JP2010020481A - Reference voltage generation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain output of a reference voltage to the utmost, even when a power supply voltage is reduced. <P>SOLUTION: When a cathode side voltage V104 of a Zener diode ZD101 of a reference voltage generating circuit 100 is reduced, as compared to a Zener voltage which is to be originally generated, first and second reference voltage support circuits 200, 300 makes a replenishment current flow through a voltage division resistor 103 on a low-voltage side of the reference voltage generation circuit 100. Accordingly, even when voltages applied to a voltage division resistor 102 and the voltage division resistor 103 are reduced, as compared to the Zener voltage to be originally applied because the power supply voltage VB is reduced, the Zener diode ZD101 of the reference voltage generating circuit 100 cannot generate the Zener voltage; and since the voltage V102 of the voltage dividing resistor 103 on the lower voltage side is increased by the amount of current replenished, reduction in the reference voltage VO can be suppressed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a reference voltage generating device that generates a desired reference voltage when a power supply voltage is supplied.

  Conventionally, for example, a Zener diode has been used as a device for generating a reference voltage necessary for operating various electronic circuits with high accuracy, such as an A / D converter and a determination circuit incorporated in an electronic control device including a microcomputer. There is known a reference voltage generator configured to generate a reference voltage using a Zener voltage that is a constant voltage generated by the Zener diode.

  FIG. 4 shows a configuration of an example of a conventional reference voltage generator. As shown in FIG. 4, the conventional reference voltage generator includes a reference voltage circuit 105 including a Zener diode. A constant current circuit 101 is connected in series to the reference voltage circuit 105 in order to prevent an overcurrent from flowing through the Zener diode and damage the Zener diode. Therefore, when the power supply voltage VB is supplied from a power supply (not shown), the Zener diode of the reference voltage circuit 105 receives a constant current from the constant current circuit 101 and generates a Zener voltage that is a constant voltage.

  The Zener voltage generated by the Zener diode of the reference voltage circuit 105 is applied to the series circuit of the resistors 102 and 103. As a result, a voltage obtained by dividing the Zener voltage according to the resistance values of the resistors 102 and 103 is generated at the midpoint between the resistors 102 and 103. The voltage divided by the resistors 102 and 103 is output via an operational amplifier 104 that constitutes a voltage follower. Therefore, by selecting the resistance values of the resistors 102 and 103, a voltage having a desired value can be output as the reference voltage VO.

  For example, it is conceivable that the power supply voltage VB decreases because the electrical load to be driven by the power supply temporarily becomes excessive. In the above-described conventional reference voltage generator, when the power supply voltage VB decreases and the Zener diode cannot generate the Zener voltage, the voltage applied to the series circuit of the resistors 102 and 103 is higher than the Zener voltage. It gets smaller. As a result, the conventional reference voltage generator cannot maintain the reference voltage VO having a desired voltage value, and the output voltage is lower than the original reference voltage VO.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a reference voltage generator capable of maintaining the output of the reference voltage as much as possible even when the power supply voltage is lowered. And

In order to achieve the above object, a reference voltage generating device according to claim 1 comprises:
A reference voltage that includes a Zener diode and a voltage dividing resistor. When the power supply voltage is supplied, the Zener voltage generated by the Zener diode is divided by the voltage dividing resistor and a reference voltage is output based on the divided voltage. Generating circuit;
A reference voltage support circuit that monitors the voltage on the cathode side of the Zener diode and suppresses the drop in the reference voltage by flowing a supplementary current into the voltage dividing resistor on the low voltage side when the cathode side voltage drops below the Zener voltage. And.

  As described above, the reference voltage generation device according to the first aspect includes the reference voltage support circuit, and the reference voltage support circuit is configured such that when the cathode side voltage of the Zener diode is lower than the Zener voltage, Supply supplementary current to the voltage dividing resistor on the low voltage side. Therefore, when the power supply voltage is lowered, the Zener diode of the reference voltage generation circuit cannot generate the Zener voltage, and the voltage applied to the voltage dividing resistor is lower than the Zener voltage to be originally applied. Even so, since the terminal voltage of the voltage dividing resistor on the low voltage side is increased by the amount of the supplementary current, it is possible to suppress a decrease in the reference voltage.

  According to the second aspect of the present invention, it is preferable that the reference voltage support circuit feeds a supplementary current that increases as the cathode side voltage of the Zener diode becomes lower than the Zener voltage into the voltage dividing resistor on the low voltage side. As a result, even if the degree of decrease in power supply voltage increases, a voltage corresponding to the reference voltage can be continuously output.

As described in claim 3, the reference voltage generation circuit further includes a rectifier diode connected in series with the Zener diode,
The reference voltage support circuit is
A Zener diode that generates the same Zener voltage as the Zener diode of the reference voltage generation circuit;
A comparison unit that compares the cathode side voltage of the Zener diode of the reference voltage generation circuit and the cathode side voltage of the Zener diode of the reference voltage support circuit;
When the power supply voltage decreases, the Zener diode of the reference voltage support circuit generates a Zener voltage, but the Zener diode of the reference voltage generation circuit to which a voltage lower by the voltage drop of the rectifier diode is applied is turned off. As a result of stopping the generation of the Zener voltage, when the comparison unit determines that the cathode side voltage of the Zener diode of the reference voltage generation circuit is lower than the Zener voltage that is the cathode side voltage of the Zener diode of the reference voltage support circuit. And a control unit that generates a supplementary current according to the voltage difference and applies the replenishment current to the voltage dividing resistor on the low voltage side of the reference voltage generating circuit.

  Zener diodes generally have a positive temperature characteristic and the generated Zener voltage tends to increase as the temperature increases. On the other hand, the rectifier diode has a negative temperature characteristic, contrary to the Zener diode, and the forward voltage (that is, the voltage applied to the rectifier diode) tends to decrease as the temperature rises.

  Therefore, as described above, by connecting the rectifier diode in series with the Zener diode in the reference voltage generation circuit, the positive temperature characteristic of the Zener diode can be offset by the negative temperature characteristic of the rectifier diode. Even when a change occurs, it is possible to ensure the accuracy of the reference voltage.

  Thus, when the reference voltage generating circuit is configured by connecting the Zener diode and the rectifier diode in series, the reference voltage support circuit can be configured as described in the third aspect. That is, the above-mentioned claim 3 shows a preferable specific configuration of the reference voltage support circuit.

  According to a third aspect of the present invention, the reference voltage support circuit includes a Zener diode that generates the same Zener voltage as the Zener diode of the reference voltage generation circuit, and the comparison unit compares the cathode side voltages of these Zener diodes. Here, as described above, in the reference voltage generation circuit, the rectifier diode is connected in series with the Zener diode. For this reason, a voltage lower than the Zener diode of the reference voltage support circuit by a voltage drop due to the rectifier diode is applied to the Zener diode of the reference voltage generation circuit. Therefore, when the power supply voltage decreases, the Zener diode of the reference voltage support circuit generates a Zener voltage, but the Zener diode of the reference voltage generation circuit may stop generating the Zener voltage. In this case, the cathode side voltage of the Zener diode of the reference voltage generation circuit is a voltage that is lowered from the power supply voltage by the voltage drop of the rectifier diode, and is therefore smaller than the Zener voltage generated by the Zener diode of the reference voltage support circuit. In the control unit, a supplementary current corresponding to such a voltage difference is generated and applied to the voltage dividing resistor on the low voltage side of the reference voltage generating circuit. Therefore, even when the power supply voltage is lowered to a level at which the Zener diode of the reference voltage generation circuit cannot generate the Zener voltage, the reference voltage generation circuit can continuously output a voltage corresponding to the reference voltage. .

The fourth aspect of the present invention shows another preferable specific configuration of the reference voltage support circuit. That is, as described in claim 4, the reference voltage support circuit is
A comparison voltage generator that generates a comparison voltage that is larger than the cathode side voltage of the Zener diode by dividing the power supply voltage when the Zener diode of the reference voltage generation circuit is turned off;
A comparison unit that compares the cathode side voltage of the Zener diode of the reference voltage generation circuit with the comparison voltage generated by the comparison voltage generation unit;
When the power supply voltage drops, the Zener diode of the reference voltage generation circuit is turned off and the generation of the Zener voltage is stopped. As a result, the cathode side voltage of the Zener diode of the reference voltage generation circuit is lower than the comparison voltage by the comparator. A controller that generates a supplementary current corresponding to the voltage difference and applies it to the voltage dividing resistor on the low voltage side of the reference voltage generation circuit.

  Even when the reference voltage support circuit having the above-described configuration is used, when the power supply voltage decreases and the Zener diode of the reference voltage generation circuit cannot generate the Zener voltage, the supplementary current that increases as the power supply voltage decreases is reduced to the low voltage side. Can be given to the partial pressure resistance. Therefore, even when the power supply voltage is lowered, the reference voltage generation circuit can continuously output a voltage corresponding to the reference voltage.

  When the reference voltage support circuit described in claim 4 is adopted, as described in claim 5, the comparison voltage generation unit reduces the generated comparison voltage to be equal to or lower than the Zener voltage of the Zener diode of the reference voltage generation circuit. It is preferable to have a voltage limiting unit for limiting. As a result, the comparison voltage becomes higher than the cathode voltage of the Zener diode of the reference voltage generation circuit only when the Zener diode of the reference voltage generation circuit can no longer generate the Zener voltage. By generating a supplementary current according to the voltage difference when this voltage magnitude relationship occurs, the supplementary current can be applied only when there is a possibility that the reference voltage is lowered.

According to a sixth aspect of the present invention, both of the circuits described in the third and fourth aspects are provided as the reference voltage support circuit. That is, the reference voltage generation circuit further includes a rectifier diode connected in series with the Zener diode,
The reference voltage support circuit includes a first reference voltage support circuit and a second reference voltage support circuit.
The first reference voltage support circuit is
A Zener diode that generates the same Zener voltage as the Zener diode of the reference voltage generation circuit;
A first comparison unit that compares the cathode side voltage of the Zener diode of the reference voltage generation circuit with the cathode side voltage of the Zener diode of the first reference voltage support circuit;
When the power supply voltage drops, the Zener diode of the first reference voltage support circuit generates a Zener voltage, but the Zener diode of the reference voltage generation circuit to which a voltage lower by the voltage drop of the rectifier diode is applied is turned off. Then, as a result of stopping the generation of the Zener voltage, the first comparison unit causes the Zener voltage of the Zener diode of the reference voltage generating circuit to be the cathode voltage of the Zener diode of the first reference voltage support circuit. A first control unit that generates a supplementary current according to the voltage difference and applies it to the voltage dividing resistor on the low voltage side of the reference voltage generation circuit.
The second reference voltage support circuit is
When the power supply voltage drops and the Zener diode of the first reference voltage support circuit is turned off, a comparison voltage equal to or higher than the cathode side voltage of the Zener diode of the reference voltage generation circuit is generated by dividing the power supply voltage. A comparison voltage generator;
A second comparison unit that compares the cathode side voltage of the Zener diode of the reference voltage generation circuit with the comparison voltage generated by the comparison voltage generation unit;
When it is determined by the second comparison unit that the cathode side voltage of the Zener diode of the reference voltage generation circuit is lower than the comparison voltage, a supplementary current corresponding to the voltage difference is generated to generate a reference voltage generation circuit. And a second control unit that applies to the voltage dividing resistor on the low voltage side.

  As described above, the reference voltage support circuit includes the first reference voltage support circuit and the second reference voltage support circuit, and the comparison voltage generation unit of the second reference voltage support circuit includes the first reference voltage. When the Zener diode of the support circuit is turned off, a comparison voltage that is equal to or higher than the cathode side voltage of the Zener diode of the reference voltage generation circuit is generated by dividing the power supply voltage, thereby outputting a voltage corresponding to the reference voltage. The power supply voltage range that can be maintained can be expanded. That is, when the power supply voltage starts to decrease, first, the first reference voltage support circuit operates to support generation of the reference voltage. When the power supply voltage further decreases and it becomes difficult for the first reference voltage support circuit to support the output of the reference voltage, the supply of supplementary current is started by the second reference voltage support circuit. As described above, since the first and second reference voltage support circuits cooperate to support the output of the reference voltage, the power supply voltage range capable of maintaining the output of the voltage corresponding to the reference voltage is expanded to a lower range. Can do.

  In addition, since the effect regarding Claim 7 is the same as that regarding the above-mentioned Claim 5, description is abbreviate | omitted.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit block diagram schematically showing the overall configuration of the reference voltage generator according to the present embodiment. Note that the same reference numerals are assigned to the same configurations as those of the conventional example described with reference to FIG.

  As shown in FIG. 1, the reference voltage generating apparatus according to the present embodiment mainly includes a reference voltage generating circuit 100, a first reference voltage support circuit 200, and a second reference voltage generating circuit 300. .

  Similar to the conventional example, the reference voltage generation circuit 100 divides a Zener voltage (for example, about 5 V), which is a constant voltage generated by the Zener diode of the reference voltage circuit 105, by the voltage dividing resistors 102 and 103, and after voltage division Is output via an operational amplifier 104 constituting a voltage follower. Therefore, as long as the power supply voltage VB does not decrease to a level at which the Zener diode of the reference voltage circuit 105 cannot generate the Zener voltage, the reference voltage generation circuit 100 is desired to be determined by the Zener voltage and the resistance values of the voltage dividing resistors 102 and 103. The reference voltage VO can be output. In the present embodiment, a voltage of about 1V is output as the reference voltage VO.

  101 is a constant current circuit. The constant current circuit 101 is for preventing an excessive current from flowing through the Zener diode and damaging the Zener diode. Therefore, as long as an excessive current can be prevented, the constant current circuit 101 may be replaced with a normal resistor.

  The first reference voltage support circuit 200 inputs the cathode side voltage of the Zener diode of the reference voltage circuit 105, and determines whether or not the cathode side voltage is lower than the Zener voltage that the Zener diode should originally generate. To do. When the Zener diode of the reference voltage circuit 105 is turned off due to the drop in the power supply voltage VB, the cathode voltage of the Zener diode is lowered from the Zener voltage that should be originally generated. Then, the reference voltage generation circuit 100 cannot generate a desired reference voltage VO based on the Zener voltage. Therefore, when the first reference voltage support circuit 200 determines that the cathode side voltage of the Zener diode of the reference voltage generation circuit 100 is lower than the Zener voltage that should originally be generated, these cathode side voltage and the Zener voltage that should be generated A current (replenishment current) having a magnitude corresponding to the voltage difference is generated and flows into the voltage dividing resistor 103 on the low voltage side (GND side). As a result, even if the Zener diode of the reference voltage generating circuit 100 is turned off and the voltage applied to the series circuit of the voltage dividing resistors 102 and 103 is reduced, the terminal voltage of the voltage dividing resistor 103 on the low voltage side is the supplementary current. Therefore, the voltage output from the operational amplifier 104 can be maintained at a voltage substantially corresponding to the reference voltage VO. The detailed circuit configuration and operation of the first reference voltage support circuit 200 will be described later.

  The second reference voltage support circuit 300 operates when the power supply voltage VB further decreases so that the operation (support operation) for maintaining the output of the reference voltage VO by the first reference voltage support circuit 200 becomes difficult. Thus, the voltage corresponding to the reference voltage VO can be continuously output from the reference voltage generating circuit 100. The circuit configuration and operation of the second reference voltage support circuit 300 will also be described in detail later.

  As described above, in the present embodiment, the first and second reference voltage support circuits 200 and 300 are provided, and when the power supply voltage VB starts to decrease, first, the first reference voltage support circuit 200 operates and the reference voltage support circuit 200 operates. The support operation is performed so that generation of a voltage corresponding to the voltage VO can be maintained. When the power supply voltage VB further decreases and it becomes difficult for the first reference voltage support circuit 200 to support the output of the voltage corresponding to the reference voltage VO, the second reference voltage support circuit 300 changes to the reference voltage VO. The support operation for maintaining the output of the corresponding voltage is started. As described above, since the first and second reference voltage support circuits 200 and 300 cooperate to perform the support operation so as to maintain the output of the reference voltage VO as much as possible, the output of the voltage corresponding to the reference voltage VO can be maintained. The range of the power supply voltage VB can be expanded to a lower range.

  Next, a detailed circuit configuration of each part of the reference voltage generator according to the present embodiment will be described with reference to FIG.

In FIG. 2, first, the constant current generation circuit 400 will be described. In constant current generating circuit 400, when power supply voltage VB is applied, base current is supplied to transistor Q404 via resistor R401, and transistor Q404 is turned on. Then, the base current is also supplied to the transistor Q405 via the transistor Q404, and the transistor Q405 is also turned on. As a result, each collector current of transistors Q401 and Q402 having a current mirror configuration flows through transistors Q404 and Q405, respectively. At this time, a voltage corresponding to the voltage between the emitter and the base of the transistor Q405 _{V BE} (about 0.7 V) is applied to the resistor R402. Therefore, the current flowing through the resistor R402 becomes a constant value obtained by dividing the base-emitter voltage V _BE in the resistance value of the resistor R402.

  Here, the base currents of the transistors Q401, Q402, Q404, and Q405 are small enough to be ignored with respect to the emitter current and the collector current. Therefore, the constant current flowing through the resistor R402 can be regarded as the emitter current (collector current) of the transistor Q401. Further, since the transistor Q402 forms a current mirror with the transistor Q401, the same emitter current (collector current) flows through the transistor Q402. In this way, a substantially constant current flows through each of the transistors Q401, Q402, Q404, and Q405 of the constant current generating circuit 400 regardless of fluctuations in the power supply voltage VB.

  The reference voltage generation circuit 100 includes transistors Q401 and Q402 of the constant current generation circuit 400 and a transistor Q101 that forms a current mirror circuit. That is, since the base of the transistor Q101 is connected to the bases of the transistors Q401 and Q402 of the constant current generation circuit 400, when the constant current generation circuit 400 is operated, the current is the same as or proportional to the current flowing through the transistors Q401 and Q402. A current (collector current) flows through the transistor Q101 of the reference voltage generation circuit 100. Thus, the constant current generating circuit 400 and the transistor Q101 constitute the constant current circuit 101 of the reference voltage generating circuit 100.

  In the reference voltage generating circuit 100, a series circuit of a rectifier diode D101 and a Zener diode ZD101 is connected to the collector of the transistor Q101. Accordingly, a constant collector current output by the transistor Q101 flows through the rectifier diode D101 and the Zener diode ZD101, and the Zener diode ZD101 generates a Zener voltage. That is, in the present embodiment, the reference voltage circuit 105 in the reference voltage generation circuit 100 is configured by the rectifier diode D101 and the Zener diode ZD101.

  Here, the reason why the reference voltage circuit 105 is configured by a series circuit of a rectifier diode D101 and a Zener diode ZD101 will be described.

  The Zener diode ZD101 generally has a positive temperature characteristic, and the generated Zener voltage tends to increase as the temperature increases. On the other hand, the rectifier diode D101 has a negative temperature characteristic, contrary to the Zener diode ZD101, and the forward voltage Vf (that is, the voltage applied to the rectifier diode) tends to decrease as the temperature rises. .

  Accordingly, by connecting the rectifier diode D101 in series with the Zener diode ZD101 in the reference voltage generation circuit 100, the positive temperature characteristic of the Zener diode ZD101 can be canceled by the negative temperature characteristic of the rectifier diode D101. Regardless of the change, a substantially constant voltage V103 can be applied to the voltage dividing resistors 102 and 103. As a result, the accuracy of the reference voltage VO can be ensured even when a temperature change occurs.

  Next, the configuration of the first reference voltage support circuit 200 will be described. The first reference voltage support circuit 200 includes a Zener diode ZD201 that generates the same Zener voltage as the Zener diode ZD101 of the reference voltage generation circuit 100. The Zener diode ZD201 is connected to the transistors Q401 and Q402 of the constant current generating circuit 400 and the transistor Q205 constituting a current mirror circuit. Therefore, the Zener diode ZD201 generates a Zener voltage when a constant current is applied from the transistor Q205. The transistor Q205 is configured to output a constant current having the same current value as that of the transistor Q101 of the reference voltage generation circuit 100.

  The first reference voltage support circuit 200 includes a transistor Q203 to which the cathode side voltage V104 of the Zener diode ZD101 of the reference voltage generation circuit 100 is applied to the base, and a cathode of the Zener diode ZD201 of the first reference voltage support circuit 200. It has a transistor Q204 to which the side voltage V201 is applied to the base. The emitter of the transistor Q203 and the emitter of the transistor Q204 are short-circuited through resistors R201 and R202, respectively, and the short-circuit point is connected to the ground potential GND through the resistor R203.

  On the other hand, the transistor Q201 is connected between the collector of the transistor Q203 and the power supply line that supplies the power supply voltage VB, and the transistor Q202 is connected between the collector of the transistor Q204 and the power supply line. The bases of the transistor Q201 and the transistor Q202 are connected to each other to form a current mirror circuit.

  In addition, a wiring connecting the connection line between the transistor Q201 and the transistor Q203 and the connection line between the voltage dividing resistor 102 and the voltage dividing resistor 103 of the reference voltage generating circuit 100 is provided, and the first reference voltage support is provided in this wiring. A rectifier diode D201 having a forward direction from the circuit 200 toward the reference voltage generation circuit 100 is connected. The rectifier diode D201 forms a path for supplying a supplementary voltage to the low-voltage-side voltage dividing resistor 103 when the Zener diode ZD101 of the reference voltage generation circuit 100 cannot generate the Zener voltage. Is for.

  The operation of the first reference voltage support circuit 200 configured as described above will be described.

When the cathode side voltage V104 of the Zener diode ZD101 is applied to the base of the transistor Q203, the upper end (on the side of the transistor Q203) of the resistor R201 has a voltage V _BE between the cathode side voltage V104 and the base-emitter voltage of the transistor Q203. Only a lowered voltage is applied. Similarly, the cathode-side voltage V201 of the Zener diode ZD201 is applied to the base of the transistor Q204, so that the end on the upper side (on the transistor Q204 side) of the resistor R202 is connected between the cathode-side voltage V201 and the base-emitter of the transistor Q204. A voltage lowered by the voltage V _BE is applied.

  The lower side (short circuit point side) of the resistors R201 and R202 is short-circuited. Therefore, when the resistance values of the resistor R201 and the resistor R202 are the same, if the cathode side voltage V104 of the Zener diode ZD101 and the cathode side voltage V201 of the Zener diode ZD201 are the same, the resistor R201 and the resistor R202 are the same. A large current flows. As shown in FIG. 3, when the power supply voltage VB is sufficiently higher than the Zener voltage of each Zener diode ZD101, ZD201, each Zener diode ZD101, ZD201 generates the same Zener voltage. The cathode side voltages V104 and V201 are the same.

  Here, it is assumed that the base currents of the transistors Q201, Q202, Q203, and Q204 are negligibly small with respect to the emitter current and the collector current. Then, the current flowing through the resistor R201 becomes the collector current of the transistor Q203, and the current flowing through the resistor R202 becomes the collector current of the transistor Q204.

  Since the transistors Q201 and Q202 connected to the transistors Q203 and Q204 respectively constitute a current mirror circuit as described above, the collector currents of the transistors Q201 and Q202 are the same. Accordingly, when the cathode-side voltages V104 and V201 of the respective Zener diodes ZD101 and ZD201 are the same, the same current flows through the transistors Q203 and Q204, so that the low-voltage side from the transistor Q201 via the rectifier diode D201. The supplementary current flowing into the voltage dividing resistor 103 becomes zero.

  Next, a case where replenishment current occurs will be described. Since the rectifier diode D101 is connected in series to the Zener diode ZD101 of the reference voltage generation circuit 100, the Zener diode ZD101 is applied with a voltage lower than the Zener diode ZD201 by the voltage drop of the rectifier diode D101. It will be. For this reason, when the power supply voltage VB decreases, the Zener diode ZD201 of the reference voltage support circuit 200 generates a Zener voltage, but the Zener diode ZD101 of the reference voltage generation circuit 100 stops generating the Zener voltage. Can occur. In this case, the cathode-side voltage V104 of the Zener diode ZD101 is a voltage that is reduced by the voltage drop of the rectifier diode D101 from the reduced power supply voltage VB, and thus becomes smaller than the Zener voltage that is the cathode-side voltage V201 of the Zener diode ZD201. .

  Thus, when the cathode side voltage V201 of the Zener diode ZD201 becomes larger than the cathode side voltage V104 of the Zener diode ZD101, the voltage applied to both ends of the resistor R202 is larger than the voltage applied to both ends of the resistor R201. Become. For this reason, the current flowing through the resistor R202, that is, the collector current of the transistor Q204, is larger than the current flowing through the resistor R201, that is, the collector current of the transistor Q203.

  However, the collector currents of the transistors Q201 and Q202 having the current mirror configuration are the same. Therefore, as described above, a current corresponding to the difference between the collector current of the transistor Q203 and the collector current of the transistor Q204 is supplied to the voltage dividing resistor R103 via the rectifier diode D201.

  That is, in the first reference voltage support circuit 200, when the cathode side voltage V104 of the Zener diode ZD101 is lower than the cathode side voltage V201 of the Zener diode ZD201, as shown in FIG. A current corresponding to the voltage difference (V201−V104) divided by the resistance value of the resistor R201 (= resistor R202) flows into the voltage dividing resistor 103 and operates so as to raise the midpoint potential V102 of the voltage dividing resistors 102 and 103. .

Here, if the cathode side voltage V104 of the Zener diode ZD101 is lower than the cathode side voltage V201 of the Zener diode ZD201 by the voltage VA, the voltage V103 applied to the series resistance of the voltage dividing resistors 102 and 103 is also the voltage VA. Only drops. In this case, the voltage drop ΔV102 of the midpoint potential V102 of the voltage dividing resistors 102 and 103 can be expressed by the following equation.
(Formula 1)
ΔV102 = VA × R103 / (R102 + R103)
On the other hand, the supplementary current I flowing into the voltage dividing resistor 103 via the rectifier diode D201 can be expressed by the following equation.
(Formula 2)
I = VA / R201
Therefore, in order to prevent the midpoint potential V102 from decreasing when the cathode side voltage V104 of the Zener diode ZD101 decreases, the following expressions 3 and 4 may be satisfied.
(Formula 3)
(V103−V102) / R102 = V102 / R103
(Formula 4)
(V103−VA−V102) / R102 + VA / R201 = V102 / R103
Solving for Equations 3 and 4 yields the following relationship:
(Formula 5)
R102 = R201 (= R202)
If the relationship of Equation 5 is satisfied, as shown in FIG. 3, even when the cathode side voltage V104 of the Zener diode ZD101 decreases, the Zener diode ZD201 generates a Zener voltage that is a constant voltage. As long as the output voltage V101 (reference voltage VO) of the operational amplifier 104 is reduced, it can be prevented. That is, in FIG. 3, if the supplementary current I is not supplied, the output voltage V101 is reduced to V101-1, so that the supply of the supplementary current I can maintain the V101 line. It is.

  Next, the second reference voltage support circuit 300 will be described. The second reference voltage support circuit 300 has the same circuit configuration as that of the first reference voltage support circuit 200. In other words, the second reference voltage support circuit 300 also has one end connected to the emitters of the transistors Q303 and Q304 to which the cathode side voltage V104 of the Zener diode ZD101 and a comparison voltage V301, which will be described later, are respectively applied to the base. The other ends of the resistors R301 and R302 are short-circuited, the resistors R301 and R302 are connected to the ground potential, and the resistor R303, transistors Q303 and Q304 are connected between the power supply voltage VB and the resistor R303. Transistors Q301 and Q302 constituting a current mirror circuit, and a rectifier diode D301 forming a part of a supplementary current path from the second reference voltage support circuit 300 to the reference voltage generation circuit 100 are provided.

  However, in the first reference voltage support circuit 200, the cathode side voltage V201 of the Zener diode ZD201 is used as a comparison target of the cathode side voltage V104 of the Zener diode ZD101. However, in the second reference voltage support circuit 300, the voltage dividing resistor The difference is that a voltage obtained by dividing the power supply voltage VB by R304 and R305 is a comparison target.

  Thus, in the second reference voltage support circuit 300, the comparison voltage V301 is generated by dividing the power supply voltage VB using the voltage dividing resistors R304 and R305. For this reason, even if the power supply voltage VB is lowered to such an extent that the first reference voltage support circuit 200 cannot perform the support operation for maintaining the output of the voltage corresponding to the reference voltage VO, the second The reference voltage support circuit 300 can perform a support operation for maintaining the output of a voltage corresponding to the reference voltage VB.

  In particular, in the present embodiment, as shown in FIG. 3, the comparison voltage V301 is at the timing when the power supply voltage VB decreases and the Zener diode ZD201 of the first reference voltage support circuit 200 can no longer generate the Zener voltage. The resistance values of the voltage dividing resistors R304 and R305 are set so as to be larger than the cathode side voltage V104 of the Zener diode ZD101. As described in the operation of the first reference voltage support circuit 200, when this comparison voltage becomes larger than the cathode side voltage V104 of the Zener diode ZD101, the supplementary current is supplied to the voltage dividing resistor 103 on the low voltage side. Is started.

  Therefore, in this embodiment, when the power supply voltage VB starts to decrease, first, the first reference voltage support circuit 200 operates to perform a support operation so that generation of a voltage corresponding to the reference voltage VO can be maintained. By this support operation, as shown in FIG. 3, the output voltage V101 does not decrease like V101-1, and the line of V101 can be substantially maintained.

  When the power supply voltage VB further decreases and the Zener diode ZD201 cannot generate the Zener voltage, it becomes difficult for the first reference voltage support circuit 200 to support the output of the voltage corresponding to the reference voltage VO. (In the vicinity of 5V in FIG. 3), the second reference voltage support circuit 300 starts a support operation for maintaining the output of a voltage corresponding to the reference voltage VO. With this support operation, the output voltage V101 does not decrease like V101-2, and the decrease width can be reduced.

  FIG. 3 shows that the output voltage V101 can be maintained by the support operation of the second reference voltage support circuit 300. In practice, however, the voltage slightly lower than the line of the output voltage V101 is reduced. Output. In FIG. 3, the output voltage V101 is shown to decrease when the power supply voltage VB becomes a value around 3V. This is because the power supply voltage VB is lower than the operable voltage of the operational amplifier 104. This is because it was lowered.

  As described above, in this embodiment, the first and second reference voltage support circuits 200 and 300 cooperate to perform the support operation so as to maintain the output of the reference voltage VO as much as possible. Therefore, a voltage corresponding to the reference voltage VO Can be expanded to a lower range.

  Here, the second reference voltage support circuit 300 is configured such that a series circuit of voltage dividing resistors R304 and R305 is connected in parallel with the Zener diode ZD301, and further a transistor that supplies a constant current to the Zener diode ZD301. Q305 is provided. The reason why the Zener diode ZD301 is connected in parallel with the series circuit of the voltage dividing resistors R304 and R305 will be described below.

  As described above, when the comparison voltage V301 generated by the voltage dividing resistors R304 and R305 becomes higher than the cathode side voltage V104 of the Zener diode ZD101, the low voltage side of the reference voltage generation circuit 100 is connected via the rectifier diode D301. A supplementary current is supplied to the voltage dividing resistor 103. For this reason, if the Zener diode ZD301 is not provided, when the power supply voltage VB is at a sufficiently high level, the comparison voltage V301 by the voltage dividing resistors R304 and R305 becomes larger than the cathode side voltage V104 of the Zener diode ZD101. A supplementary current is supplied to the voltage generation circuit 100. Such a supplementary current becomes a disturbance when the reference voltage generation circuit 100 outputs the reference voltage VO, and causes a fluctuation (rise) of the reference voltage VO.

  In order to avoid this, a Zener diode ZD301 is provided, and the Zener diode ZD301 is divided so that the comparison voltage V301 by the voltage dividing resistors R304 and R305 is at most equal to or lower than the Zener voltage of the Zener diode ZD101. The voltage applied to the series circuit of R304 and R305 is limited. As a result, the comparison voltage V301 becomes higher than the cathode side voltage V104 of the Zener diode ZD101 only when the power supply voltage VB decreases and the Zener diode ZD101 cannot generate the Zener voltage. As shown in FIG. 3, when the comparison voltage V301 becomes larger than the cathode side voltage V104 of the Zener diode ZD101, the Zener diode ZD301 is turned off to stop the generation of the Zener voltage, and the voltage dividing resistor R304. , R305 generates a comparison voltage V301 by dividing the lowered power supply voltage VB.

  As mentioned above, although preferable embodiment by this invention was described, this invention is not restrict | limited at all to the embodiment mentioned above, In the range which does not deviate from the main point of this invention, it can implement in various deformation | transformation.

  For example, the above-described embodiment includes the first and second reference voltage support circuits 200 and 300 as circuits that support the maintenance of the output of the reference voltage VO even when the power supply voltage VB is lowered. there were. However, it goes without saying that the first and second reference voltage support circuits 200 and 300 may be used alone.

1 is a circuit block diagram schematically showing an overall configuration of a reference voltage generator according to an embodiment. It is a circuit diagram which shows the detailed circuit structure of each part of a reference voltage generator. It is the graph which showed the mode of the voltage change of each part of a reference voltage generator with respect to the change of a power supply voltage. It is a block diagram which shows the structure of the reference voltage generator by a prior art example.

Explanation of symbols

100 reference voltage generation circuit 101 constant current circuit 102, 103 voltage dividing resistor 104 operational amplifier 105 reference voltage circuit 200 first reference voltage support circuit 300 second reference voltage support circuit

Claims (7)

A Zener diode and a voltage dividing resistor are included. When a power supply voltage is supplied, the Zener voltage generated by the Zener diode is divided by the voltage dividing resistor, and a reference voltage is output based on the divided voltage. A reference voltage generation circuit;
The cathode side voltage of the Zener diode is monitored, and when the cathode side voltage is lower than the Zener voltage, a supplementary current is supplied to the voltage dividing resistor on the low voltage side to suppress a decrease in the reference voltage. And a reference voltage support circuit.   2. The reference according to claim 1, wherein the reference voltage support circuit feeds a supplementary current that increases as a cathode side voltage of the Zener diode becomes lower than the Zener voltage to the voltage dividing resistor on the low voltage side. Voltage generator. The reference voltage generation circuit further includes a rectifier diode connected in series with the Zener diode,
The reference voltage support circuit is:
A Zener diode that generates the same Zener voltage as the Zener diode of the reference voltage generation circuit;
A comparison unit that compares the cathode side voltage of the Zener diode of the reference voltage generation circuit and the cathode side voltage of the Zener diode of the reference voltage support circuit;
When the power supply voltage decreases, the Zener diode of the reference voltage support circuit generates a Zener voltage, but the Zener diode of the reference voltage generation circuit to which a voltage lower by the voltage drop of the rectifier diode is applied As a result of turning off and stopping the generation of the Zener voltage, the comparison unit causes the Zener diode cathode voltage of the reference voltage generating circuit to be higher than the Zener voltage of the Zener diode cathode voltage of the reference voltage support circuit. And a control unit that generates a supplementary current according to the voltage difference and applies it to the voltage dividing resistor on the low voltage side of the reference voltage generation circuit. Item 3. The reference voltage generator according to Item 1 or 2. The reference voltage support circuit is:
A comparison voltage generator for generating a comparison voltage that is larger than the cathode voltage of the Zener diode when the Zener diode of the reference voltage generation circuit is turned off by dividing the power supply voltage;
A comparison unit for comparing a cathode side voltage of a Zener diode of the reference voltage generation circuit with a comparison voltage generated by the comparison voltage generation unit;
When the power supply voltage is reduced, the Zener diode of the reference voltage generation circuit is turned off and the generation of the Zener voltage is stopped.As a result, the comparison unit causes the cathode side voltage of the Zener diode of the reference voltage generation circuit to A control unit that generates a supplementary current according to the voltage difference when it is determined that the voltage is lower than the comparison voltage, and supplies the replenishment current to the voltage dividing resistor on the low voltage side of the reference voltage generation circuit. The reference voltage generator according to claim 1 or 2.   The reference voltage generation device according to claim 4, wherein the comparison voltage generation unit includes a voltage limiting unit that limits a generated comparison voltage to a zener voltage of a zener diode of the reference voltage generation circuit. The reference voltage generation circuit further includes a rectifier diode connected in series with the Zener diode,
The reference voltage support circuit includes a first reference voltage support circuit and a second reference voltage support circuit,
The first reference voltage support circuit includes:
A Zener diode that generates the same Zener voltage as the Zener diode of the reference voltage generation circuit;
A first comparison unit that compares the cathode side voltage of the Zener diode of the reference voltage generation circuit with the cathode side voltage of the Zener diode of the first reference voltage support circuit;
When the power supply voltage decreases, the Zener diode of the first reference voltage support circuit generates a Zener voltage, but a voltage that is lower than the voltage drop of the rectifier diode is applied. As a result of turning off the Zener diode and stopping the generation of the Zener voltage, the first comparison unit causes the cathode side voltage of the Zener diode of the reference voltage generating circuit to be changed to that of the Zener diode of the first reference voltage support circuit. If it is determined that the voltage is lower than the Zener voltage, which is the cathode side voltage, a supplementary current is generated according to the voltage difference between the first voltage and the first voltage applied to the voltage dividing resistor on the low voltage side of the reference voltage generation circuit. A control unit,
The second reference voltage support circuit includes:
When the power supply voltage decreases and the Zener diode of the first reference voltage support circuit is turned off, the comparison voltage that is equal to or higher than the cathode side voltage of the Zener diode of the reference voltage generation circuit is divided. A comparison voltage generator generated by
A second comparison unit that compares a cathode side voltage of a Zener diode of the reference voltage generation circuit with a comparison voltage generated by the comparison voltage generation unit;
When it is determined by the second comparison unit that the cathode voltage of the Zener diode of the reference voltage generation circuit is lower than the comparison voltage, a supplementary current corresponding to the voltage difference is generated, 3. The reference voltage generating device according to claim 1, further comprising: a second control unit that applies the voltage dividing resistor on the low voltage side of the reference voltage generating circuit.   The comparison voltage generation unit of the second reference voltage support circuit includes a voltage limiting unit that limits a generated comparison voltage to be equal to or lower than a Zener voltage of a Zener diode of the reference voltage generation circuit. The reference voltage generator described.

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