Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2002-12-04
2004-11-02
Sherry, Michael (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S282000
Reexamination Certificate
active
06812682
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a step-down chopper-type switching power supply unit of a non-insulated type, in which the input side and the output side are not electrically insulated from each other. More particularly, the present invention relates to a switching power supply unit with which the power consumption can be reduced in a light-load operation and in a stand-by operation, and also to a semiconductor device for such a switching power supply.
A conventional switching power supply unit will be described with reference to the drawings.
FIG. 6
illustrates a schematic circuit configuration of a non-insulated step-down switching power supply unit, and
FIG. 7
illustrates current/voltage waveforms during the operation of the switching power supply unit.
The general configuration and the operation of the switching power supply unit illustrated in
FIG. 6
will now be described.
First, before the start-up of a control circuit
100
, a switch
101
in the control circuit
100
is in a closed state, whereby an internal circuit current supply circuit
102
and a control circuit power supply capacitor
103
are connected to each other.
When an input voltage VIN is applied to a main input terminal
104
, a control current flows from the internal circuit current supply circuit
102
via the switch
101
to the control circuit power supply capacitor
103
, thereby increasing a power supply voltage Vcc of the control circuit
100
. When the power supply voltage Vcc reaches the start-up voltage of the control circuit
100
, a start-up/shut-down circuit
105
starts operating and the control circuit
100
starts up.
When the start-up/shut-down circuit
105
starts operating, the switch
101
is opened, thereby stopping the current supply from the internal circuit current supply circuit
102
to the control circuit power supply capacitor
103
. Thereafter, a control current is supplied to the control circuit
100
from the control circuit power supply capacitor
103
. At this point, an output voltage VOUT at a main output terminal
106
is 0 V.
Then, the control circuit
100
starts operating, thereby starting the switching (i.e., ON/OFF) operation of a switching device
107
, which is an N-channel MOSFET. When the switching device
107
is ON, a drain current IDS flows from the main input terminal
104
via the switching device
107
into a coil
110
a
of a voltage conversion circuit
110
. Then, when the switching device
107
is turned OFF, the electric energy accumulated in the coil
110
a
is supplied to the main output terminal
106
via a regenerative diode
110
b
, thereby increasing the output voltage VOUT at the main output terminal
106
.
When the switching device
107
is turned OFF, with the output voltage VOUT having increased to be greater than the sum of a breakdown voltage Vz of a Zener diode
111
, which is an output voltage detection circuit, a forward voltage Vf of a diode
112
, which is a feedback circuit, and a power supply voltage Vcc of the control circuit
100
, i.e., Vz+Vf+Vcc, a current flows into the control circuit power supply capacitor
103
from the main output terminal
106
via the Zener diode
111
and the diode
112
. As a result, the voltage value of the output voltage VOUT is fed back to the control circuit
100
, and the power supply voltage Vcc is supplied from the main output terminal
106
to the control circuit
100
.
When the power supply voltage Vcc is increased by the voltage supplied from the main output terminal
106
to the control circuit
100
, and the power supply voltage Vcc reaches a predetermined value, a switching element
114
is turned ON by a shunt regulator
113
, and a PWM control current I
PWM
is supplied from the control circuit power supply capacitor
103
to a resistor
115
, whereby a voltage is applied across the resistor
115
.
The on-duty ratio of the switching device
107
is determined by the voltage across the resistor
115
and the output signal of a comparator
117
, which receives a triangular-wave signal from an oscillator
116
, whereby the pulse width to be applied to the switching device
107
is determined.
As described above, the conventional switching power supply unit variably controls the duty ratio of the switching device
107
, thereby controlling the output voltage VOUT at the main output terminal
106
to be a predetermined value.
As described above, the conventional switching power supply unit employs a pulse width modulation (PWM) method for improving the precision of the output voltage VOUT. Typically, a switching frequency fc in the PWM method is set to a constant value of about 100 kHz to 200 kHz, for example. Moreover, the comparator
117
determines the on-duty ratio &dgr; of the switching device
107
as described above, and operates with a constant frequency and with the minimum on-duty ratio during a light-load operation, including a stand-by operation, as illustrated in FIG.
7
.
In recent years, there is a demand for reducing the amount of energy use, i.e., energy conservation, from an environmental point of view. Thus, there is a demand for further reduction in the power consumption and further improvement in the efficiency for power supply units, particularly for switching power supply units.
However, in the conventional switching power supply unit, the switching device
107
is in the switching operation regardless of the magnitude of the load. Therefore, power is constantly wasted while being supplied to, and consumed by, the main output terminal
106
. Moreover, there is an increased switching loss because the switching frequency fc is relatively high, i.e., 100 kHz or more.
SUMMARY OF THE INVENTION
The present invention has been made in order to solve these problems in the prior art, and has an object to reduce the power consumption and increase the efficiency of a switching power supply unit or a semiconductor device for a switching power supply.
In order to achieve the object set forth above, the present invention provides a switching power supply unit or a semiconductor device for a switching power supply, in which the application of a switching signal to a switching element is stopped depending on a power supply voltage of a control circuit that is detected by an output voltage detection circuit and fed back to the control circuit.
Specifically, a switching power supply unit of the present invention includes: a smoothing input capacitor for receiving a first DC voltage; a switching element for receiving the first DC voltage; a control circuit for controlling an operation of the switching element; a control circuit power supply capacitor provided between an output terminal of the switching element and a reference voltage terminal of the control circuit; a voltage conversion circuit for receiving an output signal from the switching element and converting the first DC voltage into a second DC voltage whose absolute voltage value is smaller than that of the first DC voltage; an output voltage detection circuit provided on an output side; and a feedback circuit for receiving a detection signal from the output voltage detection circuit and feeding back the received detection signal to the control circuit, the control circuit including: a regulator provided between an input terminal of the switching element and the reference voltage terminal for holding a voltage at the reference voltage terminal at a predetermined value; an output load detection circuit for receiving a feedback signal from the feedback circuit; an error amplifier for producing an error voltage signal that represents a difference between an output signal from the output load detection circuit and a reference voltage; an element current detection circuit for detecting a current flowing through the switching element with an output signal of the error amplifier being a reference; and a light load detection circuit for stopping a switching operation of the switching element when the error voltage signal is lower than a lower limit voltage while resuming the switching operation
Laxton Gary L.
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
Sherry Michael
LandOfFree
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