Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2003-09-09
2004-08-31
Berhane, Adolf (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
Reexamination Certificate
active
06784648
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a DC stabilized power supply, and more particularly to a switching signal generator for use in a switching power supply employing a &Dgr; &Sgr;-modulator, in which a switching signal for a power switch element is fed back from a gate driver circuit output to the modulator, and to a DC-DC converter utilizing &Dgr; &Sgr;-modulation in which the gain of an integrator inside a &Dgr; &Sgr;-modulator can be adjusted in accordance with output of the DC-DC converter.
2. Description of the Related Art
Description will first be made in connection with the switching signal generator for the switching power supply.
A conventional PWM (pulse-width modulation) switching signal generator modulates an input signal by varying its pulse width. In other words, as shown in the block diagram of a PWM switching signal generator in
FIG. 5
, a PWM oscillator
18
generates a gate signal from an input signal
1
, which gate signal is amplified by a gate driver circuit
6
to drive a power switch element
7
. In the PWM system, the distortion produced at the gate driver circuit
6
has been unable to be corrected.
A block diagram of a conventional PWM switching signal generator applied to a step-down chopper is shown in FIG.
6
. The voltage applied to a load and a reference voltage
17
are compared, and its result is inputted into a PWM oscillator
18
so that a power switch element
7
is controlled by the output of the PWM oscillator
18
. In this generator, however, because there is provided no direct feedback path from the gate driver circuit
6
, the distortion generated at the gate driver circuit
6
has been impossible to correct.
Another conventional switching signal generator has been known in which, as shown in
FIG. 7
, a &Dgr; &Sgr;-modulator
5
is used to output a gate drive signal to and drive a power switch element
7
. In the &Dgr; &Sgr;-modulator
5
, an input signal is integrated by an integrator
3
instead of using the PWM oscillator and quantized to provide a one-bit output signal. With this generator, however, because the feedback is performed upstream of a gate driver, the distortion produced at the gate driver circuit
6
may not be corrected.
A block diagram of a conventional &Dgr; &Sgr; switching signal generator applied to a step-down chopper is shown in FIG.
8
. The voltage applied to a load and a reference voltage
17
are compared, and its result is inputted into a &Dgr; &Sgr;-modulator
5
so that a power switch element
7
is controlled by the output of the &Dgr; &Sgr;-modulator
5
. In this generator, however, because there is provided no direct feedback path from the gate driver circuit
6
, the distortion generated at the gate driver circuit
6
has been impossible to correct.
As a result, because distortion has not been removed from the gate driver circuit
6
which directly drives the power switch element
7
, the linearity of the &Dgr; &Sgr;-modulator has been impaired.
Due to the distortion produced at the gate driver circuit both in the conventional PWM system and &Dgr; &Sgr; system, there is caused an error between, in the PWM system, the output signal of the PWM oscillator and the gate driver output signal and, in the &Dgr; &Sgr; system, between the output signal of the &Dgr; &Sgr;-modulator and the gate driver output signal. Thus, when these conventional switching signal generators are used for controlling a switching power supply, especially when operated at a high frequency, there will be obtained only a small phase margin, resulting in unstable control.
Furthermore, the addition of a phase correction circuit, which is necessary to prevent oscillation, increases the number of parts and thus the cost. In addition, with these conventional generators, in order for an optimum circuit to be designed, an experiment with an actual circuit used has been conducted in many cases, resulting in stable circuit design being made difficult and increasing in development time.
Another method has been known in which the linearity is improved by inputting an analog signal and feeding back the output signal of a power switch element, as in a switching amplifier utilizing &Dgr; &Sgr; modulation proposed in Japanese Patent Application Laid-Open Specification No. 2000-307359.
FIG. 9
is a block diagram of a conventional &Dgr; &Sgr;-modulation system in which the output signal of a power switch element is fed back. This conventional method, however, has the following drawbacks when used for controlling a switching power supply.
If the output current of a switching power supply is small, there will occur a discontinuity region in which the current flowing through an inductance located in a power supply circuit becomes discontinuous. If in this discontinuity region the current flowing through the inductance becomes zero, an oscillation is caused by a capacity component and an inductance component inside the power supply circuit.
As shown in
FIG. 9
, with the method of feeding back the output signal of a power switch element to a &Dgr; &Sgr;-modulator, the noise caused by this oscillation is also fed back, thereby considerably increasing the number of switchings of the &Dgr; &Sgr;-modulation output. Consequently, an increase is made in the switching loss, and a reduction is made in the power supply efficiency.
In other words, with a conventional switching signal generator, because the distortion produced at the gate driver is difficult to remove, an impaired linearity of direct-current transmission characteristics results, which in turn results in a small phase margin, thereby readily giving rise to oscillation.
With the conventional &Dgr; &Sgr;-modulation-utilizing method in which the feedback path extends from downstream of the power switch element to improve the linearity, a reduction is made in the power supply efficiency due to the noise caused by the current discontinuity.
Description will now be made in connection with the DC-DC converter utilizing the &Dgr; &Sgr;-modulation.
&Dgr; &Sgr;-modulation is a modulation system in which an input signal is integrated, the integrated value is compared with a reference voltage to perform quantization, and its output is fed back to a modulator input. Shown in
FIG. 13
is a block diagram of a primary &Dgr; &Sgr;-modulator. By using this modulation system, switching of a switching element can be performed to make a DC-DC converter.
With a conventionally widely-used DC-DC converter employing a pulse width modulation system (PWM), the switching frequency is constant, whereas with a DC-DC converter utilizing &Dgr; &Sgr;-modulation, the switching frequency varies responsive to a converter output. Thus, the latter has an advantage that a reduction may be made in the switching loss under light load, and has attracted attention.
Shown in
FIG. 14
is one example of a conventional step-down chopper DC-DC converter utilizing &Dgr; &Sgr;-modulation in which, comparison is made between a converter output voltage and a reference voltage to &Dgr; &Sgr;-modulate an error-amplified signal voltage of the compared voltages as an input voltage of the &Dgr; &Sgr;-modulator, switching of a switching element is made by the output signal of the modulator, and the switching output is inputted into a smoothing circuit to obtain a constant voltage output.
The &Dgr; &Sgr;-modulator has at least one integrator, and shown in
FIG. 15
is one example of an integrator employing an operational amplifier. The gain that represents the gradient of variation of the output voltage relative to the input voltage of the integrator, is determined, if the frequency component of the signal inputted into the integrator is within the operational amplifier band, only by the value of resistance and the capacitance value irrespective of the gain of the operational amplifier, and is proportional to the inverse of the product of the resistance value and the capacitance value.
Where &Dgr; &Sgr;-modulation is employed in a DC-DC converter, care must be taken so as not to saturate the output of an
Mitamura Atsushi
Ono Hideyuki
Berhane Adolf
Nixon & Vanderhye P.C.
Shindengen Electric Manufacturing Co. Ltd.
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