JP4894425B2 - Voltage source circuit - Google Patents

Description

  The present invention relates to a voltage source circuit using an output capacitor, and more particularly to a voltage source circuit that drops a terminal voltage of an output capacitor linearly to a ground potential in a certain time.

  When dropping the terminal voltage of the output capacitor charged by the reference voltage source to the ground potential (0 V) with time, for example, a voltage source circuit as shown in FIG. 9 is used. FIG. 9 is a diagram showing a configuration of a conventional voltage source circuit. In this voltage source circuit, charges are stored in the output capacitor C101 via the switch SW101 by the reference voltage source 101 to give an initial voltage value. Then, the switch SW101 is disconnected to cut off the supply of electric charge, and the terminal voltage is lowered by discharging the electric charge of the output capacitor C101 by the resistor R101.

  Here, the capacitance value of the output capacitor C101 is also represented by C101 (F), the voltage value (initial voltage value) of the reference voltage source 101 is V101 (V), and the current value flowing through the resistor R101 is I101 (A). The end time, that is, the time t101 until the terminal voltage of the output capacitor C101 drops to the ground potential is expressed by the following equation.

t101 = C101 × V101 / I101 (1)
Note that a constant current circuit may be used instead of the resistor R101 for the discharge circuit of the output capacitor C101.
Japanese Patent Laid-Open No. 10-322914

  By the way, in the conventional voltage source circuit as described above, the initial charge stored in the output capacitor, that is, the reference voltage source that determines the initial voltage value of the output capacitor, and the resistor (or constant) that determines the discharge current amount of the output capacitor. Current circuit) is composed of different elements, and when the characteristics of each element and circuit fluctuate due to changes in power supply voltage, temperature changes, manufacturing variations, etc., the rate of fluctuation of those characteristics is independent of each other. Become.

  For this reason, for example, when the voltage value of the reference voltage source, the discharge current amount and the capacitance value of the output capacitor fluctuate to kv times, ki times, and kc times due to temperature changes, for example, the discharge end time is (kc Xkv / ki) times, and there is a problem that the time from the start of the drop of the terminal voltage of the output capacitor to the arrival at the ground potential varies.

  The present invention has been made in view of these points, and the terminal voltage of the output capacitor is always maintained even if the characteristics of the reference voltage source, the output capacitor, each element constituting the discharge system, and the circuit vary. An object of the present invention is to provide a highly reliable voltage source circuit that can be lowered linearly to a ground potential in a certain time.

In the present invention, in order to solve the above-described problem, a reference voltage source that charges an output capacitor to give an initial voltage value, second and third voltage sources having the same characteristics as the reference voltage source, and the second voltage A voltage is supplied to the inverting input terminal from the first transistor to which a driving current is supplied from a source through a first magnification circuit and a reference resistor, and from the third voltage source through a second magnification circuit. A constant current circuit having a first operational amplifier for supplying a voltage at a connection point between the reference resistor and the first transistor to a non-inverting input terminal and controlling a driving current of the first transistor, and the output capacitor There is provided a voltage source circuit comprising: a discharge circuit that discharges at a current value correlated with a current value flowing through the constant current circuit.

According to such a voltage source circuit, it has a characteristic variation with a correlation constant current circuit and characteristic variations of the reference voltage source, discharging the output capacitor with a current value having a correlation with the current value flowing to the constant current circuit Therefore, even if the characteristics of the reference voltage source, the output capacitor, each element constituting the discharge system, and the circuit vary, the terminal voltage of the output capacitor can always be lowered linearly to the ground potential in a certain time. .

  The voltage source circuit of the present invention includes a constant current circuit having a characteristic variation correlated with the characteristic variation of the reference voltage source, and discharges the output capacitor with a current value correlated with the current value flowing through the constant current circuit. Even if there are fluctuations in the characteristics of the reference voltage source, the output capacitor, each element constituting the discharge system, and the circuit, the terminal voltage of the output capacitor can always be lowered linearly to the ground potential in a certain time. There is an advantage of improving the performance.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a voltage source circuit according to a first embodiment of the present invention. The voltage source circuit includes a reference voltage source 1 that charges an output capacitor C1 through a switch SW1 to give an initial voltage value, two second voltage sources 2 and a third voltage source having the same characteristics as the reference voltage source 1. 3, the second voltage source 2 and the third voltage source 3, the magnification circuits 4 and 5, the reference resistor R 1, and the drive current from the second voltage source 2 through the magnification circuit 4 and the reference resistor R 1. The supplied transistor (MOSFET) Q1 and the operational amplifier ( first operational amplifier) OP1 that controls the drive current of the transistor Q1 constitute a constant current circuit having a characteristic variation correlated with the characteristic variation of the reference voltage source 1. Has been. Further, a transistor Q2 that is the same as the transistor Q1 is connected in parallel with the output capacitor C1 as a discharge circuit, and the output capacitor C1 is discharged with a current value that correlates with the current value flowing through the constant current circuit. In the circuit of FIG. 1, a current mirror circuit is constituted by the transistor Q1 of the constant current circuit and the transistor Q2 of the discharge circuit, and the output capacitor C1 is discharged at a current value proportional to the current value flowing through the constant current circuit. The voltage source circuit can be formed on a single semiconductor substrate.

  In the voltage source circuit configured as described above, the initial charge is stored in the output capacitor C1 by the reference voltage source 1 for determining the initial value, and the voltage value of the second voltage source 2 for determining the discharge current is the reference resistance. A constant current is converted by a circuit using R1 and the operational amplifier OP1, and the electric charge stored in the output capacitor C1 is discharged by the constant current. Then, the terminal voltage of the output capacitor C1 is output from the output terminal To and used as a linear drop type voltage source.

  More specifically, a charge proportional to the initial voltage value determined by the reference voltage source 1 is stored in the output capacitor C1 via the switch SW1. Further, the voltage values of the second voltage source 2 and the third voltage source 3 having the same circuit configuration as that of the reference voltage source 1 are multiplied or attenuated by arbitrary multiplier circuits 4 and 5 by resistance voltage division or the like, and the operational amplifier OP1. A reference current for discharging the output capacitor C1 is generated together with the reference resistor R1 and the transistor Q1.

  Since the voltage value at point c in FIG. 1 becomes equal to the voltage value at point b by the feedback loop of the operational amplifier OP1-transistor Q1, the voltage value applied across the reference resistor R1 is the voltage value at points a and b. Is equal to the difference. At this time, since the second voltage source 2 and the third voltage source 3 have the same circuit configuration as that of the reference voltage source 1, the differential voltage value at the point a and the point b is the point d output from the reference voltage source 1. In proportion to the voltage value, there is also a correlation in the fluctuation ratio of the voltage values. If the reference voltage source 1, the second voltage source 2, and the third voltage source 3 are arranged close to each other on the substrate, their characteristics are closer to each other, and the correlation of the fluctuation ratio can be strengthened.

  Here, by using a high-concentration N-type Poly-Si resistor that varies as the reference resistor R1 and has a small temperature dependence, the fluctuation of the resistance value is suppressed to be sufficiently small, so that the reference resistor R1 and the transistor Q1 have d points. It is possible to pass a current that is proportional to the voltage value of and that has a correlation with the fluctuation rate. Since the transistors Q1 and Q2 have a current mirror configuration, the current value of the transistor Q2 that discharges the output capacitor C1 is proportional to the current value of the transistor Q1, and has similar characteristics. Therefore, by adjusting the mirror ratio of the transistors Q1 and Q2 to keep the impedance of the transistor Q2 sufficiently high, the influence on the voltage value at the point d given by the transistor Q2 can be sufficiently reduced.

  In the above circuit configuration, the resistance value of the reference resistor R1 is also expressed as R1, the voltage value at the point d is Vd, the magnification values of the magnification circuits 4 and 5 are k1 and k2, and the mirror ratio of the transistors Q1 and Q2 is M1. The discharge current I1 flowing through the transistor Q2 is expressed by the following equation.

I1 = M1 × (k1−k2) × Vd / R1 (2)
Then, by disconnecting the switch SW1 at an arbitrary time, the charge supplied to the output capacitor C1 is cut off, and the discharge by the transistor Q2 starts. When the capacitance value of the output capacitor C1 is also expressed as C1, Equation (2) Thus, the discharge end time t1 is expressed by the following equation.

t1 = C1 * R1 / (M1 * (k1-k2)) (3)
According to equation (3), even when the initial voltage value determined by the reference voltage source 1 fluctuates due to changes in power supply voltage, temperature changes, manufacturing variations, etc., the discharge current also fluctuates in the same way, and the fluctuations in both characteristics are offset. The discharge current end time is not affected. Therefore, the terminal voltage of the output capacitor C1 is linearly determined by the time determined by the magnification value of the magnification circuits 4 and 5, the resistance value of the reference resistor R1, the mirror ratio of the transistors Q1 and Q2, and the capacitance value of the output capacitor C1. Drops to ground potential. Since these characteristic fluctuations are small, the voltage value of the output terminal To always drops linearly to the ground potential in a stable time.

  FIG. 2 is a diagram illustrating a discharge time of the output capacitor C1 due to a temperature change according to the embodiment. Even if the voltage value Vd at the point d, which is the initial voltage value, fluctuates as the temperature changes, the difference voltage Va-Vc between the points a and b for determining the discharge current is also equal in temperature characteristic. As a result, the discharge time of the output capacitor C1 becomes substantially constant. For this reason, as shown in FIG. 3, even when the initial voltage value of the output terminal To is different, the time from the voltage drop start time until reaching the ground potential is constant. FIG. 3 is a diagram showing the time during which the voltage value of the output terminal To drops to the ground potential according to the embodiment, and shows the time when the temperature is 100 ° C. and 25 ° C.

  As described above, in the first embodiment, the initial voltage value is determined by using the reference voltage source 1 for determining the initial voltage value and the second voltage source 2 and the third voltage source 3 that are correlated with the characteristic variation. And a constant current circuit having a current amount that is proportional to the initial voltage value and whose fluctuation ratio is correlated with the initial voltage value, and discharges the output capacitor C1 with a current amount proportional to the current amount. For this reason, even if the initial voltage value or the amount of discharge current fluctuates due to a change in power supply voltage, temperature change, manufacturing variation, etc., the fluctuation ratio has a correlation, so that those equations (3) are correlated. The fluctuation can be canceled out, and the fluctuation of the discharge end time can be suppressed only to the fluctuation of the output capacitor C1.

  In general, since the fluctuation ratio due to the power supply voltage, temperature, and manufacturing variation of the capacitor is small, the characteristics of the elements and circuits constituting the reference voltage source 1, the output capacitor C1, and the discharge system thereof vary due to the above configuration. However, the terminal voltage of the output capacitor C1 can always be linearly dropped to the ground potential in a certain time, and the reliability is improved.

  FIG. 4 is a diagram showing the configuration of the voltage source circuit according to the second embodiment of the present invention. In the second embodiment, the reference voltage source 1 shown in FIG. 1 is shared with the voltage source of the constant current circuit, and the constant voltage circuit is configured by using the reference voltage source 1 and the second voltage source 2. ing. The rest of the configuration is the same as that of the circuit of FIG. 1, and a constant current circuit having a characteristic variation correlated with the characteristic variation of the reference voltage source 1 is provided. Since the output capacitor C1 is discharged, the terminal voltage of the output capacitor C1 can always be lowered linearly to the ground potential in a certain time.

  FIG. 5 is a diagram showing the configuration of the voltage source circuit according to the third embodiment of the present invention. Also in the third embodiment, the reference voltage source 1 shown in FIG. 1 is shared with the voltage source of the constant current circuit, and the constant current circuit is configured by using the reference voltage source 1 and the second voltage source 2. Has been. The rest of the configuration is the same as that of the circuit of FIG. 1, and a constant current circuit having a characteristic variation correlated with the characteristic variation of the reference voltage source 1 is provided. Since the output capacitor C1 is discharged, the terminal voltage of the output capacitor C1 can always be lowered linearly to the ground potential in a certain time.

  FIG. 6 is a diagram showing a configuration of a voltage source circuit according to the fourth embodiment of the present invention. Also in the fourth embodiment, the reference voltage source 1 shown in FIG. 1 is shared with the voltage source of the constant current circuit, and the constant current circuit is configured by using one reference voltage source 1. The rest of the configuration is the same as that of the circuit of FIG. 1, and a constant current circuit having a characteristic variation correlated with the characteristic variation of the reference voltage source 1 is provided. Since the output capacitor C1 is discharged, the terminal voltage of the output capacitor C1 can always be lowered linearly to the ground potential in a certain time.

FIG. 7 is a diagram showing the configuration of the voltage source circuit according to the fifth embodiment of the present invention. Also in the fifth embodiment, the reference voltage source 1 shown in FIG. 1 is shared with the voltage source of the constant current circuit, and the constant current circuit is configured by using one reference voltage source 1. The output capacitor C1 is given an initial voltage value from the reference voltage source 1 via an operational amplifier (second operational amplifier) OP2, and the voltage of the reference voltage source 1 is divided by resistors R2 and R3 and divided. Voltage is input to the inverting input terminal of the operational amplifier OP1. The other configuration is the same as that of the circuit of FIG. 6, and includes a constant current circuit having a characteristic variation correlated with the characteristic variation of the reference voltage source 1, and a current value correlated with a current value flowing through the constant current circuit. Since the output capacitor C1 is discharged, the terminal voltage of the output capacitor C1 can always be lowered linearly to the ground potential in a certain time.

  FIG. 8 is a diagram showing the configuration of the voltage source circuit according to the sixth embodiment of the present invention. In the sixth embodiment, the second voltage source 2 shown in FIG. 1 is shared with the third voltage source 3, and a constant current circuit is configured by using one second voltage source 2. Yes. The other configuration is the same as that of the circuit of FIG. 7, and includes a constant current circuit having a characteristic variation correlated with the characteristic variation of the reference voltage source 1, and a current value correlated with the current value flowing through the constant current circuit. Since the output capacitor C1 is discharged, the terminal voltage of the output capacitor C1 can always be lowered linearly to the ground potential in a certain time.

It is a figure which shows the structure of the voltage source circuit of the 1st Embodiment of this invention. It is a figure which shows the discharge time of the output capacitor by the temperature change of embodiment. It is a figure which shows the time when the voltage value of the output terminal of embodiment falls to ground potential. It is a figure which shows the structure of the voltage source circuit of the 2nd Embodiment of this invention. It is a figure which shows the structure of the voltage source circuit of the 3rd Embodiment of this invention. It is a figure which shows the structure of the voltage source circuit of the 4th Embodiment of this invention. It is a figure which shows the structure of the voltage source circuit of the 5th Embodiment of this invention. It is a figure which shows the structure of the voltage source circuit of the 6th Embodiment of this invention. It is a figure which shows the structure of the conventional voltage source circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reference voltage source 2 2nd voltage source 3 3rd voltage source 4,5 Multiplier circuit C1 Output capacitor OP1, OP2 Operational amplifier Q1, Q2 Transistor R1 Reference resistance R2, R3 Resistance SW1 Switch To Output terminal

Claims (9)

A reference voltage source that charges the output capacitor to provide an initial voltage value;
Second and third voltage sources having the same characteristics as the reference voltage source , a first transistor to which a drive current is supplied from the second voltage source via a first multiplier circuit and a reference resistor, and the second transistor Voltage is supplied from the voltage source 3 to the inverting input terminal via the second magnification circuit, and the voltage at the connection point between the reference resistor and the first transistor is supplied to the non-inverting input terminal. A constant current circuit having a first operational amplifier for controlling a driving current of the transistor ;
A voltage source circuit comprising: a discharge circuit that discharges the output capacitor at a current value correlated with a current value flowing through the constant current circuit. 2. The voltage source circuit according to claim 1, wherein the second voltage source is configured as a common voltage source with the reference voltage source . 2. The voltage source circuit according to claim 1, wherein the third voltage source is configured as a common voltage source with the reference voltage source . 2. The voltage source circuit according to claim 1, wherein the second voltage source and the third voltage source are configured as a common voltage source with the reference voltage source . 2. The voltage source circuit according to claim 1, wherein the second voltage source and the third voltage source are configured as one common voltage source.   The first magnification circuit is a second operational amplifier in which an output terminal is connected to an inverting input terminal, and a voltage of the common voltage source is supplied to a non-inverting input terminal;
  6. The voltage source circuit according to claim 4, wherein the second magnification circuit is constituted by a resistance voltage dividing circuit.   6. The operational amplifier according to claim 1, wherein the first magnification circuit is an operational amplifier having an output terminal connected to an inverting input terminal and a voltage of the second voltage source supplied to a non-inverting input terminal. The voltage source circuit according to any one of the above.   6. The voltage source circuit according to claim 1, wherein the second magnification circuit is configured by a resistance voltage dividing circuit.   2. The discharge circuit according to claim 1, wherein the discharge circuit is a second transistor connected in parallel with the output capacitor, and constitutes a current mirror circuit with the first transistor of the constant current circuit. 9. The voltage source circuit according to claim 8.

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