JP4908889B2 - Low voltage detection circuit - Google Patents

Description

  The present invention relates to a low voltage detection circuit, and more particularly to a low voltage detection circuit for detecting a decrease in operating voltage (power supply voltage) in a semiconductor integrated circuit such as an IC.

  In general, in a semiconductor integrated circuit such as an IC, when its operating voltage (also referred to as an auxiliary power supply voltage) decreases, it is necessary to stop the operation of the semiconductor integrated circuit in order to prevent malfunction. For this reason, in the semiconductor integrated circuit, a low voltage detection circuit for detecting a decrease in the auxiliary power supply voltage is used.

  FIG. 5 is a circuit diagram showing an example of a conventional low voltage detection circuit. In FIG. 5, a drain (D) of an NMOS transistor 12 is connected to an input terminal 11 to which an external input voltage is applied, and a resistor. 13 is connected, and the resistor 13 is connected to the gate (G) of the NMOS transistor 12 and the drain of the NMOS transistor 14. The gate of the NMOS transistor 14 is connected to the output terminal of the operational amplifier (comparator) 15, and the source (S) of the NMOS transistor 14 is grounded.

  Further, the source of the NMOS transistor 12 is connected to an internal power supply terminal to which an internal power supply voltage is applied and the auxiliary power supply terminal 16, and the internal power supply terminal and the auxiliary power supply terminal 16 are grounded via resistors 17, 18 and 19. The connection point between the resistor 17 and the resistor 18 is connected to the non-inverting terminal of the operational amplifier 20. The connection point between the resistor 18 and the resistor 19 is connected to the non-inverting terminal of the operational amplifier 15. The inverting terminals of the operational amplifiers 15 and 20 are connected to each other, and a reference voltage source 21 is disposed between the inverting terminals and the ground. The power supply of the operational amplifiers 15 and 20 is supplied from the reference voltage terminal 22, and the output terminal of the operational amplifier 20 is connected to the low voltage detection terminal 23.

  In the low voltage detection circuit described above, when an input voltage (for example, 30V to 80V) is applied to the input terminal 11, the NMOS transistor 12 is turned on, and the voltage appearing at the internal power supply terminal and the auxiliary power supply terminal 16 is reduced. After the IC voltage shown in FIG. 2 starts operating after gradually increasing to an initial voltage value (also referred to as an auxiliary power supply voltage value, for example, constant at 7 V), the transistor 25 can be turned on / off. become. At that time, since energy is transmitted to the secondary side of the transformer, energy is similarly transmitted to the control winding 16a. As shown in FIG. 2, the output of the control winding 16a is connected to the reference numeral 16 of the IC 24, which is an internal power supply terminal and an auxiliary power supply terminal. That is, the internal power supply terminal and the auxiliary power supply terminal 16 gradually increase from the initial value voltage value and reach the auxiliary power supply voltage (for example, constant at 15 V).

  On the other hand, the voltage value appearing on the internal power supply terminal and auxiliary voltage terminal 16 side is a predetermined voltage value (low voltage detection set voltage value, for example, (internal power supply voltage value + α) V, and α is a preset setting. Exceeding the value), the output terminal voltage of the operational amplifier 15 becomes higher, and the current driving capability of the NMOS transistor 14 increases. Similarly, the output terminal voltage of the operational amplifier 20 is further increased. As a result, a high level appears at the low voltage detection terminal 23. As a result, an auxiliary power supply voltage value (for example, 15 V) is applied to the internal power supply terminal and the auxiliary power supply terminal 16.

  On the other hand, when the voltage appearing on the internal power supply terminal and auxiliary power supply terminal 16 side becomes equal to or lower than the low voltage detection setting threshold, the output terminal of the operational amplifier 20 becomes low level, and the low voltage detection terminal 23 also becomes low level (here, the low level is low level). Low voltage detection signal). The low voltage detection signal detects that the auxiliary power supply voltage has become low. As a result, the auxiliary power supply voltage applied to the internal power supply terminal and the auxiliary power supply terminal 16 is cut off. In the operational amplifier 15, the non-inverting terminal is connected to the contact point between the resistor 18 and the resistor 19, so that the output terminal voltage does not show a change yet (high level).

In order to improve the current detection accuracy in the semiconductor integrated circuit, a current detection resistor using a metal wiring is provided, and the reference voltage corresponding to a predetermined current value is compensated while compensating the temperature characteristic of the resistance value of the metal wiring. And the current flowing through the current detection section of the metal wiring is determined based on the voltage drop and the reference voltage in the current detection section of the metal wiring to determine whether or not the current value exceeds a predetermined current value. Here, the output voltage is limited according to the determination result (see Patent Document 1).
JP-A-9-93912 (paragraph (0018) to paragraph (0032), FIGS. 1 to 5)

  By the way, in the conventional low voltage detection circuit, since a decrease in the internal power supply voltage is detected using a plurality of operational amplifiers (comparators), not only the layout area is inevitably increased and the circuit scale is increased, There is a problem that the circuit configuration becomes complicated.

  Furthermore, the aforementioned low voltage detection set voltage value is set to the internal power supply voltage value + α, and the operating point of the operational amplifier changes when the ambient temperature changes, that is, when viewed from the operational amplifier, the ambient environment temperature As a result, the set value α varies, and as a result, the low voltage detection set voltage value slightly changes according to changes in the ambient environment temperature. And if a low voltage detection setting voltage value changes, there exists a subject that a low voltage state cannot be detected accurately. In other words, there is a problem that the relationship between the internal power supply voltage value and the low voltage detection set value cannot be kept constant because the set value α varies.

  In the conventional low voltage detection circuit, in order to detect a low voltage state with high accuracy, it is necessary to provide a temperature compensation circuit for performing temperature compensation of the operational amplifier, and considering this point, the circuit scale is further increased. In addition, the temperature compensation control becomes complicated.

  In order to solve the above-described problems, an object of the present invention is to provide a low-voltage detection circuit that can detect a low-voltage state with high accuracy and with a simple configuration.

  According to the present invention, in the low voltage detection circuit for detecting a decrease in the internal power supply voltage that is an operating voltage of the electronic / electrical device, the first switching element that operates according to the input voltage, and the first switching A second switching element that operates in accordance with the operation of the element and defines an auxiliary power supply voltage that is higher than the internal power supply voltage; and operates in accordance with the operation of the first switching element; A third switching element for defining a low voltage detection voltage between the internal power supply voltage, a first operating point defining element for defining an operating point of the second switching element, and the third switching element A second operating point defining element that defines an operating point of the second switching point, and when the auxiliary power supply voltage becomes equal to or lower than the low voltage detection voltage, the third switching element has a low auxiliary power supply voltage. Low voltage detection circuit is obtained which is characterized in that so as to detect the. In the present invention, the second and third switching elements have the same temperature characteristics, and the first and second operating point defining elements have the same temperature characteristics.

  In the present invention, after the third switching element is turned on when the internal power supply voltage is increased, the second switching element is turned on. When the internal power supply voltage is decreased, the third switching element is turned off. When the second switching element is turned off and the auxiliary power supply voltage becomes equal to or lower than the low voltage detection voltage, the second and third switching elements are turned off, and the third switching element The decrease of the auxiliary power supply voltage is detected by turning off.

  In the present invention, for example, the first and second operating point defining elements are first and second resistors, respectively.

  In the present invention, the first, second and third switching elements are first, second and third transistors, respectively, and the input voltage is applied to the drain of the first transistor and the first The input voltage is applied to the gate of the first transistor via the resistor, and the input voltage is applied to the drain of the second transistor via the first resistor. Is connected to the internal power supply terminal to which the internal power supply voltage is applied and the auxiliary power supply terminal, and is connected to the gate of the second transistor through a constant voltage source, and the source of the second transistor is grounded. The constant voltage source is grounded via third and fourth resistors, and the connection point between the third resistor and the fourth resistor is the third transistor. A low voltage detection terminal to which a reference voltage is applied to the drain of the third transistor via the second resistor and a low voltage detection signal indicating low voltage detection is transmitted. And the source of the third transistor is grounded.

  For example, the constant voltage source includes a diode having an anode connected to the source of the first transistor, and a Zener diode having a cathode connected to the cathode of the diode, and the anode of the Zener diode is the second transistor. Connected to the gate of the transistor.

  As described above, according to the present invention, in the low voltage detection circuit for detecting a decrease in the internal power supply voltage that is the operating voltage of the electronic / electrical device, the first switching element that operates according to the input voltage is operated. A second switching element that operates to define an internal power supply voltage, and a second switching element that operates in conjunction with the operation of the first switching element to define a low voltage detection voltage between the auxiliary power supply voltage and the internal power supply voltage. 3 switching elements, a first operating point defining element that defines the operating point of the second switching element, and a second operating point defining element that defines the operating point of the third switching element. When the auxiliary power supply voltage becomes lower than the low voltage detection voltage, the low voltage state is detected by the third switching element, and the second and third switching elements have the same temperature characteristics. At the same time, since the first and second operating point defining elements have the same temperature characteristics, the set value α, which is the difference between the internal power supply voltage and the low voltage detection voltage, is set regardless of variations in the ambient environment temperature. Since it can always be kept constant and there is no need to use a comparator, there is an effect that a low voltage state can be detected with high accuracy with a simple configuration.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a low voltage detection circuit according to an embodiment of the present invention. The low voltage detection circuit 10 shown in FIG. 1 is used, for example, when detecting a decrease in auxiliary power supply voltage applied to an IC. The IC 24 shown in FIG. 2 includes the low voltage detection circuit 10 shown in FIG. 1. When the low voltage detection circuit 10 detects a low voltage state, the low voltage detection circuit 10 as shown in FIG. A low level low voltage detection signal is output from the detection terminal 23.

  As a result, the transistor 25 that has been repeatedly turned on / off until then is turned off, the current flowing in the primary winding of the transformer 26 is cut off, and no output appears on the secondary winding side. The auxiliary power supply voltage supplied from the side to the internal power supply terminal 16 is cut off.

  In FIG. 1, the input terminal 11 is connected to the drain of an NMOS transistor (first transistor) 31 and also connected to a resistor (first operating point defining element) 32, and the resistor 32 is the gate of the NMOS transistor 31. And the drain of the NMOS transistor (second transistor) 33. The source of the NMOS transistor 33 is grounded. The source of the NMOS transistor 31 is connected to the internal power supply terminal and the auxiliary power supply terminal 16, and is connected to the anode side of the diode 34. The cathode side of the diode 34 is connected to the cathode side of the Zener diode 35 (the diode 34 and the Zener). The anode side of the Zener diode 35 is connected to the gate of the NMOS transistor 33 and grounded via resistors 36 and 37 (third and fourth resistors). Has been.

  The connection point between the resistor 36 and the resistor 37 is connected to the gate of an NMOS transistor (third transistor) 38, and the source of the NMOS transistor 38 is grounded. The drain of the NMOS transistor 38 is connected to the low voltage detection terminal 23 via the inverter 39 and is connected to the reference voltage terminal 22 via the resistor (second operating point defining element) 40. Here, the NMOS transistors 33 and 38 have the same temperature characteristics. Moreover, the resistor 32 and the resistor 40 have the same temperature characteristic.

Here, the operation of the low voltage detection circuit 10 will be described with reference to FIGS.
In the low voltage detection circuit 10, when an input voltage is applied to the input terminal 11, the NMOS transistor 31 is turned on, and the voltage appearing at the internal power supply terminal and the auxiliary power supply terminal 16 gradually increases as shown in FIG. 2. After increasing to the internal power supply voltage value, it further increases.

  The forward voltage Vf of the diode 34 and the voltage value dropped by the Zener voltage Vz of the Zener diode 35 are applied to the gate of the NMOS transistor 33, and the NMOS transistor 33 is turned on. The NMOS transistor 33 defines the aforementioned internal power supply voltage value.

  On the other hand, a voltage value that is further reduced by the resistance value of the resistor 36 is applied to the gate of the NMOS transistor 38, the NMOS transistor 38 is turned on, whereby the reference voltage terminal 22 is grounded, and the inverter 39 is low level. Is input, and the inverter 39 outputs a high level. Therefore, the low voltage detection signal is not output from the low voltage detection terminal 23, the transistor 25 shown in FIG. 2 is turned on / off, and the internal power supply voltage is applied to the internal power supply terminal and the auxiliary power supply terminal 16. Will be.

  The NMOS transistors 33 and 38 are turned on when a voltage higher than a predetermined gate voltage (threshold voltage) is applied to the gate, respectively, and when the internal power supply voltage exceeds the low voltage detection set voltage (internal power supply). Voltage value <low voltage detection set voltage value <auxiliary power supply voltage), and the resistors 32 and 40 apply voltages equal to or higher than the threshold voltage to the gates of the NMOS transistors 33 and 38, respectively. That is, the resistors 32 and 40 are resistors that define the operating points of the NMOS transistors 33 and 38, respectively.

  Now, as shown in FIG. 3, if the internal power supply voltage drops and the internal power supply voltage value becomes the low voltage detection set voltage value at the time indicated by the point P, the gate voltage of the NMOS transistor 38 is less than the threshold voltage. Thus, the NMOS transistor 38 is turned off. As a result, the NMOS transistor 38 is turned off, a high level appears on the input side of the inverter 39, a low voltage detection signal that is at a low level is sent from the inverter, and the transistor 25 shown in FIG. 2 is turned off. The internal power supply voltage applied to the internal power supply terminal and the auxiliary power supply terminal 16 is cut off (the NMOS transistor 38 is a transistor defining a low voltage detection set voltage value).

  In the low voltage detection circuit shown in FIG. 1, when the ambient environment temperature changes, the operating points of the NMOS transistors 33 and 38 also change, but the NMOS transistors 33 and 38 have the same temperature characteristics. The NMOS transistor 33 that defines the internal power supply voltage and the NMOS transistor 38 that defines the low voltage detection set voltage always have a set value α that is the difference between the internal power supply voltage value and the low voltage set voltage value, regardless of temperature fluctuations. It will be kept constant.

  That is, as shown in FIG. 4, even if the internal power supply voltage fluctuates, the set value α is always kept constant (the relationship between the internal power supply voltage value and the low voltage detection set value is kept constant), the comparator and A low voltage detection circuit capable of accurately detecting a drop in the auxiliary power supply voltage can be obtained with a simple configuration using a switching element such as an NMOS transistor without using a temperature compensation circuit.

  In the above-described example, the example of detecting the decrease in the auxiliary power supply voltage in the semiconductor integrated circuit has been described. However, regardless of the semiconductor integrated circuit, the decrease in the operating voltage is similarly detected in other electric and electronic devices. be able to.

  A second switching element that operates in accordance with the operation of the first switching element that operates in accordance with the input voltage and defines an auxiliary power supply voltage; an internal power supply voltage that operates in accordance with the operation of the first switching element; A third switching element for defining a low voltage detection voltage between the auxiliary power supply voltage and a first operating point defining element for defining an operating point of the second switching element; A second operating point defining element for defining an operating point, and when the internal power supply voltage becomes lower than the low voltage detection voltage, the low voltage state is detected by the third switching element; As a result of being able to detect a low voltage state with high accuracy, it can be applied to detection of a decrease in driving voltage applied to an electric / electronic device.

It is a circuit diagram which shows an example of the low voltage detection circuit by embodiment of this invention. It is a figure for demonstrating the power supply system of the semiconductor integrated circuit in which the low voltage detection circuit shown in FIG. 1 is used. FIG. 2 is a diagram showing a relationship among an input voltage, an internal power supply voltage, a low voltage detection setting voltage, and an auxiliary power supply voltage in the low voltage detection circuit shown in FIG. 1. In the low voltage detection circuit shown in FIG. 1, it is a figure for demonstrating the state by which the difference of an internal power supply voltage and a low voltage detection voltage is kept constant irrespective of the change of ambient environment temperature. It is a circuit diagram which shows the conventional low voltage detection circuit.

Explanation of symbols

11 Input terminal 12, 14, 31, 33, 38 NMOS transistor 13, 17, 18, 19, 32, 36, 37, 40 Resistor 15, 20 Operational amplifier (comparator)
21 Reference voltage source 22 Reference voltage terminal 23 Low voltage detection terminal 24 IC
25 Transistor 26 Transformer 34 Diode 35 Zener diode 39 Inverter

Claims (6)

In a low voltage detection circuit for detecting a drop in the internal power supply voltage, which is the operating voltage of electronic and electrical equipment,
A first switching element that operates in response to an input voltage;
A second switching element that operates in conjunction with the operation of the first switching element to define an auxiliary power supply voltage that is higher than the internal power supply voltage;
A third switching element that operates in conjunction with the operation of the first switching element to define a low voltage detection voltage between the auxiliary power supply voltage and the internal power supply voltage;
A first operating point defining element that defines an operating point of the second switching element;
A second operating point defining element that defines an operating point of the third switching element;
The low voltage detection circuit according to claim 3, wherein when the auxiliary power supply voltage becomes equal to or lower than the low voltage detection voltage, the third switching element detects a decrease in the auxiliary power supply voltage. The second and third switching elements have the same temperature characteristics;
2. The low voltage detection circuit according to claim 1, wherein the first operating point defining element and the second operating point defining element have the same temperature characteristic. When the internal power supply voltage increases, the second switching element is turned on after the third switching element is turned on,
When the internal power supply voltage decreases, the third switching element is turned off and then the second switching element is turned off.
When the auxiliary power supply voltage becomes equal to or lower than the low voltage detection voltage, the second and third switching elements are turned off, and a decrease in the auxiliary power supply voltage is detected by turning off the third switching element. The low voltage detection circuit according to claim 2, wherein   4. The low voltage detection circuit according to claim 2, wherein the first and second operating point defining elements are first and second resistors, respectively. The first, second and third switching elements are first, second and third transistors, respectively;
The input voltage is applied to the drain of the first transistor, the input voltage is applied to the gate of the first transistor via the first resistor, and the first resistor is applied via the first resistor. The input voltage is applied to the drain of the second transistor;
The source of the first transistor is connected to an internal power supply terminal to which the internal power supply voltage is applied and an auxiliary power supply terminal, and is connected to the gate of the second transistor via a constant voltage source, The source of the transistor is grounded,
The constant voltage source is grounded through third and fourth resistors, and a connection point between the third resistor and the fourth resistor is connected to a gate of the third transistor, and A reference voltage is applied to the drain of the third transistor via the second resistor, and a low voltage detection terminal to which a low voltage detection signal indicating low voltage detection is sent is connected, and the third transistor 5. The low voltage detection circuit according to claim 4, wherein the source of the low voltage detection circuit is grounded. The constant voltage source includes a diode having an anode connected to a source of the first transistor;
A Zener diode having a cathode connected to the cathode of the diode;
6. The low voltage detection circuit according to claim 5, wherein an anode of the Zener diode is connected to a gate of the second transistor.

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