Power circuit

Abstract

An object of the present invention is to provide a power supply circuit that can detect and protect against overvoltages for a plurality of DC voltages without increasing the circuit size or costs. [Configuration] The present invention comprises a voltage generation unit that generates 1st to nth voltages (n is an integer of 2 or more), a voltage adjustment unit that generates 1st to nth adjusted voltages by individually adjusting the voltage values ​​of these 1st to nth voltages and outputs the largest adjusted voltage among them as a unified voltage, an overvoltage detection unit that includes a single Zener diode that receives this unified voltage at its cathode and generates an overvoltage detection signal indicating that at least one of the 1st to nth voltages is in an overvoltage state based on the current sent from the anode of the Zener diode, and a stop control unit that stops the operation of the voltage generation unit in response to the overvoltage detection signal.

Description

[Technical Field]

[0001] The present invention relates to a power supply circuit having an overvoltage protection function. [Background technology]

[0002] A power supply circuit that generates a DC voltage to operate an electronic circuit has been proposed that has a function of detecting an overvoltage state, in which the generated DC voltage exceeds the maximum allowable voltage for some reason, and protecting the electronic circuit from the overvoltage state (see, for example, Patent Document 1). The power supply circuit includes a DC-DC converter that generates the DC voltage based on an externally supplied power supply voltage, and an overvoltage protection circuit that forcibly stops operation of the DC-DC converter when an overvoltage is detected. Note that the overvoltage protection circuit includes a Zener diode as an overvoltage detection means. The diode receives the DC voltage generated by the DC-DC converter at its cathode and sends out a current from its anode when the DC voltage exceeds the maximum allowable voltage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-133538 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the power source required for electronic circuits is not only a single DC voltage, but also a plurality of DC voltages each having a different voltage value.

[0005] Therefore, in order to provide overvoltage protection to such electronic circuits using conventional overvoltage protection circuits, it is necessary to provide a Zener diode for each of the multiple DC voltages, taking into account the maximum allowable voltage of each, which poses the problem of increasing the circuit size and cost.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a power supply circuit that is capable of detecting and protecting against overvoltages for a plurality of DC voltages without increasing the circuit size or costs. [Means for solving the problem]

[0007] The power supply circuit of the present invention includes a voltage generation unit that generates first to nth voltages (n is an integer of 2 or more), a voltage adjustment unit that receives the first to nth voltages, generates first to nth regulated voltages by individually adjusting the voltage values ​​of the first to nth voltages, and outputs the largest regulated voltage among the first to nth regulated voltages as a unified voltage, an overvoltage detection unit that includes a single Zener diode that receives the unified voltage at its cathode and generates an overvoltage detection signal indicating that at least one of the first to nth voltages is in an overvoltage state based on a current sent from the anode of the Zener diode, and a stop control unit that stops operation of the voltage generation unit in response to the overvoltage detection signal. [Effects of the Invention]

[0008] According to the power supply circuit of the present invention, overvoltage detection can be performed for a plurality of DC voltages with different voltage values ​​using a single Zener diode, thereby making it possible to suppress increases in circuit size and costs. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram showing a configuration of a power supply circuit 100 as a power supply circuit according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] FIG. 1 is a block diagram showing the configuration of a power supply circuit 100 according to the present invention.

[0011] The power supply circuit 100 includes a DC / DC converter 20, an overvoltage detection unit 30 as an overvoltage protection circuit, an input switch unit 40, and a voltage adjustment unit 50.

[0012] When DC / DC converter 20 receives DC power supply voltage VDD from input switch unit 40, it generates three systems of DC voltages V1 to V3, each having a different nominal voltage, by stepping up or stepping down power supply voltage VDD. DC / DC converter 20 outputs the generated DC voltages V1 to V3 and supplies them to voltage adjustment unit 50. When the supply of power supply voltage VDD from input switch unit 40 stops, DC / DC converter 20 stops generating DC voltages V1 to V3.

[0013] The overvoltage detection unit 30 includes a rectifying diode 31, a Zener diode 32, and a latch circuit .

[0014] The diode 31 has its cathode connected to the latch circuit 34 and its anode connected to the anode of the Zener diode 32. The Zener diode 32 receives the unified voltage Vuf supplied from the voltage adjustment unit 50 at its cathode. The Zener diode 32 has its anode connected to the latch circuit 34.

[0015] The latch circuit 34 includes a PNP transistor 340 , an NPN transistor 341 , and resistors 342 and 343 .

[0016] The resistor 342 has one end connected to the cathode of the diode 31, and the other end connected to the collector of the transistor 340 and the base of the transistor 341. The resistor 343 receives the power supply voltage VDD at one end, and the other end connected to the emitter of the transistor 340 and the input switch section 40 via the output node nd0. The transistor 340 has its base connected to the collector of the transistor 341. The transistor 341 has its emitter connected to a ground line GL that receives a ground voltage (for example, zero volts).

[0017] The input switch section 40 includes a resistor 401, an NPN transistor 402, a resistor 403, a capacitor 404, and a P-channel MOS (metal oxide semiconductor) transistor 405 as the input switch.

[0018] The resistor 401 receives at one end the overvoltage detection signal Exv output from the output node nd0 of the overvoltage detection unit 30. The other end of the resistor 401 is connected to the base of the transistor 402, and supplies a current based on the overvoltage detection signal Exv to the base of the transistor 402. The transistor 402 has its emitter connected to the ground line GL and its collector connected to one end of the resistor 403, one end of the capacitor 404, and the gate of the transistor 405. A power supply voltage VDD is applied to the other end of each of the resistor 403 and the capacitor 404. The transistor 405 receives the power supply voltage VDD at its source. When the transistor 405, which serves as the input switch described above, is set to an ON state in response to the voltage received at its gate, it supplies the power supply voltage VDD to the DC / DC converter 20 via its drain. On the other hand, when the transistor 405 is set to an OFF state in response to the voltage received at its gate, it stops supplying the power supply voltage VDD to the DC / DC converter 20.

[0019] The voltage adjusting unit 50 includes resistors 510-515 and rectifying diodes 520-522.

[0020] The resistor 510 receives the DC voltage V1 generated by the DC / DC converter 20 at one end. The other end of the resistor 510 is connected to one end of the resistor 511 and the anode of the diode 520. The resistor 512 receives the DC voltage V2 generated by the DC / DC converter 20 at one end. The other end of the resistor 512 is connected to one end of the resistor 513 and the anode of the diode 521. The resistor 514 receives the DC voltage V2 generated by the DC / DC converter 20 at one end. The other end of the resistor 514 is connected to one end of the resistor 515 and the anode of the diode 522. The other ends of the resistors 511, 513, and 515 are connected to the ground line GL. The cathodes of the diodes 520 to 522 are commonly connected to a line DL and are connected to the cathode of the Zener diode 32 of the overvoltage detection unit 30 via the line DL.

[0021] The operation of the power supply circuit 100 will now be described.

[0022] When the DC / DC converter 20 receives the supply of the power supply voltage VDD from the input switch section 40, it generates DC voltages V1 to V3 and supplies them to the voltage adjustment section 50, respectively.

[0023] Resistors 510 and 511 of voltage adjustment unit 50 divide DC voltage V1 to adjust its voltage value and supply the adjusted voltage Va to the anode of diode 520. Resistors 512 and 513 of voltage adjustment unit 50 divide DC voltage V2 to adjust its voltage value and generate adjusted voltage Vb, which is supplied to the anode of diode 521. Resistors 514 and 515 of voltage adjustment unit 50 divide DC voltage V3 to adjust its voltage value and generate adjusted voltage Vc, which is supplied to the anode of diode 522.

[0024] In the voltage adjustment unit 50, the voltage division ratios of the voltage dividing resistor pairs (510, 511), (512, 513), and (514, 515) are individually set so that the voltage values ​​of the adjustment voltages Va to Vc obtained when the DC voltages V1 to V3 have their respective nominal voltages are equal, as follows:

[0025] (R511·Vn1) / (R510+R511)=(R513·Vn2) / (R512+R513)=(R515·Vn3) / (R514+R515) R510~R515: Resistance values ​​of resistors 510~515 Vn1: Nominal voltage of DC voltage V1 Vn2: Nominal voltage of DC voltage V2 Vn3: Nominal voltage of DC voltage V3 For example, the nominal voltages Vn1 to Vn3 are Vn1=3.3 volts Vn2=5 volts Vn3=12 volts in the case of, For example, the resistance values ​​of resistors 510 to 515 are Resistance 510: 3kΩ Resistance 511: 30kΩ Resistor 512: 20kΩ Resistance 513: 30kΩ Resistance 514: 30kΩ Resistor 515: 10kΩ Let's say.

[0026] As a result, even if DC / DC converter 20 outputs DC voltages V1 to V3 with different nominal voltages (3.3 volts, 1.5 volts, 12 volts), the corresponding regulated voltages Va, Vb, and Vc are all regulated to 3 volts.

[0027] However, if some malfunction occurs and at least one of the DC voltages V1 to V3 becomes higher than its nominal voltage, only the regulated voltage corresponding to that DC voltage will become higher than 3 V. For example, if only DC voltage V2 of DC voltages V1 to V3 becomes 6 V, which is higher than its nominal voltage of 5 V, regulated voltage Vb will become 3.6 V, which is higher than the 3 V of regulated voltages Va and Vc.

[0028] Here, the regulated voltage Va is supplied to the anode of the diode 520, the regulated voltage Vb is supplied to the anode of the diode 521, and the regulated voltage Vc is supplied to the anode of the diode 522. At this time, the cathodes of the diodes 520 to 522 are commonly connected to the line DL.

[0029] Therefore, the diode OR connection of these diodes 520 to 522 selects the maximum voltage from among the regulated voltages Va to Vc, and the voltage obtained by subtracting the forward voltages of the diodes (520, 521, 522) from this maximum voltage is applied to the line DL. At this time, the voltage applied to the line DL is supplied to the cathode of the Zener diode 32 of the overvoltage detection unit 30 as the unified voltage Vuf.

[0030] In this way, the voltage adjustment unit 50 receives the DC voltages V1 to V3, divides each of them individually using first to third voltage division ratios to generate adjusted voltages Va to Vc whose voltage values ​​are adjusted, and outputs the maximum adjusted voltage among these adjusted voltages Va to Vc as a unified voltage Vuf to the overvoltage detection unit 30.

[0031] The Zener diode 32 of the overvoltage detection unit 30 receives the unified voltage Vuf at its cathode and is turned off when the reverse voltage applied between its cathode and anode is lower than its Zener voltage Vz. Therefore, no Zener current is output from the Zener diode 32 at this time. On the other hand, when the reverse voltage applied between the cathode and anode of the Zener diode 32 becomes equal to or greater than the Zener voltage Vz, the Zener diode 32 is turned on, and the Zener diode 32 outputs a Zener current corresponding to the unified voltage Vuf to the latch circuit 34 via the diode 31.

[0032] When the Zener diode 32 is in the off state, the transistor 341 of the latch circuit 34 is turned off because no current is supplied to its base, and accordingly, no base current flows to the transistor 340, so that the transistor 340 is also turned off. As a result, a high-voltage signal based on the power supply voltage VDD is output from the output node nd0 to the input switch section 40 as the overvoltage detection signal Exv indicating "no overvoltage."

[0033] On the other hand, when the Zener diode 32 is in the ON state, the Zener current sent from the Zener diode 32 is supplied to the base of the transistor 341 via the diode 31 and the resistor 342, turning the transistor 341 ON. As a result, the Zener current is sent from the emitter of the transistor 341 to the ground line GL, and as a result, a current also flows to the base of the transistor 340 via the collector and emitter of the transistor 341, turning the transistor 340 ON. At this time, a current is drawn from the output node nd0 via the emitter of the transistor 340, and the voltage of the output node nd0 drops. As a result, a low-voltage signal on the output node nd0 is output from the output node nd0 to the input switch unit 40 as an overvoltage detection signal Exv indicating "the presence of an overvoltage." Even if the Zener current from the Zener diode 32 subsequently stops flowing, a current based on the power supply voltage VDD continues to flow to the base of the transistor 341 via the resistor 343 and the emitter and collector of the transistor 340, maintaining the on state of the transistors 340 and 341. In other words, the latch circuit 34, consisting of the transistors 340, 341, and the resistors 342 and 343, maintains the overvoltage detection signal Exv at a high voltage indicating "overvoltage present." The voltage regulator 50 described above prevents the unified voltage Vuf received by the Zener diode 32 from changing even if the nominal voltages of the DC voltages V1 to V3 are different. Therefore, even if any of the DC voltages V1 to V3 enters an overvoltage state, the Zener current sent from the Zener diode 32 to the transistor 341 does not change significantly. This allows the overvoltage detector 30 to generate a stable overvoltage detection signal Exv without malfunctioning, even if the DC voltages V1 to V3, which are subject to overvoltage, have different voltage values.

[0034] As described above, when the voltage across the Zener diode 32 becomes equal to or greater than the Zener voltage Vz due to the reception of the unified voltage Vuf, the overvoltage detection unit 30 generates a low-voltage overvoltage detection signal Exv indicating "overvoltage present," i.e., indicating that at least one of the DC voltages V1 to V3 is in an overvoltage state. On the other hand, when the voltage across the Zener diode 32 is lower than the Zener voltage Vz despite receiving the unified voltage Vuf, the overvoltage detection unit 30 generates a low-voltage overvoltage detection signal Exv indicating "no overvoltage present," i.e., indicating that none of the DC voltages V1 to V3 is in an overvoltage state.

[0035] That is, the overvoltage detection unit 30 detects whether or not at least one of the DC voltages V1 to V3 is in an overvoltage state based on the unified voltage Vuf. At this time, in the overvoltage detection unit 30, the Zener voltage Vz of the Zener diode 32 serves as a threshold value for determining whether or not an overvoltage state exists.

[0036] For example, in the circuit configuration shown in FIG. 1, the voltage VK applied to the cathode of the Zener diode 32 is, for example, VK=Vuf=Va-VF520 VF520: Forward voltage of diode 520 is expressed as The voltage VA applied to the anode of the Zener diode 32 is VA=VF31+Vr+VBE VF31: Forward voltage of diode 31 Vr: Voltage across resistor 342 VBE: Base-emitter voltage of transistor 341 It is expressed as:

[0037] Therefore, for example, if it is desired to detect a state in which the nominal voltage exceeds 10% as an overvoltage state, the Zener diode 32 of the overvoltage detection unit 30 should be: Vz=[(VaQ-VF520)-(VF31+Vr+VBE)] VaQ: Va obtained when the voltage is 10% higher than the nominal voltage of V1 A Zener diode having a Zener voltage Vz that satisfies the above is used.

[0038] The overvoltage detection unit 30 supplies the input switch unit 40 with the overvoltage detection signal Exv, which is generated as described above and indicates "no overvoltage" or "existence of overvoltage."

[0039] When the input switch unit 40 receives a high-voltage overvoltage detection signal Exv indicating "no overvoltage," a base current is supplied to the transistor 402 via the resistor 401. This turns on the transistor 402, and a ground potential (for example, zero volts) is supplied to one end of each of the resistor 403 and the capacitor 404, and to the gate of the transistor 405. Therefore, in the input switch unit 40, the transistor 405 turns on and supplies the power supply voltage VDD to the DC / DC converter 20. Therefore, the DC / DC converter 20 continues to generate the DC voltages V1 to V3 based on the power supply voltage VDD.

[0040] On the other hand, when a low-voltage overvoltage detection signal Exv indicating "the presence of an overvoltage" is received, no base current is supplied to transistor 402 of input switch unit 40, and transistor 402 is therefore turned off. At this time, after the time constant defined by resistor 403 and capacitor 404 has elapsed since transistor 402 switched from the on state to the off state, power supply voltage VDD is supplied to the gate of transistor 405 via resistor 403. This turns off transistor 405 as an input switch, and the supply of power supply voltage VDD to DC / DC converter 20 is stopped. Therefore, at this time, DC / DC converter 20 stops generating DC voltages V1-V3. That is, if, for some reason, at least one of DC voltages V1-V3 becomes an overvoltage state higher than the nominal voltage, power supply circuit 100 forcibly stops the operation of DC / DC converter 20, thereby protecting DC / DC converter 20 itself or the electronic circuits receiving DC voltages V1-V3.

[0041] As described above in detail, the power supply circuit 100 can detect an overvoltage state with one Zener diode 32 for the DC voltages V1 to V3 generated by the DC / DC converter 20. Therefore, the power supply circuit 100 can provide overvoltage protection without increasing the circuit size or costs, even if the overvoltage detection targets are a plurality of voltages with different voltage values.

[0042] 1, the connection positions of the diode 31 and the Zener diode 32 may be interchanged. That is, the cathodes of the diode 31 and the Zener diode 32 may be connected to each other, and the anode of the Zener diode 32 may be connected to the resistor 342, so that the anode of the diode 31 receives the unified voltage Vuf.

[0043] In addition, in the voltage adjustment unit 50 shown in FIG. 1, the voltage value of each of the DC voltages V1 to V3 is adjusted by voltage dividing resistor pairs (510, 511), (512, 513), and (514, 515), but the configuration is not limited as long as it is possible to obtain the adjusted voltages Va to Vc by individually adjusting the voltage value of each of the DC voltages V1 to V3.

[0044] 1, the number of DC voltages targeted for overvoltage detection is three, but it may be two, four, or more. In this case, according to the power supply circuit 100, even if the number of DC voltages targeted for detection increases, the only additional circuitry is the voltage-dividing resistor pair and the normal diode for rectification, and no additional Zener diode is required, thereby minimizing the increase in circuit size. Furthermore, simply changing the resistance value of the voltage-dividing resistor pair allows the voltage value of the DC voltage targeted for overvoltage detection to be changed, thereby avoiding problems that may arise when changing the design.

[0045] Furthermore, in the embodiment shown in FIG. 1, when an overvoltage is detected, the input switch unit 40 stops the supply of the power supply voltage VDD to the DC / DC converter 20 serving as the voltage generation unit, thereby stopping the operation of generating the DC voltages V1 to V3. However, the operation of generating the DC voltages V1 to V3 may also be stopped by setting the DC / DC converter 20 to a disabled state.

[0046] In short, the power supply circuit 100 may include the following voltage generation unit, voltage adjustment unit, overvoltage detection unit, and stop control unit.

[0047] The voltage generating section (20) generates first to n-th (n is an integer of 2 or more) voltages (V1 to V3).

[0048] The voltage adjustment unit (50) receives these first to nth voltages, adjusts the voltage values ​​of each voltage individually to generate first to nth adjusted voltages (Va to Vc), and outputs the maximum adjusted voltage among these first to nth adjusted voltages as a unified voltage (Vuf).

[0049] The overvoltage detection unit (30) includes a single Zener diode (32) that receives the unified voltage at its cathode, and generates an overvoltage detection signal (Exv) that indicates that at least one of the first to nth voltages (V1 to V3) is in an overvoltage state in response to a current sent from the anode of the Zener diode. [Explanation of symbols]

[0050] 20 DC / DC converter 30 Overvoltage detection section 32 Zener diode 40 Input switch section 50 Voltage adjustment unit 510~515 Resistance 520~522 Diodes

Claims

1. a voltage generating unit that generates first to n-th voltages (n is an integer of 2 or more); a voltage adjusting unit that receives the first to n-th voltages, generates first to n-th adjusted voltages by individually adjusting the voltage values ​​of the first to n-th voltages, and outputs the maximum adjusted voltage among the first to n-th adjusted voltages as a unified voltage; an overvoltage detection unit including a single Zener diode receiving the unified voltage at its cathode, and generating an overvoltage detection signal indicating that at least one of the first to n-th voltages is in an overvoltage state based on a current sent from an anode of the Zener diode; a stop control unit that stops operation of the voltage generation unit in response to the overvoltage detection signal.

2. the voltage generating unit generates the first to nth voltages having voltage values ​​according to first to nth nominal voltages, respectively; the voltage adjusting unit generates the first to n-th adjusted voltages by dividing the first to n-th voltages individually at first to n-th voltage division ratios, respectively; 2. The power supply circuit according to claim 1, wherein in the voltage adjustment unit, the first to n-th voltage division ratios are set so that n voltages obtained by individually dividing the first to n-th nominal voltages by the first to n-th voltage division ratios all have the same voltage value.

3. The voltage adjusting unit first to n-th voltage dividing resistor circuits that obtain the first to n-th adjusted voltages by individually dividing the first to n-th voltages at the first to n-th voltage dividing ratios; first to n-th diodes, the cathodes of which are commonly connected and which receive the first to n-th regulated voltages at their anodes, 3. The power supply circuit according to claim 2, wherein the voltages of the cathodes of the first to n-th diodes are output as the unified voltage.

4. 2. The power supply circuit according to claim 1, wherein the voltage generating unit receives a DC power supply voltage and generates the first to n-th DC voltages by stepping up or stepping down the power supply voltage.

5. 5. The power supply circuit according to claim 1, wherein the stop control unit stops supplying the power supply voltage to the voltage generation unit in response to the overvoltage detection signal.

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