TNY279ꢀtoꢀprovideꢀtwoꢀoutputꢀvoltages:ꢀ-5ꢀVꢀatꢀ2
atꢀ250ꢀmAꢀcontinuousꢀandꢀ600ꢀmAꢀpeak.
Aꢀandꢀ-12ꢀVꢀ
Design Idea DI-122
®
TinySwitch-III
13 W (17.2 W Peak) Non-Isolated Power Supply
for White Goods: <150 mW No-load Power Consumption
Application
Device
Power Output Input Voltage
Output Voltage
Topology
White Goods TNY279P 13 W / 17.2 W Pk 85-265 VAC -5 V, 2.0 A / -12 V, 0.25 A / 0.6 A Pk
Flyback
Design Highlights
Feedback is taken directly from the -5 V output. Once the
output exceeds the voltage defined by the VBEꢀofꢀQ1ꢀandꢀ
ratingꢀofꢀVR1,ꢀQ1ꢀisꢀbiasedꢀon.ꢀThisꢀpullsꢀcurrentꢀoutꢀofꢀtheꢀ
EN/UV pin of U1 and disables the next switching cycle. By
adjusting the number of enabled to disabled cycles, output
regulationꢀisꢀmaintained.
•ꢀ Lowꢀcost,ꢀlowꢀcomponentꢀcountꢀsolution
•ꢀ ImpedanceꢀfreeꢀpathꢀfromꢀNeutralꢀtoꢀoutputꢀRTN,ꢀidealꢀ
forꢀapplicationsꢀdrivingꢀtriacs
•ꢀ <150ꢀmWꢀno-loadꢀconsumptionꢀatꢀ230ꢀVACꢀinput
•ꢀ Bothꢀoutputsꢀexhibitꢀgoodꢀcrossꢀregulation
•ꢀ Maximumꢀambientꢀtemperatureꢀofꢀupꢀtoꢀ70ꢀ°C
•ꢀ MeetsꢀCISPR-22ꢀClassꢀB/EN55022ꢀBꢀEMIꢀlimitsꢀ
withoutꢀanꢀinputꢀcommonꢀmodeꢀchoke
TheꢀvalueꢀofꢀR7ꢀsetsꢀtheꢀbiasꢀcurrentꢀthroughꢀVR1,ꢀoperatingꢀ
theZenerclosertoitsspecifiedtestcurrent.ResistorR6limits
the base current of Q1, R5 and C8 roll-off of high frequency
gain and R3 limits the current out of the EN/UV pin.
Operation
The non-isolated flyback converter shown in Figure 1 uses a
Diode D3 ensures the EN/UV pin is clamped to >ꢀ-0.3ꢀVꢀwithꢀ
respect to the SOURCE pin of U1.
Powerꢀ Integrationsꢀ E-Shield™ꢀ transformerꢀ constructionꢀ
techniques, the RCD clamp, a simple π filter (C4, C5 and
L1), small X-type (C1) and Y-type (C2) capacitors and the
frequencyjitterfunctionoftheTinySwitch-IIIfamily, provide
good EMI margin (see Figure 3). Using a one square inch
metal shield, located underneath U1 and T1 (connected
to the SOURCE pin of U1) can further reduce EMI noise
generation.
The MOSFET integrated within U1 switches the primary of
transformer T1. Each time it turns on, the primary current
rampsuntilitreachesaninternalcurrentlimitandtheMOSFET
is turned off. During the off time, the energy stored in T1
transfers to the secondary where it is rectified and filtered by
D4 and C11 and D5 and C9. The primary side RCD clamp
(D2,ꢀC6,ꢀR1ꢀandꢀR2)ꢀlimitsꢀtheꢀpeakꢀDRAINꢀvoltageꢀspikeꢀ
caused by transformer leakage inductance.
T1
EF20
D1
1N4007
L1
1000 µH
F1
3.15 A
Line
RTN
1
10
8
R1
200 kΩ
0.5 W
C6
1 nF
1 kV
C12
47 µF
16 V
C11
2200 µF
10 V
D4
SB530
L3
3.3 µH
-5 V, 2 A
R2
C2
1 nF
250 VAC
200 Ω
C9
C10
47 µF
25 V
*
D5
SB3100
-12 V, 250 mA
(600 mA pk)
470 µF
25 V
7
D2
1N4007GP
3
Safety Earth
Ground
R4
TinySwitch-III
**
**
47 Ω
U1
TNY279P
EN/UV
C1
C4
33 µF
400 V
C5
33 µF
400 V
R3
4.7 kΩ
47 nF
D
S
275 VAC
Q1
PN2222A
R6
5.1 kΩ
VR1
BZX79-B4V7
4.7 V, 2%
BP/M
R5
1 kΩ
C7
100 nF
50 V
D3
1N5817
R7
620 Ω
C8
100 nF
50 V
Neutral
PI-4498-112906
*One square inch metal shield (connected to the S pin of U1) under U1 and T1 eliminates the need for C2.
**For high-line only operation (180 VAC input, minimum), 10 µF (400 V) capacitors can be used for C4 and C5.
Figure 1. TinySwitch-III 13/17.2 W White Good Power Supply.
January 2007
DI-122
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