W
R10 R8 200 680 k 1% 0.5 W R9 10 VR4 1N5245B 15 V U1 LNK304P VR2 P6KE150A VR3 P6KE150A
S
C2 470 F 16 V
C3 100 F 16 V J6
Q1 IRFBC20 R11 330
D
R5 1k L1 1 mH VR1 P6KE150A
FB BP
U2B PC817A
U2A PC817A R12 1 k
C4 100 nF 50 V
VR6 BZX79-C11 11 V
PI-4487-081506
Figure 1. Schematic Diagram of 3 W Bias Supply using LinkSwitch-TN in StackFET Configuration.
DI-124 September 2006
DI-89 DI-124
75 70
PI-4493-081806
with load, scaling switching losses and maximizing efficiency. The use of LinkSwitch-TN further improves efficiency due to its 66 kHz switching frequency.
80
Key Design Points
* The input stage (to the left of C9) can be omitted in applications that have a high-voltage DC bus. Capacitor C9 is still required to provide local decoupling. * Long cores (EEL) are ideal for this application to provide greater bobbin width to accommodate the increased margins required to meet safety spacings at the high operating voltage. * Zener diodes VR1-3 can be replaced with a single P6KE540 device. * The value of capacitors C5 to C8 can be reduced to 10 F if operation down to 57 VAC is not required (100 VAC minimum). * Use 0.5 W resistors for R13-16 and R6-8 to provide adequate voltage rating. * Efficiency falls at high line due to switching losses. Reducing transformer capacitance by adding layers of tape between the primary winding layers minimizes this.
EN55022B Limits
QP AV
PI-4492-090706
Efficiency (%)
65 60 55 50 45 40
50
150
250
350
450
550
AC Input Voltage (V)
Figure 3. Full Load Efficiency vs. Input Voltage.
TRANSFORMER PARAMETERS Core Material Bobbin EEL16, gap for ALG of 70 nH/T2 6+4 pin (Ying Chin YC-1604-1) with 3 mm + 3 mm tape margins Shield: 23T, 2 x 36 AWG Primary: 184T, 36 AWG Shield: 12T, 2 x 29 AWG Secondary: 30T, 29 AWG TIW Shield (5-NC), tape, primary (7-5), tape between layers, shield (9-10), tape, 12 V / (4-1), tape Primary: 3.5 mH 10% Leakage: 160 H (max)
80 70 60 50 40
Winding Details
Winding Order (pin numbers) Inductance
dBV
30 20 10 0 -10 -20 0.15 1.0
QP AV
Primary Resonant 500 kHz (min) Frequency
Table 1. Transformer Design Parameters.
TIW = Triple Insulated Wire, NC = No Connect, FL = Flying Lead
10.0
100.0
MHz
Figure 2. Conducted EMI (230 VAC, EN55022B Limits, AV and QP Results).
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 09/06
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