JP2001021590A - Current detecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect a supply current value by means of a current detecting circuit without being affected by variations in resistance values of two resistances constituting a potential dividing part and fluctuations of two source voltages, in a circuit detecting the supply current value of a power supply device which supplies electric power from a first power supply part to the external by the measuring means of a second power supply part of a low voltage value. SOLUTION: A switch part 424 which can be on/off-controlled is provided in parallel with a current detecting resistance provided inward of a resistive potential dividing means. The switch is turned on to cause a current to bypass the current detecting resistance, and a voltage divided by the resistance under this state is measured by an A/D converter 422. Next, the switch is turned off, and under this state the divided voltage is measured again by the A/D converter 422. Since the difference between the measured voltages equals a voltage proportional to a current supplied to the external, the current supplied to the external is detected with accuracy by dividing the voltage difference by the resistance inserted in a current path.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit on the receiver side for supplying a current to a preamplifier or the like which is usually installed at a remote place via a coaxial cable or the like, and judges whether or not the supply current is normal. The present invention relates to a current detection circuit which constitutes a part of a self-diagnosis circuit which performs the operation.

[0002]

2. Description of the Related Art Conventionally, in a GPS receiver or the like in which a coaxial cable is used to connect an antenna with a built-in preamplifier to a receiver, abnormalities such as forgetting to connect the antenna, failure of the preamplifier, short circuit of the coaxial cable, and the like are determined by the supply current Is measured by a current detection circuit, and a self-diagnosis circuit is provided for calling attention to the user of the receiver.

FIG. 2 is a general configuration diagram of a self-diagnosis circuit of a GPS receiver, wherein 1 is an antenna, 2 is a preamplifier,
3 is a coaxial cable and 4 is a GPS receiver. The GPS receiver 4 has at least a coil 41 and a current detection circuit 42.

The antenna section of the GPS receiver shown in FIG. 2 includes an antenna 1 and a preamplifier 2, and the antenna section is installed, for example, on a roof of a car that can see a satellite. Since the GPS receiver 4 is usually installed inside a vehicle, the antenna unit and the G
The PS receiver 4 is installed at a little distance, and the PS receiver 4 is connected with the coaxial cable 3 therebetween.

[0005] The power supply of the preamplifier 2 built in the antenna section is connected to a current detection circuit 42 and a coil 41 in the GPS receiver 4.
Through the coaxial cable 3 connected to the GPS receiver 4. On the other hand, GPS received by antenna 1
Is amplified by the preamplifier 2, passes through the coaxial cable 3, and is guided to the GPS receiver 4. That is, the DC power and the RF signal are superimposed on the coaxial cable 3.

[0006] The coil 41 in the GPS receiver 4 includes a DC power supplied from the current detection circuit 42 to the preamplifier 2,
This is a component for separating the high-frequency RF signal sent from the preamplifier 2, and the high-frequency RF signal is guided to an RF amplifier circuit not shown in FIG. Here, the coil 41 is shown as an example of a component for separation, but instead, a strip line or a microstrip line used as a transmission line of an RF signal in the GPS receiver 4 is used, and the RF signal is used. A similar effect can be obtained by using a strip line or microstrip line having a predetermined length and width (for example, 1/4 wavelength, ultrafine) for the frequency of.

The current detection circuit 42 in the self-diagnosis circuit
Measures the voltage dropped by a resistor provided in the path of the supply current, which is converted into a digital value by an internal A / D converter. In this case, the power supply voltage of the GPS preamplifier 2 is 5 V
Since the A / D converter included in the current detection circuit 42 provided on the receiver side was operated in the same 5 V system, the power supply voltage was unified in the 5 V system, and the use of the A / D converter There was no problem above.

In recent years, ASICs (Application Sp
ecific integrated circuit), the power supply voltage of the ASIC has been reduced due to the miniaturization of the CMOS circuit used.
As a result, the reference voltage of the A / D converter built in the ASIC and the allowable voltage range of the A / D input terminal have to be reduced to the power supply voltage of the ASIC or less. For example, the power supply voltage of a CMOS ASIC with a design rule of 0.25 μm is 2.5
V is standard, and the power supply voltage of the A / D converter, the reference voltage, and the allowable voltage range of the A / D input terminal, which are created according to the design rule, are also 0 to 2.5 V.

On the other hand, although analog circuits such as preamplifiers tend to lower the voltage, the voltage has not been reduced as much as the ASIC, and the power supply voltage of the 5V system is still large. Since the preamplifier is a 5V system, the current detection voltage of the conventional current detection circuit is also a 5V system. If this is directly input to the A / D input of the A / D converter, there is no input withstand voltage of the A / D converter.
The ASIC is messing around. Therefore, in order to prevent the ASIC from being broken, the 5V system current detection voltage is divided by resistance division, and the current detection voltage is divided into the allowable voltage of the A / D input terminal of 2.5V.
V. FIG. 3 shows a conventional current detection circuit having a voltage dividing section.

In FIG. 3, reference numeral 421 denotes a detecting resistor for causing a voltage drop due to the supplied power.
1 also includes the internal resistance of the power supply unit. 423 is the resistor 42
A voltage divider 422 composed of 3a and 423b is a 10-bit A / D converter. Power supply voltage V of A / D converter 422
dd and the reference voltage Vref are 2.5V. On the other hand, since the preamplifier 2 having a 5 V system and a current consumption of 20 mA is connected from the output terminal Vout via the coil 41 and the coaxial cable 3, the power supply voltage Vcc is DC 5 V. Since the power supply voltage Vdd of the A / D converter 422 is 2.5 V, only a voltage of 2.5 V or less can be input to the A / D input terminal. Since the voltage Va passed from the Vcc terminal to the resistor 421 is a 5 V system, the voltage Va cannot be directly input to the A / D input terminal of the A / D converter 422, and is divided by the resistors 423a and 423b.
It is necessary to lower the voltage to 2.5 V or less and input.

In the example of FIG. 3, the resistor 421 is 22 ohms,
The resistance 423a is 15k ohm, and the resistance 423b is 10k ohm. The current flowing out of the output terminal Vout is 20
Assuming mA, 0.44 V (= 22 ×
0.02), and the voltage Va of the voltage divider 423
Becomes 4.56 V (= 5-0.44). Therefore, A /
The divided voltage Vdiag of the D input terminal is 1.824 V (=
(4.56 × 10/25). The A / D conversion value output from the A / D converter 422 is 746 (= 1.824 / 2.
5 × 1023). Here, in consideration of the tolerance of the preamplifier current, the preamplifier current is 10 mA to 30 mA.
If a self-diagnosis circuit for determining normal is configured, the output of the A / D converter 422 corresponding to this current is 7
It corresponds to the range of 46 soils 36. Therefore, the A / D converter 4
An abnormality such as forgetting to connect an antenna, a failure in a preamplifier, or a short circuit in a coaxial cable is determined according to the output level of the power supply 22 or within a predetermined range (746 soil 36). can do.

However, the resistors 423a, 423b
When using resistors which are usually commercially available, these resistors usually have an error of typically within 5%. As an example, the most severe condition, the resistance 423a
Is 14.25k ohm (-5%) and the resistance 423b is 1
Suppose that it was 0.5 kOhm (+ 5%). in this case,
Since the preamplifier current is 20 mA in a standard state, the divided voltage Vdiag is obtained by dividing 4.56 V of the voltage Va.
1.9345V (= 4.56 × 10.5 / 24.75)
And the A / D conversion value is 791, which deviates from the normal monitoring range of 746 soil 36. in this way,
An error in the resistance value of the voltage dividing resistor determines that the preamplifier is abnormal and issues an alarm. Even if the detection resistor 421 has an error of about several percent, the resistance error does not significantly affect the detection value.

The power supply voltage Vd of the A / D converter 422
d, the reference voltage Vref is 2.5 V, while the power supply voltage Vcc of the preamplifier is 5 V, and is configured as another power supply. Therefore, each voltage value also changes separately. For example, the power supply voltage Vd of the A / D converter 422
d, If the reference voltage Vref does not change at 2.5 V and the power supply voltage Vcc of the preamplifier is reduced by 5%, the preamplifier current is 20 mA in a standard state, so the divided voltage Vdi
The ag voltage was 1.72 obtained by dividing 4.31 V of the voltage Va.
4V (= 4.31 × 10/25), the A / D conversion value becomes 705, which is a normal monitoring range, 746 soil 36
Greatly deviates. As described above, the self-diagnosis circuit determines that the preamplifier is abnormal and issues an alarm even though a normal current of 20 mA flows through the preamplifier due to the fluctuation error between the two power supply voltages Vcc and Vdd.

[0014]

As described above, the current supplied to the preamplifier and the like is usually about 20 mA.
The mere configuration of the resistor voltage dividing unit may cause variations in the resistance value of the voltage dividing resistor or the power supply voltages Vcc and Vdd of the two systems.
, The supply current cannot be measured accurately, and a malfunction of the self-diagnosis circuit that determines that the supply current is abnormal despite the normal supply current occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has been made in consideration of the variation in the resistance values of the two resistors constituting the voltage dividing section and the difference between the two power supply voltages Vcc and Vdd. An object of the present invention is to provide a current detection circuit that can accurately detect a supply current value without being affected by fluctuations.

[0016]

A current detection circuit according to the present invention is a current detection circuit for detecting a supply current value of a power supply device for supplying power from a first power supply unit to the outside. Voltage dividing means for dividing the voltage, and a divided voltage of the resistive voltage dividing means as a signal to be measured, and a measuring means having as a control power supply a second power supply having a voltage value lower than the supply voltage of the first power supply. A current detection resistor provided on the inner side of the resistance voltage dividing means; and switch means capable of on / off control in parallel with the current detection resistance, wherein the divided voltage when the switch means is in an on state. And measuring the divided voltage when the switch means is in an off state by the measuring means, and detecting a supply current value of the power supply device based on the measured values.

According to this configuration, switch means capable of on / off control is provided in parallel with the current detection resistor provided on the inner side of the resistance voltage dividing means, and by turning on this switch, the current detection resistor is bypassed. In this state, the voltage divided by the resistance is measured by the A / D converter. Next, the switch means of the current detection circuit is turned off, and in this state, the divided voltage is measured again by the A / D converter. Since the difference between the two measured voltages is a voltage proportional to the current supplied to the outside, the current supplied to the outside can be obtained by dividing the voltage difference by the resistance inserted in the current path. Therefore, the current detection circuit of the present invention can compensate for the resistance error used in the voltage dividing section without interrupting the current supplied to the outside, and can perform accurate measurement even with a small current. In addition, accurate measurement can be performed without being affected by fluctuations in the power supply voltages of the two systems.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A self-diagnosis circuit of a GPS receiver will be described below as a preferred embodiment of a current detection circuit according to the present invention with reference to FIG.

FIG. 1 shows a current detecting circuit according to an embodiment of the present invention.
And a switch unit 424 is provided in parallel. The switch unit 424 includes a PNP transistor 424c, an NPN transistor 424d, a resistor 424a, and a resistor 424b, and a control signal (control terminal voltage) Vcon to a control terminal.
It is turned on and off by t. Other configurations are the same as those of the conventional FIG. 3, and corresponding components are denoted by the same reference numerals.

The operation of the embodiment according to the present invention will now be described.

First, when the control terminal voltage Vcont is set to the high potential (2.1 V or more), the transistor 424d is turned on, and as a result, the transistor 424c is also turned on. Here, the resistance value of the resistor 421 is selected so that the on-resistance of the transistor 424c is sufficiently smaller than the resistance value of the resistor 421 and can be ignored, so that the output terminal voltage Vout can be considered to be equal to the power supply voltage Vcc. in this case,
Regardless of the value of the current flowing from the output terminal to the outside, the voltage Va of the voltage dividing section 423 becomes the same 5 V as the power supply voltage Vcc, and the divided voltage Vdiag is Vcc × R423b / (R4
23a + R423b), and the resistors 423a and 423b
If there is no error, the divided voltage Vdiag becomes 2.00 V and the A / D converted value becomes 818.

Next, when the control terminal voltage Vcont is set to a low potential (0.5 V or less), the transistor 424d is turned off, and as a result, the transistor 424c is also turned off.
The output terminal is connected to the power supply voltage Vcc through the resistor 421. When a current of 20 mA flows from the output terminal to the outside,
The divided voltage Vdiag is 1.824 V, A / A
Since the D conversion value is 746, the difference 72 (= 818−
746) is generated at the resistor 421. Therefore, the allowable current of the preamplifier 2 is set to 20
Assuming that the mA is 10 mA, if the voltage drop generated by the resistor 421 is within 72 ± 36, it is equivalent to determining that the voltage is normal.

The case where the power consumption of the preamplifier is 20 mA, the voltage dividing resistor 423a is 15k ohm, and the resistor 423b is 10k ohm will be described as an example. The magnitude of the current flowing to the outside is obtained by calculating the difference between the A / D conversion value when the control terminal voltage Vcont is set to the high potential and the A / D conversion value when the control terminal voltage Vcont is set to the low potential. = 2.5
/ 1023 × 25/220). Even if the control terminal voltage Vcont is set to the high potential or the low potential, the magnitude of the current flowing to the outside is hardly affected, so that the current value can be measured while supplying the current to the outside. .

Now, assuming that the control terminal voltage Vcont is at a low potential, the A / D converted value is read as 746 at this time.
Is obtained. Next, when the control terminal voltage Vcont is set to the high potential and the A / D converted value is read, 818 is obtained. A
After reading the / D conversion value, the control terminal voltage Vcont is returned to the low potential as before. A / D conversion values 818 and 74
6 is 72, which is within 72 ± 36, so it can be determined that a normal current is flowing through the preamplifier.

Next, a case where the voltage dividing resistor has a tolerance of ± 5% will be described. As an example, the resistance 423a is 14.25k ohm (-5%) and the resistance 423b is 1
Suppose that it was 0.5 kOhm (+ 5%). First, when the control terminal voltage Vcont is set to a high potential (2.1 V or more), the voltage Va of the voltage divider 423 becomes 5 V, which is the same as the power supply voltage Vcc, even when a current of 20 mA flows from the output terminal to the outside. . Therefore, the divided voltage Vdiag is 2.1
212V, and the A / D conversion value is 868. Next, when the control terminal voltage Vcont is set to a low potential (0.5 V or less), the divided voltage Vdiag is 1.9345 V, A / A in a state where a current of 20 mA flows from the output terminal to the outside.
Since the D conversion value is 791, an A / D value corresponding to the voltage drop generated by the resistor 421 is 77 (= 868-791). As described above, in the current detection circuit of this embodiment, the A / D value corresponding to the voltage drop generated by the resistor 421 is 72
If it is within the soil 36, it is determined to be normal.

The A / D value 77 corresponding to this voltage drop is included therein, and compensates for the error of the resistors 423a and 423b despite the errors of -5% and + 5%, respectively. Error of 1.39 mA for 20 mA ((77-72) × 2.5 / 1023 × 2
The current can be measured with an accuracy of 5/220).

Next, 5% is applied to the power supply voltage Vcc of the preamplifier.
A description will be given of the case where the voltage drop occurs. First, when the control terminal voltage Vcont is at the high potential, the voltage Va of the voltage dividing section 423 becomes 4.75 V, which is the same as the power supply voltage Vcc, the divided voltage Vdiag becomes 1.9 V, and the A / D conversion value becomes 7
77. Next, when the control terminal voltage Vcont is set to the low potential, the divided voltage Vdiag is 1.724V, and A / A
Since the D-converted value is 705, an A / D value corresponding to the voltage drop generated by the resistor 421 is 72 (= 777-705).

As described above, in the current detection circuit of this embodiment, the A / D value corresponding to the voltage drop generated by the resistor 421 is 7
If it is within two soils 36, it is determined that it is normal. The A / D value 72 is the central value of the soil 72, and can compensate for the power supply voltage fluctuation error despite the 5% drop in the power supply voltage Vcc of the preamplifier. Can measure the current.

As a method of using the current detection circuit, for example, when the power of the GPS receiver is turned on, the control terminal voltage Vc
once to high potential, read the A / D conversion value,
The value (for example, A / Dhigh) is stored in a RAM or the like. Next, the control terminal voltage Vcont is set to the low potential, the A / D conversion value is read, and the value (for example, A / Dlow) is stored in the RAM. Then, a difference between the value A / Dhigh stored in the RAM and the value A / Dlow measured this time is calculated. The difference is 7
If the current value is within the range of 2 soil 36, it is determined that the current value to the preamplifier is normal.

Thereafter, while the control terminal voltage Vcont is kept at the low potential, the A / D conversion value is read periodically (for example, every one second) and the previous A / Dlo stored in the ROM is read.
Compare with w. As a result of the comparison, if the value has not changed, the difference between A / Dhigh and the current A / Dlow is calculated without setting the control terminal voltage vcont to the high potential, and it is determined whether it is normal or abnormal.

If the previous A / Dlow and the current A / D
If the low is significantly different, there is a possibility that a large change has occurred in the value of the current flowing to the outside. Therefore, for confirmation, the control terminal voltage Vcont is set to the high potential, the A / D conversion value is read, and Store again as A / Dhigh. Thereafter, the control terminal voltage Vcont is set to the low potential, the A / D converted value is read, and stored as A / Dlow in the RAM. A / Dhigh and A / Dlow of RAM
It is determined whether the supply current is normal or abnormal based on whether the difference is within the range of 72 soil 36.

As described above, the measured voltage of the A / D converter when the current detection resistor is inserted in the power supply path to the preamplifier 2 and the A / D when the current detection resistor is bypassed by the switch 424c. Since the configuration is such that it is determined whether the supply current is normal or abnormal based on the difference from the measured voltage of the D converter, a fluctuation common to both states (used for the voltage dividing unit 423). It is possible to accurately measure the current value by compensating for the resistance error and the fluctuation of the power supply voltages Vcc and Vdd of the two systems.

Since the transistor 424c, which is a bypass switch, is provided in parallel with the current detection resistor 421, an abnormal state such as runaway of control software or failure of the transistor switches 424c and 424d occurs. Even if the transistor switch 424c is turned on or off, the power supply to the preamplifier 2 can be continued.

[0034]

According to the present invention, a switch means capable of on / off control is provided in parallel with a current detection resistor provided inside the resistance voltage dividing means, and the current detection resistor is bypassed by turning on this switch. Then, the resistance-divided voltage is measured by the A / D converter in this state. Next, the switch means of the current detection circuit is turned off, and in this state, the divided voltage is measured again by the A / D converter. Since the difference between the two measured voltages is a voltage proportional to the current supplied to the outside, the current supplied to the outside can be accurately obtained by dividing the voltage difference by the resistance inserted in the current path.

Therefore, the current detection circuit of the present invention can compensate for the resistance error used in the voltage dividing section without interrupting the current supplied to the outside, and can perform accurate measurement even with a very small current. In addition, accurate measurement can be performed without being affected by fluctuations in the power supply voltages of the two systems.

[Brief description of the drawings]

FIG. 1 is a current detection circuit including a voltage dividing unit according to an embodiment.

FIG. 2 is a general configuration diagram of a self-diagnosis circuit of the GPS receiver.

FIG. 3 is a conventional current detection circuit including a voltage dividing unit.

[Explanation of symbols]

 Reference Signs List 1 antenna 2 preamplifier 3 coaxial cable 4 GPS receiver 41 coil 42 current detection circuit 421 current detection resistor 422 A / D converter 423 voltage divider 424 switch

Continued on front page F-term (reference) 2G035 AA11 AA15 AA26 AB02 AC02 AC08 AC19 AD02 AD10 AD11 AD26 AD44 AD65 5G065 BA00 GA07 LA02 PA05 5H410 CC02 DD02 EA10 FF05 FF22 5K042 AA00 CA02 CA24 DA35 FA03 JA01 KA03

Claims (1)

[Claims] 1. A current detecting circuit for detecting a supply current value of a power supply device for supplying power from a first power supply unit to the outside, comprising: a resistor voltage dividing means for dividing a supply voltage of the power supply device; Measuring means having a divided voltage of the voltage means as a signal to be measured and having a second power supply section having a voltage value lower than the supply voltage of the first power supply section as a control power supply; A current detecting resistor, and switch means capable of on / off control in parallel with the current detecting resistor, wherein the divided voltage when the switch means is in an on state, and the divided voltage when the switch means is in an off state. A current detection circuit, wherein a divided voltage is measured by the measuring means, and a supply current value of the power supply device is detected based on the measured values.