JP2008034978A - Load drive circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a load drive circuit which reduces the temperature variance in the drive voltage that an output element supplies to a load. <P>SOLUTION: The load drive circuit is equipped with a power source 12 supplying a first voltage, the output element 13, connected to the power source 12 and outputting the drive voltage for driving the predetermined load 20, and a temperature compensation circuit connected between the power source 12 and an output element 13, wherein the temperature compensation circuit compensates the voltage drop of a first voltage due to the ON-resistance, according to the temperature of the output element 13 for transforming the voltage into a second voltage, and the output element 13 is supplied with the second voltage and supplies the drive voltage that is based on the second voltage, to the load 20. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a load drive circuit that performs temperature compensation of a power supply voltage supplied to an output element that outputs a drive voltage for driving a load.

  Japanese Unexamined Patent Publication No. 63-296506 (Patent Document 1) discloses a temperature compensation circuit for performing temperature compensation of a supplied voltage.

The temperature compensation circuit disclosed in Patent Document 1 includes variable voltage generation means, constant voltage generation means for generating a constant voltage, in order to perform temperature compensation on the voltage supplied to the voltage control type variable attenuator, A switching circuit in which the output voltage of the variable voltage generating means is a temperature compensation voltage in a certain temperature range, and the output voltage of the constant voltage generating means is a temperature compensation voltage at a temperature outside this constant temperature range. is there.
JP-A 63-296506

  However, the temperature compensation voltage generated by the temperature compensation circuit disclosed in Patent Document 1 is fixed at a certain temperature at which the inflection point of the temperature compensation voltage characteristic with respect to the temperature (change point of the change rate of the temperature compensation voltage) is present. . Therefore, the temperature compensation circuit may not be able to generate an appropriate temperature compensation voltage in the operating temperature region.

  For example, if the temperature compensation circuit is incorporated in a load drive circuit that uses a semiconductor for the output element, the output element has a resistance (on-resistance) that varies depending on the temperature. If the temperature-compensated voltage is not supplied to the output element, there is a problem that the variation of the drive voltage supplied from the output element to the external load increases.

  In this case, it is possible to relatively reduce variations in the driving voltage supplied to the external load by reducing the resistance value of the output element by sufficiently increasing the size of the output element. However, the size of the output element is large. As the cost increases, there is a problem that flexible voltage compensation according to temperature becomes difficult.

  Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to supply the output element with a voltage subjected to temperature compensation in accordance with the temperature of the output element. An object of the present invention is to provide a load driving circuit capable of reducing variations in driving voltage supplied from an element to an external load.

  In order to solve the above problems, a load driving circuit according to claim 1 is a power supply that supplies a first voltage, an output element that is connected to the power supply and outputs a driving voltage for driving a predetermined load, A temperature compensation circuit connected between the power supply and the output element, and the temperature compensation circuit performs temperature compensation on the first voltage according to the temperature of the output element and transforms it to the second voltage. The output element is supplied with a second voltage and outputs a drive voltage based on the second voltage.

  According to the load driving circuit of the first aspect, the voltage compensated by the temperature compensation circuit according to the temperature of the output element can be supplied to the output element, so that the output element is supplied to the external load. The variation in driving voltage can be reduced.

  The load driving circuit according to claims 2 and 3 embodies a temperature compensation circuit constituting the load driving circuit according to claim 1. That is, a load driving circuit according to a second aspect is the load driving circuit according to the first aspect, wherein the temperature compensation circuit includes a plurality of resistance elements, and the first voltage is divided at a predetermined ratio to obtain a divided voltage. A voltage dividing resistor to be generated; a reference voltage generating unit that generates a reference voltage; a temperature sensing element that senses the temperature of the output element; and a control unit that supplies a control voltage based on a temperature sensing result of the temperature sensing element to the voltage dividing resistor A differential amplifier having a first input terminal and a second input terminal, each of which is connected to a dividing point of a voltage dividing resistor and a reference voltage generating unit, and amplifies a potential difference between the divided voltage and the reference voltage; It is characterized by including.

  According to a third aspect of the present invention, there is provided the load driving circuit according to the first aspect, wherein the temperature compensation circuit is composed of a plurality of resistance elements, and the first voltage is divided at a predetermined ratio to provide a divided voltage. A reference voltage generating unit that generates a reference voltage from a microcomputer through a D / A converter based on a temperature sensing result of the temperature sensing element; 1 and 2 having a second input terminal, the input terminal being connected to a dividing point of the voltage dividing resistor and a reference voltage generating unit, respectively, and a differential amplifier for amplifying a potential difference between the divided voltage and the reference voltage. It is characterized by.

  The load drive circuit according to claims 4 and 5 embodies a temperature-sensitive element constituting the load drive circuit according to claim 2. The load driving circuit according to claims 6 and 7 embodies the arrangement of the temperature sensitive elements. That is, as the temperature sensitive element, a thermistor can be used as described in claim 4, and the thermistor can be arranged so as to replace the voltage dividing resistor as described in claim 6. Further, as the temperature sensitive element, a diode can be used as described in claim 5, and the diode can be arranged so as to be connected to a voltage dividing resistor as described in claim 7. In the load driving circuit according to the first to seventh aspects, as described in the eighth aspect, a MOS element or a bipolar element can be suitably used as the output element.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or is equivalent, and the description is abbreviate | omitted.

(First embodiment)
FIG. 1 is a diagram showing an outline of a load driving circuit 100 according to the first embodiment of the present invention. The load driving circuit 100 is a power output circuit using a semiconductor for driving an external load (for example, a transmission antenna) 20 including a coil 20a and a capacitor 20b, and includes a power supply 12 for supplying a first voltage, A P-type MOS element 13 as an output element that outputs a driving voltage for driving the external load 20 from the side, and a temperature compensation circuit connected between the power supply 12 and the MOS element 13 are configured. ing. Under such a configuration, the drive voltage output from the MOS element 13 that is supplied with the voltage from the power supply 12 is supplied to the external load 20 via the output terminal 14.

  By the way, the on-resistance of the MOS element 13 has a positive first-order temperature coefficient, and the resistance value of the MOS element 13 varies according to the temperature. Then, the voltage drop due to the on-resistance of the MOS element 13 fluctuates due to the influence of the fluctuation of the resistance value of the MOS element 13, and accordingly, the drive voltage output from the MOS element 13 varies, and the external The load 20 may not be able to exhibit desired performance.

  Therefore, the load driving circuit 100 according to the present embodiment compensates the voltage effect by the on-resistance according to the temperature of the MOS element 13 with respect to the first voltage supplied from the power supply 12 by the temperature compensation circuit, and the second To the voltage (temperature compensation voltage). Then, by supplying the temperature compensated second voltage to the MOS element 13, variations in the driving voltage output from the MOS element 13 are reduced.

  The MOS element 13 is connected to a wire (not shown) (for example, a wiring from the MOS element 13 to the output terminal 14) for transmitting an electric signal. Since heat due to heat generated by the MOS element 13 is transmitted to the wire, its resistance value changes. Therefore, the above temperature compensation is more effective when performed in consideration of the resistance component of the wire.

  The temperature compensation circuit in the load driving circuit 100 includes a bipolar element 19 that transforms the first voltage into a second voltage based on an amplification signal, which will be described later, a reference voltage generator 18 that generates a reference voltage, and a MOS element 13. The controller 17 includes a control unit 17 that outputs a control voltage that varies according to temperature, and a differential amplifier 15.

  The control unit 17 is connected to a temperature sensing element 16 that is disposed in the vicinity of the MOS element 13 and senses the temperature of the MOS element 13. The inverting input terminal (−) of the differential amplifier 15 is connected to the reference voltage generator 18 and supplied with a reference voltage. The non-inverting input terminal (+) is connected to the dividing point of the voltage dividing resistors R1 and R2, and the voltage obtained by subtracting the control voltage from the control unit 17 from the first voltage is divided by the voltage dividing resistors R1 and R2. Pressurized and supplied. R2 is a variable resistor.

  The differential amplifier 15 compares these voltages supplied to the inverting input terminal and the non-inverting input terminal, and outputs an amplified signal obtained by amplifying these fluctuations to the bipolar element 19. By driving the bipolar element 19 with the amplified signal, the first voltage is transformed into the second voltage. Then, the temperature-compensated second voltage is supplied to the MOS element 13. As a result, even if the temperature of the MOS element 13 changes, it is possible to reduce variations in the drive voltage that the MOS element 13 supplies to the external load 20.

  FIG. 2 is a graph showing the relationship between the temperature of the MOS element 13 in the load driving circuit 100 and the drive voltage output from the MOS element 13. FIG. 2A is a graph showing a drive voltage output from the MOS element 13 when a voltage not subjected to temperature compensation in accordance with the temperature of the MOS element 13 is supplied to the MOS element 13. FIG. 2A shows that the drive voltage output from the MOS element 13 decreases as the temperature of the MOS element 13 increases. That is, it shows that the drive voltage varies.

  On the other hand, FIG. 2B is a graph showing a drive voltage output from the MOS element 13 when a voltage subjected to temperature compensation in accordance with the temperature of the MOS element 13 is supplied to the MOS element 13. FIG. 2B shows that the MOS element 13 outputs a substantially constant drive voltage regardless of the temperature of the MOS element 13. That is, it shows that the variation in drive voltage is reduced.

(Second Embodiment)
FIG. 3 is a diagram showing an outline of the load driving circuit 110 according to the second embodiment of the present invention. As shown in FIG. 3, the load driving circuit 110 includes an N-type MOS element 21 as an output element for driving the external load 20 on the low side, and a first voltage supplied from the power source 12 by a temperature compensation circuit described later. On the other hand, temperature compensation corresponding to the temperature of the MOS element 21 is performed, and the voltage is transformed to the second voltage (temperature compensation voltage). Then, by supplying the second voltage to the load 20, variations in voltage drop due to the MOS element 21 are reduced.

  The temperature compensation circuit in the load driving circuit 110 includes a bipolar element 19 that transforms a first voltage into a second voltage, a reference voltage generation unit 18 that generates a reference voltage, a thermistor Th, and a differential amplifier 15. It is configured to include.

  The thermistor Th is formed by sintering a semiconductor mixture mainly composed of a metal oxide and providing a lead wire on the sintered semiconductor mixture, and its resistance value increases at a low temperature and increases at a high temperature. A semiconductor resistance element having a (positive primary temperature coefficient) and connected in series with a resistor R3.

  The inverting input terminal (−) of the differential amplifier 15 is connected to the reference voltage generator 18. The non-inverting input terminal (+) is connected between the thermistor Th and the resistor R3, and the first voltage is divided and supplied by the thermistor Th and the resistor R3.

  The differential amplifier 15 compares these voltages supplied to the inverting input terminal and the non-inverting input terminal, and outputs an amplified signal obtained by amplifying these fluctuations to the bipolar element 19. By driving the bipolar element 19 with the amplified signal, the first voltage is transformed into the second voltage. Then, the temperature-compensated second voltage is supplied to the MOS element 21. As a result, even if the temperature of the MOS element 13 changes, it is possible to reduce variations in the drive voltage that the MOS element 13 supplies to the external load 20.

(Third embodiment)
FIG. 4 is a diagram showing an outline of the load driving circuit 120 in the third embodiment of the present invention. As shown in FIG. 4, the load driving circuit 120 includes a P-type MOS element 23 and an N-type MOS element 24 as output elements that bridge drive the external load 20. Is subjected to temperature compensation in accordance with the temperatures of the MOS elements 23 and 24, and transformed to a second voltage (temperature compensation voltage). Then, by supplying the second voltage to the MOS elements 23 and 24, variation in the drive voltage output from the MOS elements 23 and 24 is reduced.

  The temperature compensation circuit in the load driving circuit 120 includes a bipolar element 19 to which a first voltage is supplied, a reference voltage generation unit 18 that generates a reference voltage, a diode group 22, and a differential amplifier 15. Has been.

  The diode group 22 is formed by connecting a plurality of diodes each having a negative primary temperature coefficient in series, and the diode group 22 formed in this way is connected in series to the resistors R4 and R5. .

  The inverting input terminal (−) of the differential amplifier 15 is connected to the reference voltage generator 18. The non-inverting input terminal (+) is connected to the voltage dividing resistors R4 and R5, and the voltage obtained by subtracting the forward voltage drop (Vf) of the diode group 22 from the first voltage is the voltage dividing resistor. Divided by R4 and R5 and supplied. The rate of change of the first voltage input to the non-inverting input terminal (+) of the differential amplifier 15 with respect to temperature can be changed by changing the number of diodes and the values of the voltage dividing resistors R4 and R5. .

The differential amplifier 15 compares these voltages supplied to the inverting input terminal and the non-inverting input terminal, and outputs an amplified signal obtained by amplifying these fluctuations to the bipolar element 19.
By driving the bipolar element 19 with the amplified signal, the first voltage is transformed into the second voltage. Then, the temperature compensated second voltage is supplied to the MOS elements 23 and 24. Thereby, even if the temperature of the MOS elements 23 and 24 changes, the variation in the drive voltage supplied to the external load 20 by the MOS elements 23 and 24 can be reduced.

(Fourth embodiment)
FIG. 5 is a diagram showing an outline of a load driving circuit 130 in the fourth embodiment of the present invention. Even if the elements constituting the circuit have complicated temperature characteristics, the load driving circuit 130 can suitably perform temperature compensation by storing them in the memory 33 and performing control by the microcomputer 32. It is a circuit that can.

  As shown in FIG. 5, the load driving circuit 130 includes a bipolar element 25 as an output element that drives the external load 20 on the high side, and the first voltage supplied from the power supply 12 is supplied to the first voltage supplied by the temperature compensation circuit described later. On the other hand, temperature compensation is performed according to the temperature of the bipolar element 25 and the like, and the voltage is transformed to the second voltage. Then, by supplying the second voltage to the bipolar element 25, variation in the drive voltage output from the bipolar element 25 is reduced.

  The temperature compensation circuit in the load driving circuit 130 includes a temperature characteristic of the bipolar element 19 to which the first voltage is supplied, the bipolar element 25, a wire connected to transmit an electric signal to the bipolar element 25, the external load 20, and the like. A memory 33 for storing data relating to the above, a microcomputer 32 to which a temperature sensitive result such as the bipolar element 25 is inputted, and a D / A conversion for converting a digital signal output from the microcomputer 32 into an analog signal based on the temperature sensitive result. The unit 31 and the differential amplifier 15 are included.

  The inverting input terminal (−) of the differential amplifier 15 is connected to the D / A converter 31 and is supplied with an analog signal based on temperature data of the bipolar element 25 and the like. The non-inverting input terminal (+) is connected to the dividing point of the voltage dividing resistors R5 and R6, and the first voltage is divided and supplied by the voltage dividing resistors R5 and R6.

  The differential amplifier 15 compares these voltages supplied to the inverting input terminal and the non-inverting input terminal, and outputs an amplified signal obtained by amplifying these fluctuations to the bipolar element 19. By driving the bipolar element 19 with the amplified signal, the first voltage is transformed into the second voltage. Then, the temperature-compensated second voltage is supplied to the bipolar element 25. As a result, even if the temperature of the bipolar element 25 changes, it is possible to reduce variations in the drive voltage that the bipolar element 25 supplies to the external load 20.

  The present invention is not limited to the embodiment described above, and various modifications can be made without departing from the spirit of the present invention. In the invention according to the dependent claims of the present invention, a part of the constituent features of the dependent claims can be omitted.

It is a figure which shows the load drive circuit in the 1st Embodiment of this invention. It is the graph which showed the relationship between output element temperature and drive voltage, (a) is a graph when temperature compensation is not performed, (b) is a graph when temperature compensation is performed. It is a figure which shows the load drive circuit in the 2nd Embodiment of this invention. It is a figure which shows the load drive circuit in the 3rd Embodiment of this invention. It is a figure which shows the load drive circuit in the 4th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 12 ... Power supply 13, 21, 23, 24, 25 ... Output element, 14 ... Output terminal, 15 ... Differential amplifier, 16 ... Temperature sensitive element, 17 ... Control part , 18 ... reference voltage generator, 20 ... external load, 31 ... D / A converter, 32 ... microcomputer, 33 ... memory

Claims (8)

A power supply for supplying a first voltage;
An output element connected to the power source and outputting a driving voltage for driving a predetermined load;
A temperature compensation circuit connected between the power source and the output element,
The temperature compensation circuit is:
The first voltage is subjected to temperature compensation according to the temperature of the output element and transformed to a second voltage,
The output element is
A load driving circuit that is supplied with the second voltage and outputs the driving voltage based on the second voltage. The temperature compensation circuit is:
A voltage dividing resistor configured by a plurality of resistance elements and generating a divided voltage by dividing the first voltage at a predetermined ratio;
A reference voltage generator for generating a reference voltage;
A temperature sensing element for sensing the temperature of the output element;
A control unit for supplying a control voltage based on the temperature sensing result of the temperature sensing element to the voltage dividing resistor;
A differential amplifier having first and second input terminals, each of which is connected to a dividing point of the voltage dividing resistor and the reference voltage generating unit, and amplifies a potential difference between the divided voltage and the reference voltage The load driving circuit according to claim 1, comprising: The temperature compensation circuit is:
A voltage dividing resistor configured by a plurality of resistance elements and generating a divided voltage by dividing the first voltage at a predetermined ratio;
A temperature sensing element for sensing the temperature of the output element;
A reference voltage generating unit that generates a reference voltage from a microcomputer through a D / A converter based on the temperature sensing result of the temperature sensing element;
A differential amplifier having first and second input terminals, each of which is connected to a dividing point of the voltage dividing resistor and the reference voltage generating unit, and amplifies a potential difference between the divided voltage and the reference voltage The load driving circuit according to claim 1, comprising:   The load driving circuit according to claim 2, wherein the temperature sensitive element is a thermistor.   The load driving circuit according to claim 2, wherein the temperature sensitive element is configured by a diode.   5. The load driving circuit according to claim 4, wherein the thermistor is arranged so as to replace one of the voltage dividing resistors.   The load driving circuit according to claim 5, wherein the diode is connected to the voltage dividing resistor.   The load drive circuit according to claim 1, wherein the output element is configured by a MOS element or a bipolar element.

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