JP2002300771A - Dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC-DC converter using a ΔΣ modulator, which can stably be controlled by switching using high frequency and whose output voltage is stable. SOLUTION: The ΔΣ modulator is constituted of an adder, an integrator and a quantizer. The integrator has a mechanism to adjust a gain. The ΔΣmodulator which is resistant to generating oscillation particularly by high sampling frequencies and whose output voltage is stable can be provided by controlling the gain of the integrator to operate a comparator in high speed without saturating the output voltage amplitude of the integrator by receiving a signal from a current flowing in the DC-DC converter or a voltage in the converter or the converter output voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a D
In a C-DC converter, the present invention relates to a DC-DC converter capable of adjusting a gain of an integrator in a ΔΣ modulator according to an output of the DC-DC converter.

[0002]

2. Description of the Related Art ΔΣ modulation is a modulation method in which an input signal is integrated, the integrated value is compared with a reference voltage, quantization is performed, and the output is fed back to a modulator input. FIG. 2 is a block diagram of the first-order ΔΣ modulator. Using this modulation method, switching elements are switched and D
A C-DC converter could be made.

The switching frequency is constant in a DC-DC converter using a pulse width modulation method (PWM), which has been generally used in the past, while the DC-DC converter using ΔΣ modulation has a converter output. Since the switching frequency changes accordingly, there is an advantage that the switching loss can be reduced at a light load, and thus, attention has been paid.

FIG. 3 shows a step-down chopper DC-DC converter using .DELTA..SIGMA. Modulation, which is an example of a conventional system, in which a converter output voltage is compared with a reference voltage, and an error amplified signal voltage of the comparison voltage is converted into a .DELTA..SIGMA. Σ modulation is performed as an input voltage, and the switching element is switched by the modulator output signal, and the switching output is input to the smoothing circuit, whereby a constant voltage output can be obtained.

A .DELTA..SIGMA. Modulator has at least one integrator. FIG. 4 shows an example of an integrator using an operational amplifier. Frequency component of the signal input to the
When it is within the band of the operational amplifier, it is determined only by the resistance value and the capacitance value regardless of the gain of the operational amplifier, and is proportional to the reciprocal of the product of the resistance value and the capacitance value.

When ΔΣ modulation is used in a DC-DC converter, it is necessary to prevent the output of the integrator in the ΔΣ modulator from being saturated. If the output of the integrator is saturated, accurate modulation is performed. The constant voltage control of the DC-DC converter becomes unstable, and the output voltage of the DC-DC converter cannot be kept constant.

Therefore, in the conventional method, the gain of the integrator is determined so that the output of the integrator is not saturated.
Since the amplitude of the integrator increases when the output current of the DC converter is small, it is necessary to set the gain low so that the integrator does not saturate at that time.

When the output current of the DC-DC converter is large, the amplitude of the integrator becomes small. However, when the output current is small, the gain of the integrator is set low so that the output of the integrator is not saturated. There was a problem that the amplitude of the output of the device became a small value of the order of mV or less.

The quantizer of the ΔΣ modulator requires a comparator for comparing the output of the integrator with a reference voltage, and the difference between two voltages to be compared in the comparator is called an overdrive amount. Is large, the output voltage of the comparator changes quickly and high-speed operation becomes possible. Conversely, if the overdrive amount is small, high-speed operation cannot be performed.

In general, the minimum amount of overdrive required for the comparator to operate at high speed is several tens mV to 100 m.
V. In order to increase the overdrive amount and operate the comparator at high speed, the gain of the integrator must be increased.

However, in the conventional method, the gain of the integrator is fixed to be small when the amplitude of the integrator output voltage is the largest in order to prevent the integrator output saturation.
When the output current of the converter is large and the output voltage amplitude of the integrator is small, a sufficient overdrive amount cannot be given to the comparator, and the comparator cannot operate at high speed.

Since the operation speed of the comparator is low, the feedback loop of the DC-DC converter is low. In particular, when the DC-DC converter is switched at a high frequency,
There was a problem of oscillation.

That is, in the conventional method, if the gain of the integrator is fixed small so that the output of the integrator is not saturated, DC-DC
If the converter oscillates and the gain of the integrator is fixed to a large value so that the DC-DC converter does not oscillate, there is a trade-off that the output of the integrator is saturated and the output voltage becomes unstable.

In the conventional method, the gain of the integrator has to be small enough not to saturate the output of the integrator and large enough not to oscillate the converter due to this trade-off, making the design difficult. In addition, it has been difficult to realize a converter that operates at high speed without the integrator being saturated.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art.
Provided is a DC-DC converter using a modulator, which can perform stable control by high-frequency switching and has a stable output voltage without oscillation even at a high sampling frequency.

[0016]

According to the present invention, an analog input signal or a multi-bit digital signal is input to a ΔΣ modulator, and a switching element is switched by the modulated signal. D
The C-DC converter is characterized in that the gain of the integrator in the ΔΣ modulator is adjusted according to the state of the converter.

The ΔΣ modulator includes at least one adder, an integrator, and a quantizer, has a feedback path from the output of the ΔΣ modulator to at least one input of the adder, and is connected to the output of the adder. And at least one of the integrator outputs is connected to a quantizer.

The quantizer performs sampling on a discrete time signal. The quantizer receives an output signal of the quantizer and is connected to an input of a gate driver circuit for supplying a current and a voltage sufficient to drive a power switch element. I have.

A circuit for adjusting a gain is added to at least one integrator, and a current flowing in the DC-DC converter, a voltage in the converter, or a converter output voltage is detected. For example, by controlling the resistance value and / or the capacitance value shown in FIG. 4, the gain of the integrator can be adjusted.

Further, the output voltage of the integrator is directly detected, and the gain of the integrator is reduced according to the detected signal so that the output voltage amplitude of the integrator is not saturated, and the comparator operates at high speed. It is possible to adjust the gain of the integrator to a range as large as possible.

Since the gain of the integrator can be adjusted to a range where the output voltage amplitude does not saturate and the comparator can operate at high speed, increasing the gain when the amplitude of the integrator is small increases the over-gain applied to the comparator. The drive amount can be increased, the feedback loop becomes faster, and the constant voltage control of the converter becomes stable.

Conversely, by reducing the gain when the amplitude of the integrator is large, saturation of the output of the integrator is prevented, and stable constant voltage control becomes possible.

Further, even if the gain of the integrator changes, the change is corrected by the feedback from the output of the ΔΣ modulator, so that the operation of the modulator does not deteriorate without deteriorating the input / output linearity of the modulator. It will not be stable.

That is, according to the present invention, it is possible to adjust the gain of the integrator to a range in which the output voltage amplitude is not saturated and the comparator can operate at high speed with respect to the operating state of the DC-DC converter, and the oscillation can be achieved. It is possible to provide a stable DC-DC converter having no output voltage fluctuation.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the DC-DC converter according to the present invention will be described below with reference to the accompanying drawings. In the description of the drawings, the same members are given the same reference numerals,
Duplicate description will be omitted.

FIG. 1 shows an embodiment of the present invention.
FIG. 2 is a block diagram showing a step-down chopper DC-DC converter using Σ modulation, in which an output voltage of a detection circuit 4 is compared with a reference voltage 9, and an output voltage of an input error amplifier 8, which is a comparison voltage, is compared with a Δ の modulator 10. The ΔΣ modulation is performed as an input voltage of the adder 11, the output signal of the ΔΣ modulator 10 is passed through a gate driver circuit 17 to switch the switching element 2, and the switching output is input to the rectifying / smoothing circuit 3. You can get output.

The output of the ΔΣ modulator 10 is fed back to the adder 11 through the D / A converter 18 and at the same time, the integrator 12 has a gain control circuit 15 for adjusting the gain. The signal detected from the detection circuit 6 is amplified by the control error amplifier 13, and the amplified signal is input to the gain adjustment circuit 15, and the gain control circuit 15 adjusts the gain of the integrator 12 according to the signal. It is possible to

FIG. 5 shows a specific example of the embodiment of the present invention. In this embodiment, the output voltage of the detection circuit 6 is compared with the reference voltage 9, the output signal of the control error amplifier 13 is input to the comparator 24, and the switch element 23 in the integrator 12 including the operational amplifier 22 is controlled. Therefore, when the converter output current is large, the switch element 23 is turned off,
A control signal is output from the comparator 24 so that the switch element 23 is turned on when the converter output current is small.

As a result, the gain of the integrator 12 can be adjusted, and the gain of the integrator 12 is reduced so that the output voltage amplitude of the integrator 12 does not saturate and increased so that the comparator 24 can operate at high speed. It is possible to adjust to a range.

FIG. 6 shows an embodiment in which the output is detected and controlled in the integrator according to the present invention. FIG. 6 is a block diagram of the integrator 12 in the ΔΣ modulator 10. The output of the integrator 12 is rectified by an absolute value circuit 26, the rectified signal is averaged by an averaging circuit 25, the averaged signal is compared with a reference voltage 9 by an adjustment error amplifier 28, and the compared signal is amplified. I do.

By controlling the transistor 27 at the input of the integrator 12 with the signal amplified by the adjustment error amplifier 28, the resistance 6 of the integrator can be adjusted. As a result, the output voltage of the integrator 12 can be adjusted. The gain of the integrator 12 can be adjusted so that the amplitude becomes constant.

[0032]

In the DC-DC converter using the ΔΣ modulator, the output voltage amplitude of the integrator is optimized by adjusting the gain of the integrator so that the output voltage amplitude is not saturated and the comparator can operate at high speed. , Which enables stable constant voltage output without oscillation even at a particularly high sampling frequency
A C-DC converter can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram of an example illustrating an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional first-order ΔΣ modulator.

FIG. 3 is a block diagram of a conventional DC-DC converter.

FIG. 4 is a diagram showing a conventional integrator.

FIG. 5 is a block diagram of a specific embodiment of the present invention.

FIG. 6 is a block diagram of an integrator including a detection circuit in an integrator in a converter according to an embodiment of the present invention.

[Explanation of symbols]

 1. Input voltage 2. Power switch element 3. Rectifying smoothing circuit 4. Detection circuit 5. Capacitor 6. Resistor 7. Load 8. Input error amplifier 9. Reference voltage 10. ΔΣ modulator 11. Adder 12. Integrator 13 Control error amplifier 14. Quantizer 15. Gain control circuit 16. Sampling clock 17. Gate driver circuit 18. D / A converter 19. Input signal 20. Output signal 21. ΔΣ modulator by conventional method 22. Operational amplifier 23.Switch element 24.Comparator 25.Average circuit 26.Absolute value circuit 27.Transistor 28.Adjustment error amplifier

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[Procedure amendment]

[Submission Date] February 25, 2002 (2002.2.2)
5)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Fig. 4

[Correction method] Change

[Correction contents]

FIG. 4

[Procedure amendment 3]

[Document name to be amended] Drawing

[Correction target item name] Fig. 6

[Correction method] Change

[Correction contents]

FIG. 6

Claims (2)

[Claims] An analog signal is ΔΣ modulated by a ΔΣ modulator,
In a DC-DC converter including a ΔΣ modulator that switches a switching element in response to the signal,
At least one integrator in the ΔΣ modulator includes a means for changing a gain, and includes a detection circuit for detecting a current flowing in the DC-DC converter or a voltage in the converter or a converter output voltage. A DC-DC converter having a function of adjusting the gain of the integrator so that the output of the integrator becomes a desired voltage in accordance with the signal of (1). 2. The DC-DC converter according to claim 1, wherein the detection circuit detects an output voltage of at least one integrator having a gain adjustment function, and adjusts a gain of the integrator having the gain adjustment function. A DC-DC converter for outputting a signal.