Electricity: electrical systems and devices – Safety and protection of systems and devices – Voltage regulator protective circuits
Reexamination Certificate
2000-11-21
2003-06-03
Huynh, Kim (Department: 2182)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Voltage regulator protective circuits
C361S020000, C363S050000, C323S276000
Reexamination Certificate
active
06574081
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a DC-DC converter for converting a voltage of a DC (Direct Current) power supply, and more specifically, it relates to an improvement in an output low voltage protection function which stops supply of power when a short circuit occurs in the load.
2. Description of the Related Art
A conventional DC-DC converter is explained according to FIG.
4
.
FIG. 4
is a circuit diagram showing an example of a conventional DC-DC converter unit. Incidentally, an explanation is made by using a flyback converter as an example. As shown in
FIG. 4
, the conventional DC-DC converter consists of a DC power supply
1
, a transformer
2
, a PWM (Pulse Width Modulation) modulation section
40
, a power supply selection section
41
, a time constant determination section
42
, a thyristor
21
, a first rectifier section
43
, a first smoothing section
44
, a photocoupler
19
, a shunt regulator
22
, dividing resisters
23
and
24
, a second rectifier section
45
, and a second smoothing section
46
.
Furthermore, the PMW modulation section
40
consists of a PWM control IC
4
and a main switch
3
. The PMW control IC
4
is provided with a power supply terminal (Vcc), a signal output terminal (OUT), an operation control input terminal (OFF), and a GND terminal. The power supply selection section
41
consists of a first FET (N channel MOSFET)
5
, a first resistor
6
, a second resistor
7
and a Zener diode
8
. The time constant determination section
42
consists of a resistor
18
and a capacitor
20
. The first rectifier section
43
is provided with two diodes
9
and
10
. The first smoothing section
44
is provided with a choke coil
11
and a capacitor
12
. Moreover, the second rectifier section
45
is provided with two diodes
14
and
15
. The second smoothing section
46
is provided with a choke coil
16
and a capacitor
17
. Incidentally, in this case, the main switch
3
consists of an FET (hereinafter referred to as a second FET for discrimination).
In a first FET
5
in the power supply selection section
41
, the drain terminal (D) and the gate terminal (G) are respectively connected to a positive pole side of a DC power supply
1
via the first resistor
6
and the second resistor
7
. The gate terminal (G) of the first FET
5
is also connected to a cathode terminal (K) of the Zener diode
8
. An anode terminal (A) of the Zener diode
8
is connected to a negative pole side (hereinafter referred to as “GND”). Moreover, a source terminal (S) is connected to the power supply terminal (Vcc) of the PMW control IC
4
and to an output terminal Q of the second smoothing section
46
.
A power supply terminal of the PWM control IC
4
of the PWM modulator
40
is connected to a terminal X of the photocoupler
19
via the resistor
18
. The terminal X of this photo-coupler
19
is also connected to a gate terminal (G) of the thyristor
21
and is connected to GND via the capacitor
20
. Moreover, a terminal Y of the photocoupler
19
is connected to GND. The anode terminal (A) and the cathode terminal (K) are connected to the operation control input terminal (OFF) of the PWM control IC
4
and GND respectively. The signal output terminal (OUT) of the PWM control IC
4
is connected to the gate terminal (G) of the second FET
3
and the GND terminal of the PWM control IC
4
is further connected to GND. Incidentally, a feedback signal of the output voltage is input to this PWM control IC
4
by an output voltage detection circuit and a feedback circuit which are not illustrated. A source terminal (S) of the main switch
3
is connected to GND and a drain terminal (D) thereof is connected to the positive pole side of the DC power supply via a primary winding
2
a
of a transformer
2
.
Both ends of a secondary winding
2
b
of the transformer
2
are connected to a load
13
via the first rectifier section
43
and the first smoothing section
44
, a terminal P side of this load
13
is connected to the anode terminal of the LED of the photocoupler
19
, the cathode terminal of the photocoupler
19
is connected to the cathode terminal (K) of the shunt regulator
22
. Moreover, the anode terminal (A) of this shunt regulator is connected to the other end of the load
13
, a reference terminal (R) is connected to the terminal P side of the load
13
via the resistor
23
and is connected to the other end of the load
13
via the resistor
24
.
Both ends of the third winding
2
c
of the transformer
2
are connected to the second smoothing section
46
via the second rectifier section
45
. Incidentally, GND terminals of the second rectifier section
45
and the second smoothing section
46
are connected to GND respectively as they are shown.
Operations of the PWM modulation section
40
and the power supply selection section
41
are now explained. In the PWM modulation section
40
, the PWM control IC
4
controls conduction of the main switch
3
by a PWM-controlled output signal to control the current flowing to the primary winding
2
a
of the transformer
2
. Moreover, the PWM modulation section
40
stops output of the PWM-controlled signal when the operation control terminal (OFF) of the PWM control IC
4
is set to an L-level.
Furthermore, when the second smoothing section
46
does not supply sufficient sub-power supply voltage (when starting), the power supply selection section
41
turns the first FET
5
ON to supply power supply voltage of the DC power supply
1
supplied via the resistor
6
to the power supply terminal (Vcc) of the PWM control IC
4
. When the second smoothing section
46
supplies sufficient sub-power supply (in a steady state), the power supply selection section
41
turns the first FET
5
OFF to supply the sub-power supply voltage outputted from the second smoothing section
46
to the power supply terminal (Vcc) of the PWM control IC
4
as it is shown.
Incidentally, the time constant determination section
42
is widely known, and a choke-input rectifying method which is well known is utilized for the first rectifier section
43
, the first smoothing section
44
, the second rectifier
45
and the smoothing section
46
. Therefore, detailed explanations are omitted.
Next, operations of the conventional DC-DC converter shown in
FIG. 4
are explained. First, an operation of this DC-DC converter when starting is explained. The voltage from the DC power supply
1
is applied to the gate electrode (G) of the first FET
5
via the resistor
7
, and the gate electrode (G) is fixed at predetermined potential to GND by function of the Zener diode
8
. On the other hand, since the voltage is not applied to the source terminal (S) of the first FET
5
at first, a potential difference is generated between the gate and source terminals to turn the first FET ON, and the voltage to be applied to the drain terminal (D) of the first FET
5
via the resistor
6
is transmitted to the power supply terminal (Vcc) of the PWM control IC
4
via the source terminal (S). Then, the PWM control IC
4
is turned ON to start, and a PWM modulated voltage signal (a gate driving pulse) is outputted from the output terminal OUT. Incidentally, in this case, the PWM control IC
4
is fed back to be inputted with output voltage. Thereby, the PWM control IC
4
performs operations to control the output voltage to a predetermined value.
Subsequently, the main switch
3
is switching-controlled by the gate driving pulse outputted from the PWM control IC
4
, and a current between the drain electrode (D) and the source electrode (S), that is, the current flowing through the primary winding
2
a
of the transformer
2
from the DC power supply is converted to an AC current.
Then, a current in accordance with the number of wire turns is induced in the secondary winding
2
b
of the transformer, and a current in accordance with the number of wire turns is also induced in the tertiary winding
2
c
. A voltage signal generated on both ends of the secondary winding
2
b
of the transformer
2
is rec
Matsumoto Tadahiko
Nagai Jun
Tsuji Hitoshi
Huynh Kim
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
LandOfFree
DC-DC converter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with DC-DC converter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and DC-DC converter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3149569