Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific voltage responsive fault sensor
Reexamination Certificate
2001-07-30
2002-11-26
Riley, Shawn (Department: 2838)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific voltage responsive fault sensor
C363S056110, C363S021070
Reexamination Certificate
active
06487059
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention regards a power supply device with detection of malfunctioning.
2. Description of the Related Art
As is known, electronic power supplies are extensively used in appliances for offices, in data-acquisition systems, and in the so-called “silver boxes” for supplying motherboards, memory devices, interface circuits, etc., present inside computers.
An example of a power supply device of the off-line type is schematically illustrated in FIG.
1
. The power supply device
1
has an input terminal
2
receiving an input voltage VIN, and an output terminal
3
connected to a load
4
and supplying an output voltage VOUT. The input voltage VIN is a mains AC voltage (220 V, 50 Hz), and the output voltage VOUT is a DC voltage.
The power supply device
1
comprises the following: a first rectifier circuit
5
(of the diode-bridge type) connected between the input terminal
2
and a first terminal of a first filter capacitor
7
, the latter having a second terminal connected to a ground terminal; and a DC-DC-converter circuit
8
, of the forward type, connected between the first terminal of the first filter capacitor
7
and the output terminal
3
.
The DC-DC converter circuit
8
comprises a transformer
9
made up of a primary winding
9
a
and a secondary winding
9
b.
The primary winding
9
a
has a first terminal connected to the first terminal of the first filter capacitor
7
, and a second terminal connected to a first conduction terminal of a power switch
10
, which has a second conduction terminal connected to the ground terminal, and a control terminal
11
. The secondary winding
9
b
has a first terminal connected to the output terminal
3
by means of a second rectifier circuit
13
, and a second terminal connected to the ground terminal. The power switch
10
is a discrete-type power transistor sized for power outputs higher than 200 W. Alternatively, the power switch
10
may be a high voltage integrated power transistor sized for power outputs of the order of tens of Watts.
The second rectifier circuit
13
includes the following: a first diode
16
having its anode connected to the first terminal of the secondary winding
9
b,
and its cathode connected to a connection node
17
; a second diode
18
having its cathode connected to the connection node
17
, and its anode connected to the ground terminal; an induction coil
19
connected between the connection node
17
and the output terminal
3
; and a second filter capacitor
20
connected between the output terminal
3
and the ground terminal.
The DC-DC converter circuit
8
further comprises a driving stage
12
made of a pulse-width modulation (PWM) controller circuit integrated using, for example, BCD off-line technology. The driving stage
12
has a compensation terminal
34
connected to a compensation node
30
, and an output terminal connected to the control terminal
11
of the power switch
10
. The driving stage
12
comprises a current generator
31
having an output terminal connected to the compensation terminal
34
and supplying a biasing current I
P
. The compensation node
30
is also connected to a first terminal of a compensation capacitor
32
having a second terminal connected to the ground terminal.
The DC-DC converter circuit
8
also comprises a voltage divider
14
and a regulating circuit
15
. The voltage divider
14
is connected between the output terminal
3
and the ground terminal, and is made up of a first resistor
21
and a second resistor
22
connected together at a feedback node
23
, on which a feedback voltage V
FB
is present that is proportional to the output voltage V
OUT
. The regulating circuit
15
is connected between the feedback node
23
and the compensation node
30
, and includes an error amplifier
24
having an inverting input terminal connected to the feedback node
23
, a non-inverting input terminal connected to a voltage generator
25
supplying a reference voltage V
REF
, and an output terminal
26
supplying an error voltage V
E
correlated to the difference between the feedback voltage V
FB
and the reference voltage V
REF
. The regulating circuit
15
moreover includes a photocoupler
27
comprising the following: a photodiode
28
having its anode connected to the output terminal
3
of the power supply device
1
, and its cathode connected to the output terminal
26
of the error amplifier
24
; and a phototransistor
29
having a first conduction terminal connected to the compensation node
30
, a second conduction terminal connected to the ground terminal, and a control terminal receiving light radiation emitted from the photodiode
28
.
Operation of the power supply device
1
is described in what follows.
The input voltage V
IN
is rectified by means of the first rectifier circuit
5
and filtered by means of the first filter capacitor
7
to obtain a continuous voltage V
DC
. The continuous voltage V
DC
is applied across the primary winding
9
a
when the power switch
10
is on. The driving stage
12
causes the power switch
10
to switch at a fixed frequency, normally over 20 kHz (threshold of acoustic audibility) and with a duty-cycle &dgr; that depends upon the value of a compensation voltage V
COMP
present on the compensation node
30
and due to the charging of the compensation capacitor
32
by the current generator
31
; namely:
δ
=
T
ON
T
ON
+
T
OFF
=
f
(
V
COMP
)
(
1
)
where T
ON
designates the time interval during which the power switch
10
is on, and T
OFF
designates the time interval during which the power switch
10
is off.
The energy associated to the input voltage V
IN
is transferred to the secondary winding
9
b
of the transformer
9
(which has also the task of insulating the circuitry connected downstream of the power supply device
1
from the high voltage). The second rectifier circuit
13
supplies, on the output terminal
3
, the output voltage V
OUT
, which for a forward-type DC-DC converter in continuous mode is
V
OUT
=
T
ON
T
ON
+
T
OFF
V
DC
(
2
)
The regulating circuit
15
performs continuous regulation and stabilization of the output voltage V
OUT
, rendering it immune from the variations of the input voltage V
IN
and of the load
4
. In greater detail, initially, when the phototransistor
29
is off, the current generator
31
charges the compensation capacitor
32
, causing the compensation voltage V
COMP
to increase. As soon as the phototransistor
29
turns on, it absorbs the biasing current I
P
and fixes the compensation voltage V
COMP
, adapting it automatically to the conditions of the power supply device
1
. In this way, the duty-cycle &dgr; of the power switch
10
is fixed, and likewise the output voltage V
OUT
.
It is known that current standards require, for reasons of safety, that in off-line power supply devices there should be a physical separation (galvanic decoupling) between the circuits supplied by AC voltage and the circuits supplied by low voltage. The minimum distance required is 8 mm. For this reason, DC-DC converters are of the forward type or, alternatively, of the flyback type, in that both these configurations use transformers for transferring energy, and decoupler components (photocouplers and signal transformers) for making the regulating circuit. At present, photocouplers, on account of their low cost, are the components most extensively used for making regulating circuits.
A problem linked to the presence of photocouplers is that, if for any reason, the regulating circuit breaks or gets disconnected, the compensation voltage increases beyond a certain operating limit. In such conditions, the duty-cycle of the controlled transistor reaches its maximum value, as likewise does the energy that the transformer transfers to the load, with consequent increase in the output voltage V
OUT
.
To prevent the output voltage V
OUT
from reaching values such as might damage the circuitry connected downstream of the power supply device, the latter is modified as shown in
FIG. 2
, in which parts that are the
Adragna Claudio
Bontempo Gregorio
Fagnani Mauro
Gattavari Giuseppe
Pidutti Albino
Bennett II Harold H.
Jorgenson Lisa K.
Riley Shawn
STMicroelectronics S.r.l.
LandOfFree
Switching mode power supply device with detection of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Switching mode power supply device with detection of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Switching mode power supply device with detection of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2993758