JPH11220374A - Power source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid the generation of an over-current at the time of starting a power source by outputting a prescribed control current based on a reference current from a reference current source which generates a reference current and from a reference voltage source which generates a reference voltage so as to output a driving current to a load and adjusting the control current of a current amplifier circuit based on an output voltage added to the load and the reference voltage. SOLUTION: When the output voltage Vreg is lower than a voltage prescribed by the reference voltage Vref, a base current is not supplied for the transistor Q6 of a first current amplifier circuit 12 to turn-off the transistor Q6 to amplify the reference current Iref by a prescribed amplitude to make a controlled current Icont. When the output voltage Vreg exceeds the reference voltage Vref, a control circuit 16 supplies a base current equivalent to a voltage difference for the transistor Q6 to reduce the base current of a transistor Q4 and the reduce-controlled base current is amplified by a prescribed amplitude to operate feedback control to fix the output voltage Vreg.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device which is incorporated in, for example, a two-wire proximity switch and is suitable for driving a load such as a sensor circuit or a signal processing unit.

[0002]

[Related Background Art] Proximity switches that detect the proximity (presence or absence) of a detection target made of a magnetic material without contacting the detection target have higher operation reliability than mechanical contact switches such as microswitches. It has advantages such as high and long life,
Widely used for various applications. Above all, the detection unit is provided with a detection coil that forms a part of a high-frequency oscillation circuit, and the inductance and loss of the detection coil change due to the electromagnetic induction between the detection object and a magnetic substance. A high-frequency oscillation type proximity switch (electronic switch device) that detects the proximity of an object to be detected by utilizing changes in oscillation amplitude and oscillation frequency in a circuit has excellent features such as high detection sensitivity and fast response speed. Have.

[0003] By the way, one of such proximity switches is
There is a two-wire type in which a pair of power lines is shared with a signal line.
This two-wire type high frequency oscillation type proximity switch is, for example, shown in FIG.
As shown in FIG.
A sensor circuit section 6 including an integrating circuit 2, a comparison circuit 3, a signal processing circuit 4, and a constant voltage source 5;
And a display circuit 7 for driving the LED 7a to turn on the LED 7a in response to the output from the power supply line 7 and an output circuit 8 interposed between the pair of power supply lines La and Lb. In the proximity switch having such a configuration, for example, the pair of power supply lines La and Lb are connected to an internal power supply Vout of a monitoring device 10 including a microprocessor or the like via a load 9 including a relay circuit.
It is powered by ut and works.

The high-frequency oscillation circuit 1 has a coil (detection coil) 1a and a capacitor 1b forming an LC tank circuit and oscillates at a predetermined frequency, and the integration circuit 2 integrates (smooths) the output of the oscillation circuit 1. ) To detect the oscillation amplitude. Then, the oscillation amplitude detected as the integrated voltage is compared with a predetermined threshold value in the comparison circuit 3, whereby a decrease in the oscillation amplitude due to the proximity of the detection target (magnetic material) to the coil 1a is detected. Signal processing circuit 4
Outputs the proximity of the detection object detected in this manner in accordance with the setting state of the proximity switch.

The display circuit 7 drives the LED 7a to light up when, for example, the proximity of the detection target is detected.
An output circuit 8 comprising bipolar transistors, etc.
Is, for example, normally in a non-conducting state, and is driven to conduct in relation to the lighting of the LED 7a (when the proximity of the detection target is detected) to change the voltage Vcc between the pair of power supply lines La and Lb. Let it. The load (relay circuit) 9 is actuated by such a change in the voltage Vcc between the power supply lines La and Lb, and the monitoring device 10 detects the operating state of the load 9, for example, a change in current flowing through the load 9 by the proximity switch. The proximity of the detection target will be detected.

[0006]

A constant voltage source (power supply) 5 incorporated in a two-wire proximity switch (electronic switch device) configured as described above is connected to the pair of power supply lines La and Lb. Then, from the power supply voltage Vcc supplied from an external power supply, a drive voltage Vdrv for driving each of the circuits 1, 2, 3, and 4 serving as the load is generated. The constant voltage source (power supply device) 5 having such a role generally compares the output voltage Vdrv with the internal reference voltage Vref, and increases the output voltage Vdrv when the output voltage Vdrv is lower than the internal reference voltage Vref. Control circuit for performing feedback control as described above.

In the constant voltage source (power supply device) 5 provided with such a control circuit, the output voltage Vdrv of the constant voltage source 5 rises to a predetermined voltage value when the power supply to the proximity switch is started. During the period, that is, when the output voltage drv is low, a large current flows to the load due to the feedback action of the control circuit. Such an output current usually becomes maximum immediately before the output voltage Vdrv reaches a predetermined voltage value. Then, the load (relay circuit) 9 interposed between the power supply lines La and Lb is activated by the large current, and the behavior is as if the proximity switch detected the proximity of the detection target.

Accordingly, the present applicant first performs a constant current operation at the beginning of energization of the proximity switch to charge the load.
A power supply device that performs a constant voltage operation when the output voltage Vdrv exceeds a predetermined voltage value has been proposed. That is, the output voltage Vdrv is temporarily made higher than a predetermined target voltage value by operating the power supply device at a constant current, and then the output voltage Vdrv is controlled to the target voltage value by operating the power supply device at a constant voltage. Thus, a power supply device configured to suppress an increase in current has been proposed. However, a control circuit for monitoring the output voltage Vdrv to switch between the constant current mode and the constant voltage mode is required, and a circuit for the constant current mode and a circuit for the constant voltage mode are required. There was a problem that it became complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object the purpose of assembling it in a two-wire proximity switch, for example, since the circuit configuration is simple and undesired excessive current does not occur at the start of energization. It is another object of the present invention to provide a power supply device suitable for the above.

[0010]

In order to achieve the above-mentioned object, a power supply device according to the present invention is incorporated in, for example, a two-wire proximity switch and driven by an external power supply to supply power to a load such as a sensor circuit. A first current amplifier that outputs a constant voltage and outputs a predetermined control current based on a predetermined reference current output from a reference current source; and amplifies the control current and drives the load with respect to a load. Second to output current
And the first current amplification circuit, based on a predetermined reference voltage generated by a reference voltage source and an output voltage applied to the load by the driving current, such that the output voltage is defined by the reference voltage. A control circuit that controls the operation of the circuit and adjusts the control current output from the first current amplification circuit.

That is, according to the present invention, a constant drive current is output to a load using the second current amplifier circuit, and is output from the first current amplifier circuit to drive the second current amplifier circuit. The drive current is controlled by controlling a control current by comparing an output voltage applied to the load by the drive current with a predetermined reference voltage, thereby making the output voltage constant. And

In a particularly preferred aspect of the present invention, the first and second current amplifying circuits are each realized as a current mirror circuit as described in claim 2, and the first and second current amplifying circuits are each implemented as a current mirror circuit as described in claim 3. The first current amplifier circuit
It is characterized by being realized as a peaking current source circuit. Further, in the power supply device according to the present invention, when the gain of the current amplifying circuit that outputs a constant drive current to the load can be sufficiently secured, the predetermined power output from the reference current source is provided as described in claim 4. A current amplifier circuit for amplifying a control current consisting of a reference current or a part thereof and outputting a drive current to a load; a predetermined reference voltage generated by a reference voltage source; and an output voltage applied to the load by the drive current And a control circuit that controls a part of the reference current based on the control current, thereby varying a control current supplied to the current amplification circuit and adjusting a control current output from the current amplification circuit. Features.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a power supply device according to an embodiment of the present invention will be described with reference to the drawings, taking a constant voltage source incorporated in, for example, a two-wire proximity switch as an example. FIG. 1 is a schematic configuration diagram of the power supply device according to the first embodiment.
This power supply device is driven by a power supply voltage Vcc supplied from an external power supply via power supply lines La and Lb, and generally receives a predetermined reference current Ire by receiving the power supply voltage Vcc.
f, a constant current source 11 for amplifying the reference current Iref output from the constant current source 11 and outputting a control current Icont, and a sensor circuit for amplifying the control current Icont. And a second current amplifying circuit 14 for outputting a drive current Iout to a load circuit 13 composed of the same. Further, the power supply device includes a voltage detecting circuit 17 including voltage dividing resistors R1 and R2 for dividing and detecting an output voltage Vreg applied to the load circuit 13 based on the output of the driving current Iout to the load circuit 13; According to the power supply voltage Vcc, for example, a predetermined reference voltage V
A reference voltage source 15 for generating ref, an output voltage Vsens detected by the voltage detection circuit 17 and the reference voltage Vref.
(The divided value of the output voltage Vreg) to control the operation of the first current amplifying circuit 12 to adjust the control current Icont, whereby the second current amplifying circuit 14 amplifies and outputs. A control circuit 16 for controlling the drive current Iout.

Incidentally, the first current amplifying circuit 12
A pair of npn transistors Q4, Q5 forming a current mirror circuit with the base and the emitter commonly connected.
And a current controlling npn transistor Q connected between bases and emitters of these transistors Q4 and Q5.
6, the collector of a transistor Q5 having a base and a collector connected in common, receives the reference current Iref, and basically amplifies the reference current Iref flowing through the transistor Q5 by [n2] times by the transistor Q4. The control current Icont is output to the collector of the transistor Q4. The transistor Q6 reduces the control current Icont output from the transistor Q4 by bypassing a part of the base current applied to the base of the transistor Q4 according to the base current supplied to the base from the control circuit 16. Take the role to let.

The second current amplifying circuit 14 includes a pair of pnp transistors Q1, whose emitters are connected to a power supply line La to which a power supply voltage Vcc is applied via resistors R3 and R4, respectively, and whose bases are commonly connected. It comprises a current mirror circuit comprising a transistor Q2 and a pnp transistor Q3 having an emitter and a base connected between the base and collector of the transistor Q2. Thus, the transistor Q3 operates based on the control current Icont from the first current amplifier circuit 12, and controls the control current Icont to flow through the transistor Q2. In this way, the control current Icont flowing through the transistor Q2 is amplified [n1] times by the transistor Q1, and
From the collector of the transistor Q1.

Therefore, the load circuit 13 is basically connected to the first power supply circuit as described above, particularly at the start of supply of the power supply voltage Vcc and before the power supply apparatus has sufficiently started up and operates stably. In the current amplifier circuit 12, the reference current Ire
The control current Icont obtained by amplifying f and the constant drive current Iout obtained by amplifying the control current Icont in the second current amplifying circuit 14 are supplied.

The control circuit 16 monitors the output voltage Vreg applied to the load circuit 13 based on the output of the drive current Iout. And the output voltage Vr
When eg is lower than the voltage defined by the reference voltage Vref, specifically, the detection voltage Vsens of the output voltage Vreg detected by dividing the voltage by the resistors R1 and R2 is equal to the reference voltage Vr.
When the voltage is lower than ef [Vref> Vsens], the control circuit 1
6 does not supply a base current to the transistor Q6 of the first current amplifier circuit 12, thereby turning off the transistor Q6 (non-conduction). Therefore, in this case, in the first current amplifier circuit 12, the transistor Q4 is connected to the reference current Iref supplied to the transistor Q5.
It is amplified at a predetermined amplification factor [n2], and this is output as the control current Icont.

On the other hand, when the output voltage Vreg exceeds the voltage defined by the reference voltage Vref, specifically, the output voltage Vr detected via the resistors R1 and R2.
When the detected voltage Vsens of eg exceeds the reference voltage Vref [Vref ≦ Vsens], the control circuit 16 supplies a base current corresponding to the voltage difference to the transistor Q6. By supplying this base current, the transistor Q6
Operates (conducts) to draw a part of the reference current Iref and reduce the base current to the transistor Q4. As a result, in the first current amplifier circuit 12, the base current for the transistor Q4 is controlled to decrease by the amount bypassed by the transistor Q6 without changing the reference current Iref supplied to the transistor Q5. Then, the transistor Q4 amplifies the base current subjected to the decrease control as described above with a predetermined amplification factor [n2], and outputs this as the control current Icont. Therefore, the control current Icont output via the transistor Q4
Is reduced by the conduction of the transistor Q6. The control circuit 16 includes a transistor Q6
Is subjected to negative feedback control according to the above-mentioned output voltage Vref, thereby making the output voltage Vref constant at a predetermined voltage value defined by the reference voltage Vref.

Therefore, according to the power supply device configured as described above, the supply of the constant drive current Iout from the second current amplifying circuit 14 to the load circuit 13 is started with the supply of the power supply voltage Vcc. When the driving current Iout is accumulated in the load circuit 13 and the output voltage Vref gradually increases and the output voltage Vreg reaches the voltage defined by the reference voltage Vref, the feedback control by the control circuit 16 operates to perform the driving. The current Iout is suppressed, and the output voltage Vreg is controlled to be constant.

As a result, the relationship between the drive current Iout output from the power supply device and the output voltage Vreg applied to the load circuit 13 by the drive current Iout is as shown in FIG.
After a constant current operation is performed with the start of the supply of the power supply voltage Vcc, a constant voltage is output. Therefore, even when the supply of the power supply voltage Vcc is started, an undesired excessive current does not flow, and the current consumption as a whole can be suppressed low. Therefore, according to the power supply device that outputs a constant voltage after the constant current operation as described above at the start of energization,
Even if this is incorporated in a two-wire proximity sensor, an excessive current does not flow at the start of energization.
A stable operation can be ensured without malfunction of the relay circuit inserted between a and Lb.

In particular, according to the power supply device having the above-described configuration, the power supply device basically includes a current amplifier circuit 14 which amplifies the constant current Iref and outputs a predetermined drive current Iout to the load circuit 13. Since the control current Icont for driving the current amplifying circuit 14 is feedback-controlled in accordance with the output voltage Vreg applied to the output terminal 12 and the output voltage Vreg is constant, the circuit configuration can be simplified. In other words, there is no need to provide a circuit for the constant current mode and a circuit for the constant voltage mode as in the related art, and it is not necessary to selectively operate these circuits in accordance with the output voltage Vreg. Can be In addition, it is not necessary to take measures such as once raising the output voltage Vdrv during the constant current operation to be higher than a predetermined target voltage value to determine the switching point of the constant voltage operation mode. There are effects such as output can be prevented beforehand.

By inserting resistors R3 and R4 into the emitters of the transistors Q1 and Q2 forming the second current amplifying circuit 14, respectively, the output impedance is increased and the amplification gain is set high. Although the change in the drive current Iout due to the change in the voltage Vcc is suppressed, this power supply device
In the case where the transistor is constructed by an IC process having a high output impedance of a p-transistor or when it is not necessary to increase the amplification gain so much, the resistance R3,
It goes without saying that R4 can be omitted.

In the first embodiment described above, the first current amplifying circuit 12 that drives the second current amplifying circuit 14 that outputs a predetermined drive current Iout to the load circuit 13 is replaced with a current mirror circuit. However, as illustrated in FIG. 3 as a second embodiment, it is also possible to realize the first current amplifier circuit 12 using a peaking current source circuit.

That is, as shown in FIG. 3, the first current amplifier circuit 12 has a collector connected to a constant current source 11 via a load resistor R5 and a base connected to the constant current source 11 via a resistor R6. A constant current Iref output from the constant current source 11 is received by an npn transistor Q7 connected to the control current, and a collector current of the collector Q7 is amplified by an npn transistor Q8 to drive the second current amplifying circuit 14. It is configured to obtain Icont. The control transistor Q9 connected in parallel to the transistor Q7 receives the output of the control circuit 16 and bypasses a part of the output of the transistor Q7 to control the operation of the transistor Q8. Control current Icont
Is configured to be adjusted.

According to the first current amplifying circuit 12 configured as described above and serving as a peaking current source circuit, the output current of the constant current source 11 is set to be small in order to prevent a malfunction at power-on. The constant current source 11
Even if there is some variation in the operating characteristics of the transistor Q8 due to the device characteristics, a stable constant current can be taken out from the constant current source 11, so that the transistor Q8 can be driven stably. And the second current amplifier circuit 14 can be operated stably. As a result, it is possible to stably output the drive current Iout to the load circuit 13. Further, since the base current is supplied to the transistor Q7 via the resistor R6, it is possible to effectively suppress the influence due to the variation in the current amplification factor h _fe of the transistor Q7. Therefore, a more stable operation can be expected as compared with the power supply device having the circuit configuration shown in FIG.

On the other hand, when the current amplification factor of the second current amplification circuit 14 is sufficiently high, for example, as shown in FIG.
The current amplifier circuit 12 of FIG.
Can be directly driven. That is, in this case, basically, the control current Icont applied to the transistor Q2 of the second current amplifier circuit 14 is a constant current Iref, and the transistor Q10 provided in parallel with the second current amplifier circuit 14 is Control circuit 1
By controlling in step 6, a part of the constant current Iref is supplied.

According to the power supply device configured as described above, the transistor Q10 is turned off under the control of the control circuit 16 when the supply of the power supply voltage Vcc is started. The constant current Iref is drawn through the transistor Q2 of the circuit 14. Therefore, the second current amplifying circuit 14 outputs a constant drive current Iout in accordance with the constant current Iref (control current Icont).

Thereafter, the driving current Iout is applied to the load circuit 1
3 is applied to the load circuit 13 and applied to the output voltage Vreg.
Rises, the control device 16 operates to drive the transistor Q10 as described above. Then, the constant current source 11
Is supplied through the transistor Q10, and the current drawn through the transistor Q2 of the second current amplifier circuit 14, that is, the drive current Icont is reduced accordingly. . As a result, the drive current Iout output from the second current amplifier circuit 14 to the load circuit 13 is controlled to be reduced. The output voltage Vreg is kept constant by the negative feedback control of the drive current Iout by the control circuit 16.
Therefore, even if the power supply device is configured in this manner, the same operation and effect as those of the above-described embodiments can be obtained. In particular, since the first current amplifier circuit 12 can be omitted, the circuit configuration can be further simplified. can do.

The output voltage Vreg applied to the load circuit 13
Control circuit 1 for detecting the feedback and controlling the drive current Iout in negative feedback
6 can be specifically configured as shown in FIGS. 5 and 6, respectively. That is, the voltage detection circuit shown in FIG. 5 operates based on the internal reference voltage forming the bandgap voltage source, and operates the transistor Q6 according to the output voltage Vreg which is divided and detected via the resistors R1 and R2. And two npn transistors Q11 and Q12 whose bases are connected in common.
Is realized mainly by The resistors R9 and R10 connected in series are connected to the emitter of the transistor Q11.
The emitter of the transistor Q12 is connected to the connection point between the resistors R9 and R10 so that the emitter potential is different.

According to the voltage detection circuit thus configured, when the output voltage Vreg is low, the current exclusively through the transistor Q11 becomes larger than the current flowing through the transistor Q12. And the output voltage Vreg
Becomes higher, the difference between the currents flowing through the transistors Q11 and Q12 becomes smaller, and the current flowing through the transistor Q12 becomes larger when the detection voltage Vsens exceeds the internal reference voltage Vref. At this time, the collector voltages of the transistors Q11 and Q12 also increase with the rise of the output voltage Vreg, and the magnitude relationship changes. The output voltage Vsen detected by dividing the voltage via the resistors R1 and R2.
When s reaches a voltage defined by the internal reference voltage Vref based on the bandgap voltage, the collector voltages of the transistors Q11 and Q12 become equal and balanced, and the output voltage Vreg is stabilized.

The control circuit 16 performs negative feedback control on the control current Icont and, consequently, the drive current Iout for the load circuit 13 so that the collector voltages of the transistors Q11 and Q12 in such a voltage detection circuit become equal. As a result, the output voltage Vreg is controlled to be constant. Therefore, an output corresponding to the output voltage Vreg is obtained based on the internal reference voltage using the band gap voltage,
Thus, if the output voltage Vreg is controlled to be constant, a more stable operation can be expected.

The voltage detection circuit shown in FIG. 6 is provided with resistors R7 and R8 provided at the collectors of the transistors Q11 and Q12.
Instead, a current mirror circuit including a pair of transistors Q13 and Q14 is provided, and a current corresponding to the output voltage Vreg is obtained as an output from the current mirror circuit. According to the voltage detection circuit thus configured, the output of the current mirror circuit is connected to the third current amplification circuit 16a.
Through the transistor Q.
By controlling the operation of 6, the drive current Iout and, moreover, the output voltage Vreg can be stabilized more stably by negative feedback control. In particular, according to the power supply circuit having such a circuit configuration, it is suitable for the case where the power supply circuit is formed into an IC.

The present invention is not limited to the circuit configuration shown in each of the above-described embodiments, and the specific circuit configuration is determined according to the specifications such as the current amplification factor required for the current amplification circuit. Various modifications can be made. When the current consumption in the load circuit 13 is small, the second
Even when the current amplification factor of the current amplification circuit 14 is not high, the power supply device can be simply configured using only one current amplification circuit as shown in FIG. In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0034]

As described above, according to the present invention, after supplying a constant drive current to a load circuit with reference to a constant current obtained by a constant current source, the output voltage applied to the load circuit becomes a predetermined voltage. When the output voltage is reached, the drive current is negatively feedback-controlled in accordance with the output voltage to stabilize the output voltage. Therefore, it is possible to realize a power supply device having a simple circuit configuration in which only the operation of the current amplifier circuit is negatively feedback-controlled. it can.
In addition, at the time of power supply, the drive current necessary for the load circuit is supplied, and after reaching a steady state of operation, the drive current is reduced to keep the output voltage constant. Does not flow. In addition, effects such as a reduction in overall current consumption can be obtained.

Further, by realizing the current amplifying circuit using a current mirror circuit, a power supply device having a simple and stable circuit configuration can be realized, and an excessive current does not flow at the time of startup. Therefore, there is an advantage that it is suitable for incorporation into, for example, a two-wire proximity switch.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a power supply device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing output characteristics of the power supply device shown in FIG.

FIG. 3 is a schematic configuration diagram of a power supply device according to a second embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of a power supply device according to a third embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of a power supply device according to a fourth embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of a power supply device according to a fifth embodiment of the present invention.

FIG. 7 is a diagram showing a schematic configuration of a two-wire high-frequency oscillation proximity switch.

[Explanation of symbols]

11 Reference Current Source (Reference Current Iref) 12 First Current Amplifier (Outputs Control Current Icont) 13 Load Circuit 14 Second Current Amplifier (Outputs Drive Current Iout) 15 Reference Voltage Source (Reference Voltage Vref) 16 Control circuit R1, R2 Resistance (detection of output voltage Vreg) Q1, Q2, Q3 Transistor (current mirror circuit) Q4, Q5 Transistor (current mirror circuit) Q6, Q9, Q10 Transistor (for control of control current Icont) Q7, Q8 Transistor (peaking current source circuit)

Claims (5)

[Claims] 1. A power supply device driven by an external power supply to output a constant voltage to a load, comprising: a reference current source that outputs a predetermined reference current; a reference voltage source that generates a predetermined reference voltage; A first current amplification circuit that outputs a predetermined control current based on the reference current; a second current amplification circuit that amplifies the control current and outputs a drive current to a load; A control circuit that controls an operation of the first current amplification circuit based on an output voltage applied to a load and the reference voltage, and adjusts a control current output from the first current amplification circuit. And power supply. 2. The first and second current amplifier circuits,
The power supply device according to claim 1, wherein each of the power supply devices comprises a current mirror circuit. 3. The circuit according to claim 1, wherein said first current amplifier circuit comprises a peaking current source circuit.
A power supply according to claim 1. 4. A power supply device which is driven by an external power supply and outputs a constant voltage to a load, comprising: a reference current source for outputting a predetermined reference current; a reference voltage source for generating a predetermined reference voltage; A current amplifying circuit for amplifying a control current comprising the reference current or a part thereof and outputting a drive current to a load; and the reference current based on an output voltage applied to the load by the drive current and the reference voltage. And a control circuit that varies a control current supplied to the current amplification circuit by bypass-controlling a part of the control circuit and adjusts a control current output from the current amplification circuit. 5. The power supply device according to claim 1, wherein the output voltage applied to the load is detected by resistance division.