Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-04-11
2001-09-25
Patel, Rajnikant (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S285000, C363S089000
Reexamination Certificate
active
06294903
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a non-insulating switching power supply of a step-down chopper system, particularly to a switching power supply of a step-down chopper system which requires a technology for reducing power consumption.
BACKGROUND OF THE INVENTION
FIG. 11
is a circuit diagram showing a conventional switching power supply described in JP-A-10-191625. This circuit contains a switching device
51
, a starting power supply block
63
, a control circuit
66
, a conversion circuit
68
, and an output voltage detecting circuit
67
as main elements.
The switching device
51
comprises an n-channel MOS. An input main terminal
56
is connected to the drain terminal of the switching device. The input main terminal
56
is further connected to the anode terminal of an input capacitor
57
and to the starting power supply block
63
.
The conversion circuit
68
includes a coil
52
, a regeneration diode
53
, and a capacitor
54
. The anode terminal of the regeneration diode
53
is grounded. The node between the cathode terminal of the diode
53
and the coil
52
is connected to the source terminal of the switching device
51
. The node between the other terminal of the coil
52
and the anode terminal of the output capacitor
54
is connected to the output main terminal
55
.
The control circuit
66
comprises a PWM pulse forming circuit
69
, a comparator
62
, resistors
64
and
65
, and a triangular wave forming circuit
70
. The triangular wave forming circuit
70
forms a triangular wave carrier signal at a constant frequency (e.g. 100 kHz). The PWM pulse forming circuit
69
is connected to the gate terminal of the switching device
51
. The control circuit
66
uses the voltage between both terminals of a capacitor for control circuit power supply
60
as its power supply voltage, and controls ON/OFF of the switching device
51
according to the change in the potential difference between both terminals of the capacitor
60
. The control circuit
66
also is connected to the starting power supply block
63
through a power supply switching block
61
.
The output voltage detecting circuit
67
comprises a diode
58
and a Zener diode
59
. Its terminal at the side of the Zener diode
59
is connected to the output main terminal
55
, and its terminal at the side of the diode
58
is connected to one terminal of the capacitor for control circuit power supply
60
, respectively.
This conventional switching power supply circuit is a power supply circuit of a step-down chopper system, in which a DC voltage applied to the input main terminal
56
is stepped down and outputted from the output main terminal
55
.
FIG. 12
shows current/voltage waveforms at respective parts of the switching power supply in FIG.
11
. The signs at the left of the waveforms in
FIG. 12
correspond to the signs indicated at respective parts in FIG.
11
. The power supply switching block
61
is closed so that the starting power supply block
63
is connected to the capacitor for control circuit power supply
60
until the control circuit
66
is started. When a voltage is applied to the input main terminal
56
first, a current flows from the starting power supply block
63
into the capacitor for control circuit power supply
60
through the power supply switching block
61
, so that the voltage supplied to the control circuit
66
is increased.
The control circuit
66
operates when the supplied voltage exceeds a starting voltage of the control circuit
66
. At this time, the output voltage Vout is 0 V. A triangular wave carrier signal voltage formed in the triangular wave forming circuit
70
and a voltage obtained by dividing the power supply voltage Vc of the control circuit
66
by the resistors
64
and
65
are compared by a comparator
62
, and an output signal Vg indicated in
FIG. 12
is supplied from the PWM pulse forming circuit
69
to the gate terminal of the switching device
51
. The output signal Vg is ON for a certain duration. As described below, this duration is variable depending on the voltage between both terminals of the capacitor for control circuit power supply
60
. When the output signal Vg is ON, the switching device
51
is ON, and a current Ip flowing in the switching device
51
flows into the coil
52
. Next, when the switching device
51
is turned OFF by the output signal Vg of the control circuit
66
, an electric energy accumulated in the coil
52
is supplied to the output through the regeneration diode
53
.
If the voltage at the output main terminal
55
is increased to be greater than the sum of the puncture voltage Vz of the Zener diode
59
, the forward voltage Vf of the diode
58
, and the power supply voltage Vc of the control circuit
66
(Vz+Vf+Vc), when the switching device
51
is OFF, a current Ic flows from the output main terminal
55
into the capacitor for control circuit power supply
60
through the Zener diode
59
and the diode
58
, so that information of the output voltage is fedback to the control circuit
66
. When the power supply voltage Vc of the control circuit
66
becomes high enough, the supply switching block
61
switches so that the power supply voltage is supplied from the output main terminal
55
to the control circuit
66
.
The triangular wave carrier signal voltage formed in the triangular wave forming circuit
70
and the voltage obtained by dividing the power supply voltage Vc of the control circuit
66
by the resistors
64
and
65
(or the power supply voltage Vc) are compared by the comparator
62
, and on-duty of the switching device
51
in one triangular wave (1 carrier) is determined by the PWM pulse forming circuit
69
, and then the pulse duration to be inputted to the switching device
51
is determined.
Thus, in the conventional switching power supply, by variably controlling the duty of the switching device
51
, precision of the voltage at the output main terminal
55
is improved, and the output voltage Vout is kept constant.
In the conventional switching power supply circuit, pulse duration control system (PWM system) is used to improve the precision of the output voltage. Generally, the switching frequency fc is constant in this circuit, which is commonly 100 to 200 kHz. The PWM pulse forming circuit
69
determines the on-duty &dgr; of the switching device
51
, and allows it to operate at a constant frequency with minimum on-duty at the time of a light load.
However, when the above-mentioned conventional technology is used, the following problems occur. First, power is supplied to or consumed by the output main terminal uselessly because the switching device switches independently of the lightness or heaviness of the load. Second, switching loss is increased due to the relatively high switching frequency fc. In recent years, energy saving has been required from the point of energy or global environmental protection. Thus, a further reduction in power consumption and improvement in efficiency have been required in power supplies (primarily switching power supplies). However, because of the above two problems, a further reduction in power consumption and improvement in efficiency have been difficult to attain in a conventional control system.
SUMMARY OF THE INVENTION
The present invention intends to solve the above-mentioned two problems. It is an object of the present invention to provide a switching power supply with reduced power consumption and improved efficiency.
The switching power supply of the present invention includes: a switching device having an input terminal, an output terminal and a control terminal, which turns ON/OFF a first DC voltage supplied to the input terminal through an input main terminal, and outputs it to the output terminal; an input smoothing capacitor connected to the input main terminal; a starting power supply block connected to the input main terminal; a control circuit comprising an output signal terminal connected to the control terminal of the switching device, a power supply terminal connected to the starting power supply bl
Hachiya Yoshiaki
Mori Yoshihiro
Yamanishi Yuji
Yamashita Tetsuji
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Patel Rajnikant
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