Electrical transmission or interconnection systems – Plural load circuit systems – Control of current or power
Reexamination Certificate
2002-05-29
2003-11-04
Riley, Shawn (Department: 2838)
Electrical transmission or interconnection systems
Plural load circuit systems
Control of current or power
Reexamination Certificate
active
06642630
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a multi-output switching power source circuit to conduct constant-voltage control using a magnetic amplifier or a magamp.
Description of the Prior Art
FIG. 1
shows a conventional circuit configuration of a multi-output switching power supply circuit to conduct constant-voltage control using a magnetic amplifier or a transducer.
The power supply
20
includes a transformer
20
including a primary side which includes a direct-current (dc) power source
1
, an input smoothing condenser or capacitor
2
, a starting resistor
3
, a pulse width modulation controller
4
, detecting resistors
5
and
6
, a capacitor
7
, a smoothing choke coil
8
, a rectifying diode
9
, a commutating diode
10
, and a main switch
11
, e.g., an n-type metal-oxide semiconductor transistor (to be simply referred to as an NMOS hereinbelow).
On the primary side of the transformer
20
, a primary winding
21
and an auxiliary winding
22
are disposed. The transformer
20
includes a secondary side including secondary windings
23
a
,
23
b
,
23
c
, etc. for respective output sections A, B, C, etc., respectively.
The output section A includes a magnetic amplifier
31
, a rectifier diode
32
, a commutator diode
33
, a smoothing choke coil
34
, a capacitor
35
, a dummy resistor
36
, a constant-voltage control circuit
37
, detecting resistors
38
and
39
, a transistor
40
, a resistor
41
, and a diode
42
. The other output sections B, C, and the like are configured substantially in the same manner as for the output section A. Each section includes a load RL in its output section.
Referring next to
FIGS. 2 and 3
, description will be given of a principle of operation of the magnetic amplifier shown in FIG.
1
.
As can be seen from a graph of
FIG. 2
, the magnetic amplifier
31
is on when a pulse current having a pulse width of x &mgr;s (micro sec.) is flowing in the circuit. Even when the pulse current repeatedly changes its state between an on state and an off state, the magnetic amplifier
31
is in a magnetized state which conducts reciprocation between point A corresponding to a maximum value of the pulse current and point B corresponding to a state in which the current or a magnetic field associated therewith is zero as shown in FIG.
2
. The magnetic amplifier
31
is kept retained in the on state. However, when a current slightly flows through the amplifier
31
in a direction opposite to that of the pulse current, that is, when a reset current flows therethrough, the state of magnetization of the amplifier
31
changes to a state corresponding to point C. The amplifier
31
therefore turns off. In this situation, even when voltage E is applied to the amplifier
31
in a forward direction, the current does not flows at once. According to a relationship
Magnetic flux (&phgr;)=Product of Voltage and Time (
T×E
),
the current starts flowing with a delay of time, i.e., rising time of
&Dgr;
T=&Dgr;&phgr;/E.
By controlling the rising time delay &Dgr;T by the reset current, the pulse width modulation is carried out. In this case, if
x=&Dgr;T,
no current flows at all. In other words, by regulating the width of &Dgr;&phgr; of the amplifier
31
, the pulse modulation is conducted in a range of pulse current from 0% to 100%.
Subsequently, description will be given of operation of a multi-output switching power source circuit of the prior art shown in FIG.
1
.
In the power supply circuit, the dc power source section
1
generates a dc input voltage V
1
. The input smoothing capacitor
2
smoothes the voltage V
1
.
The PWM (power width modulation) control circuit
4
produces a control signal V
4
having a predetermined frequency and a pulse width corresponding to detected voltage, which is detected as below. The auxiliary winding
22
on the primary side of the transformer
20
generates an alternating-current (ac) voltage. The rectifying diode
9
rectifies the ac voltage into a pulsating voltage. The smoothing choke coil
8
and the smoothing capacitor
7
smooth the pulsating voltage to obtain an output dc voltage. The resistors
5
and
6
divides the dc voltage. The PWM control circuit
4
detects a change in the divided voltage to thereby produce the detected voltage. The secondary winding
23
a
produces an ac voltage determined by a turn ratio, i.e., a ratio between a number of turns of the primary winding
21
and that of the secondary winding
23
a
. By producing an ac voltage proportional to the ac voltage in the secondary winding
23
a
by the auxiliary winding
22
, the PWM control circuit
4
controls the pulse width according to the change in the ac voltage to resultantly keep the output voltage at a fixed value. The NMOS
11
turns on or off the input dc voltage V
1
according to the control signal V
4
to generate an ac voltage V
11
having a predetermined frequency and a pulse width associated with the detected voltage. The transformer
20
transforms the ac voltage V
11
to produce ac voltages V
23
a
, V
23
b
, V
23
c
, etc. respectively from the secondary windings
23
a
,
23
b
,
23
c
, etc. according to turn ratios respectively between the primary and secondary windings.
The magnetic amplifier
31
converts the ac voltage V
23
a
through on/off control using a reset current into an ac voltage V
31
having a pulse width associated with the reset current. The rectifier diode
32
rectifies the ac voltage V
31
to produce a pulsating voltage V
32
. The voltage V
32
has electromagnetic energy of, which is accumulated in the smoothing choke coil
34
. When the diode
32
on the rectifying side is off and the diode
33
on the commutating side is on, the electromagnetic energy is supplied to the smoothing capacitor
35
. The capacitor
35
smoothes the pulsating voltage V
32
into an output do voltage. The output section A feeds the do voltage V to the load RL.
The magnetic amplifier
31
stabilizes the dc voltage using a hysteresis characteristic. That is, the resistors
38
and
39
detects variation in the dc output voltage. The constant-voltage control circuit
37
adjusts the reset current
142
for the magnetic amplifier
31
to stabilize the dc voltage. During a period in which the amplifier
31
is off, the adjusted reset current
142
is delivered via the transistor
40
, the resistor
41
, and the diode
42
to the amplifier
31
. This resultantly controls the rising edge of a period in which the amplifier
31
is on to thereby stabilize the de output voltage.
Referring next to
FIG. 4
, description will be given of a circuit configuration of a second example of the multi-output switching power supply circuit of the prior art using a magnetic amplifier to control a constant voltage.
The multi-output switching power source circuit includes a main output section A and a plurality of subsidiary output sections B, C, etc. Among the output sections, the main output section A has a maximum output and small load variation. A switching duty ratio on the primary side is controlled by a negative feedback operation according to variation in an output voltage from the main section A. Each of the subsidiary output sections produces an output voltage. For the output voltage, the magnetic amplifier controls and produces an ac voltage having a duty ratio determined according to the output voltage from the main output section A.
The multi-output switching power supply circuit of the conventional example 2 shown in
FIG. 4
includes, on the primary side of a voltage transformer
60
, a de power source
51
, an input smoothing capacitor
52
, a starting resistor
53
, a PWM control circuit
54
, a capacitor
55
, a smoothing choke coil
56
, a rectifying diode
57
, a commutating diode
58
, and an NMOS
59
.
The transformer
60
includes a primary winding
61
and a subordinate winding
62
on the primary side and secondary windings
63
,
64
,
65
, etc. on its secondary side.
The main output section A includes a rectifying diode
71
, a commutating diode
72
, a smoothing choke coil
73
, a smooth
McGinn & Gibb PLLC
NEC Communication Systems Ltd.
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