JP3540946B2 - Voltage detection circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a voltage detection circuit that detects that a power supply voltage of a main circuit has become low.
[0002]
[Prior art]
In order for an electronic circuit to operate without malfunction, it is necessary to secure its power supply voltage. In addition, when the power supply voltage falls below a value required for driving the electronic circuit, it is required to stop the electronic circuit. In order to realize the above, it is necessary to constantly monitor the power supply voltage.
[0003]
FIG. 5 shows a conventional voltage detection circuit. The sources of p-channel MOSFETs M11, M12 and M17, which constitute a circuit for passing a constant current, are connected to the high potential side VDD (representing a terminal or voltage) of the power supply of the voltage detection circuit which is the same as the power supply voltage of the main circuit ing. M11 is connected to ground GND (representing a terminal or voltage) via a constant current source 12. The reference voltage VREF is divided by the dividing resistors R11 and R12 to generate a divided voltage V13 which is a voltage at the dividing point. The drain of M12 is connected to the sources of p-channel MOSFETs M13 and M14, the respective drains are connected to the drains of n-channel MOSFETs M15 and M16, and the sources of M15 and M16 are connected to GND. The voltage of VDD is divided between VDD and GND by voltage dividing resistors R13 and R14 to generate a divided voltage V14 which is a voltage at a voltage dividing point. Further, M17 and an n-channel MOSFET M18 are connected between VDD and GND, and a connection point between M17 and M18 becomes an output VOUT (representing a terminal or voltage) of the voltage detection circuit. V13 is the input voltage VIN, which is the gate voltage of M13, and V14 is the gate voltage of M14. The drain of M14 is connected to the gate of M18. The gates of M11, M12 and M17 are respectively connected, and the gate of M11 is connected to the drain of M11. The aforementioned VOUT is connected to a main circuit (not shown).
[0004]
In this figure, VDD is also a power supply voltage to be detected, and VREF is a reference voltage. The gate voltage V13 (= VIN) of M13 is a value obtained by dividing the reference voltage VREF by the voltage dividing resistors R11 and R12, and becomes V13 = VREF × R12 / (R11 + R12). The gate voltage V14 of M14 is a value obtained by dividing the power supply voltage VDD by the resistors R13 and R14, and becomes V14 = VDD × R14 / (R13 + R14). When V13 <V14, that is, when VDD> VREF × R12 (R13 + R14) / [R14 (R11 + R12)], the output voltage VOUT becomes VDD. When V13> V14, that is, when VDD <VREF × R12 (R13 + R14) / [R14 (R11 + R12)], the output voltage VOUT becomes 0V. As described above, by comparing the power supply voltage with the reference voltage, it can be detected that the power supply voltage becomes low.
[0005]
[Problems to be solved by the invention]
However, the conventional voltage detection circuit shown in FIG. 5 uses a comparator having as many as five MOSFETs, so that the circuit configuration is complicated. When the power supply voltage of the electronic circuit as the main circuit decreases, the power supply voltage of the voltage detection circuit also decreases because the power supply of the main circuit is supplied to the voltage detection circuit. The comparator of this conventional circuit is composed of M12 forming a constant current source, M13 and M14 of a differential circuit, and M15 and M16 as active loads, and three MOSFETs from the high potential side of the power supply to the ground side. They are connected in series. These three MOSFETs connected in series are operated in a saturation region where the current is constant. Therefore, it is necessary to apply a voltage of about 0.6 V between the source and the drain to one MOSFET. With three MOSFETs, the voltage between the high potential side and the ground side of the power supply is Even when the voltage becomes low, a voltage of about 2 V is required. Therefore, in the conventional circuit, the voltage detection circuit operates stably at a voltage of about 2 V or more, but malfunctions at a voltage lower than about 2 V. Further, in the conventional circuit, the voltage comparison is performed by a p-channel MOSFET in which the source terminals of M13 and M14 are connected to the high potential side of the power supply. Therefore, when the power supply voltage fluctuates, the source potentials of M13 and M14 and the gate of M14 change. The potential fluctuates, making accurate comparison difficult. Therefore, when a highly accurate comparison is required, in the conventional circuit, the power supply of the voltage detection circuit is separated from the power supply of the main circuit as another stable power supply, and the voltage dividing resistors of R13 and R14 for detecting V14 are used. Must be connected to the power supply of the main circuit. Further, in order to increase the withstand voltage of the power supply voltage, it is necessary to increase the withstand voltage of a large number of semiconductor elements forming the voltage detection circuit, and the circuit becomes expensive.
[0006]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a voltage detection circuit which solves the above-mentioned problems and consumes less current and can reliably detect a low voltage.
[0007]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, a function of detecting that the power supply voltage of the main circuit has become low voltage is provided, two stages of inverter circuits are connected, and the threshold voltage and the power supply voltage of the preceding inverter circuit are determined. comparison that is the supply voltage for the detected that becomes a low voltage, and inputs the output voltage of the preceding stage of the inverter circuit in the subsequent stage of the inverter, upon detecting a low voltage, ground and the output voltage of the subsequent stage of the inverter circuit In the voltage detection circuit in which the output voltage of the subsequent inverter circuit becomes the power supply voltage in a range where the low voltage is not detected in the voltage detection circuit, the input to the previous inverter is divided by the first and second voltage dividing resistors. The power supply voltage of the circuit, the preceding inverter circuit is a first p-channel MOSFET having a gate and a drain connected, a load resistor, and a gate are input parts of the preceding inverter. A first n-channel MOSFET is connected in series, and a second-stage inverter circuit has a second p-channel MOSFET whose gate is connected to the gate of the first p-channel MOSFET and a gate connected to the load resistor. The second n-channel MOSFET connected to the connection point of the first n-channel MOSFET is connected in series.
With the circuit configuration of the circuit is simple, no malfunction, also operates stably to a low voltage, can be manufactured with less has voltage detecting circuit current consumption.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Figure 1 is a voltage detection circuit of the first reference example of the present invention. This voltage detection circuit is composed of two stages of inverters INV1 and INV2, and a voltage obtained by dividing the power supply voltage VDD by the voltage dividing resistors R1 and R2 is input to the preceding stage inverter INV1 as an input voltage VIN, and an output voltage VOUT1 is obtained. Is output. This VOUT1 becomes the input voltage of the inverter INV2 at the subsequent stage, and the output voltage VOUT is output from the inverter INV2.
[0011]
INV1 is for monitoring VIN, and the method is to compare the threshold value of INV1 (the input voltage at which the output voltage of the inverter switches from H level to L level and from L level to H level) with VIN. Performed by VOUT1 becomes 0 V when VIN is higher than the threshold value, and becomes the power supply voltage VDD when VIN is lower than the threshold value. In response to the signal of VOUT1, the output voltage VOUT of INV2 becomes a level obtained by inverting the output voltage VOUT1 of INV1, and the output voltage VOUT of INV2 becomes the power supply voltage VDD when VIN is higher than the threshold value, and the threshold voltage is VIN. When it is lower than the value, the voltage becomes 0 V (GND). As described above, by using the two-stage inverter, the voltage detection circuit is simplified, the current consumption is suppressed, and when the voltage becomes low, the output voltage VOUT of the voltage detection circuit is set to 0 V, so that the load circuit is reduced. Power supply can be stopped.
[0012]
Figure 2 is a voltage detection circuit of the second reference example of the present invention. In this circuit, INV1 of the circuit shown in FIG. 1 is constituted by a load resistor 1 and an n-channel MOSFET 2. Monitoring of the input voltage VIN is performed by comparing the threshold value (Vth) of the n-channel MOSFET 2 with VIN. Further, INV2 can be constituted by one or two MOSFETs, and the configuration of this voltage detection circuit is simpler than that of the conventional circuit of FIG.
[0013]
The circuit operation of FIG. 2 will be described. First, when the power supply of the main circuit (not shown) is turned on, the power supply voltage VDD of the voltage detection circuit, which is the same as the power supply voltage of the main circuit, increases, and VIN, which is the divided voltage of VDD and the gate voltage of the n-channel MOSFET 2, also increases. I do. When VIN exceeds the threshold value of the n-channel MOSFET 2, the n-channel MOSFET 2 is turned on, and VOUT1 becomes 0V. Since VOUT1 becomes the input voltage of INV2, the input voltage of INV2 becomes 0V. This 0V signal is inverted by INV2, and the output voltage VOUT of INV2 becomes the power supply voltage VDD. Next, when VDD decreases and VIN falls below the threshold value of the n-channel MOSFET 2, the n-channel MOSFET 2 is turned off, the input voltage of INV2 increases, and VOUT becomes 0V. Even if VDD further decreases, VOUT is maintained at 0 V because the n-channel MOSFET 2 remains off, and the voltage detection circuit does not malfunction when VDD decreases as in the conventional circuit.
[0014]
FIG. 3 shows a voltage detection circuit according to a first embodiment of the present invention. This circuit comprises two p-channel MOSFETs M1 and M2, two n-channel MOSFETs M3 and M4, two voltage dividing resistors R1 and R2, and one load resistor R3. The circuit configuration is very simple as compared with the conventional circuit. As the input voltage VIN of this circuit, a voltage obtained by dividing the power supply voltage VDD by the voltage dividing resistors R1 and R2 is used. The n-channel MOSFET 2 in FIG. 2 is M3 in this circuit, and the load resistor 1 in FIG. 2 is a load 3 in this circuit, and the load 3 is composed of M1 and R3. INV2 in FIG. 2 is composed of M2 and M4.
[0015]
Next, the circuit operation will be described. When the power supply voltage VDD rises and the gate voltage V3 of M3 generated by dividing VDD by R1 and R2 exceeds the threshold value of M3, M3 is turned on and the gate voltage V4 of M4 becomes 0V. As a result, M4 is turned off, and the output voltage VOUT becomes VDD. Next, when VDD decreases and V3 falls below the threshold value of M3, M3 turns off, V4 increases, M4 turns on, and VOUT becomes 0V. The detection of the power supply voltage VDD is performed by comparing the input voltage VIN, which is the voltage obtained by dividing VDD with the voltage dividing resistors R1 and R2, with the threshold voltage of M3, and setting the detection voltage value by the ratio of R1 to R2. It becomes possible by adjusting. The influence of the error due to the variation of the threshold value of M3 can be eliminated by adjusting the value of R2 / (R1 + R2). The resistor R3 is provided to suppress the drain current when the transistor M3 is on.
[0016]
FIG. 4 shows an output voltage when the power supply voltage of the voltage detection circuit according to the present invention is changed. Here, the gate width of M1 and M2 shown in FIG. 3 was 4 μm, the gate length was 8 μm, the gate width of M3 and M4 was 12 μm, and the gate length was 1.6 μm. Further, R1 + R2 = 1000 kΩ was fixed. When R2 / (R1 + R2) = 2/10, the detection voltage is 3.15V, when R2 / (R1 + R2) = 3/10, the detection voltage is 1.9V, and R2 / (R1 + R2) = 4 / V. In the case of 10, the detection voltage is 1.35V. In the case of VDD of 1.35 V or less, VOUT can stably maintain 0 V. The minimum value of the detection voltage of the conventional circuit corresponding to the detection voltage of 1.35 V is about 1.9 V, and the voltage range in which the circuit of the present invention can reduce the detection voltage and stably operates the main circuit is smaller. Become wider. Excluding the current flowing through the voltage dividing resistors R1 and R2, the current consumption is about 5 .mu.A in the conventional circuit of FIG. 5, while it can be significantly reduced to about 1 .mu.A in the circuit of FIG.
[0017]
In the circuits of FIGS. 2 and 3, the voltage comparison is performed by the n-channel MOSFET 2 or M3 whose source terminal is grounded, and the operation is performed with reference to the ground point (GND). Stable operation can be ensured, and there is no malfunction. Further, since the number of MOSFETs connected in series between the high potential side terminal VDD and the ground side terminal GND of the power supply can be reduced to two or one, a stable operation can be obtained even at about 1V. Further, the number of stages from the input stage to the output stage is two, which is smaller than the four stages of the conventional circuit, and the current consumption can be reduced.
[0018]
Further, the number of elements constituting the circuit can be reduced as compared with the conventional circuit, and the cause of malfunction of the circuit can be reduced. Further, it is easy to increase the withstand voltage of the circuit because the number of MOSFETs to increase the withstand voltage is small.
[0019]
【The invention's effect】
According to the present invention, the configuration of the voltage detection circuit is simplified, stable operation is ensured, and extension to a high withstand voltage circuit is facilitated. In addition, since the number of transistors between the power supply and the ground is set to two or less, stable operation is possible even at a low voltage of about 1V. Further, since the number of stages is small, the current consumption can be significantly reduced.
[Brief description of the drawings]
[1] the first voltage detection circuit diagram of a reference example FIG. 2 voltage detecting circuit diagram of a second reference example of the present invention [3] Voltage detecting circuit diagram of a first embodiment of the present invention of the present invention FIG. 4 is a diagram showing an output voltage when the power supply voltage of the voltage detection circuit according to the present invention is changed. FIG. 5 is a diagram of a conventional voltage detection circuit.
1 load resistance 2 n-channel MOSFET
3 Load 11 Comparator 12 Constant current source INV1, INV2 Inverter R1, R2 Voltage dividing resistor R3 Load resistor VIN Input voltage VOUT1, VOUT Output voltage VDD High-potential terminal of power supply or voltage GND Ground terminal or voltage M1, M2 p-channel MOSFET
M3, M4 n-channel MOSFET
V3, V4 Gate voltage The name change notification has been submitted on October 2nd.

Claims (1)

A function of detecting that the power supply voltage of the main circuit becomes low voltage, the inverter circuit is connected two stages, the threshold voltage and that the supply voltage for comparing the power supply voltage of the preceding stage of the inverter circuit is low Voltage is detected, the output voltage of the preceding inverter circuit is input to the succeeding inverter, and when the low voltage is detected, the output voltage of the succeeding inverter circuit becomes the ground potential and the low voltage is not detected. In the voltage detection circuit in which the output voltage of the subsequent inverter circuit becomes the power supply voltage , the input to the previous inverter is the power supply voltage of the main circuit divided by the first and second voltage dividing resistors, A first p-channel MOSFET having a gate and a drain connected to a preceding inverter circuit, a first n-channel MOSFET having a load resistor and a gate serving as an input section of the preceding inverter. And a second p-channel MOSFET having a gate connected to the gate of the first p-channel MOSFET and a gate connected to the load resistance and the first p-channel MOSFET. A voltage detection circuit, wherein a second n-channel MOSFET connected to a connection point of the n-channel MOSFET is connected in series .

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