JPH05260727A - Step-down power supply equipment - Google Patents

Abstract

PURPOSE:To supply power with high efficiency and high accuracy from a low output to a high output by changing over the step-down means of DC input voltage between a chopper step-down means and a dropper step-down means in response to a signal from a current detecting means. CONSTITUTION:A resistor R12 is installed between an input terminal 2 and an output terminal 4, voltage-divider resistors R1, R2, R3 are combined, and voltage V1 and V2 for detecting output currents il is obtained. A changeover switch SW is brought to the state of a-c connection by an output from a comparator CP2 when voltage V2 is lower than reference voltage Vref2, when output currents 11 is a fixed value or less, and the output from the comparator CP2 is changed and the changeover switch is changed over to the state of a-b connection when output currents 11 exceed the fixed value and voltage V2 is made higher than reference voltage Vref2. Accordingly, a transistor Q1 is controlled through a drop system when output currents 11 are reduced and through a step-down chopper system when output currents are increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a step-down power supply device for obtaining a constant voltage DC output by stepping down a DC input voltage.

[0002]

2. Description of the Related Art A dropper method and a chopper method are known as methods for obtaining a constant voltage DC output by stepping down a DC input voltage. The dropper method is a method of operating a power transistor as an equivalent variable resistor to step down an input voltage and obtain a constant voltage output. This method has the advantages that the output voltage accuracy is good and the ripple spike voltage is small. The chopper method is a method in which a transistor is switched at high speed to step down an input voltage to obtain a constant voltage output. This method has the advantages of high efficiency, low loss, and low price.

[0003]

The dropper method described above has a large amount of heat generation and low efficiency. Therefore, it has a drawback that it is not suitable for high output. In addition, the chopper method has a problem that the ripple spike voltage becomes large. The present invention is intended to solve the above problems. That is, it is an object of the present invention to provide a step-down power supply device that can supply from low output to high output with high efficiency and high accuracy.

[0004]

A step-down power supply device according to the present invention comprises a dropper step-down means for stepping down a DC input voltage by a dropper method to obtain a constant voltage DC output, and a step-down voltage for a DC input voltage by a chopper method. A chopper step-down means for obtaining a DC output of voltage, a current detection means for detecting an output current, and a DC input voltage step-down means for switching between a chopper step-down means and a dropper step-down means in response to a signal from the current detection means. And a step-down power supply device including switching means.

[0005]

In accordance with the output current detected by the current detecting means, the switching means is the method of stepping down the DC input voltage, whichever of the dropper stepping means and the chopper stepping means is the most suitable method. Select.

[0006]

EXAMPLES Examples of the present invention will be described below. Figure 1
1 shows a circuit configuration of a step-down power supply device according to this embodiment. Figure 1
In the circuit of, the DC voltage Vin input from the input terminals 1 and 2 passes through the transistor Q1 and the chopper method,
Alternatively, the voltage is stepped down by one of the dropper methods and is output from the output terminals 3 and 4 as a stable DC voltage Vout.

The input terminal 1 is connected to the positive electrode of the electrolytic capacitor C1, the power supply terminal of the reference voltage generator reg, and the emitter electrode of the transistor Q1 (hereinafter, "connection" is an electrical connection). ). A reference voltage Vref1 is output from the reference voltage generator reg, the output terminal of which is connected to the input terminal 2 via the resistors R1, R2 and R3 connected in series, and the resistors R4 and R5 connected in series. To output terminal 4 via. Output terminal 4
Is set to the ground potential, the reference voltage Vref1 is divided by the resistors R4 and R5 as described above,
The reference voltage Vref2, which is lower than ef1, is supplied.

The emitter electrode of the transistor Q1 is a resistor
It is connected to the base electrode via R6, and the base electrode is connected to the collector electrode of the transistor Q2 via the resistor R7. The emitter electrode of transistor Q2 is
The base electrode is connected to the output terminal 4, the base electrode is connected to the emitter electrode via the resistor R8, and is also connected to the a terminal of the changeover switch SW via the resistor R9. The transistor Q2 is a driving transistor for the transistor Q1. That is, the transistor Q1 is operated in a chopper or a dropper according to a control signal sent through the changeover switch SW as described later.

The collector electrode of the transistor Q1 is connected to the output terminal 3 via the DC reactor L1. A resistor R10 and a resistor R11 are connected in series between the output terminals 3 and 4, whereby the output voltage Vout is divided and a voltage V3 for detecting the output voltage is generated. Further, a resistor R12 is provided between the input terminal 2 and the output terminal 4, and as will be described later, the resistors R1, R2, and
In combination with R3, the voltage V1 for output current detection,
A voltage V2 having a lower potential than V1 is generated. A freewheel diode D1 is provided between the collector electrode of the transistor Q1 and the input terminal 2.

The non-inverting input terminal of the current control amplifier A1 is connected to the resistors R4 and R5 via the resistor R13, whereby the reference voltage Vref2 is input. Further, the inverting input terminal is connected to the resistors R1 and R2 via the resistor R14, so that the output current detection voltage V1 is input. The output terminal of the current control amplifier A1 is a resistor.
It is connected to the inverting input terminal via R15 and capacitor C3, is also connected to the non-inverting input terminal of comparator CP1 via diode D2 and resistor R20, and is also connected to the c terminal of changeover switch SW via diode D2. Is also connected. In this way, the current control amplifier A1
The voltage corresponding to the difference between ef2 and voltage V1 is output. That is,
Output current is detected.

The inverting input terminal of the voltage control amplifier A2 is connected to the resistors R4 and R5 via the resistor R16, whereby the reference voltage Vref2 is input. Further, the non-inverting input terminal is connected to the resistors R10 and R11, so that the voltage V3 for detecting the output voltage is input. Also,
The output terminal of the voltage control amplifier A2 is connected to the inverting input terminal via the resistor R17 and the capacitor C4, and the comparator CP via the diode D3 and the resistor R20.
It is connected to the non-inverting input terminal of 1 and is also connected to the c terminal of the changeover switch SW through the diode D3. In this way, the voltage control amplifier A2
Output the voltage corresponding to the difference from V3. That is, the output voltage is detected.

The inverting input terminal of the comparator CP1 is connected to the output terminal of the triangular wave generator OSC via the resistor R21, and the output terminal of the comparator CP1 is a changeover switch.
Connected to b terminal of SW. In addition, the current control amplifier A1
The current detection output from the voltage control amplifier A2 and the voltage detection output from the voltage control amplifier A2 are OR-coupled via the diodes D2 and D3, respectively, as described above. It is input as a signal to the non-inverting input terminal of comparator CP1.

The comparator CP1 compares the oscillating triangular wave from the triangular wave generator OSC with the PWM command signal, performs pulse width modulation, and outputs a pulse width P inversely proportional to the PWM command signal.
Output WM signal. The PWM command signal is also input to the c terminal of the changeover switch SW as described above. Therefore, at the a terminal of the changeover switch SW, either the PWM command signal or the PWM signal appears due to the changeover operation of the changeover switch SW and is input to the base of the drive transistor Q2 as a control signal.

The changeover control terminal of the changeover switch SW is connected to the output terminal of the comparator CP2. comparator
The inverting input terminal of CP2 is connected to the resistor R2 and the resistor R3, whereby the voltage V2 for detecting the output current is input. In addition, the non-inverting input terminal is connected to the output terminal through the resistor R18, and is also connected through the resistor R19.
It is connected to R4 and R5, which allows the reference voltage Vref
2 is entered. In this way, the comparator CP2 compares the reference voltage Vref2 with the voltage V2, and outputs a high potential when Vref2> V2 and a low potential when Vref2 <V2, respectively.
Change the connection state of the selector switch SW.

Here, the output current i1 and the voltage V1 and
Explain the relationship with V2. As shown in the figure, assuming that the output current through the resistor R12 is i1 and the current through the resistors R1, R2, and R3 is i2, the voltages V1 and V2 are V1 = Vref1−R1 × i2 V2 = Vref1− ( It is given as R1 + R2) × i2. On the other hand, from Vref1 = (R1 + R2 + R3 + R12) × i2−R12 × i1, i2 = (Vref1 + R12 × i1) / (R1 + R2 + R3 + R12), so the above voltages V1 and V2 Is V1 = Vref1−R1 × (Vref1 + R12 × i1) / (R1 + R2 + R3 + R12) V2 = Vref1− (R1 + R2) × (Vref1 + R12 × i1) / (R1 + R2 + R3 + Both are given as a function of the output current i1 like R12).

With the above arrangement, the apparatus of this embodiment
When the voltage V2 is lower than the reference voltage Vref2, that is, the output current
When i1 is less than a predetermined value, the output of the comparator CP2 causes the changeover switch SW to be connected to the ac terminal. When the output current i1 exceeds the predetermined value and the voltage V2 becomes higher than the reference voltage Vref2, the output of the comparator CP2 is changed to switch to the ab terminal connection state. Thus, when the output current is less than the predetermined value, the comparator CP1 is bypassed, and the PWM command signal is directly input to the base of the drive transistor Q2 as a control signal. When the output current exceeds the predetermined value and becomes large, the PWM signal from the comparator CP1 is input to the base of the drive transistor Q2 as a control signal.

When the PWM command signal is directly input to the base of the drive transistor Q2, a collector current corresponding to the PWM command signal flows, and the collector current becomes a base current of the transistor Q1 to operate the transistor Q1 in a dropper system. As described above, when the output current is small, the output voltage with high accuracy and no switching noise is obtained by the dropper method.

Further, when the PWM signal which is the pulse output of the comparator CP1 is input as the control signal to the base of the driving transistor Q2, the transistor Q1 is turned on / off according to the pulse width, and the step-down chopper operation is performed. Freewheel diode D1, DC reactor L1,
A smooth DC output is produced by the smoothing electrolytic capacitor C2. Thus, when the output current becomes larger than the set predetermined value, the constant voltage output is obtained with high efficiency by the chopper method.

[0019]

As described above in detail, the step-down power supply device according to the present invention detects the output current and, based on the detection result, selects the DC input voltage step-down method from the chopper method and the dropper method. It is a device that switches to the optimum method. Therefore, from low output to high output can be supplied with high efficiency and high accuracy.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a step-down power supply device according to an embodiment.

[Explanation of symbols] 1, 2 input terminals, 3, 4 output terminals, reg reference voltage generator, SW changeover switch, L1 DC reactor, OSC
Triangular wave oscillator,

Claims (2)

[Claims] 1. A dropper step-down means for stepping down a DC input voltage by a dropper method to obtain a constant voltage DC output, and a chopper step-down means for stepping down a DC input voltage by a chopper method to obtain a constant voltage DC output. A step-down power supply device comprising: a current detection unit that detects a current; and a switching unit that responds to a signal from the current detection unit and that switches the step-down unit for the DC input voltage between a chopper step-down unit and a dropper step-down unit. 2. The step-down power supply device according to claim 1, wherein the switching means executes switching from the chopper step-down means to the dropper step-down means when the output current becomes a predetermined value or less.