JP5329840B2 - Overvoltage protection circuit and power management circuit and electronic equipment using the same - Google Patents

Description

  The present invention relates to an overvoltage protection circuit that protects a circuit from an overvoltage.

A circuit element used for a semiconductor integrated circuit cannot execute a normal function when a voltage exceeding a withstand voltage is applied. Electronic devices that operate using an external power source, especially emergency power sources that use dry batteries, or devices that are expected to use poor quality USB (Universal Serial Bus) power sources, are subject to high voltages that are not rated. Therefore, an overvoltage protection circuit for protecting circuit elements from overvoltage is required.
Japanese Patent Laid-Open No. 9-219935

  As a result of studying an overvoltage protection circuit having a voltage protection function using a Zener voltage in an input stage, the present applicant has recognized the following problems. In an overvoltage protection circuit in which an external power supply voltage is applied to the input terminal and the reference voltage terminal is grounded, an input diode is provided so that the cathode is on the input terminal side and the anode is on the reference voltage terminal side. When an overvoltage is applied to the input terminal, the power supply voltage is clamped by the Zener voltage, and the circuit element is protected.

  However, when the external power supply is connected with the polarity reversed, a large voltage is applied to the input diode in the forward direction, which may impair the reliability of the input diode. For example, when a personal computer USB power supply or an emergency power supply using a dry battery is used by the user, if the socket orientation is incorrect or the dry battery orientation is incorrect, the input diode will have a large forward voltage. In such cases, it is necessary to consider circuit design.

  The present invention has been made in view of such a problem, and an object thereof is to provide an overvoltage protection circuit having resistance against an input voltage having a reverse polarity.

  One embodiment of the present invention relates to an overvoltage protection circuit. This overvoltage protection circuit has an input terminal to which an external power supply voltage is input, an output terminal to output the power supply voltage to the outside, a reference voltage terminal to which a reference voltage is input, a drain connected to the input terminal, and a back A first transistor having a gate connected to the source; a first resistor provided between the gate and source of the first transistor; a second resistor provided between the gate of the first transistor and a reference voltage terminal; A first Zener diode disposed between a gate and a source of the first transistor in a direction in which a cathode is on a source side of the first transistor; a gate between the gate of the first transistor and a reference voltage terminal; And a second Zener diode arranged in the following direction.

  According to this aspect, the first Zener diode and the second Zener diode that are connected in series between the output terminal and the reference voltage terminal when a positive overvoltage is applied to the input terminal with reference to the potential of the reference voltage terminal. Thus, the potential of the output terminal can be clamped. At this time, since the gate-source voltage of the first transistor can be clamped by the first Zener diode, the first transistor can be protected. In addition, when a negative overvoltage is applied to the input terminal with reference to the potential of the reference voltage terminal, the body diode of the first transistor, the first Zener diode, and the second Zener diode are disposed to face each other, so that the reference voltage terminal It is possible to prevent current from flowing from the input terminal to the input terminal. At this time, since the gate-source voltage of the first transistor can be clamped by turning on the second transistor, the first transistor can be protected.

An overvoltage protection circuit according to an aspect is provided between a gate of the first transistor and a reference voltage terminal, a third resistor provided in series with the second Zener diode, and a gate and a source of the first transistor. May be further connected to the anode of the second Zener diode, and a second transistor provided in such a direction that the anode of the body diode is on the gate side of the first transistor.
When the power supply voltage sharply changes to negative, the gate voltage of the first transistor follows and changes in the negative direction. At this time, the gate-source voltage of the first transistor can be clamped by the body diode of the second transistor, and the current flowing from the reference voltage terminal to the input terminal via the first transistor can be suppressed.

  The overvoltage protection circuit may be integrated on a single semiconductor substrate. “Integrated integration” includes the case where all of the circuit components are formed on a semiconductor substrate and the case where the main components of the circuit are integrated. A resistor, a capacitor, or the like may be provided outside the semiconductor substrate.

  Another aspect of the present invention is a power management circuit. The power management circuit includes the above-described overvoltage protection circuit and a charging circuit that charges the secondary battery using the power supply voltage output from the output terminal of the overvoltage protection circuit.

  Yet another embodiment of the present invention is an electronic device. The electronic device includes a secondary battery and the above-described power management circuit that charges the secondary battery based on a power supply voltage from an external power supply.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, and the like are also effective as an aspect of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the overvoltage protection circuit which has the tolerance with respect to the input voltage of reverse polarity can be provided.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are physically directly connected, or the member A and the member B are in an electrically connected state. Including the case of being indirectly connected through other members that do not affect the above.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as an electrical condition. It includes the case of being indirectly connected through another member that does not affect the connection state.

FIG. 1 is a circuit diagram showing an overall configuration of an overvoltage protection circuit 100 according to an embodiment and an electronic apparatus 1000 using the same.
The electronic device 1000 is a battery-driven information terminal device such as a mobile phone terminal, PDA, or notebook PC. Electronic device 1000 includes overvoltage protection circuit 100, charging circuit 112, and battery 114. In addition, the electronic device 1000 includes a CPU (Central Processing Unit), a DSP (Digital Signal Processor), a digital circuit including a liquid crystal panel, and an analog circuit (not shown).

  The battery 114 is a secondary battery such as a lithium ion or NiCd (nickel cadmium) battery, and the battery voltage Vbat is supplied to other circuit blocks of the electronic device 1000.

  The external power source 110 is an emergency power source that is connected to the electronic device 1000 and uses an AC adapter that converts a commercial AC voltage into a DC voltage, a DC / DC converter that steps down a voltage of an in-vehicle battery, a USB power source, or a dry battery. . The external power supply 110 supplies a DC power supply voltage Vdc to the battery 114.

  The overvoltage protection circuit 100 includes an input terminal 102, an output terminal 104, and a reference voltage terminal 106, and is integrated on a single semiconductor substrate. A DC voltage Vdc is applied as a power supply voltage from the external power supply 110 between the input terminal 102 and the reference voltage terminal 106. The DC voltage Vdc is applied in such a direction that the input terminal 102 side is at a high potential and the reference voltage terminal 106 side is at a low potential in a normal state. The overvoltage protection circuit 100 operates using the voltage level of the reference voltage terminal 106 as a reference voltage (ground voltage).

  The charging circuit 112 receives the DC voltage Vdc output from the overvoltage protection circuit 100 and charges the battery 114. Of course, the circuit connected to the output terminal 104 of the overvoltage protection circuit 100 is not limited to the charging circuit 112, and can be applied to various circuits that operate using a DC voltage from the outside.

  Hereinafter, a specific configuration of the overvoltage protection circuit 100 will be described. The overvoltage protection circuit 100 includes a first transistor M1, a second transistor M2, a first resistor R1, a second resistor R2, a third resistor R3, a first Zener diode ZD1, and a second Zener diode ZD2.

  The first transistor M1 is a P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). One end of the first transistor M <b> 1 is connected to the input terminal 102. In this specification, for convenience, a terminal on the input terminal 102 side of the first transistor M1 is a drain (d) and a terminal on the output terminal 104 side is a source (s). That is, the drain of the first transistor M1 is connected to the input terminal 102, and the source is connected to the output terminal 104. The back gate of the first transistor M1 is connected to its source. Therefore, the body diode of the first transistor M1 is arranged in such a direction that the cathode is on the output terminal 104 side and the anode is on the input terminal 102 side.

  The first resistor R1 is provided between the gate (g) and the source of the first transistor M1. The resistance value of the first resistor R1 is sufficiently high and ranges from several hundred kΩ to several MΩ. The second resistor R2 is provided between the gate of the first transistor M1 and the reference voltage terminal 106. For example, the resistance value of the second resistor R2 may be in the range of several kΩ to several tens of kΩ. For example, R1 = 1 MΩ and R2 = 20 kΩ.

  The first Zener diode ZD1 is provided between the gate and the source of the first transistor M1. The first Zener diode ZD1 is arranged in such a direction that the cathode is the source side of the first transistor M1 and the anode is the gate side of the first transistor M1. The first Zener diode ZD1 is a general term for m (m is a natural number) Zener diodes connected in series in the same direction.

  The second Zener diode ZD2 has a cathode connected to the anode of the first Zener diode ZD1. The second Zener diode ZD2 is a generic name for n (n is a natural number) Zener diodes connected in series in the same direction. The third resistor R3 is provided between the anode of the second Zener diode ZD2 and the reference voltage terminal 106. For example, R3 = 10 kΩ.

  The second transistor M2 is an N-channel MOSFET, one end of which is connected to the output terminal 104 and the other end is connected to the cathode of the second Zener diode ZD2. From another point of view, the second transistor M2 is provided between the gate and the source of the first transistor M1. In this specification, for convenience, the terminal on the output terminal 104 side of the first transistor M1 is referred to as a source, and the other end is referred to as a drain. The gate of the second transistor M2 is connected to the anode of the second Zener diode ZD2.

  The operation of the overvoltage protection circuit 100 configured as described above will be described for each application state of the external power supply 110.

(1) When the DC voltage Vdc is applied with a normal polarity and a normal value In this case, since the gate-source voltage of the first transistor M1 exceeds the threshold voltage Vt of the MOSFET, the first transistor M1 is turned on. The power supply voltage Vdc supplied to the input terminal 102 is output from the output terminal 104 and supplied to the charging circuit 112.
At this time, the potential difference between the output terminal 104 and the reference voltage terminal 106 is Vdc. The first resistor R1 and the second resistor R2 connected in series between the output terminal 104 and the reference voltage terminal 106 include:
Ir = Vdc / (R1 + R2)
The current given by flows. This current Ir is a waste current that is not supplied to the charging circuit 112 as a load. However, as described above, when R1 = 1 MΩ and R2 = 20 kΩ, Ir≈5 μA with respect to the power supply voltage Vdc of 5 V, and the charging circuit Compared to the current supplied to 112, the value is negligibly small.

(2) When the DC voltage Vdc is applied with normal polarity and overvoltage When the value of the DC voltage Vdc increases with the first transistor M1 turned on, the voltage of the output terminal 104 increases accordingly. . That is, the voltage between the gate and the source of the first transistor M1 increases. When the DC voltage Vdc exceeds the first threshold voltage Vth1 near Vz × m, the first Zener diode ZD1 is turned on in the reverse direction, and the gate-source voltage Vgs of the first transistor M1 is clamped to Vz × m. The Here, Vz is a reverse voltage (zener voltage) of the Zener diode. Therefore, the first transistor M1 can be protected when the gate-source breakdown voltage of the first transistor M1 is low.

As the DC voltage Vdc further increases, the potential at the output terminal 104 also increases accordingly. When the DC voltage Vdc exceeds the second threshold voltage Vth2 near Vz × (m + n), both the first Zener diode ZD1 and the second Zener diode ZD2 are turned on in the reverse direction. Therefore, the potential of the output terminal 104 is
Vz × (m + n)
It is clamped in the vicinity, and an overvoltage can be prevented from being supplied to the charging circuit 112. In other words, the values of m and n are selected in consideration of the withstand voltage of the charging circuit 112 to be protected. For example, when m = 2, n = 2, and Vz = 5.5V, the potential of the output terminal 104 is clamped to 5.5 × 4 = 22V.

The current consumption of the overvoltage protection circuit 100 at this time is examined.
Since the voltage drop of the first Zener diode ZD1 is applied to the first resistor R1,
5.5 (V) × 2/1 (MΩ) = 11 μA
Flows. A voltage of Vdc−Vz × m is applied to the second resistor R2. For example, if Vdc = 30V in the overvoltage state, the second resistor R2 has
(Vdc−Vz × m) / R2 = (30−5.5 × 2) (V) / 20 (kΩ) ≈1 mA
Current flows.

A voltage of Vdc−Vz × (m + n) is applied to the third resistor R3. For example, if Vdc = 30V, the third resistor R3 has
(Vdc−Vz × (m + n)) / R3 = (30−5.5 × 4) (V) / 10 (kΩ) ≈1 mA
Current flows. Therefore, the current consumption does not increase so much even in the overvoltage state.

(3) When DC Voltage Vdc is Applied with Reverse Polarity Consider a case where a negative voltage is applied to the input terminal 102 with reference to the potential of the reference voltage terminal 106. Such a situation may occur when the external power supply 110 is connected in the reverse direction. In this situation, the first transistor M1 is turned off because neither the gate-source voltage nor the gate-drain voltage exceeds the threshold voltage Vt of the MOSFET. Therefore, the current flowing from the reference voltage terminal 106 toward the input terminal 102 is cut off by the body diode D1 arranged in such a direction that the cathode is on the reference voltage terminal 106 side.

  The above is the basic operation of the overvoltage protection circuit 100. Next, the operation when the DC voltage Vdc makes a sharp transition with the reverse polarity will be described.

  Consider a case where a negative voltage having a steep slope is applied to the input terminal 102. In order to clarify the effect of the overvoltage protection circuit 100 according to the present embodiment, the operation when the second transistor M2 is not provided will be described as a comparison technique, and then the operation when the second transistor M2 is provided will be described. .

  FIG. 2 is a waveform diagram showing a transient operation state of the overvoltage protection circuit 100 of FIG. The waveform when the second transistor M2 is not provided is indicated by a broken line, and the waveform when the second transistor M2 is provided is indicated by a solid line. The vertical axis and horizontal axis in FIG. 2 are enlarged or reduced as appropriate for easy understanding, and the waveforms shown are also simplified for easy understanding.

First, the operation when the second transistor M2 is not provided will be described with reference to the waveform indicated by the broken line.
When the potential Vdc of the input terminal 102, that is, the drain voltage of the first transistor M1 sharply transitions to a negative voltage, the gate voltage Vg of the first transistor M1 coupled via the parasitic capacitance Cgd between the gate and drain transitions negative. To do. On the other hand, since the source and gate of the first transistor M1 are coupled via the first resistor R1, the source voltage Vs changes according to a time constant determined by the resistor R1 and the capacitor Cgd. As described above, since the time constant is large when the first resistance R1 is about 1 MΩ, the source voltage Vs gradually approaches the gate voltage Vg. In this process, the first transistor M1 is turned on when the gate-source voltage Vgs exceeds the threshold voltage Vt of the MOSFET. As a result, there arises a problem that a large current I1 flows from the reference voltage terminal 106 toward the input terminal 102.

  If the resistance value of the first resistor R1 is decreased, the source voltage Vs follows the gate voltage Vg, so that the gate-source voltage Vgs becomes substantially the same potential, and the MOSFET is not turned on. However, when the resistance value of the first resistor R1 is reduced, another problem arises that the current consumption during normal operation described in (1) increases.

  That is, when the second transistor M2 is not provided, the generation of a large current and the current consumption during normal operation are in a trade-off relationship. This trade-off problem is preferably solved by providing the second transistor M2.

  Next, the operation when the second transistor M2 is provided will be described with reference to the solid line waveform. When the potential Vdc of the input terminal 102 transitions in the negative direction, the gate voltage Vg of the first transistor M1 swings in the negative direction following the transition. At this time, the gate-source voltage Vgs of the second transistor M2 is clamped to the diode forward voltage Vf (≈0.7 V) by the body diode D2 of the second transistor M2. Therefore, since the degree of ON of the first transistor M1 is limited, it is possible to prevent a large current from flowing from the reference voltage terminal 106 to the input terminal 102. At this time, since the resistance value of the first resistor R1 may be large, an increase in current consumption during normal operation is also suppressed.

  Further, by providing the second transistor M2, the following effects can be obtained. The second transistor M2 is turned on because the gate-source voltage exceeds the threshold voltage when the potential Vdc of the input terminal 102 is a negative voltage. As a result, even if a negative overvoltage is applied to the input terminal 102, the second Zener diode ZD2 conducts in the forward direction, so that the potential of the output terminal 104 is clamped by the second Zener diode ZD2. Specifically, if the voltage drop at the third resistor R3 is ignored, the potential of the output terminal 104 is clamped near (−Vf × n), and a negative overvoltage is supplied to the charging circuit 112. Can be prevented. If the second transistor M2 is not provided, the potential of the output terminal 104 decreases to −Vf × (m + n).

  Those skilled in the art will understand that the above-described embodiment is an exemplification, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  In the embodiment, the MOSFET and the bipolar transistor can be appropriately replaced as necessary. Further, the N channel and P channel of the MOSFET or the NPN type and PNP type of the bipolar transistor may be appropriately replaced.

  In the embodiment, the case where the overvoltage protection circuit 100 and the charging circuit 112 are configured as separate ICs has been described, but these may be integrated as a power management IC 116. Alternatively, the overvoltage protection circuit 100 may be configured using a discrete element.

  Although the present invention has been described based on the embodiments, the embodiments merely show the principle and application of the present invention, and the embodiments are defined in the claims. Needless to say, many modifications and arrangements can be made without departing from the spirit of the present invention.

It is a circuit diagram which shows the structure of the overvoltage protection circuit which concerns on embodiment, and the whole electronic device using the same. FIG. 2 is a waveform diagram showing a transient operation state of the overvoltage protection circuit of FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Overvoltage protection circuit, 102 ... Input terminal, 104 ... Output terminal, 106 ... Reference voltage terminal, M1 ... 1st transistor, M2 ... 2nd transistor, R1 ... 1st resistance, R2 ... 2nd resistance, R3 ... 3rd Resistor, ZD1 ... first Zener diode, ZD2 ... second Zener diode, D1 ... body diode, D2 ... body diode, 110 ... external power supply, 112 ... charge circuit, 114 ... battery, 116 ... power management IC.

Claims (4)

An input terminal to which an external power supply voltage is input;
An output terminal for outputting the power supply voltage to the outside;
A reference voltage terminal to which a reference voltage is input; and
A first transistor having a drain connected to the input terminal and a back gate connected to the source;
A first resistor provided between a gate and a source of the first transistor;
A second resistor provided between the gate of the first transistor and the reference voltage terminal;
A first Zener diode disposed between a gate and a source of the first transistor in a direction in which a cathode is a source side of the first transistor;
A second Zener diode disposed between the gate of the first transistor and the reference voltage terminal in a direction in which a cathode is on the gate side;
A third resistor provided in series with the second Zener diode between the gate of the first transistor and the reference voltage terminal;
A second transistor provided between the gate and source of the first transistor, the gate connected to the anode of the second Zener diode, and the anode of the body diode facing the gate side of the first transistor; ,
An overvoltage protection circuit comprising: 2. The overvoltage protection circuit according to claim 1 , wherein the overvoltage protection circuit is integrated on a single semiconductor substrate. An overvoltage protection circuit according to claim 1 ;
A charging circuit for charging a secondary battery using a power supply voltage output from the output terminal of the overvoltage protection circuit;
And a power management circuit that is integrated. A secondary battery;
The power management circuit according to claim 3 , wherein the secondary battery is charged based on a power supply voltage from an external power supply;
An electronic device comprising:

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