JP2013121203A - Surge voltage protection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surge voltage protection circuit capable of protecting a device from a surge voltage and removing a ripple component.SOLUTION: When a voltage Vdiv divided by a resistor R2 and a resistor R3 is lower than a Zener voltage Vzd1, a transistor TR1 is in a non-conductive state. Here, a surge voltage is applied to a power supply input terminal IN, the voltage Vdiv exceeds the Zener voltage Vzd1 to make the transistor TR1 be conductive. Thereby, an emitter voltage of a transistor TR3 is controlled so that the voltage Vdiv is substantially equal to the Zener voltage Vzd1 to make the surge voltage be restricted and outputted from a power supply output terminal OUT. In addition, a low-pass filter is configured by a resistor R1 and a capacitor C1 to remove a ripple component.

Description

  The present invention relates to a surge voltage protection circuit for protecting an electronic device mounted on a vehicle or the like from a surge voltage.

  An electronic device mounted on a vehicle or the like generates a high voltage (surge voltage) instantaneously at the time of load dump or the like, and thus it is necessary to take a countermeasure for protecting the surge voltage in the power supply circuit. FIG. 6 shows an example of a conventionally used surge voltage protection circuit for protecting such an electronic device from a surge voltage. In the surge voltage protection circuit 100 shown in FIG. 6, a resistor R100 is connected in series between a power supply input terminal IN to which a DC voltage is applied and a power supply output terminal OUT to which a load is connected. A Zener diode ZD100 is connected between the grounds. In the surge voltage protection circuit 100, when a normal voltage is input to the power supply input terminal IN, the normal voltage is equal to or lower than the Zener voltage of the Zener diode ZD100, so that the Zener diode ZD100 does not conduct. However, when a surge voltage is applied to the power supply input terminal IN, the voltage at the power supply output terminal OUT rises to be higher than the Zener voltage of the Zener diode ZD100, and the Zener diode ZD100 becomes conductive. As a result, the power supply voltage output from the power supply output terminal OUT is limited to the Zener voltage.

  In addition, in electronic devices mounted on vehicles and the like, power supply ripples are also removed. A conventional ripple elimination circuit 200 used in the power supply circuit is shown in FIG. In the ripple elimination circuit 200 shown in FIG. 8, a DC voltage is applied to the power input terminal IN, and a load is connected to the power output terminal OUT. A resistor R201 and a capacitor C201 constitute a low-pass filter whose time constant is determined. Since the capacitor C201 has a low impedance with respect to the ripple component, the ripple component is suppressed from the voltage across the capacitor C201, and control is performed so that the ripple component is removed from the emitter voltage of the emitter follower-connected transistor TR201 by this voltage. Is done. As a result, an output voltage from which the ripple component has been removed is output from the power supply output terminal OUT output from the emitter of the transistor 202.

JP-A-10-191555 JP 2002-84737 A

  As described above, in the conventional surge voltage protection circuit 100, when the surge voltage is applied, a high voltage obtained by subtracting the Zener voltage from the surge voltage is applied to both ends of the resistor R100. A large current flows through ZD100. For this reason, there is a problem that it is necessary to use the resistor R100 having a large allowable power and the Zener diode ZD100 having a large allowable current. Further, the conventional surge voltage protection circuit 100 cannot remove the ripple component of the power supply, and the conventional ripple removal circuit 200 has a problem that the surge voltage cannot be effectively limited.

  Therefore, the present invention provides a surge voltage protection circuit capable of protecting against a surge voltage without requiring a resistor having a large allowable power or a Zener diode having a large allowable current and removing a ripple component. It is an object.

  In the surge voltage protection circuit of the present invention, a first resistor and a capacitor are connected in series, a series circuit connected between a power input terminal and ground, and a cathode at a connection point between the first resistor and the capacitor. A zener diode having an anode connected to the ground, a collector connected to the power input terminal, an emitter connected to the power output terminal, and a connection point between the first resistor and the capacitor connected to the base. The most important feature is to include a transistor.

  According to the present invention, since the current flowing through the circuit when a surge voltage is applied can be greatly reduced, the load on the circuit component can be reduced, so that the circuit component can be reduced in size and the cost can be reduced. Will be able to. In addition, a low-pass filter is configured by the first resistor and the capacitor, and the ripple component is suppressed from the voltage across the capacitor, and the output voltage from which the ripple component is removed is output from the power supply output terminal. .

It is a circuit diagram which shows the circuit structure of the surge voltage protection circuit of the Example of this invention. It is a circuit diagram which shows the circuit structure which actualized the surge voltage protection circuit of the Example of this invention. It is a figure which shows the output voltage waveform when a surge voltage is input into the surge voltage protection circuit of the Example of this invention compared with a prior art example. It is a figure which shows the current waveform when a surge voltage is input into the surge voltage protection circuit of the Example of this invention compared with a prior art example. It is a circuit diagram which shows the circuit structure of the surge voltage protection circuit of the other Example of this invention. It is a circuit diagram which shows the circuit structure of the conventional surge voltage protection circuit. It is a circuit diagram which shows the circuit structure which actualized the conventional surge voltage protection circuit. It is a circuit diagram which shows the circuit structure of the conventional ripple removal circuit.

FIG. 1 is a circuit diagram showing a circuit configuration of a surge voltage protection circuit according to an embodiment of the present invention.
A surge voltage protection circuit 1 according to the present invention shown in FIG. 1 is a circuit provided on the power supply side in order to protect an in-vehicle electronic device from a surge voltage. A surge voltage protection circuit 1 shown in FIG. 1 includes a second transistor (TR) 2 and a second transistor (TR) 2 connected in series between a power input terminal IN to which a DC voltage is applied and a power output terminal OUT to which a load is connected. Three transistors (TR) 3 are connected. In this case, the power input terminal IN is connected to the collectors of TR2 and TR3, the emitter of TR2 is connected to the base of TR3, and the emitter of TR3 is connected to the power output terminal OUT. A resistor R1, a first transistor (TR) 1, and a Zener diode ZD1 are connected in series between the power input terminal IN and the ground. In this case, one end of the resistor R1 is connected to the power input terminal IN, the other end of the resistor R1 is connected to the collector of TR1, the cathode of the Zener diode ZD1 is connected to the emitter of TR1, and the anode of the Zener diode ZD1 is grounded. It is connected to the. The base of TR1 is connected to the midpoint of a series circuit of a resistor R2 and a resistor R3 connected between the power supply output terminal OUT for dividing the output voltage output from the power supply output terminal OUT and the ground.

Furthermore, the resistor R1 is connected between the collector and base of TR2, one end of the capacitor C1 is connected to the other end of the resistor R1 connected to the base of TR2, and the other end of the capacitor C1 is grounded. . Note that TR1, TR2 and TR3 are NPN bipolar junction transistors, which are silicon transistors.
In the surge voltage protection circuit 1 according to the present invention configured as described above, a low-pass filter whose time constant is determined by the resistor R1 and the capacitor C1 is configured, and the capacitor C1 has a low impedance with respect to the ripple component. Therefore, the ripple component is suppressed from the voltage across the capacitor C1. For this reason, since the ripple component is removed from the base voltage of TR2, the ripple component is also removed from the emitter voltage of TR2, which is the base voltage of TR3, and the power supply output terminal OUT to which the emitter of TR3 is connected. The output voltage from which the ripple component is removed is output.

In addition, when the divided voltage Vdiv obtained by dividing the output voltage output from the power supply output terminal OUT by the resistors R2 and R3 is lower than the Zener voltage Vzd1 of the Zener diode ZD1, TR1 is non-conductive. That is, when a steady-state input voltage is input to the power input terminal IN, TR1 is non-conductive. Here, when a surge voltage is applied to the power supply input terminal IN and the output voltage of the power supply output terminal OUT rises, the divided voltage Vdiv exceeds the Zener voltage Vzd1 of the Zener diode ZD1. As a result, current flows through the Zener diode ZD1 connected to the emitter when TR1 is turned on. In this case, when TR1 is turned on, the emitter voltage of TR1 is fixed to the Zener voltage Vzd1, but the collector voltage of TR1 is lowered, and accordingly, the base voltage and emitter voltage of TR2 are lowered. The emitter voltage of TR3 also drops. However, when the divided voltage Vdiv becomes lower than the Zener voltage Vzd1 of the Zener diode ZD1, TR1 is disabled. Become so. By performing this control, the output voltage of the power supply output terminal OUT is obtained by adding the base-emitter voltage Vbe (about 0.7 V) of the TR1 to the Zener voltage Vzd1 to obtain the reciprocal of the voltage dividing ratio of the resistors R2 and R3. It is limited to the multiplied voltage value. Thus, even if a surge voltage is applied to the power input terminal IN, the surge voltage is limited and output from the power output terminal OUT.
Since the current flowing through the series circuit of R1-TR1-ZD1 may be the current at which the Zener diode ZD1 operates, the value of the resistor R1 can be set to several tens kΩ to several hundred kΩ, so that a surge voltage is applied. In this case, the current flowing through the surge voltage protection circuit 1 can be reduced. Thereby, a circuit component can be reduced in size and cost reduction can be aimed at.

Next, FIG. 2 shows a circuit configuration of a surge voltage protection circuit 2 that embodies the surge voltage protection circuit 1 according to the present invention.
The other surge voltage protection circuit 2 shown in FIG. 2 is a circuit that embodies the surge voltage protection circuit 1. In the surge voltage protection circuit 1 shown in FIG. 1, an unnecessary high frequency component is provided between the power input terminal IN and the ground. The capacitors C2 and C3 to be removed are connected, and a resistor RL that is a load is connected between the power supply output terminal OUT and the ground. As an example of the value of each element of the surge voltage protection circuit 2, the capacitor C1 is about 0.1 μF, the capacitor C2 is about 0.01 μF, the resistor R1 is about 100 kΩ, and the Zener voltage Vzd1 of the Zener diode ZD1 is about 6. 2V, the capacitor C1 is about 1 μF, the resistance R2 is about 240 kΩ, the resistance R3 is about 100 kΩ, and the resistance RL used as a load is about 200Ω. In the surge voltage protection circuit 2 configured as described above, the ripple component can be removed and the surge voltage can be limited in the same manner as the surge voltage protection circuit 1 described above.

Therefore, in the surge voltage protection circuit 2 shown in FIG. 2, when a surge voltage (JASO-D001-94 5.7 A-1 type) is applied to the power input terminal IN, the output voltage waveform Vout2 output from the power output terminal OUT. The simulation results are shown in FIG.
Referring to FIG. 3, a normal voltage that is an output voltage of about 10 V is supplied to the power supply input terminal IN until about 0.1 seconds elapse. Then, after about 0.1 second, a surge voltage is applied to the power supply input terminal IN that suddenly rises to a peak voltage of about 72 V, then drops rapidly, and returns to the normal voltage after about 0.45 seconds. This surge voltage is shown by the waveform shown as Vin in FIG. When a surge voltage having such a waveform is applied to the power supply input terminal IN of the surge voltage protection circuit 2 shown in FIG. 2, the output voltage output from the power supply output terminal OUT is slightly higher than the surge voltage as shown in FIG. Although it rises with a delay, the output voltage waveform Vout2 is thereafter limited to a substantially constant voltage. In this case, the Zener voltage Vzd1 of ZD1 is about 6.2V, and the voltage dividing ratio of the resistor R2 and the resistor R3 is about 0.29. Therefore, the maximum voltage of the output voltage waveform Vout2 limited to a substantially constant voltage. The value is about 23.8V as shown.

  In the surge voltage protection circuit 2, when a surge voltage is input, the voltage is limited to the output voltage corresponding to the voltage dividing ratio of the Zener voltage Vzd1 of the Zener diode ZD1 and the resistors R2 and R3, but the Zener diode ZD1 The voltage Vzd1 needs to be higher than a voltage value obtained by multiplying the output voltage output from the power supply output terminal OUT at the normal time by the voltage dividing ratio of the resistors R2 and R3. However, if the Zener voltage Vzd1 is increased too much, the output voltage that is limited is also increased, which may adversely affect an electronic device that is a load connected to the power supply output terminal OUT. Therefore, it is preferable to determine the Zener voltage Vzd1 in consideration of these.

  The output voltage waveform Vout1 shown in comparison with FIG. 3 is a waveform of the output voltage output from the conventional surge voltage protection circuit, and the surge voltage is limited. This output voltage waveform Vout1 is generated by the surge voltage (JASO-D001-94 5.7 A-1 type) in the conventional surge voltage protection circuit 101 shown in FIG. 7 which embodies the conventional surge voltage protection circuit 100 shown in FIG. The simulation result of the output voltage waveform output from the power supply output terminal OUT when applied to the input terminal IN. In the conventional surge voltage protection circuit 101 shown in FIG. 7, the resistor R100 is about 15Ω, the Zener voltage of the ZD100 is about 22V, and the capacitor C101 and about 0.1 μF between the power output terminal OUT and the ground. A capacitor C102 of 0.01 μF is connected in parallel. Further, a resistor RL having a load of about 200Ω is connected between the power output terminal OUT and the ground. In this case, since the Zener voltage of the ZD 100 is about 22V, the maximum voltage value of the output voltage waveform Vout1 is limited to about 22V as illustrated.

Next, when a surge voltage (JASO-D001-94 5.7 A-1 type) is applied to the power input terminal IN, the simulation result of the current waveform I2 flowing through the surge voltage protection circuit 2 shown in FIG. FIG. 4 shows a comparison with the simulation result of the current waveform I1 flowing in the conventional surge voltage protection circuit 101 shown in FIG. The current waveform I2 and the current waveform I1 are waveforms of current flowing from the power supply input terminal IN toward the power supply output terminal OUT.
Referring to FIG. 4, when the surge voltage indicated as Vin in FIG. 3 is applied to the power input terminal IN of the conventional surge voltage protection circuit 101 shown in FIG. 7, the current waveform I1 flowing from the power input terminal IN is the surge voltage ( The peak current of about 3.2 A is reached after about 0.1 seconds in synchronism with Vin), and then decreases and returns to the normal current after about 0.3 seconds. Since the maximum current obtained by subtracting the normal current from the peak current flows in the ZD 100, the ZD 100 needs to use a Zener diode having a large allowable current of about 3.2 A or more which is the peak current. Further, since a power of about 150 W is consumed momentarily when the peak current flows in the resistor R100, it is necessary to use a resistor having a large allowable power that can withstand this power consumption.

  On the other hand, referring to FIG. 4, when the surge voltage shown as Vin in FIG. 3 is applied to the power input terminal IN of the surge voltage protection circuit 2 according to the present invention shown in FIG. 2, the current flows to the power input terminal IN. The current waveform I2 slowly rises in synchronization with the surge voltage (Vin) and becomes almost constant, but the rising current becomes a slight current of several tens of mA and returns to the normal current after about 0.45 seconds. . Thus, even if a surge voltage is applied, the increase in the current waveform I2 becomes a small amount of current, and therefore, ZD1 can use a Zener diode having a small allowable current. In addition, since there is no element that consumes a large amount of power even when a surge voltage is applied, it is not necessary to use an element with a large allowable power.

Next, FIG. 5 shows a circuit configuration of a surge voltage protection circuit 3 according to another embodiment of the present invention.
A surge voltage protection circuit 3 according to another embodiment of the present invention shown in FIG. 5 is the same as the surge voltage protection circuit 1 shown in FIG. 1, except that TR1 is omitted and the cathode of the Zener diode ZD1 is directly connected to the other end of the resistor R1. ing. Further, the voltage dividing circuit of the resistors R2 and R3 is also omitted. In the surge voltage protection circuit 3 of another embodiment configured as described above, a low-pass filter whose time constant is determined by the resistor R1 and the capacitor C1 is configured, and a ripple component is removed from the voltage across the capacitor C1. Will come to be. For this reason, an output voltage from which the ripple component is removed is output from the power supply output terminal OUT.

  When a normal voltage is input to the power input terminal IN, the normal voltage is lower than the zener voltage Vzd1 of the zener diode ZD1, so that no current flows through the zener diode ZD1, and the surge voltage protection circuit 3 It operates as a ripple rejection circuit. Here, when a surge voltage is applied to the power input terminal IN and the input voltage at the power input terminal IN exceeds the Zener voltage Vzd1 of the Zener diode ZD1, a current flows through the Zener diode ZD1, and the base voltage of the TR2 Is fixed at the zener voltage Vzd1. Accordingly, the emitter voltage of TR2 is fixed at a voltage obtained by adding the base-emitter voltage Vbe (about 0.7 V) of TR2 to the Zener voltage Vzd1. Since the emitter of TR2 is connected to the base of TR3, the emitter voltage of TR3 is fixed at a voltage obtained by adding the base-emitter voltage Vbe (about 0.7 V) of TR1 to the emitter voltage of TR2. As a result, even if a surge voltage is applied, the output voltage output from the power supply output terminal OUT is equal to the Zener voltage Vzd1, the TR2 base-emitter voltage Vbe (about 0.7V) and the TR1 base-emitter voltage Vbe ( The voltage is limited to the sum of about 0.7V).

  When a surge voltage is input to the surge voltage protection circuit 3, the output voltage waveform is substantially the same as Vout2 shown in FIG. 3, and the flowing current waveform is substantially the same as I2 shown in FIG. Note that the Zener voltage Vzd1 of the Zener diode ZD1 needs to be higher than the output voltage output from the power supply output terminal OUT at the normal time. However, if the Zener voltage Vzd1 is increased too much, the output voltage that is limited is also increased, which may adversely affect an electronic device that is a load connected to the power supply output terminal OUT. Therefore, it is preferable to determine the Zener voltage Vzd1 in consideration of these.

Since the surge voltage protection circuit according to the present invention described above can greatly reduce the current flowing through the circuit even when a surge voltage is applied, the circuit components can be reduced in size and the cost can be reduced. Further, since the surge voltage protection circuit according to the present invention also serves as a ripple removal circuit, the ripple component can also be removed.
The transistors constituting the surge protection circuit according to the present invention are not limited to the NPN type, but may be a PNP type, and the transistor may be a unipolar transistor. Note that a Darlington-connected transistor can be replaced with a single transistor.
Furthermore, the value of the circuit element in the surge protection circuit according to the present invention described above is an example, and the present invention is not limited to this. Note that the Zener voltage Vzd1 of the Zener diode ZD1 needs to be higher than the voltage obtained by multiplying the output voltage output from the power supply output terminal OUT at the normal time by the voltage dividing ratio of the resistors R2 and R3.

1 Surge voltage protection circuit, 2 Surge voltage protection circuit, 3 Surge voltage protection circuit, 100 Surge voltage protection circuit, 101 Surge voltage protection circuit, 200 Ripple elimination circuit, C1, C2, C3 capacitor, TR1, TR2, TR3 transistor, R1 , R2, R3 resistance, ZD1 Zener diode, C101, C102 capacitor, TR201, TR202 transistor, R100, R201 resistance, ZD100 Zener diode, RL resistance

Claims (2)

A series circuit in which a first resistor and a capacitor are connected in series and connected between a power input terminal and ground;
A Zener diode having a cathode connected to a connection point between the first resistor and the capacitor, and an anode grounded;
A transistor having a collector connected to the power input terminal, an emitter connected to the power output terminal, and a connection point of the first resistor and the capacitor connected to a base;
A surge voltage protection circuit comprising: A first series circuit in which a first resistor and a capacitor are connected in series and connected between a power input terminal and ground;
A second series circuit in which a second resistor and a third resistor are connected in series and connected between the power supply output terminal and the ground;
A collector is connected to a connection point between the first resistor and the capacitor, a cathode of a Zener diode whose anode is grounded is connected to an emitter, and a connection point between the second resistor and the third resistor is connected to a base. A first transistor,
A second transistor having a collector connected to the power input terminal, an emitter connected to the power output terminal, and a connection point between the first resistor and the capacitor connected to a base;
A surge voltage protection circuit comprising:

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