Application Device Power Output Input Voltage Output Voltage Topology
General Purpose TNY278PN 12 W 85 - 265 VAC 12 V Flyback
DI-91 Design Idea
TinySwitch-III
www.powerint.com February 2007
12 W Universal Input CV Adapter
®
Design Highlights
No-load consumption <50 mW at 265 VAC (R8 fi tted)
Active mode effi ciency >75% (CEC 2008, ≥72.4%)
BP/M pin capacitor value selects MOSFET current limit (ILIMIT–1,
ILIMIT, or ILIMIT+1): for design fl exibility
Output OVP function senses overvoltage on the output through
the primary bias winding
Accurate (±5%), auto-recovering, hysteretic thermal shutdown
function maintains safe PCB temperatures
Auto-restart function protects against output short circuits and
open feedback loops
>3.2 mm package pin creepage: reliable operation in high
humidity and high pollution environments
Operation
This universal input, 12 V, 1 A, fl yback converter was designed
around a member of the TinySwitch-III IC family, the TNY278PN.
Because of the many features integrated into the device family, the
supply only requires 31 through-hole components (no SMT), which
enables a simple, single-sided PCB layout to be used.
•
•
•
•
•
•
•
Figure 1. TinySwitch-III 12 W, Universal Input, CV Adapter.
The use of an E-shield™ in the transformer, a low-noise drain-
node clamp (R2, C4 and D5), a single Y capacitor (C5) and the
device’s switching frequency jitter function enable a low-cost pi π
fi lter (C1, L1 and C2) to attenuate conducted EMI enough to
provide more than 10 dB of margin to EN550022 requirements
(see Figure 4). The clamp circuit Zener (VR1) only conducts briefl y
during startup and at worst-case overload, just before the auto-
restart function is activated.
Although TinySwitch-III family members do not need a bias
winding to operate, one was used in this design to take advantage
of the IC’s output OVP detection function. If an open loop fault
causes an overvoltage on the output, VR2 will conduct. When the
current into the BP/M pin exceeds 5.5 mA, an internal latch
triggers and disables MOSFET switching (see Figure 3), until AC
power is removed and reapplied (to reset the latch). Resistor R3
limits the current through VR2, while R3 and R7 attenuate the
portion of the leakage inductance spike that appears in the bias
winding.
D
S
S BP/M
EN/UV
L1
1 mH
D1
1N4007
RV1
275 VAC
F1
3.15 A
D2
1N4007
C1
6.8 μF
400 V
C6
1 μF
60 V
C2
22 μF
400 V
C10
1000 μF
25 V
C5
2.2 nF
250 VAC
C11
100 μF
25 V
+12 V, 1 A
85-265
VAC
RTN
J4
J3
J1
J2
C7
100 nF
50 V
U1
TNY278PN
C4
10 nF
1 kV
VR1
P6KE150A
NC
8
6
4
T1
2
5
1
3
D5
1N4007GP
D6
UF4003
D7
BYV28-200
U2
PC817A
VR2
1N5255B
28 V
VR3
BZX79-C11
11 V
C7 is configurable to adjust
U1 current limit, see circuit
description
*R5 and R8 are optional
components
R5*
3.6 MΩ
R3
47 Ω
1/8 W
R4
2 kΩ
1/8 W
R6
390 Ω
1/8 W
R7
20 Ω
R8*
21 kΩ
1%
R1
1 kΩ
R2
100 Ω
D3
1N4007
D4
1N4007
L2
Ferrite Bead
3.5 × 7.6 mm
PI-4244-122007
†
†
TinySwitch-III
Power Integrations
5245 Hellyer Avenue
San Jose, CA 95138, USA.
Main: +1 408-414-9200
Customer Service
Phone: +1-408-414-9665
Fax: +1-408-414-9765
Email: usasales@powerint.com
On the Web
www.powerint.com
C
02/08
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.
©2006, Power Integrations, Inc.
DI-91
Figure 4. Conducted EMI Scan (Line): 113 VAC, Full Load.
When R8 (optional) is installed, it supplies current to the BP/M pin,
which reduces the no-load consumption of the supply. When R5
(also optional) is installed, the current it feeds into the EN/UV pin of
the IC enables the input undervoltage lockout function (UVLO),
and sets the start-up threshold at 65 VAC.
The output voltage is determined by the series sum of the voltages
across VR3, R6, and the LED in U2. The values of R4 and R6 can
be adjusted to fi ne tune the output voltage of the supply, and a
TL431 can be used in place of VR3, for tighter output voltage
regulation.
Key Design Points
In the TinySwitch-III family of devices, the MOSFET current limit
can be selected from 3 levels by the value of capacitance on
the BP/M pin. This gives the designer a number of options,
which are shown in Figure 2. First, a TNY279 could be used,
with the current limit of a TNY278, to obtain higher effi ciency.
Second, a TNY277 could be used, with the current limit of a
TNY278, to deliver the same power at a lower effi ciency. Lastly,
a TNY278 could be used, with the current limit of a TNY279, to
extend the power capability of the supply*.
The UVLO function integrated into U1 only enables MOSFET
switching to occur once the current fl owing into the EN/UV pin
exceeds 25 μA. Changing the UVLO threshold voltage requires
changing the value of R5 so that 25 μA fl ows through it at the
desired threshold voltage.
If output OVP is not required and no-load power consumption
of 150 mW (max, at 265 VAC input) is acceptable, then R7, D6,
C6, R3 and VR2 can be eliminated and the bias winding
removed from T1, for an even lower parts count.
*Note: This supply was not thermally designed to continuously
deliver the extended power range that could be obtained by
operating a TNY278 with its MOSFET current limit set at that of a
TNY279.
•
•
•
Figure 3. BP/M Pin OVP Function Shuts Down Power Supply.
Figure 2. Operating Effi ciency vs ILIMIT+, ILIMIT- and Device Size.
72
70
68
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.3 1.41.2 1.5
Output Current (A)
Efficiency (%)
76
74
82
84
86
88
80
78 TNY279 (with ILIMIT-1)
TNY278 (with std ILIMIT)
TNY277 (with ILIMIT+1)
CEC/ENERGY STAR Minimum
TNY278 (with ILIMIT+1)
PI-4274-013106
PI-4288-012506
0 250 500
15
0
Time (ms)
Voltage (V)
-20
-10
0
-10
20
30
40
50
60
70
80
0.15 1 10 30
Frequency (MHz)
Amplitude (dBμV)
PI-4289-012506
