JPH08316807A - Current detector - Google Patents

Abstract

(57) [Summary] [Object] To provide a current detection device capable of detecting a short-circuit current flowing in a high-side power voltage drive element without using a battery as a power supply means. A power supply means 1 for generating a constant reference voltage V _s with an output end potential E _O of a high-side power MOSFET 1 controlled on / off by a drive circuit 15 as a reference potential.
9 and a current detecting means 5 for converting a sense current flowing in the sense MOSFET 3 into a detection voltage V _d for detection based on a load current I _L controlled by the high-side power MOSFET, and comparing the reference voltage and the detection voltage. Means 10
In the current detection device having, the power supply means 19 includes a charge pump circuit 16 for generating a substantially constant voltage higher than the reference voltage with respect to the reference potential, and a reference voltage circuit 7 connected to the output side of the charge pump circuit. , And a voltage adjusting means 8 connected to the output side of the reference voltage circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detection device for a power voltage drive element equipped with an overcurrent limiting device, and more particularly to a current detection device for a high side power voltage drive element whose output side is connected to a load circuit.

[0002]

2. Description of the Related Art FIG. 4 is a connection diagram showing an example of a conventional current detecting device for a high-side power voltage drive device having an overcurrent limiting device. In the figure, a power MOSFET 2 as a high-side power voltage driving element is a sense MO
Drive circuit (also called drive circuit) with SFET3
The drive voltage V _G generated by 15 is received by the gate electrode and is on / off controlled, and the flow of the load current I _L flowing to the external load via the output terminal 22 is controlled.

A load current I flowing through the power MOSFET 2
_The current detection device 11 that mainly detects an abnormality (overcurrent, short-circuit current, etc.) of _L is configured by a sense MOSFET 3 and a series circuit of a sense resistor 4 connected between its source electrode and an output terminal 22. Current detection means 5 and output terminal 2
A power supply unit 9 including a reference power supply 6, a reference voltage circuit 7, and a voltage adjusting unit 8 that generate a constant voltage using the potential E _O of 2 as a reference potential, and an output reference voltage V _{s of the} power supply unit.
And a comparator 10 as a comparison means for comparing the detected voltage V _d of the current detection means 5 with the output voltage V _D thereof being supplied to the current limiting device 20.

The current detecting means 5 is a power MOSF.
The sense current flowing through the sense MOSFET 3 is detected as a voltage drop of the sense resistor 4 at a constant ratio with respect to the load current I _L flowing through ET2, and the detection voltage V _{d is} applied to the + input side of the comparator 10 via the adjustment resistor 5R. Supply as. The power supply means 9 comprises a reference power supply 6, a reference voltage circuit 7 and a voltage adjusting means 8. The reference power source 6 is composed of a battery and applies a constant voltage to the reference voltage circuit 7 with the potential E _O of the output terminal 22 of the power MOSFET 2 as a reference potential. The reference voltage circuit 7 operates as a constant current circuit in which a depletion MOSFET 6D in which the source electrode and the gate electrode are short-circuited passes a zero bias saturation current, and an enhancement MOSFET 6E in which the gate electrode and the source electrode are connected to the source electrode side is a constant voltage circuit. It functions as a voltage circuit and generates a substantially constant reference voltage V _s using the potential E _O of the output terminal 22 as a reference potential. This reference voltage V _s is applied to the voltage adjusting means 8 composed of the diode 7D, the resistance voltage divider 7R, etc., adjusted to a desired reference voltage V _S and supplied to the minus input side of the comparator 10, and the detection voltage V _d.
Compared to.

Therefore, the reference voltage V _{S is set} to the power MOSFET.
If the overcurrent detection level of T2 is set in advance, when the detection voltage V _d exceeds the reference voltage V _S , the comparator 10 determines that an overcurrent has occurred, and the output voltage V _D becomes high level. In response to this, the current limiting device 20 suppresses the output drive voltage V _G of the drive circuit 5, so that the current value of the power MOSFET 2 that can flow is limited, and the overcurrent protection of the power MOSFET 2 is performed.

By the way, the resistance value of the sense resistor 4, which is usually a semiconductor resistor, has a positive temperature coefficient with respect to a change in temperature. For this reason, when the temperature becomes low, for example, the resistance value lowers and the comparator 10 becomes overheated. Since the determination of the current state is delayed and the resistance value increases when the temperature becomes high, there is a problem that the comparator 10 erroneously determines a current value equal to or less than the overcurrent as the overcurrent state. In the current detection device 11 shown in FIG. 4, the MOSF forming the reference voltage circuit 7 is
Utilizing the fact that the threshold voltage of ET and the temperature dependence of the diode 7D are negative, not only the temperature dependence of the sense resistor 4 but also the temperature dependence of the voltage dividing resistor 7R and the temperature dependence of the semiconductor resistance in the comparator 10 are used. Since the current can be compensated for, the current detection device 11 has a temperature compensation function, and highly accurate overcurrent detection is performed.

[0007]

In the high-side power MOSFET 1 in which a load circuit is connected to the output terminal 22, the output terminal 22 is at a high potential when the current flows, so that the current detecting device 11 has its current detecting means. 4 is configured to detect the detection voltage V _d using the potential E _O of the output terminal 22 as a reference potential, and the power supply means 9 is also configured to generate the reference voltage V _s using the potential E _O of the output terminal 22 as a reference potential. Further, when a short circuit accident occurs in the load circuit, the high-side power MOSFET 1 is short-circuited, the potential difference between its drain (power supply terminal 2) and source (output terminal) 22 is almost eliminated, and the comparator 10 receives the reference voltage V. _Since it becomes impossible to supply _s , the power supply means 9 is provided with a reference power supply 6 such as a battery whose cathode is connected to the output terminal 22 so that the short-circuit current can be detected even when the high-side power MOSFET 1 is short-circuited. It is configured.

However, since a current corresponding to the zero bias saturation current of the depletion MOSFET 6D constantly flows from the reference power source 6 toward the reference voltage circuit 7, when a battery is used as the reference power source 6, its consumption is severe, Since the batteries are replaced regularly, long-term operation is hindered, and maintenance of the batteries becomes complicated.

An object of the present invention is to provide a current detecting device capable of detecting a short-circuit current flowing in a high side power voltage driving element without using a battery as a power source means.

[0010]

In order to solve the above-mentioned problems, a first aspect of the present invention provides a constant reference voltage with an output terminal potential of a power voltage drive element on / off controlled by a drive circuit as a reference potential. A comparison for comparing the reference voltage and the detected voltage with a power source means for generating, a current detecting means for converting a current flowing through the sense voltage driving element into a detection voltage for detection based on a load current controlled by the power voltage driving element And a reference voltage circuit connected to the output side of the charge pump circuit, wherein the power supply means generates a substantially constant voltage higher than the reference voltage with respect to the reference potential. And a voltage adjusting means connected to the output side of the reference voltage circuit.

Here, as in the invention described in claim 2,
It is preferable that the charge pump circuit also serves as the charge pump circuit of the drive circuit. Further, as in the invention described in claim 3, in the reference voltage source circuit, the drain electrode is connected to the output side of the charge pump circuit, and the source electrode and the gate electrode are short-circuited, and the depletion MOSFET has a gate on the source electrode side. It is preferable that the electrode and the drain electrode are connected to each other and the source electrode is an enhancement MOSFET connected to the output terminal of the power voltage driving element. Further, as in the invention described in claim 4, the voltage adjusting means is connected between the diode having the anode connected to the intermediate connection point of the reference voltage source circuit, and the cathode and the output terminal of the power voltage drive element. And a resistance voltage divider.

[0012]

According to the present invention, the load pump circuit is short-circuited by using the charge pump circuit as the power source means for generating a constant reference voltage with the output terminal potential of the high side power voltage driving element as the reference potential. By this, even if the potential difference between the power supply terminal and the output terminal of the power voltage drive element disappears, it becomes possible to supply the reference voltage to the comparison means through the reference voltage circuit and the voltage adjustment means, which requires maintenance management. It is possible to detect a short circuit current without using a battery.

According to the second aspect of the invention, the charge pump circuit also serves as the charge pump circuit of the drive circuit, so that the short-circuit current can be detected without providing a new charge pump circuit in the reference power supply. In the invention according to claim 3, the reference voltage circuit is composed of a depletion MOSFET in which the source electrode and the gate electrode are short-circuited, and an enhancement MOSFET in which the gate electrode and the drain electrode are connected to the source electrode side. The reference voltage circuit can absorb the fluctuation of the output voltage of the charge pump circuit and generate a stabilized reference voltage. Further, in the invention described in claim 4, the voltage adjusting means compensates for the positive temperature dependence of the resistances of the current detecting means and the comparing means by utilizing the negative temperature dependence of the diode, and the resistance voltage divider is used as a reference. Enables adjustment of overcurrent detection level by fine adjustment of voltage.

[0014]

EXAMPLES The present invention will be described below based on examples.
Since the members having the same reference numerals as those of the conventional example have the same functions as those of the conventional example, the description thereof will be omitted. FIG. 1 is a connection diagram showing an embodiment of the current detecting device of the present invention. In the figure, a current detection device for mainly detecting an abnormality of a load current I _L flowing through a high-side power MOSFET 2 is constituted by a series circuit of a sense MOSFET 3 and a sense resistor 4, and a sense current is detected by a sense resistor 4 at a detection voltage V.
Current detection means 5 for converting to _d for detection, and output terminal 22
Power supply means 19 including a charge pump circuit 16 for generating a constant voltage higher than the reference voltage V _s with the potential E _O of the reference voltage as the reference potential, the reference voltage circuit 7, and the voltage adjusting means 8.
And the output reference voltage V _s of this power supply means and the current detection means 5
The comparator 10 is composed of an operational amplifier as a comparison means for comparing the detected voltage V _{d of the above-mentioned} output voltage V _d with the output voltage V _D of the operational amplifier.

The difference of this embodiment from the above-mentioned conventional example is that the battery as the reference power source 6 of the power source means 9 in FIG. 4 is replaced with the charge pump circuit 16, and the load is changed by the configuration as described above. Even when a short circuit accident occurs in the circuit and the high-side power MOSFET 1 is short-circuited, and the potential difference between the drain (power supply terminal 2) and the source (output terminal 22) is almost eliminated,
Since the charge pump circuit 16 supplies the reference voltage circuit 7 with a constant voltage higher than the reference voltage V _s with the potential E _O of the output terminal 22 as the reference potential, the short-circuit current can be detected.
In addition, it is not necessary to replace the battery and it is not necessary to stop the operation of the device to replace the battery, so maintenance management can be saved compared to the conventional example, and a current that enables continuous operation for a long period of time. A detection device is obtained.

FIG. 2 is a connection diagram showing another embodiment of the current detecting device of the present invention. This embodiment differs from the embodiment shown in FIG. 1 in that a high-side power MOSFET is used.
The charge pump circuit 26 normally provided in the drive circuit 15 for supplying the drive voltage V _G to
9 is a point that is configured. In this way, by using the charge pump circuit also, the structure of the current detection device can be simplified and the manufacturing cost thereof can be reduced.

FIG. 3 is a connection diagram showing another embodiment of the current detecting device of the present invention. The difference between this embodiment and the embodiment shown in FIG. 1 or FIG. 2 is that a high-side power voltage drive element which is a target of overcurrent detection and overcurrent protection is sensed by an IGBT (insulated gate bipolar transistor) 3.
3 is that the power IGBT 31 is provided, and in this case as well, the short-circuit current can be detected as in the above-described embodiment. The same applies to current detection devices for other voltage-driven semiconductor elements such as GTO thyristors.

[0018]

As described above, the current detecting device of the present invention uses the charge pump circuit as the reference power source of the power source means for generating the reference voltage to be compared with the detection voltage, and the output terminal potential of the high side power voltage driving element. Is configured to generate a constant voltage. As a result, similar to the conventional example in which a battery is used as a reference power supply, short-circuit current can be detected even when the potential difference between the power supply terminal and output terminal of the high-side power voltage drive element disappears due to a short circuit in the load circuit. At the same time, it is possible to provide a highly reliable current detection device that does not require battery replacement and operation stoppage due to this, is easy to maintain and can be operated continuously for a long period of time.

Further, by sharing one charge pump circuit for the drive circuit and the current detecting device, there is an advantage that the current detecting device having a simple structure and low cost can be economically advantageously provided.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of a current detection device of the present invention.

FIG. 2 is a connection diagram showing another embodiment of the current detecting device of the present invention.

FIG. 3 is a connection diagram showing another embodiment of the current detection device of the present invention.

FIG. 4 is a connection diagram showing an example of a conventional current detection device for a high-side power voltage drive element equipped with an overcurrent limiting device.

[Explanation of symbols]

1 high side power MOSFET (power supply voltage driving element) 2 power supply terminal (drain terminal) 3 sense MOSFET 4 sense resistor 5 current detecting means 6 reference power supply (battery) 6D depletion MOSFET 6E enhancement MOSFET 7 reference voltage circuit 7D diode 7R resistance component Pressure device 8 Voltage adjusting means 9 Power supply means 10 Comparison means (comparator circuit) 11 Current detection device 15 Drive circuit 16 Charge pump circuit 19 Power supply means 20 Current limiting device 22 Output terminal 26 Charge pump circuit (also used as drive circuit) 29 Power supply means 31 High-side power IGBT 33 Sense IGBT E _O Output terminal potential (reference potential) V _d Detection voltage V _s Reference voltage V _D Comparator output voltage I _L Load current

Claims (4)

[Claims] 1. A power supply means for generating a constant reference voltage with an output terminal potential of a power voltage drive element being on / off controlled by a drive circuit as a reference potential, and a sense voltage based on a load current controlled by the power voltage drive element. Current detecting means for detecting the current flowing through the drive element by converting it into a detection voltage;
In a current detection device having a comparison means for comparing the reference voltage and a detected voltage, the power supply means generates a substantially constant voltage higher than the reference voltage with respect to the reference potential, and the charge pump circuit. A current detecting device, comprising: a reference voltage circuit connected to the output side of and a voltage adjusting means connected to the output side of the reference voltage circuit. 2. The current detecting device according to claim 1, wherein the charge pump circuit also serves as a charge pump circuit of the drive circuit. 3. A reference voltage circuit is a depletion MOSFET having a drain electrode connected to the output side of a charge pump circuit and a source electrode and a gate electrode short-circuited, and a gate electrode and a drain electrode connected to the source electrode side, and a source. 2. The current detecting device according to claim 1, wherein the electrode comprises an enhancement MOSFET connected to the output terminal of the power voltage driving element. 4. The voltage adjusting means has a diode whose anode is connected to an intermediate connection point of the reference voltage source circuit, and a resistance voltage divider connected between its cathode and the output terminal of the power voltage driving element. The current detection device according to claim 1 or 2, characterized in that.