JP4001685B2 - Load disconnection detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention generally relates to an apparatus for detecting disconnection of a load, and more particularly to a load disconnection detection apparatus for a moving body using a current detection circuit.
[0002]
[Prior art]
Conventionally, a load current is passed through a shunt resistor, a minute potential difference between both ends of the shunt resistor is amplified by a current detection circuit that is usually composed of a differential amplifier, and the output signal is analogized by an A / D converter. A system is known in which a signal is converted into a digital signal, the digital signal is read by a microcomputer, and the read value is compared with a preset threshold value to determine the presence or absence of load disconnection. In particular, the system has been used to detect the disconnection of a lamp as a load for a moving body such as an automobile. Hereinafter, the “load” is referred to as “lamp load” or simply “lamp”.
[0003]
In the current detection circuit used in the lamp disconnection detection device of the prior art, a current I _L equal to the load current of the lamp flows through the shunt resistor having the resistance value R _{S due} to the power supply voltage V _B , and the potential difference between both ends of the shunt resistor. as an input signal, the output voltage V _O from the amplifying circuit 7 is expressed by the following equation is output.
[0004]
[Expression 1]
V _O = G * (R _S * I _L ± V _OS ± V _TD )
= G * [R _S * [V _B / (R _S + R _L )] ± V _OS ± V _TD ] (1)
[0005]
Here, G is the gain of the amplifier circuit, R _L is the resistance value of the lamp, V _OS is the input offset voltage of the differential amplifier, and V _TD is the input equivalent drift voltage of the differential amplifier due to temperature change.
[0006]
As apparent from the above equation (1), when the power supply voltage V _B varies with respect to the set value, a problem that also vary the load current I _L of the lamp, as a result, the output voltage V _O of the current detection circuit changes was there.
[0007]
In order to solve this problem, conventionally, not only the output voltage V _O of the current detection circuit but also the power supply voltage V _B is input to the A / D converter, and the fluctuation of the power supply voltage is read by the microcomputer, thereby This prevented erroneous determination of lamp breakage.
[0008]
[Problems to be solved by the invention]
However, since it is necessary to perform A / D conversion twice for the output voltage V _O and the power supply voltage V _B , the conversion error increases and the detection accuracy of the lamp breakage is lowered.
[0009]
Accordingly, an object of the present invention is to provide a lamp load disconnection detecting device capable of removing the influence of power supply voltage fluctuations and improving the load current detection accuracy of the lamp.
[0010]
[Means for Solving the Problems]
To achieve the above purpose, the load disconnection detecting apparatus of the invention described in claim 1, amplification with the input and the resistance of the resistance value R s which current flows to the lamp load from the power supply, the voltage between the terminals of the resistor comprising a current detection circuit including an amplifier circuit rate G, a, in determining lamp load disconnection detecting device whether the disconnection of the lamp load from the output voltage Vo of the current detection circuit, the lamp normally in the setting power source voltage V _BS the load current at the I _LS, the source voltage V maximum value V _BH of _B, and the minimum value V _BL, the supply voltage fluctuation and ΔV _B = V _BH -V _BL, corresponding to the V _BH and V _BL When the lamp normal load current is I _LH and I _LL , and the load current fluctuation is ΔI _L = I _LH −I _LL ,
Correcting the output voltage Vo of the current detection circuit so as to cancel a voltage proportional to the power supply voltage V _B represented by _{G * Rs * ΔI L / ΔV} B * V B constituting the output voltage Vo of the current detection circuit The first correcting means for canceling out the constant voltage independent of the power supply voltage V _B indicated by G * Rs * ΔI _L / ΔV _B * V _BS constituting the output voltage Vo of the current detection circuit. And second correction means for correcting the input voltage of the current detection circuit.
[0011]
Improve lamp load current detection accuracy by limiting the load current value of the lamp for which the highest detection accuracy is required and the current value range in which correction of power supply voltage fluctuations works effectively using the first correction means And minimizing the current detection circuit configuration at the same time.
[0012]
Furthermore, by using the second correction means, not only the constant term of the correction voltage unrelated to the fluctuation of the power supply voltage but also the first correction means and the offset voltage of the amplifier circuit (differential amplifier) can be corrected. It becomes possible.
[0013]
In order to achieve the above object, the load disconnection detecting device of the invention described in claim 2 is characterized in that the first correction means includes a voltage dividing circuit for a power supply voltage. The power supply voltage dividing circuit can detect the fluctuation proportional term and convert it to a desired level.
[0014]
In order to achieve the object, the load disconnection detecting device of the invention described in claim 3 is characterized in that the first correction means includes an addition / subtraction circuit. By the addition / subtraction circuit, it becomes possible to correct the output voltage of the current detection circuit in accordance with the fluctuation proportional term converted to the desired level.
[0015]
In order to achieve the object, in the load disconnection detecting device according to the invention described in claim 4, the second correction means includes a constant current circuit for operating the input voltage of the current detection circuit according to a current value. It is characterized by that. By changing the constant current value using the constant current circuit, the input bias condition can be changed, the output offset voltage can be corrected, and the variation among lots can be eliminated.
[0016]
In order to achieve the object, in the load disconnection detecting device according to the invention described in claim 5, the second correction means comprises a variable resistor for operating the input voltage of the current detection circuit by a resistance value. It is characterized by. By varying the resistance value using a variable resistor, the input bias condition can be changed, the output offset voltage can be corrected, and variations among lots can be eliminated.
[0017]
In order to achieve the object, the load disconnection detecting device according to the invention described in claim 6 is characterized in that the second correction means is a constant current circuit for operating an input voltage of the current detection circuit according to a current value, and a resistor. A variable resistor for operating an input voltage of the current detection circuit according to a value is provided, and the temperature coefficient of the constant current circuit current is set so as to cancel the temperature coefficient of the variable resistor.
[0018]
By setting the temperature coefficient of the constant current circuit current so as to cancel the temperature coefficient of the variable resistor, it is possible to minimize the drift voltage of the current detection circuit due to a temperature change and further improve the detection accuracy.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0020]
FIG. 1 is a block diagram showing the overall configuration of a lamp breakage detection device 1 according to the present invention. The apparatus 1 includes a lamp power source 2, a current detection circuit 3, a lamp load 4, an A / D converter 5, and a microcomputer 6. A load current I _L flowing through the lamp load 4 is detected by the current detection circuit 3 and output as an analog voltage V _O. Next, the analog output voltage V _O is converted into a digital value by the A / D converter 5, and this value is read by the microcomputer 6, and the read value is compared with a preset threshold value. The presence or absence is determined.
[0021]
FIG. 2 is a block diagram showing a reference example of the current detection circuit 3 according to the present invention, and FIG. 3 is a block diagram showing a first embodiment of the current detection circuit 3 according to the present invention . The current detection circuit 3 includes a shunt resistor R _S , an amplifier circuit 7, a first correction unit 8, and a second correction unit 9 . The load current I _L of the lamp 4 flows through the shunt resistor R _S for current detection, and the voltage drop R _S I _L is brought to a predetermined level necessary as an input of the subsequent A / D converter 5 by the amplifier circuit 7. It is amplified to be outputted as a voltage V _O. The first correction means 8 is connected to the amplifier circuit 7. Here, when the power supply voltage V _B supplied to the lamp 4 fluctuates from the set value V _BS , the first correction means 8 amplifies in proportion to the magnitude of the fluctuation ΔV _B and according to the polarity. A control signal V _C for correcting the output voltage V _O of the circuit 7 is output. The control signal V _C is supplied to the feedback and output stage in the amplifier circuit 7, and the output voltage V _O is corrected in proportion to the power supply voltage V _B.
[0022]
The following series of equations derives a correction voltage term for the output voltage V _O. The gain of the amplifier circuit 7 and G, the input offset voltage V _OS and temperature drift voltage V _TD of differential amplifier is assumed to be zero, the output voltage V _O, the table as in the following equation from the equation (1) Is done.
[0023]
[Expression 2]
V _O = G * R _S * I _L (2)
[0024]
Next, the maximum fluctuation value of the power supply voltage V _B is limited to V _BH , the minimum fluctuation value is limited to V _BL , the maximum load current of the lamp is I _LH , the minimum load current is I _LL , and the set load current is I _LS When the load current I _L of the lamp in consideration of supply voltage variation is expressed as follows.
[0025]
[Equation 3]
I _L = I _LS + [(I _LH −I _LL ) / (V _BH −V _BL )] * (V _B −V _BS ) (3)
[0026]
Here, when ΔI _L = I _LH −I _LL and ΔV _B = V _BH −V _BL and substituting Equation (3) into Equation (2), the following equation is obtained.
[0027]
[Expression 4]
V _O = G * R _S * I _LS + [(G * R _S ) * ΔI _L / ΔV _B * (V _B −V _BS )] (4)
[0028]
In the equation (4), the predetermined output voltage is indicated by the first term on the right side, and the output change due to the fluctuation of the power supply voltage V _B is indicated by the second term on the right side. Therefore, the output change is offset from the output voltage V _O. The correction voltage for this is as follows.
[0029]
[Equation 5]
Correction voltage = − [(G * R _S ) * ΔI _L / ΔV _B ] * V _B
+ [(G * R _S ) * ΔI _L / ΔV _B ] * V _BS (5)
[0030]
In the equation (5), the first term on the right side indicates a fluctuation proportional term proportional to the fluctuating power supply voltage V _B, and the second term on the right side indicates a constant term unrelated to the power supply voltage fluctuation. First correction means 8 in the block diagram of a reference example shown in FIG. 2, the variation proportional term and the constant term of the correction voltage, and adding the correction to the output voltage V _O.
[0031]
FIG. 3 is a block diagram showing a first embodiment of the current detection circuit 3 according to the present invention. FIG. 3 includes second correction means 9 in addition to the configuration of FIG. 2 as a reference example . In the case of the current detection circuit shown in FIG. 2 as a reference example , the first correction means 8 is configured to correct the output voltage V _O using the correction voltage fluctuation proportional term and the constant term. For the first embodiment according to the present invention, on the other hand, charge variation proportional term of the correction voltage first correction means 8 represented by the above equation (5), the second correction means 9 described above (5 In this case, the output voltage V _O is corrected by taking a constant term out of the correction voltage expressed by the formula (1). Further, the second correction means 9 is a variation of the offset voltage caused by the characteristic variation of the first correction means 8 and the components of the amplifier circuit 7, that is, the characteristic variation of the components of the first correction means 8 and This is used to correct an error appearing in the level of the output voltage Vo after the correction by the first correction means 8 due to the characteristic variation of the components of the amplifier circuit 7.
[0032]
FIG. 4 shows a detailed circuit diagram of the current detection circuit 3 of FIG. Although a detailed circuit diagram of the current detection circuit 3 in FIG. 2 has not been presented, it is obvious that the second correction means 9 in FIG. 4 is not provided. As shown in FIG. 4, the first correction means 8 is a component composed of resistors R1 and R2 and a diode-connected transistor QB in order to detect a change in the power supply voltage V _B and convert it to a predetermined level. The output from the junction of the voltage circuit 10 and the resistors R1 and R2 in the voltage divider circuit 10 is received by the base of the transistor QA, and the fluctuation proportional term of the correction voltage, which is the collector output of the transistor QA, is fed back to the amplifier circuit 7. And an adder / subtractor circuit 11 that is input to the collector of the transistor QH8 in the output stage to change the emitter current of the transistor QH8 and consequently increase or decrease the level of the output voltage V _O. The second correction means 9 includes a variable resistor 13 and a constant current circuit 12, and by changing the input bias voltage to the amplifier circuit 7, not only the constant term of the correction voltage unrelated to the power supply voltage fluctuation, The error appearing in the level of the output voltage Vo corrected by the first correction unit 8 due to the characteristic variation of the component of the first correction unit 8 and the characteristic variation of the component of the amplifier circuit 7 is also corrected. Function. In FIG. 4, the second correction means 9 is composed of a variable resistor 13 and a constant current circuit 12 with a fixed current, but is composed of a fixed resistor and a constant current circuit with a variable current in that the bias voltage is variable. Are functionally the same.
[0033]
Correction of the error appearing in the level of the output voltage Vo after the correction by the first correction means 8 due to the characteristic variation of the components of the first correction means 8 and the characteristic variation of the components of the amplifier circuit 7 is as follows. The first characteristic function of the second correction means 9 is the correction of the input conversion drift voltage of the differential amplifier due to the temperature change as the second characteristic function. This will be described next. The variable resistor 13 has a temperature coefficient, and the voltage drop due to the current of the constant current circuit 12 also changes when the resistance value changes due to temperature change. Therefore, in the actual configuration of the second correction means 9 shown in FIG. 4, the offset temperature coefficient of the variable resistor 13 is canceled in order to cancel out the input conversion offset voltage V _OS of the differential amplifier due to temperature change, that is, the temperature drift. As described above, the current temperature coefficient of the constant current circuit 12 is set.
[0034]
FIG. 5 is a block diagram showing a second embodiment of the current detection circuit 3 according to the present invention. In the case of the current detection circuit 3 shown in FIGS. 2 to 4, the current detection shunt resistor R _S of the lamp load 4 is a fixed resistance, whereas in the case of the current detection circuit 3 shown in FIG. It is composed of resistors. This is to optimize the power supply voltage fluctuation correction even for lamp loads having different characteristics. And the load current of the lamp, the use of lamp load having different specifications from the lamp load by setting the correction range by the power supply voltage fluctuation, the load current changes in the increasing direction or decreasing direction, which can correct the output voltage V _O There is no margin in the power supply voltage range above or below, making it difficult to achieve optimal power supply voltage fluctuation correction. Therefore, the power supply voltage fluctuation correction range is optimized by changing the resistance value of the shunt resistor R _S so as to match the voltage drop R _S * I _LS caused by a preset shunt resistor. For example, when the shunt resistance of the load resistance R _{LA to} the setting lamp A is R _SA and the load current is I _LA , the shunt resistance of the load resistance R _{LB to} the lamp B is R _SB and the load current is I _LB. R _SB is obtained from the following equation.
[0035]
[Formula 6]
R _SA * [V _B / (R _SA + R _LA )] = R _SB * [V _B / (R _SB + R _LB )]
R _SB = (R _LB / R _LA ) * R _SA (6)
[0036]
For example, when a 5W3 lamp load is set in advance and then a 21W2 lamp load is used, the shunt resistance value is [1 / (21 * 2)] / [1 / (5 * 3)] = 1 / 2.8 times It becomes.
[0037]
【The invention's effect】
As described above, the load disconnection detecting device according to the first aspect of the present invention has a resistance value R s through which a current from the power source to the lamp load flows, and an amplification factor G having the voltage between the terminals of the resistance as inputs. of the amplifier circuit, comprising a current detection circuit including, in determining lamp load disconnection detecting device whether the disconnection of the lamp load from the output voltage Vo of the current detection circuit, when the lamp normal in setting the power supply voltage V _BS The load current is I _LS , the maximum value of the power supply voltage V _B is V _BH , the minimum value is V _BL , the power supply voltage fluctuation is ΔV _B = V _BH −V _BL, and the lamps corresponding to the V _BH and V _BL When normal load currents are I _LH and I _LL , and load current fluctuations are ΔI _L = I _LH −I _LL , G * Rs * ΔI _L / ΔV _B constituting the output voltage Vo of the current detection circuit proportional to the power supply voltage V _B which * indicated by V _B Represented by the first correction means and constitutes the output voltage Vo of the current detection circuit _{G * Rs * ΔI L / ΔV} B * V BS for correcting the output voltage Vo of the current detection circuit so as to offset the voltage And a second correction means for correcting the input voltage of the current detection circuit so as to cancel out the constant voltage that does not depend on the power supply voltage V _B. Using the first correction means, the load current value of the lamp for which the highest detection accuracy is required and the current value range in which the correction of the power supply voltage variation is effective are limited, thereby improving the load current detection accuracy of the lamp. And minimizing the current detection circuit configuration at the same time. Furthermore, by using the second correction means, not only the constant term of the correction voltage unrelated to the fluctuation of the power supply voltage but also the first correction means and the offset voltage of the amplifier circuit (differential amplifier) can be corrected. It becomes possible.
[0038]
According to a second aspect of the present invention, there is provided the load disconnection detecting device, wherein the first correction means includes a voltage dividing circuit for a power supply voltage. The power supply voltage dividing circuit can detect the fluctuation proportional term and convert it to a desired level.
[0039]
According to a third aspect of the present invention, there is provided the load disconnection detecting device according to the first aspect, wherein the first correction means includes an addition / subtraction circuit. By the addition / subtraction circuit, it becomes possible to correct the output voltage of the current detection circuit in accordance with the fluctuation proportional term converted to the desired level.
[0040]
According to a fourth aspect of the present invention, the second correction means includes a constant current circuit for operating an input voltage of the current detection circuit 3 according to a current value. By changing the constant current value using the constant current circuit, the input bias condition can be changed, the output offset voltage can be corrected, and the variation among lots can be eliminated.
[0041]
According to a fifth aspect of the present invention, the second correction means includes a variable resistor for operating the input voltage of the current detection circuit 3 by a resistance value. By varying the resistance value using a variable resistor, the input bias condition can be changed, the output offset voltage can be corrected, and variations among lots can be eliminated.
[0042]
According to a sixth aspect of the present invention, in the load disconnection detecting device, the second correction means includes a constant current circuit for operating the input voltage of the current detection circuit by a current value, and a resistance value of the current detection circuit. A variable resistor for operating an input voltage is provided, and the temperature coefficient of the constant current circuit current is set so as to cancel the temperature coefficient of the variable resistor. By setting the temperature coefficient of the constant current circuit current so as to cancel the temperature coefficient of the variable resistor, it is possible to minimize the drift voltage of the current detection circuit due to temperature change and further improve the detection accuracy.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an overall configuration of a lamp breakage detection device of the present invention.
FIG. 2 is a block diagram showing a reference example of a current detection circuit 3;
FIG. 3 is a block diagram showing a first embodiment of a current detection circuit according to the present invention.
4 is a detailed circuit diagram of the current detection circuit shown in FIG. 3;
FIG. 5 is a block diagram showing a second embodiment of a current detection circuit according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Lamp load disconnection detection apparatus 2 Lamp power supply 3 Current detection circuit 4 Lamp load 5 A / D converter 6 Microcomputer 7 Amplification circuit 8 First correction means 9 Second correction means 10 Voltage dividing circuit 11 Addition / subtraction circuit 12 Constant current Circuit 13 Variable resistance

Claims (6)

Resistance value through which current flows from the power supply to the lamp load R s resistance and amplification factor with input of voltage between terminals of the resistance G And an output voltage of the current detection circuit. Vo From the lamp load disconnection detecting device for determining the presence or absence of disconnection in the lamp load from
  Set power supply voltage V _BS Is the load current when the lamp is normal _LS And the power supply voltage V _B The maximum value of V _BH , The minimum value is V _BL , ΔV _B = V _BH -V _BL And V _BH And V _BL The load current when the lamp corresponding to _LH And I _LL , Load current fluctuation
ΔI _L = I _LH -I _LL When
  Output voltage of the current detection circuit Vo G * Rs * ΔI constituting _L / ΔV _B * V _B The power supply voltage V indicated by _B The output voltage of the current detection circuit so as to cancel the voltage proportional to Vo First correction means for correcting
  Output voltage of the current detection circuit Vo G * Rs * ΔI constituting _L / ΔV _B * V _BS The power supply voltage V indicated by _B Second correction means for correcting the input voltage of the current detection circuit so as to cancel the constant voltage independent of
A load disconnection detecting device comprising:   2. The load disconnection detection device according to claim 1, wherein the first correction means includes a voltage dividing circuit for the power supply voltage.   3. The load disconnection detecting device according to claim 1, wherein the first correction unit includes an addition / subtraction circuit for increasing / decreasing an output voltage of the current detection circuit.   2. The load disconnection detection device according to claim 1, wherein the second correction means includes a constant current circuit for operating an input voltage of the current detection circuit according to a current value.   5. The load disconnection detection device according to claim 4, wherein the second correction means includes a variable resistor for operating an input voltage of the current detection circuit according to a resistance value.   The second correction means includes a constant current circuit for operating the input voltage of the current detection circuit by a current value, and a variable resistor for operating the input voltage of the current detection circuit by a resistance value, 2. The load disconnection detecting device according to claim 1, wherein the temperature coefficient of the constant current circuit current is set so as to cancel the temperature coefficient of the variable resistance.

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