JPH065644Y2 - Power supply voltage inspection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a power supply voltage inspection circuit.

[Conventional technology]

2. Description of the Related Art Conventionally, a power supply voltage inspection circuit used in battery-powered electronic equipment has the configuration of the comparator shown in FIG. The power supply voltage V _{CC includes the} transistors Q _{1 to} Q ₄ and the constant current source I _1.
Voltage divided by resistors R ₁ and R ₂ and reference voltage Vref
And the output is output to the output terminal V _O by the transistor Q ₅ and Q ₆ constant current source I ₂ and the resistor R ₃ . A voltage obtained by dividing the power supply voltage V _CC by the resistors R ₁ and R ₃ is applied to the non-inverting terminal of this comparator, while the reference voltage Vref is applied to the inverting terminal and the power supply voltage of the battery or the like is Vk. Is the judgment voltage Then, the output terminal V _O changes from the H level to the L level, and the drop of the power supply voltage is detected.

[Problems to be solved by the invention]

The reference voltage Vref used in FIG. 2 is given by constituting a reference voltage source circuit, and the circuit is a power supply voltage V _CC.
Since it is usually operated by, as shown in FIG. 3, depending on the power supply voltage characteristic of the circuit that forms the reference voltage Vref,
The reference voltage source Vref sharply drops when the power source voltage V _T becomes lower than a certain level. Now, the minimum battery voltage at which the comparator operates is V
_{In the case of BMIN} , when V _T > V _BMIN , the voltage of the output terminal Vo _changes from H level to L bell at the determination voltage V _K given by the equation (1) as the battery voltage V _CC decreases.
When the battery voltage V _CC further decreases to V _CC V _T , the reference voltage Vref sharply decreases, so that the output terminal V _O changes from the L level to the H level again, giving a signal as if the power supply voltage is normal and giving an error. There was a problem of making a decision.

An object of the present invention is to set the minimum operating voltage of each of the comparator and the reference voltage source constituting the power supply voltage inspection circuit to V _BMIN <V.
An object of the present invention is to provide an inspection circuit that prevents an erroneous determination signal from being generated at the output at _T.

[Means for solving problems]

According to the present invention, when the power supply voltage is between the determination voltage V _K and the voltage V _T that produces an erroneous output, it has an auxiliary circuit and a comparator that change from H level to L level. A power supply voltage inspection circuit in which an output and an output of an auxiliary circuit are wire-connected.

〔Example〕

 The present invention will now be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. The L level is output from the terminal output V _O between the predetermined power supply voltage (voltage at which the comparator produces an erroneous output) V _T and the determination voltage V _K by the resistors R ₅ and R ₆ , the transistor Q ₃ , and the load resistor _4. To do so. now Then, the resistors R ₅ and R ₆ are selected so that the voltage V _S becomes V _T <V _S <V _K.

V _BE of the equation (2) is a base-emitter voltage when the transistor Q ₈ operates. Connect the collector of the transistor Q ₈ to the base of the transistor Q _7, to wired connection to the collector of the transistor Q ₇ to the output terminal V _O of the comparator.

As a result, when V _CC > V _S , the collector of the transistor Q ₇ becomes H level, and when V _CC <V _S , the collector of the transistor Q ₇ becomes L level, and the power supply voltage V _CC is between the base and emitter of the transistor Q _7. The level of the output terminal V _O of the comparator is fixed to “L” until the voltage of the output terminal V _O becomes about 0.7 V, and the level of the output terminal V _O is re-inverted at V _CC V _T in FIG. There is no. V _CC 0.7V
After that, the level of the output terminal V _O again becomes V _CC , but in order to further set the level of the output terminal V _O to the L level, the transistor Q ₇ may be an NMOSFET having a low threshold voltage.

[Devise Effect] As described above, when the present invention is in the voltage V _T of the comparator power supply voltage determination voltage V _K and the reference voltage source to the output of which constitutes the supply voltage test circuit is rapidly lowered, By wire-connecting the output of the auxiliary circuit that changes from the H level to the L level, the output of the comparator will not be inverted again even if the power supply voltage becomes V _T or less. There is an effect that can be lost.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a power supply voltage inspection circuit according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional power supply voltage inspection circuit, and FIG. 3 is a power supply voltage and output of a conventional power supply voltage inspection circuit. It is a graph which shows the relationship of. Q ₁ , Q ₂ , Q ₃ , Q ₄ , Q ₅ , Q ₆ , Q ₇ , Q _8, ...
Transistors, I ₁ , I ₂ ... Constant current source, R ₁ , R ₂ ,
_{R 3, R 4, R 5} , R 6 ...... resistance, Vref ...... reference voltage _{source, V CC} ...... supply voltage, _{V O} ...... comparator output terminal voltage, _{V K} ...... supply determination voltage, _{V T} ...... The power supply voltage at which Vref drops sharply.

Claims (1)

[Scope of utility model registration request] 1. A comparison circuit for comparing a resistance-divided voltage of a power supply voltage with a reference voltage, wherein a minimum operating voltage of the comparison circuit is lower than a minimum operating voltage of a reference voltage source for generating the reference voltage, and the power supply. A power supply determination circuit that outputs a detection output of a predetermined potential level when the voltage becomes equal to or lower than the power supply determination voltage,
The power supply voltage changes to the same potential level as the detection output when the power supply voltage is between the power supply determination voltage and the minimum operating voltage of the reference voltage source, and the power supply potential is lower than the minimum operating voltage of the reference voltage source. Also has an auxiliary circuit having an output characteristic for maintaining the predetermined potential level, and the output of the power supply determination circuit and the output of the auxiliary circuit are connected by wire.