JP2008125176A - Hysteresis comparator circuit and power supply switching circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform a stable switching operation without causing dependence on a power supply voltage in hysteresis characteristics of a comparator, in a power supply switching circuit using a hysteresis comparator. <P>SOLUTION: A battery voltage Vbat is compared with an adaptor voltage Vadp by the comparator OP1 and MOS transistors connected to a battery and an adaptor are controlled to perform power supply switching. In this case, the battery voltage Vbat and the adaptor voltage Vadp are divided by resistors R11, R12 and R21, R22 based on the same voltage dividing ratio, and the MOS transistor M1 connected in parallel to one voltage supply VS2 of voltage supplies VS1, VS2 connected between the division resistors and the ground is turned on or off according to a control signal from the comparator OP1, thereby providing the output switching level of the comparator OP1 with the hysteresis characteristics. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a comparator circuit for comparing two systems of voltages and switching each power source, and more particularly to a hysteresis comparator circuit and a power source switching circuit having hysteresis characteristics.

  When an external power source such as an AC adapter is connected to a portable electronic device that operates on an internal power source such as a battery, and the internal power source is disconnected so that power is supplied from the external power source to the portable electronic device, the power source that switches between these power sources A switching circuit is required. Therefore, it has been proposed to switch the power supply by comparing two systems of voltages and turning the MOS switch on and off (see, for example, Patent Document 1). FIG. 4 is a diagram showing the configuration of such a conventional power supply switching circuit.

  The power supply switching circuit shown in FIG. 4 includes a P-channel MOS transistor Q101 having a drain (D) connected to an input node T1 to which the battery voltage Vbat is input, and a drain (D to the input node T2 to which the adapter voltage Vadp is input. ) Connected to the P-channel MOS transistor Q102 and a comparator OP101 that compares the battery voltage Vbat and the adapter voltage Vadp and outputs a control signal to the MOS transistors Q101 and Q102. G) receives a control signal, which is an output signal of the comparator OP101, via the driver 101, and the gate (G) of the MOS transistor Q102 receives a signal obtained by inverting the control signal from the comparator OP101 by the inverter INV101. It is input via the driver 102. The sources (S) of the MOS transistors Q101 and Q102 are connected to the output node To, and the output capacitor C101 and the load R101 are connected to the output node To. D101 and D102 indicate parasitic diodes of the MOS transistors Q101 and Q102.

  In the power supply switching circuit, the comparator OP101 is composed of an operational amplifier, and the output voltage Vout is supplied as a power supply voltage. The inverter INV101 inverts the output of the comparator OP101. For this reason, the on and off states of the two MOS transistors Q101 and Q102 are opposite to each other, and the power supply of the battery and the adapter is switched and output.

  In other words, the two MOS transistors Q101 and Q102 are turned on when a gate receives an L (Low) level signal, and are turned off when an H (High) level signal is received. When Vbat> Vadp, the output of the comparator OP101 is L level, and the MOS transistor Q101 is turned on. In response to the output of the comparator OP101, the output of the inverter INV101 becomes H level, and the MOS transistor Q102 is turned off. Therefore, the output voltage Vout = battery voltage Vbat, and the higher voltage (battery voltage Vbat) of the battery voltage Vbat and the adapter voltage Vadp is selectively output.

  On the other hand, when Vbat <Vadp, the logic of the signal input to the gates of the MOS transistors Q101 and Q102 is reversed as in the case of Vbat> Vadp, so that the MOS transistor Q101 is turned off and the MOS transistor Q102 is turned on. . Therefore, the output voltage Vout = adapter voltage Vadp, and similarly, the higher voltage (adapter voltage Vadp) of the battery voltage Vbat and the adapter voltage Vadp is selectively output.

  Since the two MOS transistors Q101 and Q102 are often required to have a high breakdown voltage and a large current, discrete components are considered first. Therefore, the source names (S) and drains (D) of the two MOS transistors Q101 and Q102 use the terminal names designated by the discrete components. That is, in the normal usage method, the side connected to the anode of the parasitic diode is the drain, and the side connected to the cathode side is the source, so the source (S) and drain (D) are designated as discrete components according to this connection. Therefore, the present specification follows this. This is a consideration for easily confirming and implementing the background art and the present invention using commercially available MOS transistors, but the actual currents of the two MOS transistors Q101 and Q102 flow from the drain to the source. Yes.

  The comparator OP101 uses the output voltage Vout as the power supply voltage, but other control power supplies can also be used. FIG. 5 is a diagram showing the configuration of such another conventional power supply switching circuit. This power supply switching circuit includes a regulator 103 as a stabilized power supply circuit that obtains the control voltage Vreg from the output voltage Vout, and the control voltage Vreg is used as the power supply voltage of the comparator OP102.

  Here, in the power supply switching circuit shown in FIGS. 4 and 5 described above, as the input voltage of the comparators OP101 and OP102, a voltage having a level higher than the power supply voltage of the comparators OP101 and OP102 (for example, the difference between the battery voltage Vbat and the adapter voltage Vadp). The battery voltage Vbat and the adapter voltage Vadp range from 5V to 12V is input to Vreg = 3V, and the common mode input range of the comparators OP101 and OP102 is exceeded, and the comparators OP101 and OP102 operate normally. In some cases, the higher voltage of the two voltages cannot be selectively output.

  Thus, it has been proposed that the battery voltage Vbat and the adapter voltage Vadp are divided by resistance and input to the comparator so that the input voltage to the comparator falls within the common-mode input range (see, for example, Patent Document 2). FIG. 6 is a diagram showing the configuration of a conventional power supply switching circuit that applies resistance voltage division to the input of such a comparator.

  In the power supply switching circuit shown in FIG. 6, the battery voltage Vbat is divided by resistors R111 and R112, the divided voltage is input to the inverting input terminal of the comparator OP102, and the adapter voltage Vadp is divided by resistors R121 and R122. The divided voltage is input to the non-inverting input terminal of the comparator OP102. As described above, by applying the resistance voltage division to the input of the comparator OP102, the input voltage of the comparator OP102 becomes the in-phase input range.

  Here, assuming that the resistance values of the resistors R111 and R112 and the resistors R121 and R122 are also expressed as R111, R112 and R121 and R122 (hereinafter the same), for example, R111 = R121, R112 = R122, R111 / R112 = 5 When the battery voltage Vbat and the adapter voltage Vadp change within the range from 5V to 12V, the voltage input to the inverting input terminal and the non-inverting input terminal of the comparator OP102 becomes 0.83V to 2V, and the control of the comparator OP102 Even at the voltage Vreg = 3V, the input signal can sufficiently enter the common-mode input range, and can operate normally and selectively output.

  In order to perform a stable power supply switching operation with the above-described circuit, it is effective to give a hysteresis width to the switching level. FIG. 7 is a diagram showing a configuration of a conventional power supply switching circuit in which hysteresis characteristics are given to the power supply switching level.

  In the power supply switching circuit shown in FIG. 7, a resistor R123 is connected between the resistor R122 and GND (ground), an N-channel MOS transistor M101 is connected in parallel with the resistor R123, and the gate of the MOS transistor M101 is connected to the output signal of the inverter INV101. It is controlled by. The MOS transistor M101 is turned on when the gate signal is at the H level and turned off when the gate signal is at the L level.

  When Vbat> Vadp, the output of the comparator OP102 is at the L level, so that the MOS transistor M101 is turned on, the connection point between the resistor R123 and the resistor R122 is at the GND level, and the resistor R123 is divided by the divided voltage of the adapter voltage Vadp. Does not contribute. On the other hand, when Vbat <Vadp, the output of the comparator OP102 is at the H level, the MOS transistor M101 is turned off, and the resistor R123 contributes as a voltage dividing resistor for the adapter voltage Vadp.

  Here, when k1 and k2 are constants, for example, R121 = R111, R122 = k1 × R112, and R122 + R123 = k2 × R112 are set, the battery voltage Vbat is used as a reference to switch from the battery voltage Vbat side to the adapter voltage Vadp side. The level is expressed by the following formula.

Vadp−Vbat = (1−k1) / k1 × R111 / (R111 + R112) × Vbat (= ΔV111) (1)
Similarly, the level at which the adapter voltage Vadp is switched to the battery voltage Vbat with respect to the battery voltage Vbat is expressed by the following equation.

Vadp−Vbat = (1−k2) / k2 × R111 / (R111 + R112) × Vbat (= ΔV112) (2)
Specifically, for example, when R111 / R112 = 5, k1 = 0.978, and k2 = 1.022, ΔV111 = 0.187 Vbat and ΔV112 = −0.0179Vbat.

  FIG. 8 is a diagram showing the power supply switching level in the conventional power supply switching circuit having the hysteresis characteristics described above. A solid line indicates a switching level from the battery to the adapter, and indicates a differential voltage ΔV111. A broken line indicates a switching level from the adapter to the battery, and indicates a differential voltage ΔV112.

From the state where Vbat> Vadp, the MOS transistor Q101 is on, and the MOS transistor Q102 is off, when Vadp becomes higher than Vbat by ΔV111, the MOS transistor Q101 is turned off and the MOS transistor Q102 is turned on. Conversely, when Vbat <Vadp, the MOS transistor Q101 is turned off, and the MOS transistor Q102 is turned on, when Vadp becomes lower than Vbat by ΔV112, the MOS transistor Q101 is turned on and the MOS transistor Q102 is turned off.
JP 2005-18514 A JP-A-9-130996 (FIGS. 3, 6, 8, and 11)

  However, in the power supply switching circuit using the conventional hysteresis comparator as described above, the power supply switching level is dependent on the power supply voltage, and if the power supply switching level is optimally set at the higher power supply voltage, the power supply switching level is low. There is a problem that the switching level becomes small and malfunctions due to noise, or if the setting is optimally performed at a lower power supply voltage, the switching level becomes higher in a region where the power supply voltage is high and switching is impossible.

  That is, in the conventional configuration, the difference voltages ΔV111 and ΔV112 must be set to a voltage lower than the on-voltage VF (generally about 0.6V) of the parasitic diodes D101 and D102 of the MOS transistors Q101 and Q102. If the differential voltages ΔV111 and ΔV112 are higher than the on-voltage VF of the parasitic diodes D101 and D102, Vout = Vbat when the MOS transistor Q101 is on, and in this state, the adapter voltage Vadp rises and exceeds the voltage of (Vbat + VF). Since the parasitic diode D102 of the MOS transistor Q102 is turned on and Vout = (Vadp−VF), and the MOS transistor Q101 is turned on, Vbat = Vout = (Vadp−VF), and the battery is reversely charged from the adapter side. The potential difference for switching determination is fixed to (Vadp−Vbat) = VF.

  Therefore, if ΔV111> VF is set, the differential voltage does not increase beyond the switching level, and power supply switching is not performed. Similarly, when ΔV112> VF is set, switching from the adapter voltage Vadp side to the battery voltage Vbat side cannot be performed. For this reason, it is necessary to set the difference voltages ΔV111 and ΔV112 at the switching level to be equal to or lower than the lowest on-voltage in consideration of the operating temperature conditions and load current of the parasitic diodes D101 and D102.

  The present invention has been made in view of these points, and provides a hysteresis comparator circuit and a power supply switching circuit capable of always performing a stable switching operation without causing voltage dependence in the hysteresis characteristics of the comparator. Objective.

  In the present invention, in order to solve the above problem, in a comparator circuit having a comparator for comparing a voltage from a first power supply with a voltage from a second power supply, the voltage from the first power supply and the second power supply are compared. A voltage dividing resistor that divides the voltage from the power supply and inputs the divided voltage to the comparator; and a voltage source connected between each voltage dividing resistor and a reference potential, and the voltage dividing ratio of each voltage dividing resistor is equal. And setting the output switching level of the comparator to have a hysteresis characteristic by switching the output voltage to the voltage dividing resistor of one of the voltage sources according to the output signal of the comparator. A hysteresis comparator circuit is provided.

  According to such a hysteresis comparator circuit, the voltage from the first power supply and the voltage from the second power supply are respectively divided by the same voltage dividing ratio, and one of the voltage sources connected to the voltage dividing resistors is divided. Since the output voltage to the voltage dividing resistor of the source is switched according to the output signal from the comparator, a stable switching operation is always possible without causing voltage dependency in the hysteresis characteristic of the comparator.

  According to the present invention, in order to solve the above problem, in a comparator circuit having a comparator for comparing the voltage from the first power supply with the voltage from the second power supply, the voltage from the first power supply and the first power supply are compared. A voltage dividing resistor for dividing a voltage from each of the two power sources and inputting the divided voltage to the comparator; a voltage generating resistor connected between each of the voltage dividing resistors and a reference potential; and a voltage generating resistor connected to each of the voltage generating resistors. A constant current source, wherein the voltage dividing ratio of each of the voltage dividing resistors is set to be equal, and the current flowing from one constant current source of each of the constant current sources to one of the voltage generating resistors is output from the comparator Provided is a hysteresis comparator circuit characterized in that the output switching level of the comparator has a hysteresis characteristic by switching according to a signal. That.

  According to such a hysteresis comparator circuit, the voltage from the first power supply and the voltage from the second power supply are respectively divided by the same voltage dividing ratio, and one of the constant current sources connected to the voltage dividing resistors is divided. Since the output current to the voltage dividing resistor of the constant current source is switched according to the output signal from the comparator, a stable switching operation is always possible without causing voltage dependence in the hysteresis characteristics of the comparator.

  Further, in the present invention, in order to solve the above-described problem, the voltage from the first power source is compared with the voltage from the second power source, and each connected to the first power source and the second power source, respectively. In a power supply switching circuit using a comparator that outputs a control signal of a switch element, a voltage dividing resistor that divides the voltage from the first power supply and the voltage from the second power supply and inputs the divided voltage to the comparator, A voltage source connected between each voltage dividing resistor and a reference potential, and setting the voltage dividing ratio of each voltage dividing resistor to be equal to the voltage dividing resistor of one of the voltage sources. By switching the output voltage according to the control signal, there is provided a power supply switching circuit characterized in that the output switching level of the comparator has a hysteresis characteristic.

  According to such a power supply switching circuit, the voltage from the first power supply and the voltage from the second power supply are respectively divided by an equal voltage dividing ratio, and one voltage of the voltage sources connected to the voltage dividing resistors is divided. Since the output voltage to the voltage dividing resistor of the source is switched according to the control signal from the comparator, a stable switching operation is always possible without causing voltage dependency in the hysteresis characteristics of the comparator.

  Further, in the present invention, in order to solve the above-described problem, the voltage from the first power source is compared with the voltage from the second power source, and each connected to the first power source and the second power source, respectively. In a power supply switching circuit using a comparator that outputs a control signal of a switch element, a voltage dividing resistor that divides the voltage from the first power supply and the voltage from the second power supply and inputs the divided voltage to the comparator, A voltage generating resistor connected between each voltage dividing resistor and a reference potential, and a constant current source connected to each voltage generating resistor, respectively, and setting the voltage dividing ratio of each voltage dividing resistor equal, By switching the output current from one of the constant current sources to one of the voltage generation resistors according to the control signal, the output switching level of the comparator is set. Power supply switching circuit, characterized in that which gave hysteresis characteristic is provided.

  According to such a power supply switching circuit, the voltage from the first power supply and the voltage from the second power supply are respectively divided by the same voltage dividing ratio, and one of the constant current sources connected to the voltage dividing resistors is divided. Since the output current to the voltage generating resistor of the constant current source is switched in accordance with the control signal from the comparator, a stable switching operation is always possible without causing voltage dependence in the hysteresis characteristics of the comparator.

  A hysteresis comparator circuit and a power supply switching circuit according to the present invention each divide a voltage from a first power supply and a voltage from a second power supply at an equal voltage dividing ratio, and are connected to these voltage dividing resistors. With respect to the voltage generation resistor, the output voltage of the voltage source or the current flowing from the current source to the voltage generation circuit is switched according to the control signal from the comparator, so the hysteresis characteristic of the comparator is always stable without causing power supply voltage dependency There is an advantage that the switching operation becomes possible.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a power supply switching circuit according to a first embodiment of the present invention. This power source switching circuit switches between two power sources, a battery as a first power source and an adapter as a second power source, using a hysteresis comparator, and is configured as follows.

  A MOS transistor Q1 which is a switch element having a drain (D) connected to an input node T1 to which a battery voltage Vbat from a battery is input, and a drain (D) to an input node T2 to which an adapter voltage Vadp from an adapter is input. A MOS transistor Q2 which is a connected switch element, and a comparator OP1 which compares the battery voltage Vbat and the adapter voltage Vadp and outputs a control signal to the MOS transistors Q1 and Q2 are provided. The two MOS transistors Q1 and Q2 are turned on when an L level signal is received at the gate (G), and are turned off when an H level signal is received. A control signal which is an output signal of the comparator OP1 having hysteresis characteristics is input to the gate of the MOS transistor Q1 via the driver 1, and a signal obtained by inverting the control signal from the comparator OP1 by the inverter INV1 is input to the gate of the MOS transistor Q2. Is input via the driver 2. The sources (S) of the MOS transistors Q1 and Q2 are connected to the output node To, and the output capacitor C1 and the load R1 are connected to the output node To. D1 and D2 indicate parasitic diodes of the MOS transistors Q1 and Q2.

  Like the MOS transistors Q101 and Q102 in the background art, the two MOS transistors Q1 and Q2 are often required to have a high breakdown voltage and a large current. Not limited to parts). Therefore, like the MOS transistors Q101 and Q102, the source names (S) and drains (D) of the two MOS transistors Q1 and Q2 use terminal names designated by discrete components. This is a consideration for enabling the present invention to be easily confirmed and implemented using a commercially available MOS transistor, but the actual currents of the two MOS transistors Q1 and Q2 flow from the drain to the source.

  The comparator OP1 comprises an operational amplifier, and a control voltage Vreg from a regulator (stabilized power supply) 3 that obtains the control voltage Vreg from the output voltage Vout is supplied as a power supply voltage. Further, the inverter INV1 inverts the output of the comparator OP1. For this reason, the on / off states of the two MOS transistors Q1 and Q2 are opposite to each other, and the power source of the battery and the adapter is switched and output.

  The battery voltage Vbat is divided by resistors R11 and R12, and the connection point of the voltage dividing resistors is connected to the inverting input terminal of the comparator OP1. The adapter voltage Vadp is divided by resistors R21 and R22, and the connection point of the voltage dividing resistors is connected to the non-inverting input terminal of the comparator OP1. As described above, by applying the resistance voltage division to the input of the comparator OP1, the input voltage of the comparator OP1 becomes the in-phase input range.

  A voltage source VS1 of the output voltage V1 is connected between the resistor R12 and the reference potential (GND (ground)), and a voltage source VS2 of the output voltage V2 is connected between the resistor R22 and GND, and one voltage source VS2 is connected. In parallel, an N-channel MOS transistor M1 is connected. The MOS transistor M1 is turned on / off by the output signal of the inverter INV1. The MOS transistor M1 is turned on when the gate signal is at the H level and turned off when the gate signal is at the L level.

  The voltage dividing ratio between the resistors R11 and R12 and the resistors R21 and R22 is set to be equal, and the output voltage to the resistors R21 and R22 of one voltage source VS2 is switched according to the control signal from the comparator OP1, so that the comparator OP1 The output switching level has hysteresis characteristics.

  Here, for example, when the relationship of R21 = R11 = R1 and R22 = R12 = R2 is set (or when the relationship of R11 / R12 = R21 / R22 = R1 / R2 is set), the battery voltage Vbat is used as a reference. The level at which the battery voltage Vbat side is switched to the adapter voltage Vadp side is expressed by the following equation.

Vadp−Vbat = R1 / R2 × V1 (= ΔV11) (3)
Similarly, the level at which the adapter voltage Vadp is switched to the battery voltage Vbat with respect to the battery voltage Vbat is expressed by the following equation.

Vadp−Vbat = R1 / R2 × (V1−V2) (= ΔV12) (4)
Specifically, for example, when R1 / R2 = 5, V1 = 30 mV, and V2 = 60 mV, ΔV11 = 5 × 30 mV = 150 mV and ΔV12 = 5 × (30−60) mV = −150 mV.

  The above formula (3) will be described in detail. The condition that the two input voltages of the comparator OP1 are equal when the output voltage V2 = 0 of the voltage source VS2 in the configuration of FIG. 1 is R21 = R11 = R1, Since R22 = R12 = R2 (or R11 / R12 = R21 / R22 = R1 / R2), it is as follows.

V1 + (Vbat−V1) × R2 / (R1 + R2) = Vadp × R1 / (R1 + R2)
Since the left side of the above equation is Vbat × R2 / (R1 + R2) + V1 × R1 / (R1 + R2), multiplying both sides by (R1 + R2) / R2 yields Vbat + R1 / R2 × V1 = Vadp, and Equation (3) is obtained. It is done.

Further, the expression (4) will be described. The condition in which the two input voltages of the comparator OP1 are equal when V2 ≠ 0 in the configuration of FIG. 1 is as follows.
V1 + (Vbat−V1) × R2 / (R1 + R2) = V2 + (Vadp−V2) × R2 / (R1 + R2)
Than this,
Vbat × R2 / (R1 + R2) + V1 × R1 / (R1 + R2) = Vadp × R2 / (R1 + R2) + V2 × R1 / (R1 + R2)
When both sides are multiplied by (R1 + R2) / R2, Vbat + R1 / R2 × V1 = Vadp + R1 / R2 × V2 is obtained, and Expression (4) is obtained.

  FIG. 2 is a diagram showing an example of a power supply switching level in the power supply switching circuit according to the first embodiment having the hysteresis characteristics described above. A solid line indicates a switching level from the battery to the adapter, and indicates a differential voltage ΔV11. A broken line indicates a switching level from the adapter to the battery, and indicates a differential voltage ΔV12.

  In the power supply switching circuit according to the first embodiment, the term Vbat does not exist on the right side of the equations (3) and (4), and as can be seen from the graph of FIG. , ΔV12 have no voltage dependency and are at a constant level. Therefore, when the difference voltages ΔV11 and ΔV12 are set optimally, a stable power supply switching operation can be performed regardless of the magnitude of the power supply voltage.

  FIG. 3 is a diagram showing the configuration of the power supply switching circuit according to the second embodiment of the present invention. The same reference numerals as those in FIG. 1 denote the same components. In the second embodiment, voltage generation resistors R13 and R23 are connected instead of the voltage sources VS1 and VS2 of FIG. 1, a constant current source IS1 is connected to a connection point between the resistor R12 and the voltage generation resistor R13, and the resistor R22. And a constant current source IS2 is connected to the connection point of the voltage generating resistor R23. In addition, a MOS transistor M1 is connected in parallel with the voltage generating resistor R23, and the MOS transistor M1 is turned on and off by an output signal of the inverter INV1.

  In the above power supply switching circuit, the output switching level of the comparator OP1 has hysteresis characteristics by switching the output current to the voltage generating resistor of one constant current source IS2 in accordance with the control signal from the comparator OP1. .

  That is, the constant current I1 output from the constant current source IS1 is led to the connection point between the resistor R12 and the voltage generation resistor R13, and the constant current output from the constant current source IS2 is connected to the connection point between the resistor R22 and the voltage generation resistor R23. A current I2 is introduced. At this time, the resistance value of the voltage generating resistor R13 is set to be sufficiently smaller than the resistor R12, the resistance value of the voltage generating resistor R23 is set to be sufficiently smaller than the resistor R22, and the values of the constant currents I1 and I2 are set to the battery voltage Vbat, When the adapter voltage Vadp is set to a value sufficiently larger than the current value flowing through the resistors R11 and R12 and the resistors R21 and R22, the voltage at each connection point can be regarded as a voltage source. Therefore, the voltage V11 at the connection point between the resistor R12 and the voltage generation resistor R13 is approximately equal to I1 × R13, and the voltage V12 at the connection point between the resistor R22 and the voltage generation resistor R23 is approximately equal to I2 × R23. Thus, a stable power supply switching operation is always possible without causing voltage dependence in the hysteresis characteristics.

It is a figure which shows the structure of the power supply switching circuit of the 1st Embodiment of this invention. It is a figure which shows an example of the power supply switching level in the power supply switching circuit of 1st Embodiment. It is a figure which shows the structure of the power supply switching circuit of the 2nd Embodiment of this invention. It is a figure which shows the structure of the conventional power supply switching circuit. It is a figure which shows the structure of the other conventional power supply switching circuit. It is a figure which shows the structure of the conventional power supply switching circuit which applies a resistance voltage dividing to the input of a comparator. It is a figure which shows the structure of the conventional power supply switching circuit which gave the hysteresis characteristic to the power supply switching level. It is a figure which shows the power supply switching level in the conventional power supply switching circuit which gave the hysteresis characteristic.

Explanation of symbols

1, 2 Driver 3 Regulator C1 Output capacitor D1, D2 Parasitic diode INV1 Inverter IS1, IS2 Constant current source M1, Q1, Q2 MOS transistor OP1 Comparator R1 Load R11, R12, R21, R22 Resistance R13, R23 Voltage generation resistance T1, T2 Input node To Output node VS1, VS2 Voltage source

Claims (8)

In a comparator circuit having a comparator for comparing the voltage from the first power supply with the voltage from the second power supply,
A voltage dividing resistor that divides the voltage from the first power supply and the voltage from the second power supply and inputs the divided voltage to the comparator;
A voltage source connected between each of the voltage dividing resistors and a reference potential, and
By setting the voltage dividing ratio of each of the voltage dividing resistors to be equal and switching the output voltage to the voltage dividing resistor of one of the voltage sources according to the output signal of the comparator, the output of the comparator A hysteresis comparator circuit characterized in that the switching level has hysteresis characteristics. A transistor connected in parallel with the one voltage source;
2. The hysteresis comparator circuit according to claim 1, wherein the transistor is turned on / off in accordance with an output signal of the comparator. In a comparator circuit having a comparator for comparing the voltage from the first power supply with the voltage from the second power supply,
A voltage dividing resistor that divides the voltage from the first power supply and the voltage from the second power supply and inputs the divided voltage to the comparator;
A voltage generating resistor connected between each of the voltage dividing resistors and a reference potential;
A constant current source connected to each of the voltage generating resistors,
By setting the voltage dividing ratio of the voltage dividing resistors equal to each other and switching the current flowing from one constant current source of the constant current sources to one of the voltage generating resistors in accordance with the output signal of the comparator. A hysteresis comparator circuit characterized in that the output switching level of the comparator has hysteresis characteristics. A transistor connected in series with the one constant current source;
4. The hysteresis comparator circuit according to claim 3, wherein the transistor is turned on / off according to an output signal of the comparator. A power source using a comparator that compares a voltage from the first power source with a voltage from the second power source and outputs a control signal of each switch element connected to the first power source and the second power source, respectively. In the switching circuit,
A voltage dividing resistor that divides the voltage from the first power source and the voltage from the second power source and inputs the divided voltage to the comparator;
A voltage source connected between each of the voltage dividing resistors and a reference potential, and
By setting the voltage dividing ratio of each of the voltage dividing resistors to be equal, and switching the output voltage to the voltage dividing resistor of one of the voltage sources according to the control signal, the output switching level of the comparator A power supply switching circuit characterized by having hysteresis characteristics. A transistor connected in parallel with the one voltage source;
6. The power supply switching circuit according to claim 5, wherein the transistor is turned on / off according to the control signal. A power source using a comparator that compares a voltage from the first power source with a voltage from the second power source and outputs a control signal of each switch element connected to the first power source and the second power source, respectively. In the switching circuit,
A voltage dividing resistor that divides the voltage from the first power supply and the voltage from the second power supply and inputs the divided voltage to the comparator;
A voltage generating resistor connected between each of the voltage dividing resistors and a reference potential;
A constant current source connected to each of the voltage generating resistors,
The voltage dividing ratio of each of the voltage dividing resistors is set equal, and the current flowing from one constant current source of each of the constant current sources to one of the voltage generating resistors is switched according to the control signal, A power supply switching circuit characterized in that a hysteresis characteristic is given to the output switching level of the comparator. A transistor connected in series with the one constant current source;
8. The power supply switching circuit according to claim 7, wherein the transistor is turned on / off according to the control signal.

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