TW201629504A - Detection circuit - Google Patents

Abstract

Provided is a detection circuit configured to avoid erroneous detection that may occur immediately after a detection circuit is powered on. The detection circuit includes: an output transistor connected between a voltage input terminal and a voltage output terminal; and a load open-circuit detection circuit configured to detect an open circuit of a load connected to the voltage output terminal, in which an output circuit of the load open-circuit detection circuit includes a first transistor and a second transistor connected in series, the first transistor having a gate connected to the output transistor in common, the second transistor having a gate to which a signal indicating that the open-circuit of the load is detected, and in which the first transistor is in an off state when the output transistor is in an off state.

Description

Detection circuit

The present invention relates to a detection circuit for detecting an open of a connected load.

Fig. 6 is a conventional detection circuit. The conventional detection circuit includes a voltage input terminal 401, a voltage output terminal 402, an output transistor 403, a control circuit 404, a load open circuit detecting circuit 405 that detects an open circuit of a load connected to the voltage output terminal 402, and a load. The output terminal 406 of the open circuit detection circuit 405.

The control circuit 404 performs ON/OFF control of the output transistor 403. The load open circuit detecting circuit 405 outputs a detection signal to the output terminal 406 when detecting an open circuit of the load connected to the voltage output terminal 402.

In the load open circuit detecting circuit 405, in order to detect an open circuit of a load connected to the voltage output terminal 402, a method of monitoring the current of the output transistor 403 is often used. For example, a resistor 410 is provided between the voltage input terminal 401 and the output transistor 403, and the voltage generated at both ends thereof is used for determination. In the open state of the load connected to the voltage output terminal 402, no current flows through the output transistor 403, so the open circuit of the load connected to the voltage output terminal 402 is detected as described above. Prior art literature

Patent Document 1: Japanese Patent Laid-Open No. Hei 6-289087 [Problem to be Solved by the Invention]

The output transistor 403 has a large component size and a large input capacity to allow a large current to flow corresponding to the load connected to the voltage output terminal 402. It is necessary to charge and discharge the large input capacity of the output transistor 403 for on-off control, and physical time is required. Therefore, when the power supply of the detection circuit is activated, the output transistor 403 is difficult to be immediately turned on. Therefore, after the power supply of the detecting circuit has just started, the output transistor 403 is in an off state, and although it is not actually in an open state of the load, no voltage is generated in the resistor 410.

Therefore, the conventional detection circuit shown in FIG. 6 has a problem that the voltage generated in the resistor 410 is small after the power supply of the detection circuit is started, and the load open circuit detection circuit 405 generates an erroneous determination.

The present invention has been made in order to eliminate the above-mentioned problems, and provides a detecting circuit which avoids erroneous detection immediately after the power of the detecting circuit is started. [Means for solving the problem]

In order to solve the conventional problems, the detection circuit of the present invention adopts the configuration described below. The detection circuit is configured to include an output transistor provided between the voltage input terminal and the voltage output terminal, and a load open circuit detecting circuit for detecting an open circuit of the load connected to the voltage output terminal, and the output circuit of the load open circuit detecting circuit has the first a structure in which the transistor and the second transistor are connected in series, wherein a gate of the first transistor is connected in common to an output transistor, and a gate of the second transistor receives a signal for detecting an open load, and outputs When the transistor is turned off, the first transistor is turned off. (Effect of the invention)

According to the detecting circuit of the present invention, it is possible to provide a detecting circuit which avoids erroneous detection immediately after the power source is turned on.

Hereinafter, the present embodiment will be described with reference to the drawings. Fig. 1 is an explanatory view showing a detecting circuit of the embodiment. The detection circuit of the present embodiment includes a voltage input terminal 401, a voltage output terminal 402, an output transistor 403 connected between the voltage input terminal 401 and the voltage output terminal 402, a control circuit 404, a load open circuit detecting circuit 405, and a load open circuit detecting circuit. Output terminal 406 and resistor 410 of 405. The load open circuit detecting circuit 405 detects an open circuit of the load connected to the voltage output terminal 402. In order to monitor the current of the output transistor 403, the resistor 410 generates a voltage corresponding to the current.

The load open circuit detection circuit 405 includes a voltage circuit 101, a voltage source 102, a comparator 103, a transistor 104, a transistor 105, and a current source 106. The voltage circuit 101 generates a voltage VSIG of a VSS reference which is based on a voltage generated across the resistor 410. Voltage source 102 produces a reference voltage VREF. The comparator 103 compares the voltage VSIG with the reference voltage VREF and controls the on and off of the transistor 104. The gate of the transistor 105 is commonly connected to the output transistor 403, and the transistor 105 is connected in series with the transistor 104. The current source 106 is connected in series with the transistor 104 and the transistor 105 connected in series, and its connection point is connected to the output terminal 406. The transistor 104 and the transistor 105 and the current source 106 constitute an output circuit of the load open circuit detecting circuit 405.

FIG. 5 is a circuit diagram showing an example of the voltage circuit 101. The voltage circuit 101 shown in FIG. 5 includes an input terminal 300 and an input terminal 301, an amplifier 302, a resistor 304 and a resistor 305, a transistor 303, and an output terminal 306. The input terminal 300 is connected to the terminal of the voltage input terminal 401 of the resistor 410. The input terminal 301 is connected to the other terminal of the resistor 410.

The voltage circuit 101 outputs a voltage VSIG which is a VSS reference to the terminal 306 which multiplies the voltage across the resistor 410 based on the voltage of the voltage input terminal 401 by the resistance ratio. In addition, the voltage circuit 101 is not limited to this configuration as long as it is configured to generate the voltage VSIG of the VSS reference, and the voltage VSIG of the VSS reference is based on the voltage generated across the resistor 410.

Next, the operation of the detection circuit of this embodiment will be described. The control circuit 404 performs on-off control of the output transistor 403. The load open circuit detecting circuit 405 outputs a detection signal (high (H) level) to the output terminal 406 when detecting an open circuit of the load connected to the voltage output terminal 402. Since the voltage generated in the resistor 410 is based on the current of the output transistor 403, no current should flow through the output transistor 403 in the open state of the load connected to the voltage output terminal 402, and thus by determining the resistance 410 The voltage is below a certain value to detect the open circuit of the load.

The voltage VSIG is based on the voltage generated in the resistor 410, so when the voltage generated in the resistor 410 is small, the voltage VSIG is small. Therefore, in the open state of the load connected to the voltage output terminal 402, the voltage VSIG becomes small. When the comparator 103 determines that VSIG < VREF, it conducts conduction control of the transistor 104.

The output transistor 403 has a large component size and a large input capacity so that a large current flows, so that the power of the detecting circuit is not turned on immediately when the power is turned on. Here, the transistor 105 is set to be in an off state when the power of the detection circuit is activated, similarly to the output transistor 403. That is, when the power supply of the detection circuit is activated and the output transistor 403 is in the off state, the transistor 105 is also turned off, so even if the transistor 104 is turned on by the output of the comparator 103, the detection signal is not outputted to The output terminal 406 of the load open circuit detection circuit 405. As described above, according to the detecting circuit of the present embodiment, it is possible to provide a detecting circuit that avoids erroneous detection immediately after the power supply of the detecting circuit is started.

In addition, it should be understood that the transistor 105 may perform the same operation as the output transistor 403 according to the control signal of the control circuit 404 immediately after the power supply of the detection circuit is started, and its configuration or characteristics are not limited. For example, transistor 105 is of the same type as output transistor 403 and has the same threshold.

Moreover, the transistor 105 is a single transistor, but can also be inserted into a diode that is diode-connected to the source of the transistor 105, or a Darlington connection. The structure is such that the threshold of the transistor 105 is higher than that of the output transistor 403.

Moreover, the transistor 105 does not necessarily need to connect the gates to the output transistor 403 in common, or may be spaced apart by a voltage level shift. The voltage level shifting section may be, for example, as long as it includes a source follower amplification section. At this time, it is clear that the magnitude of the gate/source voltage of the transistor 105 is smaller than that of the output transistor 403, so that erroneous detection can be more reliably avoided.

Here, the detection circuit of FIG. 1 cannot output a signal indicating the open state of the load when the control circuit 404 turns off the output transistor 403. For example, when the load open circuit detecting circuit 405 detects an open circuit of the load, the ambient temperature may become high, and the control circuit 404 performs off control of the output transistor 403.

Fig. 2 is an explanatory view showing another example of the detecting circuit of the embodiment. The difference from FIG. 1 is that the transistor 110 controlled by the control circuit 404 is newly included in parallel with the transistor 105. The control circuit 404 turns on the transistor 110 based on, for example, the state described above, whereby the transistor 105 can be disabled, so that even if the output transistor 403 is in the off state, the output terminal 406 of the load open circuit detecting circuit 405 can be turned on. The detection signal is output.

Fig. 3 is an explanatory view showing another example of the detecting circuit of the embodiment. The difference from the detection circuit of FIG. 1 is that the output circuit of the load open circuit detection circuit 405 includes a transistor 104 and a current source 106 connected in series, a transistor 105 and a current source 107 connected in series, and an AND circuit. ) 201. The same effect as the detection circuit of Fig. 1 can also be obtained by this configuration.

Further, it is clear that the same effect can be obtained as long as it is constituted by a suitable circuit that uses an OR circuit, as long as it is related to a condition that a circuit is forcedly fixed by an output or a combination thereof.

Fig. 4 is an explanatory view showing another example of the detecting circuit of the embodiment. Similarly to the circuit of Fig. 2, a circuit including the transistor 202 in parallel with the transistor 105 can obtain the same effects as the circuit of Fig. 2.

Further, the load open circuit detecting circuit 405 has been described with reference to the circuits shown in Figs. 1 to 4, but this is only an example, and the embodiment is not limited as long as the same effect can be obtained. In the above description, the level of each output is defined by the H level or the low (L) level for convenience, but it is not particularly limited.

101, 102, 301‧‧‧ voltage source
103‧‧‧ comparator
104, 105, 110, 202, 303, 403‧‧‧ transistors
106, 107‧‧‧ Current source
201‧‧‧ and gate circuit
300‧‧‧Input terminal
302‧‧‧Amplifier
304, 305, 410‧‧‧ resistance
306, 406‧‧‧ output terminals
401‧‧‧Voltage input terminal
402‧‧‧Voltage output terminal
404‧‧‧Control circuit
405‧‧‧Load open circuit detection circuit
VSIG‧‧‧ voltage
VREF‧‧‧ reference voltage

Fig. 1 is an explanatory view showing a detecting circuit of the embodiment. Fig. 2 is an explanatory view showing another example of the detecting circuit of the embodiment. Fig. 3 is an explanatory view showing another example of the detecting circuit of the embodiment. Fig. 4 is an explanatory view showing another example of the detecting circuit of the embodiment. FIG. 5 is an explanatory diagram showing an example of a voltage circuit of the detection circuit of the embodiment. Fig. 6 is an explanatory view showing a conventional detecting circuit.

101‧‧‧Voltage circuit

102‧‧‧voltage source

103‧‧‧ comparator

104, 105‧‧‧Optoelectronics

106‧‧‧current source

401‧‧‧Voltage input terminal

402‧‧‧Voltage output terminal

403‧‧‧Output transistor

404‧‧‧Control circuit

405‧‧‧Load open circuit detection circuit

406‧‧‧Output terminal

410‧‧‧resistance

VSIG‧‧‧ voltage

VREF‧‧‧ reference voltage

Claims (5)

A detection circuit includes a voltage input terminal, a voltage output terminal, an output transistor disposed between the voltage input terminal and the voltage output terminal, a control circuit for controlling the output transistor, and a pair connected to the voltage output A load open circuit detecting circuit for detecting an open circuit of a load of the terminal, wherein the output circuit of the load open circuit detecting circuit has a structure in which a first transistor and a second transistor are connected in series, and the first power a gate of the crystal is commonly connected to the output transistor, and a gate of the second transistor has a signal for detecting an open circuit of the load, and when the output transistor is disconnected, the first transistor is broken open. The detecting circuit according to claim 1, wherein the first transistor is a transistor of the same type as the output transistor and having the same threshold or a higher threshold. The detecting circuit according to claim 1, wherein the gate of the output transistor and the gate of the first transistor are connected via a voltage level shifting section. The detection circuit of claim 3, wherein the voltage level shifting segment is a source follower amplification segment. The detection circuit according to any one of claims 1 to 4, further comprising: a third transistor controlled by the control circuit in parallel with the first transistor.