AN1948
Application note
DVD combo power supply with the VIPer53-E
Introduction
The VCR is available on the market despite of the presence of the DVD readers. This
document offers a typical solution to efficient supply applications where logic, DC motor
drive and LCD display are implemented together in the 35 W power range and with any
input voltage standard (85 Vac to 265 Vac).
Low standby consumption and cost saving meet the market needs and the key features for
this application are shown in
Table 1:
Figure 1. VIPer53-E board
Table 1. Output specifications
Voltage
+/-5%
Output 1
Output 2
Output 3
Output 4
Output 5
Output 6
Output 7
Output 8
3.3 V
5 V standby
5 V power
12 V power
12 V audio
-12 V power
-25 V
4.2 V display
Maximum
current
1.5 A
100 mA
1.5 A
1.5 A
200 mA
15 mA
25 mA
50 mA
Output
power
4.95 W
500 mW
7.5 W
18 W
2.4 W
180 mW
625 mA
210 mA
Normal operation:
35 W max. output
power
Standby operation:
750 mW max. input
power
with 40 mA on the
5 V standby output
Maximum power
Board size
LxWxH
170 x 70 x 40
(mm)
November 2014
DocID10413 Rev 2
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www.st.com
23
Contents
AN1948
Contents
1
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1
1.2
1.3
General features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Overload protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Standby operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2
DVD combo power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1
Schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.1
2.1.2
2.1.3
2.1.4
2.1.5
2.1.6
Normal operation mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Standby mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Drain voltage clamping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Plasma display outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2
Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.1
2.2.2
2.2.3
2.2.4
2.2.5
2.2.6
2.2.7
2.2.8
2.2.9
2.2.10
Startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Switch-off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Transitions between normal and standby mode . . . . . . . . . . . . . . . . . . 10
Load and cross regulation in normal mode . . . . . . . . . . . . . . . . . . . . . . 10
Efficiency in normal mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Load regulation and input power in standby mode . . . . . . . . . . . . . . . . 13
Line regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Dynamic load variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Short-circuit operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3
Board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.3.1
2.3.2
Board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Transformer specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
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DocID10413 Rev 2
AN1948
Description
1
Description
The VIPer53-E is the first multichip device of the VIPer
®
family with a very low R
(DS)on
=
1
Ω,
which can go up to 35
Ω
in a standard DIP8 package without the heatsink. It meets the
high efficiency and reduced space features thanks to a lower power dissipation.
1.1
General features
The block diagram can be seen in
Figure 2.
An adjustable oscillator drives a current
controlled PWM to a fixed switching frequency. The peak drain current is set for each cycle
by the voltage present on the COMP pin. The useful range of the COMP pin extends from
0.5 V to 4.5 V, with a corresponding drain current range from 0 A to 2 A.
This COMP pin can be used either as an input, in case of secondary feedback configuration,
or as an output when the internal error amplifier connected on the VDD pin operates in
primary feedback to regulate the VDD voltage to 15 V.
The VDD undervoltage comparator drives a high voltage start-up current source, which
switches off during the normal operation of the device. This feature, together with the burst
mode capability, allows a very low level of input power to be reached in standby mode, when
the converter is lightly loaded.
Figure 2. VIPer53-E block diagram
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Description
AN1948
1.2
Overload protection
A 4.35 V typical threshold is present on the COMP pin. This overload threshold is 150 mV
below the clamping voltage of 4.5 V which corresponds to the current limitation of the
device. In case of a COMP voltage exceeding the overload threshold, the pull-up resistor on
the TOVL pin is released and the external capacitor connected on this pin begins to charge.
When a value of 4 V typical is reached, the device stops switching and remains in this state
until the V
DD
voltage reaches V
DDoff
, or resumes normal operation if the COMP voltage
returns to a value below the overload threshold. The drain current that the device delivers
without triggering the overload threshold is called “current capability”, specified as I
Dmax
in
the datasheet. This value must be used to correctly size the converter versus its maximum
output power. When an overload occurs on secondary side of the converter, the output
power is limited by the current limitation of the device. If this overload lasts for more than a
time constant defined by a capacitor connected on the TOVL pin, the device is reset, and a
new sequence restarts by turning on the start-up current source. The capacitors on the VDD
pin and on the TOVL pin are defined together in order to insure a correct startup and a low
restart duty cycle in overload or short-circuit operation. Here are the typical corresponding
formulas:
C
OVL
>
12.5
⋅
10
–
6
⋅
tss
C
VDD
>
8
⋅
10
–
4
C
OVL
⋅
I
DDch2
1
⋅
------------- –
1
⋅
----------------------------------
-
-
D
RST
V
DDhyst
I
DD1
⋅
tss
C
VDD
>
-----------------------
-
V
DDhyst
Where tss and D
RST
are respectively the time needed for the output voltages to pass from
0 V to their nominal values at startup, and the restart duty cycle in overload or short-circuit
condition. A typical value of 10% is generally set for this last parameter, as it insures that the
output diodes and the transformer don’t overheat. The other parameters can be found in the
datasheet of the device. As the V
DD
capacitor has to respect two conditions, the maximum
value is retained to define its value.
1.3
Standby operation
On the opposite load configuration, the converter is lightly loaded and the COMP voltage
decreases until it reaches the shutdown threshold typically 0.5 V. At this point, the switching
is disabled and energy doesn’t pass on the secondary side. So, the output voltage
decreases and the regulation loop rises again above the shutdown threshold, thus resuming
the normal switching operation. A burst mode with pulse skipping takes place, as long as
the output power is below the one corresponding to the minimum turn-on of the device. As
the COMP voltage works around 0.5 V, the peak drain current is very low (it is defined by the
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AN1948
Description
minimum turn-on time of the device, and by the primary inductance of the transformer) and
no audible noise is generated.
In addition, the minimum turn-on time depends on the COMP voltage. Below 1 V (V
COMPbl
),
the blanking time increases till 400 ns, whereas it is 150 ns for higher voltages. The
minimum turn-on times resulting from these values are respectively 600 ns and 350 ns,
when the internal propagation time is taken into account. This feature gives the following
benefits:
–
–
–
this brutal change induces the hysteresis between normal operation and burst
mode, which is reached earlier when the output power decreases.
a short value in normal operation insures a good drain current control in case of
short-circuit on the secondary side.
long value in standby operation reinforces the burst mode by skipping more
switching cycles, thus decreasing switching losses.
More details regarding the standby operation can be found in the datasheet.
DocID10413 Rev 2
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