JP2001356139A - Current detecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current detecting circuit capable of performing a current detection with a simple circuit structure without causing an increase in power loss by an increase in measuring current. SOLUTION: In this current detector circuit, a diode 3 is connected to a current supplying circuit between a DC power source 1 and a load 2 serially to the normal direction, and a PNP transistor 4 having an emitter connected to the anode of the diode and a base connected to the cathode thereof through a base resistor 5 is arranged. The voltage drop of a collector resistor 6 connected between the PNP transistor and an earth is detected to detect the current of the current supplying 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 circuit capable of detecting a current at a power supply with a simple circuit configuration.

[0002]

2. Description of the Related Art Conventionally, a resistor is generally used for current detection. When performing current detection on the power supply side, FIG.
As shown in (1), a resistor 102 for current detection is inserted on the power supply 101 side (high side), and the voltage drop Vs is applied to the differential amplifier 10.
3 to take out the current detection output. In FIG. 3, reference numeral 104 denotes a load.

On the other hand, when current detection is performed on the ground side,
As shown in FIG. 6, a resistor 105 for current detection is inserted on the ground side, and this voltage drop (to ground) Vs is similarly applied to the differential amplifier.
Removed at 103, and a detection output of the load current I _L, the method is a current detecting method that is normally used.

[0004]

By the way, in the conventional current detection system using the voltage drop of the resistor on the power supply side shown in FIG. 5, the detection voltage does not become the ground potential, so that a differential amplifier is required. In addition, since the current is detected by the voltage drop of the resistor, the voltage drop increases in proportion to the increase of the current, and there is a problem that the power loss increases. Further, the conventional current detection method on the ground side shown in FIG. 6 has a drawback that the load rises above the ground, and similarly to the current detection method on the power supply side shown in FIG. There is a problem that loss increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional current detection method, and can perform current detection with a simple circuit configuration without increasing power loss due to an increase in measured current. It is an object of the present invention to provide a current detection circuit as described above.

[0006]

In order to solve the above problems, the invention according to claim 1 is to connect a diode in series in a forward direction to a current supply circuit between one side of a DC power supply and a load, Bipolar transistors each having an emitter and a base connected via a base resistor connected to both poles of the diode are arranged, and a voltage drop of a collector resistor connected between the collector of the bipolar transistor and the other side of the DC power supply is detected. And a current detection circuit configured to detect the current of the current supply circuit.

In the current detecting circuit according to the first aspect of the present invention, the current is detected by using a diode connected in a forward series instead of the resistor. The voltage drop is only the forward voltage of the diode and is not proportional to the detected current. Therefore,
Even if the detection current increases, current detection can be performed with a simple circuit configuration without increasing power loss as in the case of using a resistor.

According to a second aspect of the present invention, in a current supply circuit between one end of an AC power supply and a load, a diode pair formed by connecting diodes having the same characteristics in parallel in opposite directions is connected in series. A bipolar transistor having an emitter and a base connected via a base resistor respectively connected to both ends of a diode pair, and a collector connected between a collector of the bipolar transistor and a collector resistor connected between the other end of the AC power supply. A current detection circuit is configured to detect a voltage drop of a resistor and detect a current of the current supply circuit.

The current detecting circuit according to claim 2 configured as described above can perform current detection with a simple circuit configuration in an AC power supply circuit without increasing power loss.

[0010]

Next, an embodiment will be described. FIG. 1 is a circuit configuration diagram showing a first basic embodiment of a current detection circuit according to the present invention. In FIG. 1, 1
Is a DC power supply, 2 is a load, and a current detection circuit is a pn junction diode 3 connected in series in a forward direction to a current supply circuit between the DC power supply 1 and the load 2, and an emitter e is an anode of the diode 3. , The base b is connected to the cathode of the diode 3 via the base resistor 5, and the collector c is grounded via the collector resistor 6.
The load current I _L is detected based on the voltage drop of the collector resistor 6.

Next, the operation of the current detection circuit thus configured will be described. First, when the load 2 is open and no load is applied, the forward voltage Vf of the pn junction diode 3 such as a general-purpose rectifying silicon diode and the base-emitter voltage Vbe of the PNP transistor 4 are compared. Under no load and no current, if the diode and the transistor are formed of the same material, they are the same. Therefore, in this state, no current flows from the emitter e to the base b of the transistor 4 and, of course, no collector current flows. Therefore, the collector potential is the ground potential, and the collector-ground voltage Vc is zero.

On the other hand, when the load 2 is connected and the load current _IL flows, the forward voltage Vf of the diode 3 increases according to the rectification characteristic curve. When Vf> Vbe, the base current Ib of the transistor 4 flows from the emitter e to the base b via the base resistor 5.
When the base current Ib flows, a collector current flows according to the current amplification factor of the transistor 4, and the collector potential of the transistor 4 increases due to a voltage drop caused by the collector resistor 6. Therefore, by monitoring the collector voltage, it is possible to detect the presence or absence of a current I _L to the load 2. Further, by inverting the collector potential by adding an NPN transistor, a TTL / CMOS level detection signal is obtained.

When a resistor is used for current detection as in the prior art, the voltage drop across the resistor increases proportionally with an increase in current, resulting in a large power loss.
Since a diode is used as described above, the voltage drop across the diode is only the forward voltage of the diode and is not proportional to the current. Therefore, even if the load current increases, the loss does not increase proportionally as in the case of using a resistor.

As described above, according to the present invention, the forward voltage Vf of the diode is used for the current measurement, and the measurement principle utilizes the non-linearity. Therefore, the absolute value of the current cannot be obtained accurately. However, it is not suitable for measuring the presence or absence of a current, that is, the presence or absence of a load, and can be sufficiently used for measurement such as disconnection. Further, since the forward voltage Vf of the diode is used, it is not necessary to consider the value of the resistance as in the case of the measurement using a resistor, and depending on the withstand capacity of the diode to be used, several mA to several A Current measurement up to is possible.

Next, a second embodiment will be described with reference to FIG. This embodiment enables detection even when the detected current (load current) is a pulsating current or a pulsed current. In FIG. 2, the basic first embodiment shown in FIG. The same or corresponding components are denoted by the same reference numerals. In the second embodiment, as shown in FIG. 2, a diode 7 forming a rectifier circuit is connected to a collector resistor 6 connected to the collector of a PNP transistor 4.
And the capacitor 8 are connected in parallel. An NP for potential shift and current amplification is connected via a base input resistor 9 to a connection point between a diode 7 and a capacitor 8 which is an output terminal of the rectifier circuit.
The base of the N transistor 10 is connected,
Further, a resistor 11 for fixing the base potential to ground is connected to the base, the emitter is grounded, one end of the current detection LED 12 is connected to the collector, and the other end of the LED 12 is connected to the LED via the resistor 13. It is connected to a power supply (+5 V) to form a current detection circuit.

In FIG. 2, DS + is a main power supply (DC
(10 V to 36 V DC) 1 input terminal, DS- is a load side terminal, and SNS is a current detection terminal and is an open collector. The time constant of the rectifier circuit composed of the diode 7 and the capacitor 8 is determined by the capacitance of the capacitor 8 and the resistance of the resistor 9.

In the second embodiment configured as described above, even if the current to be detected is a pulsating current or a pulse current, the detection output is rectified by the rectifier circuit including the diode 7 and the capacitor 8, NPN transistor 10
And the current is amplified, so that the presence or absence of the current can be easily detected by turning on the LED 12.

In each of the above embodiments, the current is detected by a combination of a diode and a PNP transistor. However, as shown in FIG.
The diode 3 is connected to the ground side of the NPN transistor.
Current detection can also be performed in combination with a transistor. In this case, when the load current _IL flows, the anode side of the diode rises by Vf from the ground side (cathode side), and the base current Ib is supplied to the NPN transistor 4 '.
Flows, and a voltage drop Vc due to the collector current is obtained across the collector resistor 6.

In each of the above embodiments, the present invention is applied to a current supply circuit using a DC power supply.
As shown in FIG. 4, by using a diode pair in which two pn junction diodes 3 and 3 'having the same characteristics are connected in parallel in opposite directions, current detection of a current supply circuit using an AC power supply 1' can also be performed. it can. In this case, the voltage drop Vc appearing at the collector resistor 6 of the transistor 4 becomes a half-wave rectified waveform of the AC power supply 1 '. Further, any of a PNP type and an NPN type can be used as a transistor.

[0020]

As described above with reference to the embodiment, according to the first aspect of the present invention, current detection is performed using a diode connected in a forward series instead of a resistor. Current detection can be performed with an inexpensive and simple circuit configuration using only general-purpose components without increasing power loss due to an increase in measurement current. Further, according to the second aspect of the present invention, also in the AC power supply circuit, current detection can be performed with a simple circuit configuration without increasing power loss.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram showing a first embodiment of a current detection circuit according to the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit configuration diagram showing a modified example of the first embodiment shown in FIG.

FIG. 4 is a diagram showing a circuit configuration when the present invention is applied to an AC power supply circuit.

FIG. 5 is a diagram illustrating a configuration example of a conventional current detection circuit.

FIG. 6 is a diagram showing another configuration example of a conventional current detection circuit.

[Explanation of symbols]

 Reference Signs List 1 DC power supply 1 'AC power supply 2 Load 3, 3' pn junction diode 4 PNP transistor 4 'NPN transistor 5 Base resistor 6 Collector resistor 7 Rectifier circuit diode 8 Capacitance 9 Base input resistance 10 NPN transistor 11 Base potential fixing resistor 12 LED 13 resistance

Claims (2)

[Claims] 1. A bipolar transistor in which a diode is connected in series in a forward direction to a current supply circuit between one side of a DC power supply and a load, and an emitter and a base via a base resistor are connected to both poles of the diode, respectively. Wherein a current drop of the current supply circuit is detected by detecting a voltage drop of a collector resistance connected between the collector of the bipolar transistor and the other side of the DC power supply. Detection circuit. 2. A current supply circuit between one end of an AC power supply and a load is connected in series with a diode pair formed by connecting diodes having the same characteristics in parallel in opposite directions, and an emitter and a diode are provided at both ends of the diode pair. Bipolar transistors each connected to a base via a base resistor are arranged, and a voltage drop of a collector resistor connected between the collector of the bipolar transistor and the other end of the AC power supply is detected, and the current of the current supply circuit is detected. A current detection circuit configured to detect a current.