JPH0353804B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a voltage detection circuit that outputs different signals depending on whether the input voltage is higher or lower than a reference voltage. be.

[Conventional technology]

This type of voltage detection circuit conventionally consists of a reference voltage generation circuit 1 and a comparison circuit 2 with hysteresis as shown in FIG. 5, and these circuits are specifically shown in FIG. The circuit is as shown. That is, the reference voltage generation circuit 1
is a series body 7 consisting of a constant current source 4 and a resistor 5 connected in series from the high potential point of the power source 3 to the ground potential point, and an NPN transistor 6 with the collector and base shorted, and a series body 7 from the constant current source 3 to the ground potential point. A series body 11 consisting of a connected resistor 8, an NPN transistor 9, and a resistor 10, the base of which is connected to the collector of the NPN transistor 9, and the collector and emitter of which are connected between the constant current source 3 and the ground potential point. The collector is composed of an NPN transistor 12 whose collector is the output terminal of the reference voltage generation circuit 1, and the comparator circuit 2 with hysteresis has one input of the reference voltage output from the reference voltage generation circuit 1, and the input terminal A differential amplifier 15 compares these two inputs with the input voltage (V _IN ) input from 13 as the other input, and outputs the comparison result from the output terminal 14 . and an output circuit 17 which receives a signal from the output terminal 14 of the differential amplifier 15 and outputs an "H" level or "L" level signal according to this signal. The output circuit includes a series body 20 consisting of a current source 18 and a third NPN transistor 19 connected in series from a high potential point of the power supply 3 to a ground potential point;
A load transistor 21 consisting of a multi-collector PNP transistor whose emitter is connected to the collector of the NPN transistor 19 and whose collector is short-circuited to the base and connected to the bases of the NPN transistors 6 and 9; The fourth NPN transistor 23 has its collector and emitter connected to the output terminal 22 and the ground potential point, respectively.

In the voltage detection circuit configured as described above, when the reference voltage from the reference voltage generation circuit 1 is higher than the input voltage, the transistor 24 of the differential amplifier 15
is OFF and transistors 25, 26, and 27 are ON, so transistor 19 in output circuit 17 is
OFF, transistor 23 turns ON, and output terminal 22
When the reference voltage from the reference voltage generation circuit 1 is lower than the input voltage, the transistor 24 of the differential amplifier 15 is turned on, and the transistors 25, 26,
27 turns off, transistor 19 in the output circuit 17 turns on and transistor 23 turns off.
However, an "H" level voltage is output to the output terminal 22.

[Problem that the invention seeks to solve]

In the conventional voltage detection circuit as described above, since the reference voltage generation circuit 1 and the comparison circuit 2 are configured separately and independently, there is a problem that the number of elements configuring the voltage detection circuit naturally increases. It was hot.

The present invention has been made to solve these problems, and an object of the present invention is to provide a voltage detection circuit that has a small number of constituent elements and that performs accurate voltage detection.

[Means for solving problems]

The voltage detection circuit according to the present invention includes first and second transistors that input an external input voltage to a control electrode, one end of which is connected directly to the output electrode of the first transistor, and a load that is connected to the output electrode of the second transistor. first and second current mirror circuits whose current determining side output sides are connected to the input electrodes of the first and second transistors; and a third current mirror circuit whose input end is connected to the other output end of each of the second current mirror circuits, and the input end of the third current mirror circuit and the other output end of the first current mirror circuit. and an output circuit with an input terminal connected between the two.

[Effect]

In this invention, since the level of the signal output from the output circuit is determined by comparing the magnitude of the input current of each of the first and second transistors, the reference voltage generation circuit and the comparison circuit are independent. A voltage detection circuit can be configured without providing a voltage detection circuit.

〔Example〕

FIG. 1 is a circuit diagram showing one embodiment of the present invention. In the figure, 28 is a first NPN transistor whose base is connected to the input terminal 13, and 29 is n compared to the emitter size of this NPN transistor 28. a second NPN transistor with double the emitter size;
30, 31 are these NPN transistors 28, 29
The base and collector were connected to each collector, and the emitter was connected to the high potential point of power supply 3.
Two first and second transistors consisting of PNP transistors.
A current mirror circuit; 32 is a first load consisting of a resistor whose one end is connected to the emitter of the NPN transistor 29; 33 is the other resistor 32;
A first resistive load 34 whose one end is connected to the emitter of the NPN transistor 28;
A second load 36 has a collector connected to the collector of the current mirror circuit 30 made of the NPN transistor, and an emitter connected to the ground potential point. The connected NPN transistor 37 has a collector connected to the collector of the current mirror circuit 31 consisting of the above NPN transistor, a base short-circuited to its own collector, and connected to the base of the above NPN transistor 37, and an emitter connected to the ground potential point. 39 is a current mirror circuit consisting of the above-mentioned first and second transistors 28, 29, and the first and second
and third current mirror circuits 30, 31, 36
and a first and second load 32, 33.

In the potential detection circuit described above, the input voltage when the voltage at the output terminal 22 shifts from the "L" level to the "H" level, that is, the threshold voltage (V _TH ), is determined as follows.

Since the NPN transistor 23 in the output stage is ON
In the state of transition to OFF, the NPN transistor 19 is in a state of transition from OFF to ON. Therefore, in the threshold voltage (V _TH ) input state, NPN
Since the collector current (I _C30 ) of the current mirror circuit 30 consisting of a transistor is equal to the collector current (I _C37 ) of the NPN transistor 37, the collector current (I _C31 ) of the current mirror circuit 31 consisting of an NPN transistor becomes equal. The collector current (I _C30 ) and the collector current (I _C31 ) are equal.

By the way, in the figure, NPN transistor 2
The base-emitter voltage of 8,29 is V _BE28 ,
When V _BE29 is assumed and the resistance value of the resistor 32 is R ₃₂ , V _BE28 = V _BE29 + I _C31・R ₃₂ ...(1) Therefore, the emitter size of the NPN transistor 29 is set to n times the emitter size of the NPN transistor 28, Let k be the Boltzmann constant, q be the electron charge, and T be the absolute temperature, kT/q・lnI _C30 ／I _S =kT/q ・lnI _C31 ／nI _S ＋I _C31 R ₃₂ ……(2) Therefore, I _C31 R ₃₂ =kT/q(ln n+lnI _C30 /I _C31 )...The relationship shown in (3) holds true.

Here, if the input voltage is the threshold voltage, I _C30 = I _C31
Therefore, the relationship I _C31 R ₃₂ =kT/qln n...(4) is established, and the load transistor 21 is turned off.
_{Assuming that _ _}
The relationship between this and the base-emitter voltage (V _BE28 ) of the NPN transistor 28 is as follows: V _TH =V _BE28 + 2(R ₃₄ +R ₃₅ )·kT/R ₃₂ ·qln n (5).

By the way, in the voltage detection circuit, one essential factor is that the threshold voltage (V _TH ) does not depend on temperature, but the threshold voltage (V _TH ) in the above equation (5)
is 1.25 [V] when the circuit shown in Figure 1 is formed on a semiconductor substrate, and it is generally known that this voltage does not depend on the temperature coefficient.
This sufficiently satisfies the conditions for a voltage detection circuit.

Next, the operation of the voltage detection circuit configured as described above will be explained.

First, let us explain the case where the input voltage (V _IN ) from the input terminal 13 is equal to the threshold voltage (V _TH ). In this case, the collector currents (I _C30 ) (I _C31 ) of the NPN transistors 28 and 29 are equal.
Collector current (I _C30 ) of PNP transistor 30 and
Since the collector current (I _C37 ) of the NPN transistor 37 is almost equal to that of the NPN transistor 37, the NPN transistor 19 cannot obtain a sufficient base current, so it becomes OFF or incompletely ON, and the voltage at the output terminal 22 becomes unstable. .

Next, a case where the input voltage (V _IN ) is smaller than the threshold voltage (V _TH ) will be explained. The current I flowing through the resistors 34 and 35 depends on the input voltage (V _IN ), and I=V _IN −V _BE28 /R ₃₄ +R ₃₅ =I _C30 +I _C31 (6), so V _IN <V Under _{the TH} condition, I also becomes small. When the input voltage is small, the left-hand side of equation (3) above becomes small, and the first term on the right-hand side of equation (3) is a fixed value, so for equation (3) to hold, the second term on the right-hand side must be negative. The value must be , and the relationship I _C30 < I _C31 (7) holds true. Therefore, since the collector current (I _C30 ) of the NPN transistor 28 is smaller than the collector current (I _C31 ) of the NPN transistor 29, the collector current (I _C30 ) of the NPN transistor 30 is smaller than the collector current (I _C37 ) of the NPN transistor 37. becomes smaller than NPN transistor 1
9 is perfect because no base current can be obtained.
In the OFF state, an "L" level output is obtained from the output terminal 22.

When the input voltage (V _IN ) is larger than the threshold voltage (V _TH ), the collector current (I _C30 ) of the NPN transistor 28 becomes larger than the collector current (I _C31 ) of the NPN transistor 29 due to the opposite principle to the above. , the collector current (I _C30 ) of NPN transistor 30 becomes larger than the collector current (I _C37 ) of NPN transistor 37, and NPN transistor 1
Sufficient base current is supplied to 9 and it is completely turned on.
state, and an "H" level output is obtained from the output terminal 22.

FIG. 7 is a diagram showing the potential relationship when a specific calculation is performed with the area ratio of the NPN transistor 28 and the NPN transistor 29 being 10 times. FIG. 7a shows the potential relationship when the input voltage (V _IN ) is the threshold voltage (V _TH ), and FIG. 7b shows the potential relationship when the input voltage (V _IN ) is 1.0V. It can also be seen from this figure that when the input voltage (V _IN ) is smaller than the threshold voltage (V _TH ), the relationship of equation (7) above holds true.

Next, hysteresis will be explained. In FIG. 1, the hysteresis width is determined by the load transistor 21 consisting of a multi-collector PNP transistor and the second resistive load 35.
When the collector division ratio of each PNP transistor 21 is 1:1, the load transistor 21
In the ON state, that is, when "L" is output from the output terminal 22, the voltage on the low potential side of the resistor 35 is R ₃₅ · I ₁₈ /2 (here R ₃₅
is the resistance value of the resistor 35, and _I18 is the current value of the constant current source 18. ), the input voltage (V _IN ) when the voltage at the output terminal 22 shifts from the "L" level to the "H" level becomes 1.25 [V] as shown in FIG. In the OFF state, that is, when "H" is output from the output terminal 22, the voltage on the low potential side of the resistor 35 becomes equal to the ground potential as shown in the equivalent circuit of FIG. 3, so the voltage at the output terminal 22 becomes The input voltage (V _IN ) when transitioning from the "H" level to the "L" level is smaller than 1.25 [V] as shown in FIG.

In the voltage detection circuit configured as described above, if the constant current source 18 is configured with one element, the total number of components is 13, and the voltage detection circuit can be configured with a smaller number of elements than conventional ones. Also, even if the hysteresis width is determined, the resistor 35
Since it is only necessary to determine the resistance value (R ₃₅ ) of the constant current source 18 and the current value (I ₁₈ ) of the constant current source 18, the hysteresis width can be determined easily and accurately.
Moreover, since the potential detection circuit described above can operate even at a voltage as low as 1.5 [V] from the power supply 3, it can be widely applied to various voltage detection circuits, battery check circuits, waveform shaping circuits, etc. It is.

In addition, in the above embodiment, the output voltage (V _OUT )
multi-collector so that it has hysteresis.
Load transistor 2 consisting of a PNP transistor
1 is provided, and the second load 33 is made up of a first resistive load 34 and a second resistive load 35, but if it is not necessary to provide hysteresis, the load transistor 21 is deleted and that part is short-circuited.
The first resistive load 34 and the second resistive load 35 may be used as the second load 33 consisting of one resistive load.

〔Effect of the invention〕

As explained above, the present invention includes first and second transistors which input an external input voltage to the control electrode, and one end of which is directly connected to the output electrode of the first transistor and connected to the output electrode of the second transistor through a load. a second load connected to the circuit and whose other end is grounded; first and second current mirror circuits whose current determining side output ends are connected to the input electrodes of the first and second transistors; a third current mirror circuit whose input end is connected to the other output end of each of the second current mirror circuits, and a connection between the input end of the third current mirror circuit and the other output end of the first current mirror circuit; and an output circuit with an input end connected therebetween, forming a voltage detection circuit, and determining the level of the signal output from the output circuit by comparing the magnitude of the input current of each of the first and second transistors. Since the reference voltage generation circuit and the comparison circuit are not provided independently, there is an advantage that accurate voltage detection can be performed with a circuit having a small number of constituent elements.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIGS. 2 and 3 are equivalent circuit diagrams of the hysteresis circuit in FIG. 1, FIG. 4 is a characteristic diagram of output voltage with respect to input voltage, and FIG. Figure 5 is a block diagram of a conventional potential detection circuit, Figure 6 is a circuit diagram of the conventional potential detection circuit in Figure 5, and Figure 7 is a diagram of the circuit shown in Figure 1 when specific calculations are performed. FIG. 3 is a diagram showing potential relationships. In the figure, 3 is a power supply, 17 is an output circuit, 2
8 and 29 are first and second transistors, respectively;
0, 31, and 36 are first, second, and third current mirror circuits, respectively, and 32, 33 are first and second loads, respectively. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. First and second current mirror circuits each outputting the same magnitude of current from a plurality of output terminals; one current determining side of each of the first and second current mirror circuits; first and second transistors, each of which has an input electrode connected to its output terminal and whose control electrode is commonly applied with an input voltage from the outside; one end of which is directly connected to the output electrode of the first transistor; A second output electrode is connected to the output electrode via the first load and the other end is grounded.
a load; a third current mirror circuit whose input terminal is connected to the other output terminal of each of the first and second current mirror circuits, and receives the same amount of current from these input terminals; An input terminal is connected between the other output terminal of the mirror circuit and the input terminal of the third current mirror circuit, and a voltage of "H" level or "L" level is output to the outside according to the current from this input terminal. A voltage detection circuit with an output circuit to output. 2. The second load is composed of a first resistive load and a second resistive load, and the output circuit is such that the control electrode becomes the input terminal of the output circuit, the input electrode is connected to a constant current source, and the output electrode is grounded. an input electrode is connected to the input electrode of the third transistor, and one of the plurality of output electrodes is connected between the first resistive load and the second resistive load,
A load transistor in which a control electrode is connected to the other output electrode, and a control electrode is connected to the other output electrode of this load transistor, and the output electrode is grounded, and the input electrode is at an "H" level or "L" level. 2. The voltage detection circuit according to claim 1, further comprising a fourth transistor that outputs the voltage to the outside. 3 The first and second current mirror circuits are one transistor, each input electrode is connected to a power supply, and the third current mirror circuit connects the control electrodes of the two transistors and their Claim 1, characterized in that the control electrode is connected to the input electrode of one transistor and to one output end of the second current mirror circuit, and each output electrode is grounded. The voltage detection circuit according to item 1 or 2.