JPS6031267B2 - voltage detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage detection circuit capable of accurately detecting a voltage even if the voltage to be detected fluctuates over a wide range.

For example, if there is an input voltage whose level fluctuates over time like a sine wave, and whose peak value fluctuates over a wide range from mV units to several tens of volts, does the level of this voltage exceed a predetermined percentage of the peak value at that time? There are cases where it is desired to detect whether or not the

If the input voltage is as high as several tens of volts, and noise of ±several percent is expected to occur, the voltage detection is performed over a wide range from the low voltage to the high voltage using the same detection circuit. This is extremely difficult. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a voltage detection circuit that can accurately detect voltage even if the voltage to be detected fluctuates over a wide range and even if a certain amount of noise is added to the detected voltage. It is something to do.

An embodiment of the present invention will be described below with reference to the drawings.

In Fig. 1, 1 is an input terminal to which an external input signal Vin such as a sine wave is supplied, and this terminal 1 is connected to the ground via the collector and emitter of resistors Rx, R, and NPN transistor Q in an attenuator section 2. Connected to terminal 3.
The base of the transistor Q is connected to the output of the amplifier 4, and the collector is connected to the non-inverting input terminal of the amplifier 4 (
The reference voltage Vref supply terminal 5 is connected to the inverting input terminal of the amplifier 4. The connection terminal between the resistors Rx and R (the voltage here is assumed to be V) is connected to the "10" terminal of the oven amplifier 6 and the comparator 7. The output terminal of the OBE amplifier 6 is the base and emitter of the NPN transistor Q2 (the voltage here is assumed to be V2).
It is connected to its own “one” terminal via. Further, the output terminal of the obeamp 6 is grounded via a capacitor C, and the emitter of the transistor Q2 is grounded via a resistor R2. The collector of the transistor Q2 is connected to the base connections of the NPN transistors Q3 and Q4 of the current mirror circuit 8 and the collector of the transistor Q3. The emitters of the transistors Q3 and Q4 are connected to the supply terminal 9 of the power supply Vcc, and constant current sources 10 and 11 are connected between the emitters and collectors of the transistors Q3 and Q4. The collector of transistor Q is grounded via diode D, resistor R3,
A connection between the diode D and the resistor R3 (the voltage here is V3) is connected to the "1" terminal of the comparator 7. The output terminal of comparator 7 is connected to the bases of NPN transistors Q5 and Q6, the collector of this transistor is connected to the collector of transistor Q, the collector of transistor Q6 is connected to output terminal 12, and the transistor is connected to the emitter of Q6. is grounded. FIG. 2a shows a specific example of the attenuator section 2 in FIG. 1, where the voltage V4 at one end of the resistor R is expressed as V4=
Vref.

That is, the emitter voltages of the differential input stage transistors Q2, Q, and 3 are the same, and the emitter voltages of the transistors Q, . At the base of
Resistance R,. , R, 2, the base voltage V4 of the transistor Q4 is Vref in the normal state. Here, if V4 tries to rise, transistors Q, 4, Q
, 3 are turned off, and Q, . , Q,2 become more on-state. Therefore, transistors Q, 6, Q, 5 are turned off,
As a result, transistors Q, 7 are turned off, transistors Q, 8, and Q are turned on, and V4 is lowered. On the other hand, when V4 attempts to fall below the reference VrM, transistors Q, 4, Q, 3 become more on, and transistors Q.., Q.2 become off. As a result, transistors Q, 6, Q, 5 are turned on, Q, 7 is turned on, Q, 3, Q, are turned off, and V4
rises. Therefore, V4=Vref always, and the input V
When in is supplied with V, the V4 level between the resistors R, and Rx is determined by the value of Vrd and the resistance ratio of the resistors Rx, R, and V
．． ! V mourning band - 10 V blue; XR. 10V Hana r...[
It becomes 11. The equivalent circuit of the attenuator section 2 at this time is shown in FIG. 2b. Next, the operation of the circuit shown in FIG. 1 will be explained.

First, as an example, the following conditions are set, and the input voltage V of the oven amplifier 6 and the output threshold voltage Vth (inversion voltage of the comparator) when the input V:n changes are determined. Vref Ni 0.1V, Rx = 1st class Q, R, = Autumn○
, R2=10kQ, R3:5kQ, 1,! 20 Buddha A, 1
2 Ni 15 Buddha A ・■ When Vin=0.2V: V. =The art of meeting; XR. 10V similar = ¥3rd class x 300.1≠0.114
[V]≠V2 The reason why V and V2 become equal here is due to the action of the oven amplifier 6.

From the above calculation results, the current flowing through the resistor R is V2/R2
=11.4 [A], and this value is less than the current a caused by one constant current, =20 A, so the current mirror 8 does not operate in this state. Therefore, the current flowing through the resistor R3 is only the current 12 from the constant current source 11, and the voltage V
3 is V3 = 12 x R3 = 75 [mV]
...'2), and in this case, the output threshold voltage Vth is 75 mV.

That is, the voltage V, is 1. The potential V2 becomes 0.2 [V] until it exceeds the value of ×R2=0.2 [V], and the V ratio is determined by the formula {2}. Here, the voltage V, exceeds the value of 1,×R2, and the current mirror circuit 8 starts operating.
When calculating the value of n, from the m formula, V; n = position x + R, ) W,
1 Vref) + VrefiR, Q8 13) (Art-2-.

-1) Ten. -・:. -8 [V]. ■ Vin=5
When V: V. = voice ¥X300-1=0-8 [V] At this time V2=
0.8 [V], and capacitor C has V2=
A voltage of 0.8 [V] is accumulated, and at that time, the current IR2 flowing through the resistor R2 is V2 - 0.8 IR2 = R2 10,000 ryo = 80 [A] 1, = 20 A flows through the resistor R2. Therefore, this difference is 6
0 French A is supplied from the current mirror circuit 8 to R2.

In the current mirror 8, a current equal to the collector side current of the transistor Q3 (=60 mm A) flows through the resistor R3, and if that current is IR3, then IR3 = 60 112 75 mm A
] V3 IR3 x R3 = 75 x 6 = 0.375 [V] The output threshold voltage Vth at this time is V, = 0.37
Since this is the value when exceeding 5 [V], V mountain = (R, 10R
XXV, -Vref) Vref=7×〇. 275 hundred.
・R, 2.03 [V] This is the threshold voltage for the next sine half wave voltage of Vin, that is, the next sine wave Vin=
While the voltage is 2.03 [V], the output transistor Q,
The output terminal 12 of is at ground level.

■ When Vin=50 [V]: V. = Holy back! X30 o-1 = 7-23 [V] In the same way as in the case of section ■ above, the ship = poison, etc. = o-723 [mA] Also, 0.723 - 1, = 0.703 [mA] Therefore, IR
3 = 0.703 + 12 = 0.718 [mA]/. V3=
3.59 [V].・．． Vth=7×(3.59-0.1
) 10.1〒24.5 [V].

FIG. 3 is a V;n-Vth characteristic diagram according to the above calculation example.

That is, in the circuit of FIG. 1, the value of V is 1. and resistance R2
current 12 and resistance R3 if the set value is not exceeded by
Voltage detection is performed according to the set value of , and after the level of input Vin becomes large and the value of V exceeds the set value of 1, R2, the voltage is detected at approximately the value of R3/R2. .
The voltage detection circuit as described above has the following advantages.

That is, since the threshold voltage Vth changes according to the input Vin, it is not affected by the noise of the input Vin, and it is possible to accurately detect an input voltage that fluctuates over a wide range. Also, the amplifier input voltage V. The value of is the reference voltage Vref and the resistance Rx
, R, can be compressed to an arbitrary value by changing the voltage division ratio, so a voltage higher than the power supply Vcc can be used for the input Vin for detection. Further, since the reference voltage V4 (=Vr sealed) is obtained by the oven amplifier 4 and the transistor Q, a reference voltage error, that is, a voltage detection error does not occur due to the current values of the resistors Rx and R. Note that the present invention is not limited to the above-mentioned embodiments. For example, if the input Vin does not need to be compressed, the attenuator section 2 may be omitted, and depending on the application, the constant current sources 10 and 11 may be omitted. However, various applications are possible, such as the transistors Q5 and Q may be omitted.

As explained above, according to the present invention, since the output threshold voltage can be changed according to the level of the input voltage to be detected, it is possible to provide a voltage detection circuit that can accurately detect input voltages that change over a wide range. .

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an embodiment of the present invention, Figure 2a is a partial detailed circuit diagram of the same circuit, Figure 2b is its equivalent circuit diagram, and Figure 3 is a Vin diagram of the circuit in Figure 1. 1 is a Vth characteristic diagram. 1...Input terminal, 2...Attenuator section, 4...5...Obe amplifier, 6...Obe amplifier, 7...Comparator, 8...Current Mirror circuit, 10, 11...constant current source, Rx, R,
~R3... Resistor, Q, ~Q6... Transistor, C, """ Capacitor. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A voltage supply unit that supplies a voltage according to an input voltage, an operational amplifier that inputs the voltage from this voltage supply unit, and a current that corresponds to the output of this operational amplifier to a first current-carrying path. a current mirror circuit that causes a current corresponding to the current in this current-carrying path to flow through a second current-carrying path; and a current mirror circuit that stores a voltage corresponding to a peak value of the input voltage, and stores the voltage corresponding to the peak value of the input voltage, and the first and second current-carrying paths that correspond to this voltage. voltage storage means for holding the current of the current, and comparison means for comparing the voltage according to the current value of the second current-carrying path and the voltage given by the voltage supply unit. circuit. 2. The voltage detection circuit according to claim 1, wherein the voltage supply section is an attenuator in which a plurality of resistors and a constant voltage source are connected in series. 3. A voltage supply section that supplies a voltage according to the input voltage, an operational amplifier that receives the voltage from this voltage supply section, and a current that corresponds to the output of this operational amplifier is passed through a first current-carrying path to generate a current in this current-carrying path. a current mirror circuit that causes a current to flow in the second current path according to the input voltage; a first constant current source that supplies a first current obtained by adding a constant current to the current in the first current carrying path; Voltage detection characterized by comprising: a second constant current source that flows a current of No. 2; and comparison means that compares a voltage according to the value of the second current and a voltage provided by the voltage supply unit. circuit. 4. The voltage detection circuit according to claim 3, wherein the voltage supply section is an attenuator in which a plurality of resistors and a constant voltage source are connected in series.