JP2018169874A - Load control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a load control device capable of controlling the amount of voltage applied to a load without detecting current flowing through a load using a shunt resistor.SOLUTION: A load control device for controlling the amount of electric power to be supplied to a load R1 by turning on and off a first switching element Q1 provided in a power supply path comprises: a constant current section (constant current circuit 11) for supplying a constant current Ito the load R1; an error detection section (amplifier circuit AMP1) for detecting an error between voltage Vbetween both ends of the load R1 due to the constant current Iand a reference voltage Vwhen the first switching element Q1 is OFF; and a load control unit (comparator COMP1 and oscillator 13) for controlling an ON period of the first switching element Q1 so that the voltage Vbetween both ends across the load R1 by the constant current Ibecomes the reference voltage Von the basis of a detection result by the error detection section.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a load control device that controls the amount of power supplied to a load.

  There has been proposed a load control device that controls a voltage applied to a load based on a voltage across the load detected when power is supplied to the load and a current flowing through the load (see, for example, Patent Document 1).

JP 2012-164096 Gazette

  However, in the prior art, since the resistance value of the load varies depending on the temperature like a heater, the current flowing through the heater is detected using a shunt resistor. Therefore, there is a problem that a loss of the shunt resistor occurs.

  An object of the present invention is to solve the above-described problems of the prior art and provide a load control device capable of controlling the amount of voltage applied to a load without detecting a current flowing through the load using a shunt resistor. is there.

The load control device of the present invention is a load control device that controls the amount of power supplied to the load by turning on and off the first switch element provided in the power supply path, and a constant current unit that supplies a constant current to the load; An error detector for detecting an error between a voltage across the load due to the constant current and a reference voltage when the first switch element is off, and the load due to the constant current based on a detection result by the error detector; And a load control unit that controls an ON period of the first switch element so that a voltage between both ends of the first switch element becomes the reference voltage.
Furthermore, in the load control device of the present invention, the load control device further includes a reference voltage input terminal that receives an input of the reference voltage from an external reference voltage source, and the error detection unit includes the voltage across the load by the constant current and the reference An error from the reference voltage input from the voltage input terminal may be detected.
Furthermore, in the load control device of the present invention, a second switch element that turns on and off the supply of the constant current from the constant current unit to the load, and the first switch element is turned off and a preset delay time elapses. Then, an error detection period by the error detection unit and a constant current control unit for turning on the second switch element may be provided.
Furthermore, in the load control device of the present invention, a constant current control terminal to which an external resistor is connected is provided, and the constant current unit supplies a current whose voltage between both ends becomes the reference voltage when flowing through the external resistor. May be generated as
Further, in the load control device according to the present invention, the load control unit may be configured such that the voltage across the load when the first switch element is on, the voltage across the load due to the constant current, and the constant current. The ON period of the first switch element may be controlled so that the target power value is obtained.

  According to the present invention, the resistance value of the load is detected as a voltage across the load by a constant current, and the current flowing through the load is detected using a shunt resistor by controlling the voltage across the load to be the reference voltage. Therefore, it is possible to control the amount of voltage applied to the load, and it is possible to reduce the loss required for controlling the amount of voltage.

It is a circuit block diagram which shows the circuit structure of 1st Embodiment of the load control apparatus which concerns on this invention. It is an operation | movement waveform diagram of the load control apparatus shown in FIG. It is a figure which shows the temperature-resistance value characteristic example of the load shown in FIG. It is a circuit block diagram which shows the circuit structure of 2nd Embodiment of the load control apparatus which concerns on this invention. It is a circuit block diagram which shows the circuit structure of 3rd Embodiment of the load control apparatus which concerns on this invention. It is a circuit block diagram which shows the circuit structure of 4th Embodiment of the load control apparatus which concerns on this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that in the following embodiments, the same reference numerals are given to configurations showing similar functions, and description thereof will be omitted as appropriate.

(First embodiment)
Referring to FIG. 1, the load control device 1 of the first embodiment has a power input terminal BATT to which a power source E1 is connected, a power output terminal OUT that outputs power to the load R1, and a ground terminal GND. The power supply to the load R1 connected between the power output terminal OUT and the ground terminal GND is controlled.

  The load control device 1 includes a first switch element Q1, a second switch element Q2, a constant current circuit 11, a reference voltage source E2, an amplifier circuit AMP1, a sample hold circuit 12, an oscillator 13, and a comparator COMP1. And a delay one-shot circuit 14.

  The first switch element Q1 is provided in a power supply path between the power input terminal BATT and the power output terminal OUT, and controls energization to the load R1, that is, the amount of power by turning on and off. In the present embodiment, an NMOS transistor is used as the first switch element Q1.

A constant current circuit 11 and a second switch element Q2 are connected in series between the power input terminal BATT and the power output terminal OUT. Thus, the second switching element Q2 when it is turned on, a constant current I ₁ from the constant current circuit 11 is supplied to the load R1. In the present embodiment, an NMOS transistor is used as the second switch element Q2.

In the amplifier circuit AMP1, a non-inverting input terminal is connected to the power supply output terminal OUT, and an inverting input terminal is connected to the ground terminal GND via the reference voltage source E2. Amplifier circuit AMP1, the voltage value of the power supply output terminal OUT, and that is compared with the voltage value V _R1 generated across the load R1, and a reference voltage V _ref generated by the reference voltage source E2, corresponding to the difference The voltage is output from the output terminal. That is, the amplifier circuit AMP1, the first switching element Q1 is in the OFF state, which functions as an error detecting unit for detecting an error _{V ref} and the voltage across value _{V R1} and the reference voltage of the load Ri by constant current _{I 1.}

The sample and hold circuit 12 is a circuit that samples and holds the voltage output from the amplifier circuit AMP1, and includes a capacitor C1 and a switch SW1. The output terminal of the amplifier circuit AMP1 is connected to one terminal of the switch SW1, and the other terminal of the switch SW1 is connected to one terminal of the capacitor C1. The other terminal of the capacitor C1 is connected to the ground terminal GND. As a result, the voltage output from the amplifier circuit AMP1 when the switch SW1 is on is charged in the capacitor C1, and the voltage across the capacitor C1 is held as the hold voltage V _c1 when the switch SW1 is turned off.

In the comparator COMP1, the non-inverting input terminal is connected to the oscillator 13 that generates and outputs the “sawtooth wave V _saw ”, and the inverting input terminal is connected to the output terminal of the sample hold circuit 12 (a connection point between the switch SW1 and the capacitor C1). Has been. The output terminal of the comparator COMP1 is connected to the gate of the first switch element Q1. The comparator COMP1 compares the “sawtooth wave V _saw ” output from the oscillator 13 with the hold voltage V _c1 of the sample hold circuit 12 to generate a PWM signal for controlling on / off of the first switch element Q1. Output.

The output terminal of the comparator COMP1 is connected to the input terminal of the delay one-shot circuit 14. The delay one-shot circuit 14 detects the falling edge of the PWM signal output from the comparator COMP1, that is, the turn-off of the first switch element Q1. The delay one-shot circuit 14, the delay time T _d that is set in advance by detecting the falling edge of the PWM signal after the elapse outputs a pulse signal having a preset pulse width T _w from the output terminal. The delay time _Td is a waiting time until the first switch element Q1 is completely turned off. As a result, the delay one-shot circuit 14
The first switching element Q1 is turned off, after a delay time T _d elapses, during the pulse width T _w to ensure error detection period by the error detection unit functions as a constant current control unit for turning on the second switching element Q2 .

  The output terminal of the delay one-shot circuit 14 is connected to the gate of the second switch element Q2 and the control terminal of the sample hold circuit 12. Thus, the second switch element Q2 and the switch SW1 of the sample hold circuit 12 are turned on only while the pulse signal is output from the delay one-shot circuit 14.

Next, the operation of the load control device 1 will be described in detail with reference to FIG.
FIG. 2 is an operation waveform of the load control device 1. From both of (a) and (b), a “saw wave V _saw ” output from the oscillator 13 compared by the comparator COMP 1 and a sample hold circuit are shown. 12 shows output waveforms of a hold voltage V _{c1 of} 12, a PWM signal output from the comparator COMP1, and a pulse signal output from the delay one-shot circuit 14.

Referring to FIG. 2, when it falls below the “saw wave V _saw ” output from the oscillator 13 at time t ₁ and the hold voltage V _c1 of the sample hold circuit 12, the first switch element Q 1 output from the comparator COMP 1 is turned off. To do.

Delay one-shot circuit 14, PWM signal detects the fall delay time T _d is later passed, and outputs a pulse signal having a preset pulse width T _w from the output terminal.

The pulse signal output from the delay one-shot circuit 14, the second switching element Q2 is turned on, a constant current I ₁ flows through the load R1, the voltage V _R1 generated by the voltage drop across the load R1. The voltage V _R1 generated at both ends of the load R1 is compared with the reference voltage V _ref of the reference voltage source E2 in the amplifier circuit AMP1, and an error between the voltage V _R1 and the voltage V _ref is amplified and output.

The reference voltage V _ref generated by the reference voltage source E2 is a value serving as a reference for temperature control of the load R1. For example, when the temperature-resistance characteristic of the load R1 is shown in FIG. 3, the target temperature is 1000 ° C., and the constant current I ₁ flowing through the load R1 is 100 mA, the reference voltage V _ref is 1000 ° C. at the load R1. Is set to V _ref = 1Ω × 100 mA = 0.1 V, which is obtained by multiplying the resistance value 1Ω by a constant current I ₁ : 100 mA.

In the sample-hold circuit 12, the pulse signal output from the delay one-shot circuit 14, while the pulse width T _w, the switch SW1 is turned on. As a result, the error value amplified by the amplifier circuit AMP1 is held in the capacitor C1 as the hold voltage V _C1 .

The hold voltage V _C1 is input to the inverting input terminal of the comparator COMP1. A “sawtooth wave V _saw ” generated by the oscillator 13 is inputted to the non-inverting input terminal of the comparator COMP1, and the first switch element Q1 is turned on / off by comparing the hold voltage V _C1 with the “sawtooth wave V _saw ”. The on-duty of the PWM signal to be controlled is determined. That is, the comparator COMP1 and the oscillator 13 are based on the hold voltage _Vc1 that is a detection result by the error detector, so that the voltage V _R1 across the load R1 due to a constant current becomes the reference voltage _Vref. It functions as a load control unit that controls the on-period.

In FIG. 2 (a), the temperature of the load R1 is higher than the target temperature, has been shown an example in which the voltage _{V R1} exceeds the _{V ref.} In this case, the hold voltage V _C1 is increased and the on-duty of the PWM signal is decreased, so that the energization amount to the load R1 is decreased. As a result, the temperature of the load R1 is lowered and controlled to reach the target temperature (resistance value).

In FIG. 2 (b), the temperature of the load R1 becomes lower than the target temperature, has been shown an example in which the voltage _{V R1} falls below the _{V ref.} In this case, the hold voltage V _C1 decreases and the on-duty of the PWM signal increases, so that the energization amount to the load R1 increases. As a result, the temperature of the load R1 is increased and controlled to reach the target temperature (resistance value).

In this embodiment, at the OFF time of the first switching element Q1, passing a constant current _{I 1} to the load R1, holds the error between the voltage _{V R1} and the voltage _{V ref} as a hold voltage _{V C1.} Therefore, an upper limit of 90%, for example, is set for the on-duty of the PWM signal in order to secure a time (delay time T _d + pulse width T _saw ) until the hold voltage V _C1 is held.

Further, in this embodiment, by turning on and off the second switching element Q2, has been a constant current I ₁ only when off the first switch element Q1 to flow in the resistor R1, always a constant current I ₁ May flow through the resistor R1. In this case, it can be calculated as base energization amount to heat the constant current I ₁ also load R1.

Further, when the power is turned on, a low initial value voltage is set instead of the reference voltage V _ref , and when the load RI rises in temperature and time passes, the initial value voltage is increased stepwise to the target reference voltage V _ref. good. In this case, since the error signal does not become too large even when the load RI at the time of power-on is not warm, the on-duty control in the PWM signal can be performed satisfactorily.

(Second Embodiment)
Referring to FIG. 4, the load control device 1a of the second embodiment has a reference voltage input terminal VREF that receives an input of the reference voltage Vref instead of the reference voltage source E2. Thus, the reference voltage Vref can be arbitrarily set by the external reference voltage source E3 connected between the reference voltage input terminal VREF and the ground terminal GND, so that the target temperature (resistance value) of the load R1 can be easily set. It becomes possible to change.

(Third embodiment)
Referring to FIG. 5, the load control device 1b of the third embodiment has a constant current control terminal IREF, and is set by an external resistor R2 connected between the constant current control terminal IREF and the ground terminal GND. Is configured to do.

The load control device 1b, and a current mirror circuit by the PMOS transistor Q3 and the PMOS transistors Q4, an amplifier circuit AMP2, the NMOS transistor Q5 is provided as a constant current circuit for generating a constant current _{I 1} flowing through the load R1.

  The sources of the PMOS transistor Q3 and the PMOS transistor Q4 whose gates are connected to each other are connected to the power input terminal BATT. The drain of the PMOS transistor Q3 is connected to the gate of the PMOS transistor Q3 and is connected to the drain of the NMOS transistor Q5 through the second switch Q2. The drain of the PMOS transistor Q4 is connected to the power supply output terminal OUT.

  The amplifier circuit AMP2 has an inverting input terminal connected to the drain of the NMOS transistor Q5 and the constant current control terminal IREF, a non-inverting input terminal connected to the reference voltage source E2, and an output terminal connected to the gate of the NMOS transistor Q5. Yes.

  Thus, the resistance value of the resistor R2 connected to the constant current control terminal IREF is set to the resistance value at the target temperature of the load R1, so that the load R1 is controlled to have the target temperature (resistance value).

That is, constant current I ₁ = V _ref ÷ R2
The resistance value of the load R1 is controlled so that V _ref ÷ I ₁ = R2. Thereby, the target temperature (resistance value) of the load R1 can be easily changed by the external resistor R2 connected between the constant current control terminal IREF and the ground terminal GND.

(Fourth embodiment)
Referring to FIG. 6, the load control device 1c according to the fourth embodiment is an analog circuit (reference voltage source E2, amplifier circuit AMP1, sample hold circuit 12, oscillator 13, comparator COMP1, The function realized by the delay one-shot circuit 14) is constituted by an analog-digital converter (ADC) 21 and an arithmetic circuit 22.

ADC21 is a voltage _{V R1} generated across the load R1 is converted to a digital value input to the arithmetic circuit 22.

  The arithmetic circuit 22 is an arithmetic processing circuit such as a microcomputer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The ROM stores a control program for performing operation control. The CPU of the arithmetic circuit 22 controls the load control device 1c by reading the control program stored in the ROM and developing the control program in the RAM.

Arithmetic circuit 22 turns on the second switching element Q2 in the OFF period of the PWM signal by itself to output a constant current is supplied I ₁ to the load R1. Then, the voltage V _R1 converted into a digital value by the ADC 21 is received, and the on-duty of the PWM signal is controlled by comparing the voltage V _R1 with a threshold corresponding to the reference voltage V _ref .

  In the load control device 1c of the fourth embodiment, simple power control for the load R1 is possible by changing the calculation method of the arithmetic circuit 22.

A voltage generated in the load R1 when the first switch element Q1 is on is V _{R1_on,} and a voltage generated when the first switch element Q1 is off is V _{R1_oFF} . V _{R1_oFF} becomes V _{R1_oFF} = I ₁ × R1, and when rewritten, R1 = V _{R1_oFF} ÷ I ₁ .

Further, it is assumed that the electric power assumed to be applied to the load R1 is Pr1. Pr1 is the product of the applied voltage Vr1 and the current Ir1 flowing at that time, and when the resistance value R1 is used,
It can be rewritten as Pr1 = (Vr1) ² ÷ R1.

Vr1 _is that of _{= V R1_on,} R1 _{is = V R1_oFF} ÷ _{I 1.} Therefore, the power Pr1 is expressed as follows using V _{R1 —} on, V _{R1 — oFF} , and I ₁ .
Pr1 = (V _{R1_on} ) ² ÷ R1 = (V _{R1_on} ) ² ÷ (V _{R1_oFF} ÷ I ₁ )

Here, V _{R1_on} and V _{R1_oFF} are values that can be detected by the ADC 21, and I ₁ is a value recognized as a set value.
Therefore, the calculation circuit 22 performs the above calculation using V _{R1_on} , V _{R1_oFF,} and I ₁ , calculates the optimum on-duty so as to obtain the target power value Pr 1, and can perform PWM control.

As described above, according to the present embodiment, the load control device controls the amount of power supplied to the load R1 by turning on and off the first switch element Q1 provided in the power supply path. constant current unit supplies the I ₁ and (constant current circuit 11), the error first switching element Q1 is in the oFF state, to detect the error between the voltage across _{V R1} and the reference voltage _{V ref} of the load R1 by constant current _{I 1} detecting section (amplifier circuit AMP1), based on the result of detection by the error detection unit, the on-period of the first switching element Q1 as the voltage across _{V R1} of the load R1 from the constant current _{I 1} becomes the reference voltage _{V ref} And a load control unit (comparator COMP1 and oscillator 13) to be controlled.
This configuration, the resistance value of the load R2 is detected as the voltage across V _R1 of the load R1 by constant current I _1, by controlling so that the voltage across V _R1 becomes the reference voltage V _ref, by using a shunt resistor Without detecting the resistance flowing through the load, it is possible to control the amount of voltage applied to the load, and to reduce the loss associated with the control of the amount of voltage.

Further, the present embodiment includes a reference voltage input terminal VREF that receives an input of the reference voltage V _ref from the external reference voltage source E3, and the error detection unit has a voltage V _R1 across the load R1 due to the constant current I _1. And the reference voltage V _ref input from the reference voltage input terminal are detected.
With this configuration, the reference voltage Vref can be arbitrarily set by the external reference voltage source E3 connected between the reference voltage input terminal VREF and the ground terminal GND, so that the target temperature (resistance value) of the load R1 can be easily set. It becomes possible to change to.

Further, in this embodiment, a second switching element Q2 to turn on and off the supply of the constant current I ₁ from the constant current unit to the load R1, the first switching element Q1 is turned off, the preset delay time T _d after lapse, and a constant-current control unit that turns on the, second switching element Q2 during the pulse width T _w to ensure error detection period by the error detection unit (delay one-shot circuit 14).
With this configuration, when off the first switching element Q1, only while ensuring the error detection period by the error detection unit, since it only supplying a small constant current I ₁ to the load R1, the voltage across V _R1 of the load R1 Loss on detection can be reduced.

Further, in this embodiment, comprises a constant-current control terminal IREF external resistor R2 is connected, the constant current unit, the current voltage across V _R1 is flowed into the external resistor R2 becomes the reference voltage V _ref Is generated as a constant current I ₁ .
With this configuration, the target temperature (resistance value) of the load R1 can be easily changed by the external resistor R2 connected between the constant current control terminal IREF and the ground terminal GND.

Further, in the present embodiment, the arithmetic circuit 22 includes a voltage _{V RI_on} across the first switching element Q1 is at the on-load R1, and the voltage _{V R1_off} across the load R1 by constant current _{I 1,} a constant current I ₁ to control the ON period of the first switch element Q1 so that the target power value is obtained.
With this configuration, the optimum on-duty can be calculated so as to achieve the target power value Pr1, and PWM control can be performed.

  As mentioned above, although this invention was demonstrated by specific embodiment, the said embodiment is an example and it cannot be overemphasized that it can change and implement in the range which does not deviate from the meaning of this invention.

1, 1a, 1b, 1c Load control device 11 Constant current circuit 12 Sample hold circuit 13 Oscillator 14 Delay one shot circuit 21 Analog to digital converter (ADC)
22 arithmetic circuit AMP1, AMP2 amplifier circuit C1 capacitor COMP1 comparator E1 power supply E2, E3 reference voltage source Q1 first switch element Q2 second switch element Q3, Q4 PMOS transistor Q5 NMOS transistor SW1 switch R1 load R2 resistor BATT power input terminal IREF Constant current control terminal GND Ground terminal OUT Power output terminal VREF Reference voltage input terminal

Claims (5)

A load control device that controls the amount of power supplied to a load by turning on and off a first switch element provided in a power supply path,
A constant current section for supplying a constant current to the load;
An error detector that detects an error between a voltage across the load due to the constant current and a reference voltage when the first switch element is off;
A load control unit that controls an ON period of the first switch element so that a voltage across the load due to the constant current becomes the reference voltage based on a detection result by the error detection unit. A characteristic load control device. Comprising a reference voltage input terminal for receiving an input of the reference voltage from an external reference voltage source;
The load control device according to claim 1, wherein the error detection unit detects an error between a voltage across the load due to the constant current and the reference voltage input from the reference voltage input terminal. A second switch element for turning on and off the supply of the constant current from the constant current unit to the load;
An error detection period by the error detection unit after the first switch element is turned off and a preset delay time has elapsed; and a constant current control unit that turns on the second switch element. The load control device according to claim 1 or 2. Comprising a constant current control terminal to which an external resistor is connected;
4. The load control device according to claim 1, wherein when the constant current section flows through the external resistor, the constant current section generates a current whose voltage between both ends becomes the reference voltage as the constant current. 5.   The load control unit has a target power value based on the voltage across the load when the first switch element is on, the voltage across the load due to the constant current, and the constant current. The load control device according to claim 1, wherein an on period of the first switch element is controlled.

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