JPH0516530Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a voltage monitoring circuit that monitors abnormalities in the power supply voltage. A voltage to be monitored is applied to both ends, and the voltage across one of these resistors is applied to the input of a comparator consisting of a differential amplifier using amplifying elements with different current densities. The comparator output is inverted according to the change in voltage, and the voltage across the series circuit of the constant voltage element and the resistor is n (limited to an integer) of the voltage corresponding to the Si energy band gap at absolute zero. (not) when
In other words, the purpose is to provide a voltage monitoring circuit with low power consumption by inverting the output of the comparator when the voltage across either of the two resistors matches the offset input voltage of the comparator. shall be.

Voltage monitoring circuits are used in devices that use CPUs, such as system resets to prevent malfunctions caused by abnormal fluctuations in power supply voltage, and battery checkers to check the level of battery consumption. A typical voltage monitoring circuit consists of a reference voltage source and a comparator.

FIG. 1 shows a conventional example of a voltage monitoring circuit. 1,2
3 is a reference voltage source, R1 and R2 are voltage dividing resistors that divide the monitored voltage, 4 is a comparator having two inputs, and 5 is the output terminal of the comparator 4, respectively.

Comparator 4 includes reference voltage source 3 and resistor R1,
It compares the voltage divided by R2 and performs on/off operation at a certain voltage level of the monitored voltage.
It is output from output terminal 5.

The reference voltage source 3 of such a voltage monitoring circuit uses a Zener diode, a band gap, etc., and it is relatively easy to obtain one with good temperature characteristics, and a comparator with differential input also has good temperature characteristics. Since it is stable and stable, a voltage monitoring circuit with good characteristics has been realized. In recent years, CPUs and their peripheral circuits have become increasingly low in power consumption, and there has been a strong demand for low power consumption in voltage monitoring circuits as well.

However, the above-mentioned conventional example has a circuit for the reference voltage source 3, which consumes power, and therefore there is a design upper limit for reducing power consumption.

The present invention has been developed in view of the problems of the conventional example, and embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows a principle circuit diagram for explaining the operating principle of voltage monitoring deviation according to the present invention. Components that are the same as those in FIG. 1 are designated by the same reference numerals, and their explanations will be omitted.

Resistors R3 and R4 and a diode D are connected in series between the input terminals 1 and 2 to which the monitored voltage Vin is applied, and the voltage across R4 is applied to the two inputs 7 and 8 of the comparator 6. This comparator 6
The power source may be the monitored voltage Vin, but it may also be a different power source.

A normal comparator has a balanced differential input in order to make the input offset voltage zero, but the comparator 6 of FIG. 2, which is an embodiment of the present invention, has the configuration shown in FIG. 3. 9 indicates an amplifier. The emitter area of transistor Q ₂ is made n ₁ times the size of transistor Q ₁ , the current density of Q ₁ and Q ₂ is set as J ₁ /J ₂ = n ₁ , and a comparator with an offset voltage of ΔV _BE is intentionally formed. are doing. In this case, the load sides of the transistors Q ₁ and Q ₂ may be changed so that the ratio of I _C1 and I _C2 is n ₂ times the collector current.
Moreover, this collector current ratio and the transistor Q ₁ ,
It is also possible to obtain a current density that is n ₀ times as large as n ₁ ×n ₂ by taking both of the area ratios of Q ₂ .

The base-emitter voltage difference ΔV _BE of the differential transistors Q ₁ and Q ₂ is expressed as ΔV _BE = ΔV _BE1 − ΔV _BE2 = kT/q1n(n ₁ ) (1).

In general, the voltage source V _BE across the diode is V _BE = V _gp (1-T/T ₀ ) + V _BE0 (T/T ₀ ) + n1kT
It is expressed as /qln(T0/T)+kT/qln(I _C /I _CO )...(2).

Here, V _gp is the voltage corresponding to the energy band gap of Si at absolute zero, q is the electron charge k is Boltzmann's constant, T is the absolute temperature, T ₀ is the reference operating temperature, I _C = I _CO (T=T ₀ )V _BE =V _BE0 (T=
T ₀ , I _C =I _CO ). By the way, n ₁ kT/qln·(T ₀ /T)+kT/qln (I _C /I _CO ) can be ignored since the degree of deviation from the theoretical expression is small. Therefore, V _BE ≒ V _gp (1-T/T ₀ ) + V _BE0 (T/T ₀ ) ...(3) Now, in Fig. 2, the voltage Vinoffset of the monitored voltage Vin at which the comparator is inverted is the voltage Vinoffset of the resistor R4. This is when the voltage across both ends matches ΔV _BE . Ignoring the input current of the comparator 6 (actually, this current is extremely small and can be ignored), Vinoffset is expressed as Vinoffset=(1+R ₃ /R ₄ )ΔV _BE +V _BE (4).

From equations (4), (1), and (3), Vinoffset≒(1+R ₃ /R ₄ )・kT/q1n (n ₁ ) +Vgo (1−T/T ₀ )+V _BE0 (T/T ₀ ) ...(5) is obtained.

In order for the temperature coefficient of Vinoffset to become zero, use equation (5) as T
The partial differentiation becomes zero. Therefore, ∂Vinoffset/∂T=(1+R ₃ /R ₄ )・k/q1n(n ₁ ) −Vgo/T ₀ +V _BE0 /T ₀ =0 ……(6) ∴Vgo=(1+R ₃ /R ₄ )・kT ₀ /q1n(n ₁ ) +V _BE0 ……(7) On the other hand, the value of Vinoffset at T=T ₀ is from equation (5), Vinoffset=(1+R ₃ /R ₄ )・kT ₀ /q1n(n ₁ ) +V _BE0 (8) From equations (7) and (8), Vinoffset=Vgo, that is, by setting Vinoffset=Vgo at the operating temperature, a voltage monitoring circuit that is stable against temperature changes can be realized. Resistances R ₃ , R ₄ and ΔV _BE at this time
The relationship is ΔV _BE = (Vgo−V _BE ) R ₄ /R ₃ + R ₄ (9).

The principle circuit diagram in Figure 2 has only one diode D, so it can only provide a voltage monitoring circuit with a Vinoffset of 1.2V, but in order to obtain a wide range of Vinoffsets, a modified principle circuit diagram as shown in Figure 4 is required. This is easily possible with the following configuration. This FIG. 4 will be explained below. Components that are the same as those in FIG. 2 are designated by the same reference numerals, and their explanations will be omitted. The difference from FIG. 2 is that the number of diodes D is _nx .

By establishing the relationship ΔV _BE = (Vgo−V _BE )R ₄ /R ₃ +R ₄・n _x ……(10), for the temperature change that Vinoffset=n _x・Vgo ……(11) A stable voltage monitoring circuit can be created. Note that ΔV _BE is expressed as kT/q1n (n), and normally n is set to 8th place, and ΔV _BE at this time is
The voltage is about 56mV, which is sufficient to construct a stable voltage comparison circuit.

By using an arbitrary number of diodes D in this way, a desired Vinoffset voltage can be obtained with a simple configuration.

FIG. 5 shows a principle circuit diagram of yet another modification. Components that are the same as those in FIG. 2 are designated by the same reference numerals, and their explanations will be omitted. The difference from FIG. 2 is that a transistor Q3 is connected to the midpoint of the series connection of resistors R5 and _R6 in the portion of the diode D. Vinoffset with this configuration is Vinoffset≈(1+R ₃ /R ₄ )ΔV _BE +K·V _BE (12) where K=1+R ₅ /R ₆ .

From equations (12), (1), and (3), Vinoffset≒(1+R ₃ /R ₄ ) kT/qIn (n ₁ ) +KVgo (1−T/T ₀ ) +K・V _BE0 (T/T ₀ ) ...(13) becomes. In order for the temperature coefficient of Vinoffset to become zero, the partial differentiation of equation (13) with respect to T must become zero.

Therefore, ∂Vinoffset/∂T=(1+R ₃ /R ₄ )k/qIn(n ₁ ) −KVgo/T ₀ )+KV _BE0 /T ₀ =0 ……(14) ∴KVgo=(1+R ₃ /R ₄ ) kT ₀ / qIn (n ₁ ) +KV _BE0 ... (15) On the other hand, the value of Vinoffset at T = T ₀ is obtained from equation (13), Vinoffset = (1 + R ₃ / R ₄ ) kT / qIn (n ₁ ) +K・V _BE0 ...(16) From equations (15) and (16), Vinoffset=K・Vgo ...(17). That is, from this equation (17), it becomes possible to select an arbitrary Vinoffset by selecting K to an arbitrary value.

As is clear from the above, the differential amplifier (Q ₁ ,
The potential difference between both input terminals when _Q2 ) is balanced, and the resistance
The voltage difference across the resistor R 4 when the voltage across the series circuit of R ₃ and R ₄ and the diode is n ₁ times the voltage Vgo corresponding to the energy band gap of Si at absolute zero should be made equal to the voltage across the resistor R ₄ . For example, the temperature coefficient of Vinoffset is zero. With such a simple configuration, the conventional reference voltage source can be omitted.

FIG. 6 shows an embodiment of the voltage monitoring circuit of the present invention constructed in accordance with the above-mentioned principles, and the same parts as those in the previous figure are given the same reference numerals and their explanation will be omitted.

Transistors Q ₁ and Q ₆ correspond to the diode D shown in FIGS. 2 and 4, and transistors Q ₄ , R ₅ , R ₆
is based on the principle diagram in Figure 5, and with this configuration V _BE (2
+K) voltage is obtained. and transistor
_Q5 simultaneously serves as a bias source for the constant current circuit of transistors _Q9 and _Q13 . Transistors Q ₁ , Q ₂
constitutes a differential amplifier with emitter area ratio n ₁ ,
It has an active load of transistors Q ₇ and Q ₈ and is amplified by transistors Q ₁₁ , Q ₁₄ , Q ₁₅ and Q ₁₆ and is configured to output a comparator output. Resistor R ₁₀ and transistor Q ₁₀ are current emitters.
Transistors Q ₁₇ and Q ₁₈ supply the collector current of Q ₁₄ as a constant current. Both are intended to prevent current consumption from increasing when the monitored voltage increases.

The transistors Q ₁₂ and Q ₁₉ , the resistors R ₃ and R ₈ are used to provide hysteresis to the comparator 6, and the amount of hysteresis is achieved by adjusting the mutual constants of the resistors ₈ and R ₃ . FIG. 7 is a diagram for explaining this hysteresis operation.

Vin is the monitored voltage, VQ _1B is the base voltage of transistor Q ₁ , and dotted line V _B1 is the inverted voltage of transistors Q ₁₉ and Q _16, respectively. Now, when the monitored voltage Vin rises and reaches the dotted line of voltage Vin ₁ , at the same time the resistance R ₄
The voltage across both ends also rises to reach the dotted line V _B1 representing the inverted voltage of transistor Q ₁ . This makes the resistance
Since the voltage across R ₄ becomes greater than ΔV _BE generated by the emitter area ratio of transistors Q ₁ and Q ₂ , transistor Q ₁ is turned on. Further, as the transistor Q ₁ turns on, the transistors Q ₁₁ , Q ₁₄ , and Q ₁₅ turn on, while the output transistor Q ₁₆ and the transistors Q ₁₉ and Q ₁₂ turn off. When transistor Q ₁ turns on, its base potential suddenly drops from point V _B1 .
V Jump to _B2 point. This jump causes hysteresis in the comparator 6.

This jump occurs at the same time as transistor _Q1 turns on.
This occurs because Q ₁₂ and _{Q 19} are turned off, and the current I ₁₂ that had been flowing through them while Q 12 and Q ₁₉ were on flows into resistor R ₄ .

Next, when the monitored voltage Vin rises and reaches Vin ₂ , the base potential of the transistor _Q1 also rises to the point _VB3 . Then, when Vin decreases and reaches the Vin ₁ ' point, transistor Q ₁ should normally be turned off at this point and output transistor Q ₁₆ should be turned on, but this is because it has a hysteresis characteristic.
The transistor will not turn off unless Vin falls to the _Vin3 point, which is the Vinoffset potential.

That is, as mentioned above, when the transistors Q ₁₂ and Q ₁₉ are on, the current I ₁₂ flows into the resistor R ₄ , so the base potential of the transistor Q ₁ increases by the voltage drop due to the resistor R ₄ . Vin to be there
Transistor _Q1 will not be inverted unless the voltage drops to the _Vin3 (Vinoffset) point, which is lower than _{the Vin1'} point. Vin like this
When V falls to the Vin ₃ point, the base potential of transistor Q ₁ reaches V _B1 and is turned off, while transistor Q ₂ is turned on. As a result, transistors Q ₁₁ , Q ₁₄ , and Q ₁₅ are turned off again, and output transistor Q ₁₆ and transistors Q ₁₉ and Q ₁₂ are turned on. Since it has hysteresis characteristics as described above, the chattering phenomenon can be prevented _.
By connecting it to a reset terminal such as, it will have the ability to automatically enter a reset state when the power supply voltage (monitored voltage) drops abnormally.

By establishing the relationship between ΔV _BE and resistances R ₃ , R ₄ , and R ₇ as follows: ΔV _BE = (2+K) (Vgo−V _BE ) R ₄ /R ₃ +R ₊ +R ₇ ...(18), Vinoffset= (2+K)Vgo . . . (19) Therefore, it is possible to realize a voltage monitoring circuit that is not stable against temperature changes and has low power consumption and does not particularly have a reference voltage circuit.

[Brief explanation of the drawing]

Fig. 1 is a conventional monitoring voltage circuit, Fig. 2 is a principle circuit diagram of the monitoring voltage circuit of the present invention, Fig. 3 is a circuit diagram of a differential amplifier applied to the present invention, and Figs. 4 and 5.
The figures are circuit diagrams of other principles of the circuit diagram of the present invention in Figure 2, Figure 6 is a specific circuit diagram of a monitoring voltage circuit which is an embodiment of the present invention, Figure 7 is a diagram showing the hysteresis circuit of the present invention. Diagrams are shown to explain the characteristics. 1, 2... Input terminal of monitored voltage, 4, 6...
Comparator, 5... Output terminal, 7, 8... Input terminal of operational amplifier (comparator), 9... Amplifier, D... Diode, Q ₁ to ₁₉ ... Transistor, R ₁ to ₁₀ ... resistance.

Claims (1)

[Claims for Utility Model Registration] In a voltage monitoring circuit that outputs an output that is switched on or off depending on the level of DC voltage, a constant voltage element consisting of a silicon diode that generates a constant voltage n _x times the forward voltage drop. The DC voltage is applied to both ends of a series circuit with a plurality of resistors, and the voltage across one of the plurality of resistors is determined by the difference between the first and second transistors having different emitter current densities. An offset input voltage of a differential voltage ΔV _BE is generated between the bases of the first and second transistors, which are the inputs of the comparator, due to the difference in current density. The comparator output is inverted according to changes in the DC voltage, and the Si energy band at absolute zero is such that the voltage across the series circuit of the constant voltage element and the plurality of resistors is stable against temperature changes. When the voltage Vinoffset is n _x times the voltage V _gp corresponding to the gap, that is, when the voltage across any one of the plurality of resistors matches the offset input voltage of the comparator, the comparator A voltage monitoring circuit characterized by an inverted output.