Power DI-59 Low cost 2.5 w cv/cc charger or adapter Datasheet

Design Idea DI-59
®
LinkSwitch Low Cost 2.5 W
CV/CC Charger or Adapter
Application
Device
Power Output
Input Voltage
Output Voltage
Topology
Charger/Adapter
LNK500
2.5 W
85-265 VAC
5.5 V
Flyback
Design Highlights
• Replaces a linear transformer based power supply at the
same or lower cost, with better output regulation
• No-load input power consumption is less than 300 mW, at
230 VAC input: meets worldwide conservation guidelines
• Extremely simple circuit – requires only 23 components!
• No alternate path of secondary-side feedback is required:
output feedback is obtained through the main transformer!
• Output Voltage (CV) tolerance ±10% at peak power point
• Output Current (CC) tolerance ±25%, when L ≤ ±10%
• Features the following auto-recovering protection functions:
output short-circuit, open feedback loop, thermal shutdown
• Typically about 68% efficient!
• Meets EN550022 B EMI limits, without a Y-1 type Safety
capacitor between the primary and the secondary
• Ultra-low leakage current: < 5 µA at 265 VAC input
Operation
Fusible resistor RF1 gives short-circuit fault protection and
limits start-up inrush current. Diodes D1–D4 provide full
bridge rectification that charges capacitors C1 and C2. Inductors
L1 and L2 and capacitors C1 and C2 form a low-cost pi (π) filter
that attenuates conducted EMI. Transformer (T1) winding
phasing and D6 orientation let no secondary winding current
flow when the MOSFET in U1 is ON, so the current that flows
through the primary winding stores its energy in the core of T1.
When the MOSFET in U1 is turned OFF, the energy stored in
L1
1.5 mH
S
C
D1-D2
1N4007
L
85-265
VAC
N
C2
4.7 µF
400 V
C1
4.7 µF
400 V
RF1
8.2 Ω
1 W Fusible
D3-D4
1N4007
L2
Ferrite
Bead
The RCD network of C3, D5 and R1 has two functions:
1) It clamps the reflection of the output voltage (VOR) on the
primary winding, as the MOSFET turns OFF.
2) It holds VOR, for use as output feedback, eliminating the
cost and complexity of a separate feedback path.
Resistor R1 attenuates the switching noise from the VOR.
Resistor R2 determines the amount of feedback current that
flows into the CONTROL pin of U1. The output voltage can
be fine-tuned by varying the value of R2. CONTROL pin
capacitor C4 stores power and supplies it back to U1 during
start-up, determines the restart “attempt” frequency in the
auto-restart mode, shunts high frequency noise around U1
and provide U1 with the instantaneous MOSFET gate-drive
current it requires. Resistor R3, capacitor C5, the 22-turn
core cancellation winding and the 5-turn shield winding all
reduce EMI.
LinkSwitch based solutions are designed to operate only in
the discontinuous conduction mode. PO ~ 0.5 L I2f, where
PO = Output Power, L = transformer primary inductance,
I = LinkSwitch peak current, f = Switching frequency and
η = Efficiency. I2f is accurately controlled for the LinkSwitch;
therefore, PO is proportional to L.
T1 EE13
LP = 2.3 mH
5
1
LinkSwitch
D
T1 drives current out of the secondary winding, forward
biasing D6, charging C6 and developing/maintaining the
output voltage across C6.
U1
LNK500
R2
17.4 kΩ
1%
D5
1N4937
C4
0.22 µF
25 V
C3
100 nF
63 V
FILM
90T, #36
15T, #30, TIW
2
22T, #34
3
6
2
5T,
#30 x 3
C6
330 µF
16 V
D6
SB1100
R3
100 Ω
C5
100 pF
500 V
R1
100 Ω
Figure 1. 2.5 W LinkSwitch Based Charger/Adapter
DI-59
5.5 V, 0.45 A
www.powerint.com
R5
22 kΩ
RTN
C7
R4
33 Ω 150 pF
100 V
PI-3692-091903
September 2003
DI-59
Typical applications are chargers for cell phones, PDAs,
portable audio devices and shavers or power sources embedded
within home appliances and consumer electronics, such as TV
standby and bias supplies.
TRANSFORMER PARAMETERS
TDK PC40 EE13, AL = 284 nH/T2
Core
Bobbin
EE13 Horizontal 8 pin
Key Design Points
• Set VOR between 36 V and 60 V (50 V is optimum)
• Transformer primary inductance tolerance must be ≤10%,
to maintain CC limit tolerance of ±25%
• If battery (load) voltage is less than 2 V, then the LinkSwitch
will not come out of its auto-restart mode
• To increase the time period allowed for regulation to be
reached at startup (or into a full-power resistive load), C4
must be increased in value to 1 µF
• To lower the ripple voltage into non-battery loads, an LC
filter or LDO must be added onto the output
4
2
0
100
200
300
400
500
Primary Resonant
300 kHz (minimum)
Frequency
350
6
0
2.3 mH ± 10%
600
PI-3693-090503
8
Primary
Inductance
Core cancellation (2-3, clockwise), tape,
Primary (1-2, clockwise), tape,
Shield (2-open, anti-clockwise), tape,
Secondary (5T: 5-7, anti-clockwise,
10T: 7-6, anti-clockwise)
Table 1. Transformer Design Parameters.
PI-3694-091803
VIN = 85 VAC
VIN = 265 VAC
Low Limit
High Limit
Winding Order
(pin numbers)
No Load Consumption (mW)
Output Voltage (V)
10
Winding Details
Core Cancellation: 22T, 34 AWG
Primary: 90T, 36 AWG
Shield: 5T, 3 x 30 AWG
Secondary: 5T, 2 x 30 AWG (TIW)
+ 10T, 30 AWG (TIW)
300
250
200
150
100
50
0
Output Current (A)
60
Figure 2. Load Regulation - CV/CC Characteristics.
90
120 150 180 210 240 270
Input Voltage (VAC)
Figure 3. No-load Input Power Consumption.
A
9/03
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