JP2000069752A - Power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a power supply device which can reduce the power loss as a whole and can improve the power conversion efficiency. SOLUTION: A DC-DC conversion circuit 1 converts the DC voltage Vin of a DC power supply E into a required voltage and supplies the voltages to the load 2. A control circuit 3 controls the on/off of the transistor Tr1 of the DC-DC conversion circuit 1 to control the output of the DC-DC conversion circuit 1. A step-up/step-down chopper circuit 4 stabilizes a voltage generated in the snubber circuit 5 of the DC-DC conversion circuit 1 and supplies the stabilized voltage to the control circuit 3. A driving frequency control circuit 7 detects the DC voltage Vin of the DC power supply E and reduces the driving frequency of the transistors Tr2 and Tr3 of the step-up/step-down chopper circuit 4 in accordance with the increase of the DC voltage Vin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply.

[0002]

2. Description of the Related Art As shown in FIG. 5, a power supply device of this type includes a DC power supply E and a DC voltage of the DC power supply E, which is switched by a switching element (not shown) to a desired DC voltage. DC converted and supplied to load 2-
A DC conversion circuit 1; a control circuit 3 for controlling the switching elements of the DC-DC conversion circuit 1 by pulse width modulation (PWM) to control the output of the DC-DC conversion circuit 1;
And a power supply circuit 4 which supplies power to the control circuit 3 from the power supply.

The operating voltage of the control circuit 3 is usually 6V to 15V
Since the voltage is as low as possible and the current consumption is small, as the power supply circuit 4, a dropper circuit including a transistor or a zener diode or a step-up / step-down chopper circuit has been used.

[0004]

In the power supply device having the above configuration, the power supply circuit 4 generates the operating power supply for the control circuit 3 from the DC power supply E. Therefore, when the voltage fluctuation of the DC power supply E is large, the power supply circuit 4 could not stably supply a constant voltage to the control circuit 3. For example, when the power supply circuit 4 is configured by a dropper circuit, since the power supply circuit 4 can only reduce the DC voltage of the DC power supply E, when the DC voltage of the DC power supply E is lower than the minimum operating voltage of the control circuit 3,
A voltage required for the operation of the control circuit 3 cannot be supplied, and the control circuit 3 may not operate. for that reason,
There is a problem that the DC power supply E can be used only when the DC voltage of the DC power supply E is higher than the minimum operating voltage of the control circuit 3. Further, when the DC voltage of the DC power supply E is too high, there is a problem that the loss in the power supply circuit 4 increases.

On the other hand, when the power supply circuit 4 is constituted by a step-up / step-down chopper circuit, the power supply circuit 4 is controlled by the control circuit 3 regardless of whether the DC voltage of the DC power supply E is higher or lower than the operating voltage of the control circuit 3. The voltage required for the operation can be generated. In particular, when the DC voltage of the DC power supply 4 is near the rated voltage of the control circuit 3, the loss of the power supply circuit 4 can be reduced and the operation can be performed with high efficiency. However, as shown in FIG. 6, when the driving frequency f of the switching element forming the buck-boost chopper circuit is constant (that is, the ON time is constant) in the operating voltage range A of the DC voltage Vin of the DC power supply E, the DC voltage When Vin greatly fluctuates with respect to the rated voltage, the power supply circuit 4 is switched over the entire operating voltage range A of the DC voltage Vin.
Cannot be suppressed, and the power conversion efficiency cannot be improved.

The power consumption of the power supply circuit 4 for supplying operating power to the control circuit 3 is relatively small in view of the power consumption of the entire power supply device. Since the power supply circuit 4 is often used as it is, there is a problem that there is a limit to improvement in power conversion efficiency and miniaturization due to loss in the power supply circuit 4 and increase in components (radiator plate).

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a power supply device that can improve the power conversion efficiency of the entire device and reduce the size. .

[0008]

In order to achieve the above object, according to the first aspect of the present invention, a DC power supply and a snubber circuit are provided, and the DC voltage of the DC power supply is converted into a desired DC voltage and supplied to a load. DC-DC conversion circuit, a control circuit for controlling the output of the DC-DC conversion circuit, a power supply circuit for switching the voltage generated in the snubber circuit by switching means to generate an operation power supply for the control circuit, A drive frequency control circuit that controls the drive frequency, wherein the drive frequency control circuit reduces the drive frequency of the switching means as the DC voltage of the DC power supply increases,
Since the power supply circuit generates the operating power supply of the control circuit from the voltage of the snubber circuit, the power conversion efficiency can be improved as a whole of the power supply device, and the higher the DC voltage of the DC power supply, the more the drive frequency control circuit becomes. Since the driving frequency of the switching means of the power supply circuit is reduced, the loss of the power supply circuit can be reduced over the entire operating voltage range of the power supply device, and the power conversion efficiency of the power supply device can be further improved. In addition, the loss of the power supply circuit is reduced, so that the temperature rise and stress of the component parts can be reduced, and the heat sink can be dispensed with and the use of elements with small ratings can be used. Can be achieved.

According to a second aspect of the present invention, in the first aspect of the present invention, the driving frequency control circuit switches the driving frequency of the switching means in two stages according to the DC voltage of the DC power supply. In addition to the function and effect, since the drive frequency control circuit merely switches the drive frequency in two stages according to the magnitude of the DC voltage, the drive frequency control circuit can be realized with a simple circuit configuration.

According to a third aspect of the present invention, in the first aspect of the present invention, the driving frequency control circuit switches the driving frequency of the switching means in multiple stages according to the DC voltage of the DC power supply. In addition to the function and effect, since the drive frequency control circuit switches the drive frequency in multiple steps according to the voltage value of the DC voltage, the drive frequency can be switched more finely than in the case where the drive frequency is switched in two steps, The loss of the power supply circuit can be further reduced.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the driving frequency control circuit linearly controls the driving frequency of the switching means in accordance with the DC voltage of the DC power supply. In addition to the function and effect, the drive frequency control circuit changes the drive frequency linearly according to the voltage value of the DC voltage, so that the drive frequency can be controlled more finely than when the drive frequency is switched stepwise. In addition, the loss of the power supply circuit can be further reduced.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a power supply device according to this embodiment. This power supply device includes a DC power supply E and a flywheel which converts a DC voltage of the DC power supply E into a desired DC voltage and supplies the DC voltage to a load 2. It comprises a DC-DC converter circuit 1 of the buck type, a control circuit 3 for controlling the output of the DC-DC converter circuit 1, and a power supply circuit 4 for supplying operating power to the control circuit 3.

The DC-DC conversion circuit 1 includes a smoothing capacitor C1 connected between both ends of a DC power supply E, a transformer T1 having one end of a primary winding n1 connected to a high potential side end of the capacitor C1, An NPN transistor Tr having a collector connected to the other end of the primary winding n1 of the transformer T1 and an emitter connected to a low potential side end of the capacitor C1.
1, a capacitor C2 having one end connected to the high potential side end of the capacitor C1, and a capacitor C3 connected between the other end of the capacitor C2 and the low potential side end of the capacitor C1.
, A resistor R1 connected in parallel with the capacitor C2, and a cathode connected to a connection point of the capacitors C2 and C3, and a primary winding n1 of the transformer T1 and a transistor Tr.
A diode D1 having an anode connected to the connection point 1;
A diode D4 is connected between both ends of the secondary winding n2 of the transformer T1.
, And a load 2 is connected in parallel with the capacitor C5. Here, the snubber circuit 5 is composed of the capacitors C2 and C3, the resistor R1, and the diode D1.

Here, the output signal of the control circuit 3 is input to the base of the transistor Tr1, and the control circuit 3 controls on / off of the transistor Tr1. When the transistor Tr1 is on, the DC voltage Vin of the DC power supply E is applied to the primary winding of the transformer T1. At this time, since the secondary winding n2 of the transformer T1 has the opposite polarity, no current flows through the diode D4 connected to the secondary winding n2,
Energy is stored in the transformer T1. Next, when the transistor Tr1 is turned off, a back electromotive force is generated in the winding of the transformer T1, and the diode D4 is turned on.
When the switch 1 is turned on, the energy stored in the transformer T1 is output to the secondary side.

In the snubber circuit 5, the transistor T
When r1 is turned off, the energy (regeneration current) of the transformer T1 is supplied to the capacitors C2 and C3 via the diode D1, and power is supplied to the power supply circuit 4 from the connection point of the capacitors C2 and C3. Immediately after turning on the DC power supply E,
The DC voltage Vin of the DC power supply E is directly applied to the power supply circuit 4, but when the DC-DC conversion circuit 1 starts operating, the voltage generated in the snubber circuit 5 increases and the voltage supplied to the power supply circuit 4 increases. Increase.

The power supply circuit 4 comprises a step-up / step-down chopper circuit 6 which converts a voltage supplied from the snubber circuit 5 into a predetermined voltage and supplies the voltage to the control circuit 3.
Is controlled by a driving frequency control circuit 7 described later.

The step-up / step-down chopper circuit 6 includes a capacitor C
An NPN transistor Tr2, which is a switching means having a collector connected to a connection point between the terminals C2 and C3, and a choke coil L having one end connected to the emitter of the transistor Tr2.
1, a diode D2 having a cathode connected to a connection point of the transistor Tr2 and the choke coil L1, an anode connected to a low potential side end of the DC power supply E, and an anode connected to the other end of the choke coil L1. Diode D3, choke coil L1 and diode D3
A collector is connected to a connection point of the DC power supply E, and an NPN transistor Tr3 serving as switching means having an emitter connected to the low potential side end of the DC power supply E, between the cathode of the diode D3 and the low potential side end of the DC power supply E. And a capacitor C4 connected to

In the step-up / step-down chopper circuit 6, the transistor Tr2, the diode D2 and the choke coil L1 operate as a step-down chopper, and the transistor Tr3, the diode D3 and the choke coil L1 operate as a step-up chopper. The transistors Tr2 and Tr3 are turned on and off in synchronization by a drive circuit 12 described later. When the transistors Tr2 and Tr3 are on, the snubber circuit 5 supplies the transistor Tr2, the choke coil L1, the transistor Tr
3, a current flows, and energy is stored in the choke coil L1. At this time, since the transistor Tr3 is also turned on, power is not supplied to the control circuit 3 via the diode D3. Next, the transistors Tr2 and Tr3
Is turned off, a back electromotive force is generated in the choke coil L1, a current flows through the path of the choke coil L1, the diode D3, the capacitor C4, the diode D2, and the choke coil L1, and power is supplied to the control circuit 3.

The drive frequency control circuit 7 detects the DC voltage Vin of the DC power supply E, and changes the output according to the magnitude of the detected value of the DC voltage Vin and a predetermined threshold value. An oscillation circuit 10 for generating a signal for driving the transistors Tr2 and Tr3 at a drive frequency corresponding to the output of the detection circuit 9 is compared with an output voltage Vs of the step-up / step-down chopper circuit 6 and a reference voltage Vref. V
a comparison circuit 11 for generating a signal according to the magnitude of s and Vref
And a drive circuit 12 that drives the transistors Tr2 and Tr3 according to the outputs of the oscillation circuit 10 and the comparison circuit 11.

Here, the voltage detection circuit 9 outputs the DC voltage Vi.
The comparator internally includes a comparator for comparing the detected value of n with a predetermined threshold value, and outputs an output signal in two stages according to the detected value of the DC voltage Vin and the predetermined threshold value. Switch. As the oscillating circuit 10, for example, a CR oscillating circuit using a charging / discharging circuit including a capacitor and a resistor is used. By controlling the charging / discharging current of the capacitor with the output signal of the voltage detecting circuit 9, the oscillation of the oscillating circuit 10 is controlled. The frequency is switched in two stages.

As shown in FIG. 2, when the DC voltage Vin of the DC power supply E is lower than a predetermined threshold value V1, the oscillation frequency of the oscillation circuit 10, ie, the transistor Tr
2, the driving frequency f of the transistor Tr3 is f1, and if it is higher, the driving frequency f is f2 (f2 <f1), and the higher the DC voltage Vin, the lower the driving frequency f of the transistors Tr2, Tr3. Further, the comparison circuit 11 generates a signal corresponding to the magnitude of the output voltage Vs of the step-up / step-down chopper circuit 6 and the reference voltage Vref, and the drive circuit 12 responds to the signal input from the comparison circuit 11 by, for example, the transistor Tr2. , T
By changing the ON time of r3, the output voltage Vs of the step-up / step-down chopper circuit 6 is controlled to be substantially constant. Therefore, the DC voltage Vin of the DC power supply E fluctuates greatly, and the snubber circuit 5
Even if the voltage supplied to the power supply circuit 4 from the
The on-time and driving frequency f of the transistors Tr2 and Tr3
, The loss of the power supply circuit 4 can be reduced, and the power conversion efficiency can be improved.

As described above, the driving frequency control circuit 7
Depending on the magnitude of the DC voltage Vin, the transistors Tr2 and T
Since the driving frequency f of r3 is only switched in two steps, the driving frequency f is switched in multiple steps or linearly controlled according to the voltage value of the DC voltage Vin.
It can be realized with a simple circuit configuration. Note that when the oscillation circuit 10 switches the drive frequency f, hysteresis may be provided so that hunting of the drive frequency f can be prevented.

In this embodiment, the oscillating circuit 10 switches the driving frequency f of the transistors Tr2 and Tr3 to two levels in accordance with the magnitude of the DC voltage Vin of the DC power supply E. The detected value of Vin is compared with a plurality of threshold values, and as shown in FIG.
0 may switch the drive frequency f in multiple stages in accordance with the output signal of the voltage detection circuit 9.
As compared with the case where the driving frequency f is switched in two steps according to the voltage value of the above, the driving frequency f can be switched more finely, the loss of the power supply circuit 4 can be further reduced, and the power conversion efficiency can be improved.

The DC voltage Vin is applied to the voltage detection circuit 9.
A constant current circuit for generating a current corresponding to the detected value of the DC voltage Vin is provided. The current of the constant current circuit determines the charging current of the capacitor constituting the oscillation circuit 10, and as shown in FIG. The oscillation circuit 10 changes the driving frequency f
May be changed linearly, and the drive frequency f can be controlled more finely than in the case where the drive frequency f is switched stepwise, and the loss of the power supply circuit 4 can be further reduced, and the power conversion efficiency can be reduced. Can be improved.

[0026]

As described above, according to the first aspect of the present invention, there is provided a DC-DC conversion circuit having a DC power supply, a snubber circuit, and converting a DC voltage of the DC power supply into a desired DC voltage and supplying the DC voltage to a load. A control circuit for controlling the output of the DC-DC conversion circuit,
A power supply circuit that generates an operating power supply of the control circuit by switching a voltage generated in the snubber circuit by switching means;
A drive frequency control circuit for controlling a drive frequency of the switching means, wherein the drive frequency control circuit reduces the drive frequency of the switching means as the DC voltage of the DC power supply increases, and the power supply circuit includes a snubber circuit. Since the operating power of the control circuit is generated from the voltage of the power supply, the power conversion efficiency can be improved as a whole of the power supply device, and the higher the DC voltage of the DC power supply, the more the drive frequency control circuit operates the switching means of the power supply circuit. Since the driving frequency is reduced, there is an effect that the loss of the power supply circuit can be reduced over the entire operating voltage range of the power supply device, and the power conversion efficiency of the power supply device can be further improved. Besides,
Since the loss of the power supply circuit is reduced, the temperature rise and stress of the component parts can be reduced, and the heat radiation plate becomes unnecessary, and an element with a small rating can be used, so that the power supply circuit can be downsized. There is an effect that can be.

According to a second aspect of the present invention, in the first aspect of the invention, the driving frequency control circuit switches the driving frequency of the switching means in two stages according to the DC voltage of the DC power supply. In addition to the function and effect, the drive frequency control circuit adjusts the drive frequency by two in accordance with the magnitude of the DC voltage.
Since only the steps are switched, there is an effect that the driving frequency control circuit can be realized with a simple circuit configuration.

According to a third aspect of the present invention, in the first aspect, the drive frequency control circuit switches the drive frequency of the switching means in multiple stages according to the DC voltage of the DC power supply. In addition to the function and effect, since the drive frequency control circuit switches the drive frequency in multiple steps according to the voltage value of the DC voltage, the drive frequency can be switched more finely than in the case where the drive frequency is switched in two steps, There is an effect that the loss of the power supply circuit can be further reduced.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the driving frequency control circuit linearly controls the driving frequency of the switching means in accordance with the DC voltage of the DC power supply. In addition to the function and effect, the drive frequency control circuit changes the drive frequency linearly according to the voltage value of the DC voltage, so that the drive frequency can be controlled more finely than when the drive frequency is switched stepwise. This has the effect of further reducing the loss of the power supply circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a power supply device according to an embodiment.

FIG. 2 is a waveform chart for explaining the operation of the above.

FIG. 3 is a waveform diagram illustrating another operation of the above.

FIG. 4 is a waveform chart for explaining another operation of the embodiment.

FIG. 5 is a block diagram showing a conventional power supply device.

FIG. 6 is a waveform chart illustrating the operation of the above.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC-DC conversion circuit 2 Load 3 Control circuit 4 Step-up / step-down chopper circuit 5 Snubber circuit 7 Drive frequency control circuit E DC power supply Tr1-Tr3 Transistor Vin DC voltage

Claims (4)

[Claims] A DC-DC converter having a snubber circuit for converting a DC voltage of the DC power into a desired DC voltage and supplying the DC voltage to a load; and a control for controlling an output of the DC-DC converter. Circuit, a power supply circuit that switches the voltage generated in the snubber circuit by switching means to generate an operation power supply of the control circuit, and a drive frequency control circuit that controls the drive frequency of the switching means. A power supply device wherein the higher the DC voltage of the DC power supply, the lower the drive frequency of the switching means. 2. The power supply device according to claim 1, wherein the drive frequency control circuit switches the drive frequency of the switching means in two stages according to the DC voltage of the DC power supply. 3. The power supply device according to claim 1, wherein the drive frequency control circuit switches the drive frequency of the switching means in multiple stages according to the DC voltage of the DC power supply. 4. The power supply device according to claim 1, wherein the drive frequency control circuit linearly changes the drive frequency of the switching means according to the DC voltage of the DC power supply.