Design Idea DI-116
TinySwitch-III
Application
DVD / Set-top Box
Device
®
28 W Multiple Output Supply with <50 mW
No-Load Consumption
Power Output
Input Voltage
90-265 VAC
Output Voltage
5 V / 12 V / -12 V / -24 V
Topology
Flyback
TNY280P 25 W (28 W pk)
Design Highlights
•
•
•
•
•
•
•
Simple, low cost, low parts count solution
Low input power at no-load: <50 mW at 265 VAC
Low standby power consumption: <90 mW input with
5 V, 5 mA load
High efficiency: >74% at 90 VAC
>10 dBµV EMI margin to EN55022B conducted EMI
limits, even with output connected to safety earth ground
Simple output overvoltage latching shutdown circuit
protects load under fault conditions
On-time extension provides 28 ms hold-up time
The internal MOSFET in U1 conducts current through the
primary winding of T1 during each enabled switching cycle.
When the primary current reaches the MOSFET current
limit, it turns off and the energy in T1 is transferred to the
secondary.
The primary clamp (D5, VR3, R1, R2 and C3) limits the
maximum peak drain voltage below the 700 V breakdown
voltage of the internal MOSFET.
Output overvoltage protection (OVP) is provided by U2, R12,
R13, VR1 and VR2. If the feedback loop were to open circuit
due to a failure of U3, VR1 or VR2 would turn on U2 causing
the current into the BP/M pins of U1 to exceed 6.5 mA, and
U1 to latch off. The values of VR1 and VR2 determine the
output voltage at which this occurs. Once triggered, cycling
the AC power resets the OVP latch.
To reduce no-load input power and increase light-load
efficiency, resistor R3 feeds the supply current for U1 from
the auxiliary bias winding on the transformer.
C6
330 pF
R3
100 V
16
Ω
D7 SB360
C9
1 nF
50 V
R4
10
Ω
C7
680
µF
16 V
L2
3.3
µH
L3
3.3
µH
C13
100 nF
50 V
R11
10
Ω
R8
56
Ω
R7
10
Ω
U3-A
R9
1 kΩ
R14
15 kΩ
1%
U2-A
R15
115 kΩ
1%
C15
100 nF
50 V
R12
100
Ω
-12 V,
20 mA
-24 V,
15 mA
Operation
The DVD or set top box supply shown in Figure 1 was designed
as a Flyback converter using a TNY280P device (U1). In this
circuit, the 10
µF
value of C4 selects the increased current
limit level of U1, which allows the supply to deliver up to
28 W of peak power during startup or load transients (opening
the DVD tray).
C18
1 nF
250 VAC
VR3
BZY97C200
200 V
D1
1N4937
D2
1N4937
R1
560
Ω
R2
200
Ω
1/2 W
C3
1 nF
1 kV
2
T1
8
VR4
BZX79-
C8
220
µF
B8V2
8.2 V
16 V
C11
220
µF
10 V
VR1
1N5244B
14 V
+12 V,
1.15 A
+5 V,
2.1 A
RTN
3
NC
6
7
D9
BAV20
10
D10
BAV20
C12
C10
D8
2.2
µF
SB530 2200
µF
50 V
10 V
R6
10
Ω
C14
2.2
µF
50 V
C5
1
µF
100 V
VR2
BZX79-B4V7
4.7 V 2%
F1
2A
L1
10 mH
C1
47
µF
400V
D5
FR107
RV1
90-265
VAC
275 VAC
C2
47
µF
400V
TinySwitch-III
EE25
U1
TNY280P
D
EN/UV
BP/M
9
4
D6
BAV21
5
R13
1 kΩ
U2-B
PC817D
R3
100 kΩ
D3
1N4007GP
D4
1N4007GP
S
C16
220 nF
50 V
C17
1
µF
50 V
U4
TL431
2%
C18
100 nF
50 V
RTN
C4
10
µF
50 V
U3-B
PC817D
R10
3 kΩ
R16
10 kΩ
1%
PI-4416-090606
Figure 1. 25 W, 28 W pk Multiple Output Supply Using TNY280P.
DI-116
September 2006
POWERINT [ POWER INTEGRATIONS, INC. ]
