阅读说明：本技术 直流电源装置、电流稳定化电路及电源线的噪声抑制方法 (DC power supply device, current stabilization circuit, and method for suppressing noise of power supply line ) 是由 栃谷浩司 于 2021-05-25 设计创作，主要内容包括：本发明抑制从电池经由比较长的电源线向负载供给直流电压的系统中的电源线的辐射噪声。直流电源装置具备开关电源装置(22),对经由有可能产生辐射噪声的电源线(11)从直流电源(10)供给的直流输入电压进行转换而输出不同电位的直流电压,在开关电源装置的前级或后级连接有电流稳定化电路(21)。并且,电流稳定化电路(21)具备：在电流输入端子与电流输出端子之间串联连接的电阻元件(R1)和晶体管(Q1)；低通滤波器(LPF),其与电流输出端子连接；以及控制电路,其根据电阻元件和晶体管的连接节点的电压与低通滤波器的输出电压的电位差来控制晶体管(Q1),在负载骤变时使恒定电流流过该晶体管。(The invention provides a power supply line for suppressing radiation noise in a system in which a DC voltage is supplied from a battery to a load via a relatively long power supply line. The DC power supply device is provided with a switching power supply device (22) which converts a DC input voltage supplied from a DC power supply (10) via a power supply line (11) which is likely to generate radiation noise and outputs DC voltages of different potentials, and a current stabilizing circuit (21) is connected to the front stage or the rear stage of the switching power supply device. The current stabilization circuit (21) is provided with: a resistance element (R1) and a transistor (Q1) connected in series between a current input terminal and a current output terminal; a Low Pass Filter (LPF) connected to the current output terminal; and a control circuit for controlling the transistor (Q1) according to the potential difference between the voltage of the connection node between the resistance element and the transistor and the output voltage of the low-pass filter, and causing a constant current to flow through the transistor when the load suddenly changes.)

1. A DC power supply device having a switching power supply device and converting a DC input voltage supplied from a DC power supply via a power supply line which is likely to generate radiation noise to output DC voltages of different potentials,

and a current stabilizing circuit is connected to the front stage or the rear stage of the switching power supply device.

2. The direct-current power supply apparatus according to claim 1,

the current stabilization circuit has:

a resistance element and a transistor connected in series between a current input terminal and a current output terminal;

a low-pass filter connected to the current output terminal; and

and a control circuit for controlling the transistor based on a potential difference between a voltage at a connection node between the resistance element and the transistor and an output voltage of the low-pass filter, and causing a constant current to flow through the transistor when a load suddenly changes.

3. The direct-current power supply device according to claim 2,

the low-pass filter sets a time constant so as to cut off a switching frequency component of the switching power supply device and pass a servo control frequency component of the switching power supply device.

4. The direct-current power supply apparatus according to claim 2 or 3,

the control circuit includes:

an operational amplifier circuit having a voltage at a connection node between the resistor element and the transistor as an input voltage of one input terminal;

a voltage control voltage source circuit connected between the current input terminal and the other input terminal of the operational amplifier circuit; and

a capacitor for stabilizing a potential of the current input terminal,

the voltage control voltage source circuit includes a pair of control terminals, and is configured to generate a voltage corresponding to a potential difference between the pair of control terminals, wherein a potential of one of the pair of control terminals is stabilized by the capacitor, and an output voltage of the low-pass filter is applied to the other of the pair of control terminals.

5. The direct-current power supply device according to claim 4,

a constant voltage source is connected between the current input terminal and the capacitor,

the voltage control voltage source circuit is configured to supply a voltage corresponding to the output voltage of the low-pass filter to the other input terminal of the operational amplifier circuit with reference to the voltage boosted by the constant voltage source.

6. A current stabilization circuit includes:

a resistance element and a transistor connected in series between a current input terminal and a current output terminal;

a low-pass filter connected to the current output terminal; and

and a control circuit for controlling the transistor based on a potential difference between a voltage at a connection node between the resistance element and the transistor and an output voltage of the low-pass filter, and causing a constant current to flow through the transistor when a load suddenly changes.

7. The current stabilization circuit of claim 6,

the control circuit has:

an operational amplifier circuit having a voltage at a connection node between the resistor element and the transistor as an input voltage of one input terminal;

a voltage control voltage source circuit connected between the current input terminal and the other input terminal of the operational amplifier circuit; and

a capacitor for stabilizing a potential of the current input terminal,

the voltage control voltage source circuit includes a pair of control terminals, and is configured to generate a voltage corresponding to a potential difference between the pair of control terminals, wherein a potential of one of the pair of control terminals is stabilized by the capacitor, and an output voltage of the low-pass filter is applied to the other of the pair of control terminals.

8. The current stabilization circuit of claim 7,

a constant voltage source is connected between the current input terminal and the capacitor,

the voltage control voltage source circuit is configured to supply a voltage corresponding to the output voltage of the low-pass filter to the other input terminal of the operational amplifier circuit with reference to the voltage boosted by the constant voltage source.

9. The current stabilization circuit of claim 8,

the current stabilization circuit includes a plurality of resistance adjusters each including a resistance adjusting resistor and a switching element connected in series to the resistance adjusting resistor,

the current stabilization circuit has: a switching unit that switches the switching element for connecting the resistance adjuster in parallel with the resistance element,

the current stabilization circuit is configured to be capable of switching the number of parallel connections of the resistance regulators according to the magnitude of the output current.

10. A DC power supply device having a switching power supply device and converting a DC input voltage supplied from a DC power supply via a power supply line which is likely to generate radiation noise to output DC voltages of different potentials,

the switching power supply device having a plurality of current stabilization circuits according to any one of claims 6 to 9 at a preceding stage or a subsequent stage thereof, the dc power supply device comprising: a switching unit that switches connection of the plurality of current stabilization circuits; and a logic circuit that generates a switching signal of the switching unit, wherein the dc power supply device is configured to be capable of switching the number of parallel connections of the current stabilization circuits according to the magnitude of the output current.

11. The direct-current power supply device according to claim 10,

a current sensing resistor for converting an output current into a voltage is connected to an output terminal of the switching power supply device,

the logic circuit generates a switching signal of the switching unit according to the voltage of the current sensing resistor.

12. The direct-current power supply apparatus according to claim 1,

the logic circuit has hysteresis so that the logic circuit does not frequently repeat switching when the load current just coincides with the switching current value.

13. A noise suppression method for suppressing radiation noise emitted from a power supply line in a DC power supply system having a switching power supply device and supplying DC voltages of different potentials to a load by converting a DC input voltage supplied from a DC power supply via the power supply line in which radiation noise is likely to occur,

by limiting a current flowing through the power supply line to the switching power supply device by a current stabilizing circuit, noise accompanying a switching operation of the switching power supply device is suppressed from being transmitted to the power supply line.

Technical Field

The present invention relates to a dc power supply device for supplying a dc voltage to a load, a current stabilization circuit used in the dc power supply device, and a method for suppressing noise in a power supply line, and relates to a technique effective for use in a system for supplying a dc voltage to a load from a battery via a power supply line such as a relatively long cable.

Background

In a system in which a DC voltage is supplied from a battery to a load via a relatively long power cable, as in a drive recorder, a switching power supply (DC-DC converter) is provided on the device side in order to prevent a voltage drop and improve efficiency. In a system in which a current is supplied from a battery to a switching power supply through a long power supply cable, there is a problem that radiation noise is emitted from the power supply cable in association with a switching operation on the power supply side, and other electronic devices such as a television broadcast receiver are adversely affected.

Conventionally, as a technique for reducing radiation noise of a power supply line, a technique of inserting ferrite beads into the power supply line is known. For example, in an electronic device requiring noise measures such as a digital amplifier incorporated in an AV device, an invention has been proposed in which a large-capacity capacitor and a small-capacity capacitor are connected in parallel to a power supply line of a D-stage driver, and a ferrite bead is connected between the capacitors to reduce noise (patent document 1).

In addition, there is also a technique of reducing radiation noise by shielding a cable, but in an in-vehicle system or the like including an electronic device such as a drive recorder, the amount of the cable tends to increase, and the shielding of the cable increases cost and weight, so that a noise countermeasure by shielding is not suitable.

Documents of the prior art

Patent document 1: japanese patent laid-open No. 2006-262121

Patent document 2: japanese patent application laid-open No. 2010-207013

Disclosure of Invention

Problems to be solved by the invention

In a system in which a DC voltage is supplied to a load via a relatively long power cable and a DC power supply device (DC-DC converter) is provided on the load side, a current flowing through the power cable in accordance with a switching operation of the DC-DC converter fluctuates sharply and becomes a cause of radiation noise. Further, since the impedance of the ferrite bead is usually several hundred Ω, it is not possible to effectively suppress the transmission of the current change upstream even in the process of inserting the ferrite bead into the power supply cable, and the radiation noise cannot be sufficiently reduced, and the selection of the optimum bead is complicated and the design burden is large, and in the case where the change needs to be made in consideration of the components used, etc., a lot of man-hours are required and the time is taken.

Conventionally, however, in a DC power supply device that converts a power supply voltage of a battery into a voltage required by an electronic device serving as a load and supplies the voltage, either a linear regulator such as a DC-DC converter of a switching control system or a series regulator is used. Among them, the linear regulator has an advantage of not generating noise, but has a disadvantage of being inefficient and generating much heat. On the other hand, the DC-DC converter has an advantage of good efficiency, but has a disadvantage of generating noise. Therefore, the power supply is used in a differentiated manner so that the linear regulator is used when low noise is preferred and the DC-DC converter is used when efficiency is preferred.

The present inventors considered whether or not radiation noise emitted from a power cable is reduced by providing a linear regulator on the upstream side of a DC-DC converter generating switching noise, and conducted detailed studies. As a result, although the radiation noise of the power cable is reduced to some extent, the efficiency varies greatly due to the variation of the battery voltage, and the noise reduction effect is difficult to be produced unless the servo band of the regulator is increased, but the regulator is likely to oscillate if the servo band is increased, and the optimum capacitance value of the input capacitor of the DC-DC converter is largely different from the optimum capacitance value of the output capacitor of the linear regulator, thereby causing a problem that a failure such as oscillation and an increase in ripple current is likely to occur.

In addition, the present inventors have considered that a linear regulator is provided on the downstream side of the DC-DC converter in order to reduce the radiation noise of the power cable. Conventionally, as an invention in which a regulator is connected to a stage subsequent to a DC-DC converter, there is an invention described in patent document 2. However, the invention of patent document 2 has a problem of preventing generation of a rush current to a large-capacity capacitor provided between an output terminal of a DC-DC converter and a load, and has a problem of reducing radiation noise of a power supply line, and it is known that the effect of reducing radiation noise by such a method is insufficient.

The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a dc power supply device capable of suppressing radiation noise of a power supply line in a system in which a dc voltage is supplied from a battery to a load via a long power supply line, a current stabilizing circuit for the dc power supply device, and a noise suppressing method for the power supply line.

Another object of the present invention is to provide a dc power supply device, a current stabilization circuit for the dc power supply device, and a noise suppression method for a power supply line, which can suppress radiation noise of the power supply line without causing a significant change in efficiency due to a change in battery voltage, or causing a regulator to easily oscillate or causing an increase in ripple current.

Means for solving the problems

In order to achieve the above object, a first invention of the present application is a dc power supply device that has a switching power supply device and converts a dc input voltage supplied from a dc power supply via a power line that is likely to generate radiation noise to output a dc voltage of a different potential,

and a current stabilizing circuit is connected to the front stage or the rear stage of the switching power supply device.

According to the DC power supply device having the above-described configuration, the current stabilizing circuit connected between the switching power supply device (DC-DC converter) and the power supply line can prevent noise generated by the switching operation of the switching power supply device from being transmitted to the power supply line, and thus can suppress emission of radiation noise from the power supply line due to a large fluctuation in the current of the power supply line.

In addition, the radiation noise of the power supply line can be suppressed without causing a large change in efficiency due to a change in the battery voltage, or causing the regulator to easily oscillate, or causing an increase in ripple current.

Here, it is preferable that the current stabilization circuit includes:

a resistance element and a transistor connected in series between a current input terminal and a current output terminal;

a low-pass filter connected to the current output terminal; and

and a control circuit for controlling the transistor based on a potential difference between a voltage at a connection node between the resistance element and the transistor and an output voltage of the low-pass filter, and causing a constant current to flow through the transistor when a load suddenly changes.

According to such a configuration, since the current stabilizing circuit operates to maintain a constant current corresponding to the low-frequency component of the front-rear potential difference with respect to the load current variation of a high frequency, it is possible to suppress radiation noise of the power supply line and to flow a current corresponding to an increase or decrease in the current in the load of the dc power supply apparatus from the current stabilizing circuit with respect to the load current variation of a low frequency.

In addition, it is preferable that the low-pass filter sets a time constant so as to cut off a switching frequency component of the switching power supply device and pass a servo control frequency component of the switching power supply device.

According to such a configuration, it is possible to effectively prevent noise generated by the switching operation of the switching power supply device from being transmitted to the power supply line, and to allow a current corresponding to an increase or decrease in current accompanying servo control of the switching power supply device to flow through the current stabilizing circuit.

Preferably, the control circuit includes:

an operational amplifier circuit having a voltage at a connection node between the resistor element and the transistor as an input voltage of one input terminal;

a voltage control voltage source circuit connected between the current input terminal and the other input terminal of the operational amplifier circuit; and

a capacitor for stabilizing a potential of the current input terminal,

the voltage control voltage source circuit includes a pair of control terminals, and is configured to generate a voltage corresponding to a potential difference between the pair of control terminals, wherein a potential of one of the pair of control terminals is stabilized by the capacitor, and an output voltage of the low-pass filter is applied to the other of the pair of control terminals.

With this configuration, noise can be reduced by the capacitor, and the current flowing through the current stabilization circuit can be prevented from varying due to potential variation on the current input terminal side.

Preferably, a constant voltage source is connected between the current input terminal and the capacitor,

the voltage control voltage source circuit supplies a voltage corresponding to the output voltage of the low-pass filter to the other input terminal of the operational amplifier circuit with reference to the voltage boosted by the constant voltage source.

With this configuration, it is possible to avoid a period in which the current stabilizing circuit does not operate due to a decrease in the potential difference between the emitter and the collector of the transistor.

A current stabilization circuit according to another aspect of the present application includes:

a resistance element and a transistor connected in series between a current input terminal and a current output terminal;

a low-pass filter connected to the current output terminal; and

and a control circuit for controlling the transistor based on a potential difference between a voltage at a connection node between the resistance element and the transistor and an output voltage of the low-pass filter, and causing a constant current to flow through the transistor when a load suddenly changes.

According to the current stabilization circuit having the above-described configuration, it is possible to suppress the transmission of high-frequency noise on the current output terminal side to the current input terminal side, and to flow a current corresponding to the potential difference between the input side and the output side at a low frequency.

Here, it is preferable that the control circuit includes:

an operational amplifier circuit having a voltage at a connection node between the resistor element and the transistor as an input voltage of one input terminal;

a voltage control voltage source circuit connected between the current input terminal and the other input terminal of the operational amplifier circuit; and

a capacitor for stabilizing a potential of the current input terminal,

the voltage control voltage source circuit includes a pair of control terminals, and is configured to generate a voltage corresponding to a potential difference between the pair of control terminals, wherein a potential of one of the pair of control terminals is stabilized by the capacitor, and an output voltage of the low-pass filter is applied to the other of the pair of control terminals.

With this configuration, noise can be reduced by the capacitor, and the current flowing through the current stabilization circuit can be prevented from varying due to potential variation on the current input terminal side.

Preferably, a constant voltage source is connected between the current input terminal and the capacitor, and the voltage control voltage source circuit is configured to supply a voltage corresponding to the output voltage of the low-pass filter to the other input terminal of the operational amplifier circuit with reference to a voltage boosted by the constant voltage source.

With this configuration, it is possible to avoid a period in which the current stabilizing circuit does not operate due to a decrease in the potential difference between the emitter and the collector of the transistor.

The resistance adjustment device is provided with a plurality of resistance adjusters each of which is composed of a resistance for resistance adjustment and a switching element connected in series to the resistance for resistance adjustment,

having a switching unit that switches the switching element for connecting the resistance adjuster in parallel with the resistance element,

the number of parallel connections of the resistance regulator can be switched according to the magnitude of the output current.

Another invention of the present application is a dc power supply device including a switching power supply device, which converts a dc input voltage supplied from a dc power supply via a power line that may generate radiation noise to output dc voltages of different potentials,

the switching power supply device having a plurality of current stabilization circuits according to any one of claims 6 to 9 at a preceding stage or a subsequent stage thereof, the dc power supply device comprising: a switching unit that switches connection of the plurality of current stabilization circuits; and a logic circuit that generates a switching signal of the switching unit, wherein the dc power supply device is configured to be capable of switching the number of parallel connections of the current stabilization circuits according to the magnitude of the output current.

According to the dc power supply device having such a configuration, it is possible to avoid an increase in voltage drop due to the resistance without changing the servo control band.

Preferably, a current sensing resistor for converting an output current into a voltage is connected to an output terminal of the switching power supply device,

the logic circuit generates a switching signal of the switching unit in correspondence to a voltage of the current sensing resistor.

Thus, the switching signal of the switching unit according to the magnitude of the output current can be easily generated.

Preferably, the logic circuit is configured to have hysteresis so that the logic circuit does not frequently repeat switching when the load current exactly matches the switching current value.

This can prevent the load current from being frequently switched around the switching current value.

Still another invention of the present application is a noise suppressing method of suppressing radiation noise emitted from a power supply line in a dc power supply system which has a switching power supply device and which converts a dc input voltage supplied from a dc power supply via the power supply line that is likely to generate radiation noise to supply a dc voltage of a different potential to a load,

the noise suppression method suppresses noise associated with a switching operation of the switching power supply device from being transmitted to the power supply line by limiting a current flowing through the power supply line to the switching power supply device by a current stabilization circuit.

According to the above method, radiation noise emitted from the power supply line can be suppressed.

Effects of the invention

According to the dc power supply device, the current stabilization circuit used for the dc power supply device, and the noise suppression method for the power supply line of the present invention, it is possible to suppress radiation noise of the power supply line in a system in which a dc voltage is supplied from a battery to a load via a long power supply line (power supply cable). Further, the radiation noise of the power supply line can be suppressed without causing a large change in efficiency due to a change in the battery voltage, and the regulator is likely to oscillate, and the ripple current is increased.

Drawings

Fig. 1 is a system configuration diagram showing an embodiment of a power supply system to which a dc power supply device of the present invention is applied.

Fig. 2 is a circuit configuration diagram showing a specific example of a DC-DC converter as a switching power supply device constituting the power supply system of fig. 1.

Fig. 3 is a circuit configuration diagram showing a first embodiment of a current stabilization circuit constituting the power supply system of fig. 1.

Fig. 4 is a circuit configuration diagram showing an example of a circuit in which the current stabilization circuit is simplified.

Fig. 5 is a circuit configuration diagram showing an example of a circuit in which a magnetic bead is incorporated in a current stabilization circuit.

Fig. 6 is a circuit configuration diagram showing a second embodiment of the current stabilization circuit.

Fig. 7 is a system configuration diagram showing another configuration example of a power supply system to which the dc power supply device of the present invention is applied.

Fig. 8 is a configuration diagram showing a modification of the power supply system to which the dc power supply device of the present invention is applied.

Fig. 9 is a circuit configuration diagram showing an example in which a current stabilization circuit is applied to a motor drive circuit.

Description of the reference numerals

A 10 … … battery, 11 … … power cable (power cord), 20 … … DC power supply, 21 … … current stabilization circuit, 22 … … DC-DC converter, AMP1, AMP2 … … amplifier, LPF … … low pass filter, VS1 … … voltage control voltage source circuit, CVS1 … … constant voltage source, L1 … … inductor (coil), Q1 … … current control drive transistor.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

Fig. 1 shows a schematic configuration of an embodiment in which a dc power supply device according to the present invention is applied to a power supply system for supplying a power supply voltage from a dc power supply such as a battery to a load via a power supply cable.

The power supply system of fig. 1 supplies a power supply voltage from a battery 10 to a dc power supply device 20 of the present embodiment via a power supply cable 11, and the dc power supply device 20 converts the input voltage into a voltage suitable for an electronic device to be a load, outputs a stable output voltage Vout, and supplies a current Iout to the load. In fig. 1, reference symbol Lw denotes an inductance component of the power supply cable 11, and reference symbol RL denotes an equivalent resistance (load resistance) of an electronic device serving as a load.

The DC power supply device 20 of the present embodiment includes a current stabilization circuit 21 that controls a current from the battery 10 via the power cable 11, and a DC-DC converter 22 of a switching control system provided at a stage subsequent to the current stabilization circuit 21. Although not particularly limited, when the current stabilization circuit 21 and the DC-DC converter 22 are mounted on 1 substrate such as a printed wiring board, the current stabilization circuit 21 and the DC-DC converter 22 are connected to each other via a power supply line 23 formed of 2 printed wiring patterns formed on the substrate. The power cable 11 includes a coaxial cable such as a PoC cable to which signals and power are supplied.

In addition, although the coaxial cable is a shield cable in the related art, it is not necessary to reduce the transmission noise, but the PoC cable simultaneously supplies a communication signal such as a digital video and a power source, and thus, reduction of the transmission noise is required. Therefore, although the reduction of the conducted noise has been achieved by a filter or the like including an inductor and a capacitor, the filter before the PoC cable connection is not required in the dc power supply device of the present invention.

Fig. 2 shows a specific circuit example of the DC-DC converter 22. As shown IN fig. 2, the DC-DC converter 22 of the present embodiment has a pair of voltage input terminals IN1, IN2 connected to the power supply line 23 of fig. 1, and a pair of voltage output terminals OUT1, OUT2, and a load RL is connected to the voltage output terminals OUT1, OUT 2. The voltage input terminal IN2 and the voltage output terminal OUT2 are connected to each other and to a ground point, and a smoothing capacitor C1 is connected between the voltage output terminals OUT1 and OUT2 (ground point). Further, series bleeder resistors Rb1 and Rb2 for dividing the output voltage Vout of the DC-DC converter are connected between the voltage output terminals OUT1 and OUT2 (ground point).

The DC-DC converter 22 includes a switching transistor M1 and an inductor L1 as switching elements each of which is formed of a P-channel MOSFET (field effect transistor) connected IN series between a voltage input terminal IN1 and a voltage output terminal OUT 1. Further, the apparatus comprises: a synchronous rectification transistor M2 connected between a connection node N1 of the transistor M1 and the inductor L1 and a voltage output terminal OUT2 (ground point); a logic circuit LGC as a switch control circuit for generating a signal for controlling on/off of the transistors M1 and M2; and an error amplifier AMP1 having a voltage divided by the bleeder resistors Rb1 and Rb2 as a feedback voltage VFB and connected to the inverting input terminal.

The reference voltage Vref is applied to a non-inverting input terminal of the error amplifier AMP1, the error amplifier AMP1 outputs a voltage corresponding to the potential difference between the feedback voltage VFB and the reference voltage Vref to the logic circuit LGC, and the logic circuit LGC controls the on time of the switching transistor M1 based on the output voltage of the error amplifier AMP1, turns off M2, turns on M1, and after energy is accumulated by flowing a current to the inductor L1, turns off M1, turns on M2, discharges the accumulated energy of the inductor L1, flows a current Iout to the voltage output terminal OUT1, and converts the input voltage to supply a dc voltage to the load.

As for the on/off control method of the switching transistors M1 and M2 in the logic circuit LGC of the DC-DC converter 22 according to the present embodiment, various control methods have been proposed in the past as described in, for example, japanese patent laid-open No. 2012-139023, and a known control method can be adopted in the DC-DC converter 22 according to the present embodiment to configure the logic circuit LGC, and therefore, a description of a specific example is omitted.

The transistors M1 and M2, the logic circuit LGC, and the error amplifier AMP1 may be formed as a semiconductor Integrated Circuit (IC) on 1 semiconductor chip.

Fig. 3 shows a first embodiment of the current stabilization circuit 21. As shown in fig. 3, the current stabilization circuit 21 of the present embodiment includes: a current control transistor Q1 formed of a PNP bipolar transistor and provided between a current input terminal IN to which a dc voltage supplied from the battery 10 via the power supply cable 11 is applied and a current output terminal OUT; a resistor R1 connected between the emitter terminal of the transistor Q1 and the current input terminal IN; an operational amplifier (operational amplification circuit) AMP2 that controls the transistor Q1; and a voltage control voltage source circuit VS1 that generates a voltage applied to the non-inverting input terminal of the operational amplifier AMP 2. A low-resistance element having a resistance value of about 10 Ω is used for the resistor R1.

The current stabilization circuit 21 has a low-pass filter LPF provided between the current output terminal OUT and the negative control terminal (-) of the voltage control voltage source circuit VS 1.

The voltage-controlled voltage source circuit VS1 has a pair of control terminals (+), (-) and a pair of output terminals, and generates a voltage between the output terminals corresponding to a potential difference between the control terminals (+), (-). Thus, IN the present embodiment, a voltage lower than the potential of the current input terminal IN by a voltage amount corresponding to the potential difference between the control terminals (+), (-) is applied to the non-inverting input terminal of the operational amplifier AMP 2. As the voltage-controlled voltage source circuit VS1, a known voltage-controlled voltage source including an operational amplifier, a transistor, or the like can be used, for example.

The low pass filter LPF includes a resistor R2 connected between the current output terminal OUT of the current stabilization circuit 21 and the negative control terminal (-) of the voltage control voltage source circuit VS1, and a capacitor C2 connected between the negative control terminal (-) of the voltage control voltage source circuit VS1 and the ground point, and sets a time constant so as to remove a high frequency component corresponding to the switching frequency of the DC-DC converter 22 at the subsequent stage from the voltage fluctuation component of the current output terminal OUT and pass a low frequency component corresponding to the servo band (servo control frequency) of the DC-DC converter 22.

The low pass filter LPF thus operates as follows: only the voltage variation of the current output terminal OUT accompanying servo control of the DC-DC converter 22 of the subsequent stage is transferred to the operational amplifier AMP2 via the voltage control voltage source circuit VS1, and the voltage variation of the current output terminal OUT accompanying switching control is not transferred to the operational amplifier AMP 2. Specifically, for example, when the switching frequency of the DC-DC converter 22 is 2MHz and the servo control frequency is 2.4kHz, an element having a resistance value of 10 k Ω is used as the resistor R2, and an element having a capacitance value of nF is used as the capacitor C2. The servo control of the current stabilization circuit is determined by the frequency band of the operational amplifier, the resistor R1, the capacitor of the output terminal of the current stabilization circuit, and the like, in addition to the LPF. The LPF part is responsible for the auxiliary pole and dominates the phase margin over the frequency band itself.

On the other hand, a constant voltage source CVS1 and a resistor R3 connected IN series are present between the current input terminal IN of the current stabilization circuit 21 and the ground point, and a capacitor C3 for reducing noise connected between the positive side control terminal (+) of the voltage control voltage source circuit VS1 and the ground point is connected, and the potential of a connection node N3 of the constant voltage source CVS1 and the resistor R3 is applied to the positive side control terminal (+) of the voltage control voltage source circuit VS 1. Specifically, an element having a resistance value of several M Ω is used as the resistor R3, and an element having a capacitance value of several μ F is used as the capacitor C3.

With the above-described configuration, the current stabilization circuit 21 operates to stabilize the potentials of the current input terminal IN and the positive control terminal (+) of the voltage-controlled voltage source circuit VS1, and to maintain the low-frequency component of the potential difference between the current input terminal IN and the current output terminal OUT before and after the stabilization.

Fig. 4 shows a modification of the current stabilization circuit 21 of fig. 3. IN this modification, the capacitor C3 is only provided between the current input terminal IN of the current stabilization circuit 21 and the ground point, and the constant voltage source CVS1 is connected between the non-inverting input terminal of the operational amplifier AMP2 and the low pass filter LPF, so that the noise reduction effect is reduced by about a few dB, but the effect substantially equivalent to that of the circuit of fig. 3 is obtained. Fig. 5 shows a modification in which a magnetic bead BD is added in series to a resistor R1 in the current stabilization circuit 21 of fig. 3. By adding the magnetic bead BD, the noise reduction effect can be further improved by about 30 dB.

The constant voltage source CVS1 is configured to generate a voltage (about 0.2V) corresponding to the collector-emitter voltage VCE of the bipolar transistor, so that the bipolar transistor can always operate, and by configuring the voltage to be as small as about 0.2V, there is an advantage that the heat loss of the bipolar transistor can be suppressed and the loss generated in the transistor can be minimized. In addition, the parasitic capacitance of the bipolar transistor is prevented from increasing by not making the voltage too small at the same time.

When the collector current flowing through the current control transistor Q1 is denoted by Ic and the potential difference between the current input terminal IN and the current output terminal OUT is denoted by Δ V, the current stabilization circuit 21 of the present embodiment having the configuration as described above operates so that a current denoted by Ic ═ Δ V-CVS1)/R1 flows.

Here, as described above, since the potential difference Δ V between the current input terminal IN and the current output terminal OUT removes the high frequency component accompanying the operation of the DC-DC converter 22 and maintains the low frequency component, the current change on the current output terminal OUT side, which is drastically changed by the switching operation of the DC-DC converter 22, is not transmitted to the upstream power supply cable 11, and the current Ic, which is changed IN accordance with the current change accompanying the servo control of the DC-DC converter 22, can flow.

As described above, the DC power supply device 20 of the present embodiment generates a DC voltage by the DC-DC converter 22 and supplies the DC voltage to a device serving as a load, and therefore, can improve conversion efficiency as compared with a DC power supply device configured only by a linear regulator. Further, since the current stabilization circuit 21 is provided in the stage preceding the DC-DC converter 22, noise generated by the switching operation in the DC-DC converter 22 is less likely to be transmitted to the upstream power supply cable 11, and radiation noise (radiation noise) leaking from the power supply cable 11 can be reduced. In addition, the radiation noise of the power supply line can be suppressed without causing a large change in efficiency due to a change in the battery voltage, causing the regulator to easily oscillate, or causing an increase in ripple current. Further, the current stabilization circuit 21 can prevent an inrush current of a rated value or more from flowing into the load at the time of power-on or the like.

Table 1 below shows values of radiation noise (magnetic field intensity at a position 3m from the cable) when a DC power supply device (DCDC) including only a DC-DC converter, a DC power supply device (DCDC + magnetic bead) including only a DC-DC converter, a DC power supply device (DCDC + current stabilizing circuit) of the present embodiment including a current stabilizing circuit 21 and a DC-DC converter 22, a DC power supply device (LDO) including only a linear regulator, and a cable (UL standard AWG20) including parallel lines each having a length of 4m and a length of 0.5mm between the lines is used as a power supply line and a switching frequency is set to 2 MHz. The "difference" in table 1 is a relative value based on the efficiency and magnetic field of the DC power supply device constituted only by the DC-DC converter. In the above simulation, Vin is 5V, Vout is 1.8V, Iout is 200mA, and fsw _ dccd is 2 MHz.

[ Table 1]

Fig. 5 shows a case where a magnetic bead is incorporated in a current stabilization circuit, but when the magnetic bead is combined without providing a current stabilization circuit, as is apparent from table 1 above, the reduction in radiation noise is almost unexpected as 3.62dB, and a direct current power supply (LDO) composed of only a linear regulator reduces radiation noise by nearly 200dB, but reduces efficiency by nearly 50%, whereas the use of the direct current power supply according to the present embodiment can reduce radiation noise by 13% and 65dB or more, which is very efficient.

On the other hand, since the radiation noise from the pattern and the cable is reduced by applying the present embodiment, the common impedance excluded to avoid the propagation of the high-frequency noise in the module can be also allowed to some extent. Further, for example, when a plurality of cables for supplying power from a common power supply to DC-DC converters provided in the vicinity of a plurality of loads (electronic devices) are laid in parallel, the need to manage mass production for complicated modeling in order to separate wires through which sensitive signals pass from the pattern of the noise source is reduced, and miniaturization and improvement in stability of the module are achieved. Also, EMI can be improved without changing the substrate.

Further, a system having a plurality of electronic devices, such as an in-vehicle system, is becoming more complicated with higher functionality, and the number of cables tends to increase exponentially, so that suppression of radiation noise from the cables is an urgent issue. If the dc power supply device of the present embodiment is used, the radiated noise from the power supply cable can be reduced without using a large-sized ferrite bead or a PoC filter, and the cable can be made slim. In addition, if the dc power supply device according to the embodiment is used, noise interference failure due to poor modeling of the cable in the module of the electronic device can be suppressed, and the reliability of the entire device can be improved.

However, the current stabilization circuit 21 shown in fig. 3 is a circuit effective for a system in which the fluctuation range of the load current is relatively small, and has a problem that it cannot cope with the fluctuation range of the load current being large to some extent. Therefore, a current stabilization circuit that can cope with a large fluctuation range of the load current to some extent, that is, that can flow a constant current even in a case of a load sudden change in which the load current fluctuates at a high frequency in a case of a relatively large current and that functions as a simple resistor in a case in which the load current fluctuates at a relatively low frequency will be described below. Fig. 6 shows a specific circuit configuration example (second embodiment) of the current stabilization circuit 21 having such a function.

As shown in fig. 6, since the resistance R1 and the resistance R2 in the current stabilization circuit of the first embodiment shown in fig. 3 can be made variable in the current stabilization circuit 21 of the second embodiment, the resistance R1a and the resistance R1b can be added in parallel to the resistance R1 (the number of additions is not limited to this), and the voltage reduction when the resistance R1 changes is reduced, so that the current stabilization circuit can be made unsaturated when a large current flows. Since the servo band also changes due to the change in the resistance R1, the servo band is not changed by changing the resistance R2 of the low pass filter LPF at the same time. In addition, a current detection resistor Rs for converting the output current Iout into a voltage is connected to generate the switching signal. Further, since the load current is caused to repeat the switching operation less frequently in the vicinity of the switching current value, the logic circuit can be made to have hysteresis. In addition, a current sensing resistor Rs for converting an output current into a voltage after being output from the DC-DC converter is connected to generate a potential to be input to the control logic circuit.

Next, a third embodiment of the present invention will be explained. In the second embodiment, the voltage drop is suppressed by adding a resistor in parallel with the resistor R1 in the transistor switch, but in this case, the servo control band greatly changes, and this control is also necessary, which complicates the circuit. Therefore, in the third embodiment, as shown in fig. 7, the plurality of current stabilization circuits 21 are provided in parallel, and the switching means (SW1, SW2) are provided so as to be switched in accordance with the output current, whereby the number of parallel connections can be sequentially increased.

In addition, a current detection resistor Rs that converts the output current Iout into a voltage is connected in order to generate the switching signal. Further, since the load current is caused to repeat the switching operation less frequently in the vicinity of the switching current value, the logic circuit can be made to have hysteresis. According to the above configuration, when the load current is increased, a voltage drop at the series resistance (the resistance connected between the emitter terminal of the transistor Q1 and the current input terminal IN) can be suppressed.

(modification example)

Next, a modified example of the dc power supply device 20 of the above embodiment will be described.

As shown in fig. 8, in the present modification, a current stabilization circuit 21 is provided at a stage subsequent to the DC-DC converter 22.

In general, in an in-vehicle system or the like, it is desirable to place a power supply near a load in consideration Of pol (point Of load), and therefore, there is a small number Of systems in which a long cable or wiring pattern exists between a DC-DC converter and a load, but there is a demand for minimizing an occupied area by collecting power using a power management IC or the like, and therefore, depending on the system to be applied, it is sufficient to consider a case where a power supply device having a configuration as shown in fig. 8 operates efficiently.

The invention made by the present inventors has been specifically described above with reference to the embodiments, but the present invention is not limited to the embodiments. For example, in the above-described embodiment, a bipolar transistor is used as a transistor constituting the current stabilization circuit 21, but a MOS transistor may be used instead of the bipolar transistor. In the above-described embodiment, the case where the present invention is applied to the DC power supply device using the DC-DC converter of the synchronous rectification system as the DC-DC converter 22 has been described, but the present invention can also be applied to a DC power supply device using a DC-D converter of the asynchronous rectification system using a diode instead of the switching transistor M2 of fig. 2.

In the embodiment of fig. 2, the case of applying the present invention to a DC-DC converter controlled in a voltage mode is shown, but the present invention is not limited to this, and a DC-DC converter controlled in a current mode or a hysteresis may be used.

In the above-described embodiment, the case where the present invention is applied to a system in which a non-insulated DC-DC converter is used as a DC power supply device has been described, but the present invention can also be applied to a system in which an insulated DC-DC converter that includes a transformer and performs switching control of a current flowing through a primary winding is used as a DC power supply device.

In the above-described embodiment, the description has been given of a system using a power supply cable as a power supply line for supplying a power supply voltage from a battery to a load, but the present invention can also be applied to a system in which a wiring pattern formed on a substrate such as a printed wiring board is used as a power supply line for supplying a power supply voltage to a load.

The current stabilization circuit 21 of the present invention is effective for all cases where a current rapidly changes by performing a switching operation, and can be applied to, for example, reducing radiation noise from a power supply cable that supplies power to a switching motor driver (M1-M4) and reducing radiation noise from a power supply cable that supplies power to a class-D amplifier, as shown in fig. 9.