ST AN1897 Application note
®
March 2004 1/11
AN1897
- APPLICATION NOTE
VIPower: LOW COST UNIVERSAL INPUT
DVD SUPPLY WITH VIPer22A
Jun-fen g Zhang
INTRODU CTI ON
In the past few years, many consumer products have been provid ed to the end user, such as DVD or
VCD players. Generally their power supply require multiple outputs to supply a variety of control circuits:
MCU, Motor, Amplifier, VFD.
ST VIPer series of off-line switch mode power supply regulators c ombines an optimized, high voltage,
avalanche rugged Vertical Power MOSFET with current mode c ontrol PWM circuitry. The result is truly
innovative AC to DC conversion that is simpler, quicker and - with component count halved - less
expensive.
The VIPer family al so represents th e ea sies t s olution to com ply with the "Blue Angel" and "Energy Star"
Eco norms, with extremely low total power consumption at stand-by mode, thanks to the burst operation.
This document would present the ap plication on DVD player pow er supply with VI Per22A satisfying the
specification See table 1 below.
Table 1: Output Specification
Note 1: The accuracy of + /- 5% is reached only for a cer tain range of loads combination. See paragraph 3. 2 for cross regulation results.
INPUT OUTPUT 1 OUTPUT 2 OUTPUT 3 OUTPUT 4 OUTPUT 5 OUTPUT 6
Universal
mains lin e
5 V +/- 5%
(See note 1)
+12 V +/- 5%
(See note 1)
-12 V +/- 5%
(See note 1)
-26 V + /- 5%
(See note 1)
3.3 V +/- 5%
(See note 1)
5V
stb
+/- 5%
(See note 1)
Min: 85Vac
Max:
265Vac
Imin: 20mA
Imax: 1.5 A
Imax: 30 mA Imax: 30 mA Imax: 50mA Imax: 150mA Imax: 100mA
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AN1897 - APPLICATION NOTE
1. APPLICATION DESCRIPTION AND DESIGN
1.1 Schematics
The overall schematic is shown in figure 2.
1.1.1 Start-up Phase
As any member of the VIPer family, VIPer22A has an integrated high voltage current source linked to
Drain pin . At the startup converter, it will charge the V
DD
capacitor until it reaches VIPer startup level
(14.5V), and then the VIPer22A starts switching.
1.1.2 Auxiliary Supply
VIPer22A has a wide operating voltage range from 8V to 42V, respectively minimum and maximum
values for under-voltage and over-voltage protections.
This function is very useful for achievin g low stand-by total power consum ption. During norma l working,
the feedback loop is connected to 5V output by D12 to regulate 5V output. At the mean time, +5Vstb
output is blocked by Q3, so +5Vstb regulation is neglected. When the stand-by signal is present, the Vce
of Q3 can not provide enough voltage to maintain D12 conducted, so the 5V output is blocked, and the
+5Vstb output is connected to the feedback loop. In this condition the +5 Vstb is regulated. Thanks to the
transformer structure, all the other secondary outputs and the auxiliary voltages are pulled down to a very
low level, also pulling down the total power consumption.
All these contents can be summarized by the following list:
• in normal full load, the V
DD
voltage of the device must be lower than the over-voltage protection;
• in short circuit, the V
DD
voltage must be lower than the shutdown vol tage. Actually, this condition leads
to the well known hiccup mode in practice;
• in no load condition, the V
DD
voltage must be higher than the shutdown voltage.
1.1.3 Burst Mode
The Viper22A integrates a current mode PWM with a Power MOSFET and includes the leading edge
blanking function. The burst mode is a feature which allows VIPer22A to skip some switching cycles
when the energy drained by the output load goes be low E =(T
b
*V
in
)
2
* f
sw
/2L
p
(T
b
=blanking time, V
in
=DC
input voltage, f
sw
=Switching frequency, L
p
=Primary Inductance).
It has the consequence to redu ce the switching losses when working in low load cond ition by reducing
the switching frequency.
1.1.4 Feedback Loop
The 5V output voltage is regulated with a TL-431 (U3) via an optocoupler (U2) to the feedback pin. If the
output voltage is high, the TL-431 will draw more current through its cat hode to t he anode and the current
increases in the optocoupler diode. The current in optocoupler NPN increases accordingly and the
current into the VIPer22A FB pin increases. When the FB current increases, the VIPer22A will skip some
cycles to decrease turn on time and lower the output voltage to the proper level (see figure 1).
The 5V output voltage is regulated thanks to the reference voltage of TL-431 and the resistive divider R8
and R9.
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AN1897 - APPLICATION NOTE
Figure 1: VIPer22A FB pin internal structure
1.1.5 Primary Driver
In a fly-back power supply, the transformer is used as an energy tank fuelled during the ON time of the
MOSFET. When the MOSFET turns off, its drain voltage rises from a low value to the input voltage plus
the reflected voltage while the secondary diode conducts, transferring on the secondary side the
magnetic energy stored in the transformer. Because primary and secondary windin gs are not perfectly
magnetically coupled, there is a serial leakage inductance that behaves like an open inductor charged at
I
pk
that causes the voltage spikes on the MOSFET drain. These voltage spikes must be clamped to keep
the VIPer22A Drain voltage below the BVds s (730Vmin) rating. If the peak voltage is higher than this
value, the device will be destroyed. The most used solution is the RCD clamp (see figure 3). This is a
very simple and chea p solution, but it impacts on the efficiency and even on the power dissipation in
stand-by condition. Also the clamping voltage varies with load current. RCD clamp circuits may allow the
drain voltage to exceed the data sheet breakdown rating of VIPer22A during overload operation or during
turn on with high line AC input voltage. So, a zener clamp is recommended (see figure 4). However such
a solution gives higher power dissipation at full load, even if the clamp voltage is exactly defined.
1.2 Transformer Consideration
On the electrical specification of a multiple output transformer (cross regulation, leakage inductance), the
main efforts focused on the proper coupling between the windings. A lower leakage inductance
transformer will allow a lower power clamp to reduce the input power. It will lead to lower power
dissipation on the primary side.
Auxiliary and secondary windings are swapped in order to decrease the coupling to the primary one. The
secondary windings act as a shielding layer to reduce the capacitive coupling. Fewer spikes are
generated on the auxiliary windings, the primary and secondary windings have better coupling.
Designing transformers for low leakage inductance involves several considerations:
•Minimize number of turns
•Keep winding build (ratio of winding height to width) small
•Increase width of windings
•Minimize insulation between windings
•Increase coupling between windings
60kHz
OSCILLATOR
PWM
LATCH
S
Q
R
0.23V
Id
DRAIN
SOURCE
FB
R1
R2
C
+Vdd
Secondary
feedback
I
FB
Is
1 kΩ
230 Ω
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AN1897 - APPLICATION NOTE
Figure 2: Application schematic
C3
0.1uF X2
U1B
817
U1A
817
1 2
34
CH1
2.2mH
C2
2200pF Y1
C1
2200pF Y1
F1
250V 1A
C4
47uF/400V
D5
FR157
C5
47pF/1KV
R3
100k/1W
U3
TL431
C7
47uF/50V
R11
680 ohm
R6
1K
R9
5.1K
R8
5.1K
C10
47pF
D9
BYW 100/ 200
C15
100uF/10V
C20
220uF/50V
3.3V
F- (3.3Vac) / 0.15A
F+ (3.3Vac)
C17
470uF/25V
C25
100uF/10V
D11
1N5818
R4
1K
D4
1N4007
D3
1N4007
D2
1N4007
D1
1N4007
D6
1N4937
--26V / 0.05A
Vin
1
GND
2
Vout
3
U4
LD33V
C9
220uF/50V
Q3
8550
Q1
9014
R5
1K
STB
CONTROL
U2
VIPER22A
--12V / 0.03A
D8
STPS5L60
C12
1000uF/16V
C13
470uF16V
+5V / 1.5A
D7
BYW 100/ 200
RT1
NTC5D-9
C19
470uF/25V
+12V / 0.03A
+5Vstb / 0.1A
VDD
DRAIN
SOURCE
1
2
J1
CON2
1
2
J2
CON2
1
2
3
4
J4
CON4
1
2
3
4
5
6
7
8
9
J5
CON9
1
2
3
4
5
J3
CON5
1
2JP1
JUMPER
R3
9.1K
C6
47nF
+ 5V 1.5A
+ 5Vstb 0.1A
- 12V 0.03A
+ 12V 0.03A
- 26V 0.05A
3.3Vac 0.15A
Auxilia ry Volt 10 Vmin
D10
BYW 100/ 200
D13
BYW 100/ 2 00
C8
1nF / 1KV
1
2
15
14
11
13
12
9
8
10
7
TX1
TFO EC28---VER3
D12
1N5818
C3
0.1uF X2
U1B
817
U1A
817
1 2
34
CH1
2.2mH
C2
2200pF Y1
C1
2200pF Y1
F1
250V 1A
C4
47uF/400V
D5
FR157
C5
47pF/1KV
R3
100k/1W
U3
TL431
C7
47uF/50V
R11
680 ohm
R6
1K
R9
5.1K
R8
5.1K
C10
47pF
D9
BYW 100/ 200
C15
100uF/10V
C20
220uF/50V
3.3V
F- (3.3Vac) / 0.15A
F+ (3.3Vac)
C17
470uF/25V
C25
100uF/10V
D11
1N5818
R4
1K
D4
1N4007
D3
1N4007
D2
1N4007
D1
1N4007
D6
1N4937
--26V / 0.05A
Vin
1
GND
2
Vout
3
U4
LD33V
C9
220uF/50V
Q3
8550
Q1
9014
R5
1K
R9
5.1K
R8
5.1K
C10
47pF
D9
BYW 100/ 200
C15
100uF/10V
C20
220uF/50V
3.3V
F- (3.3Vac) / 0.15A
F+ (3.3Vac)
C17
470uF/25V
C25
100uF/10V
D11
1N5818
R4
1K
D4
1N4007
D3
1N4007
D2
1N4007
D1
1N4007
D6
1N4937
--26V / 0.05A
Vin
1
GND
2
Vout
3
U4
LD33V
C9
220uF/50V
Q3
8550
Q1
9014
R5
1K
STB
CONTROL
U2
VIPER22A
--12V / 0.03A
D8
STPS5L60
C12
1000uF/16V
C13
470uF16V
+5V / 1.5A
D7
BYW 100/ 200
RT1
NTC5D-9
C19
470uF/25V
+12V / 0.03A
+5Vstb / 0.1A
VDD
DRAIN
SOURCE
1
2
J1
CON2
1
2
J2
CON2
1
2
3
4
J4
CON4
1
2
3
4
5
6
7
STB
CONTROL
U2
VIPER22A
--12V / 0.03A
D8
STPS5L60
C12
1000uF/16V
C13
470uF16V
+5V / 1.5A
D7
BYW 100/ 200
RT1
NTC5D-9
C19
470uF/25V
+12V / 0.03A
+5Vstb / 0.1A
VDD
DRAIN
SOURCE
1
2
J1
CON2
1
2
J2
CON2
1
2
3
4
J4
CON4
1
2
3
4
5
6
7
8
9
J5
CON9
1
2
3
4
5
J3
CON5
1
2JP1
JUMPER
R3
9.1K
C6
47nF
+ 5V 1.5A
+ 5Vstb 0.1A
- 12V 0.03A
+ 12V 0.03A
- 26V 0.05A
3.3Vac 0.15A
Auxilia ry Volt 10 Vmin
D10
BYW 100/ 200
D13
BYW 100/ 2 00
C8
1nF / 1KV
1
2
8
9
J5
CON9
1
2
3
4
5
J3
CON5
1
2JP1
JUMPER
R3
9.1K
C6
47nF
+ 5V 1.5A
+ 5Vstb 0.1A
- 12V 0.03A
+ 12V 0.03A
- 26V 0.05A
3.3Vac 0.15A
Auxilia ry Volt 10 Vmin
D10
BYW 100/ 200
D13
BYW 100/ 2 00
C8
1nF / 1KV
1
2
15
14
11
13
12
9
8
10
7
TX1
TFO EC28---VER3
D12
1N5818
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