JPS5829697B2 - electronic circuit protection device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a protection device for electronic circuits.

Conventional protection devices for electronic circuits include connecting diodes in series or parallel to the circuit as shown in Figure 4 A to C to protect against reverse voltage phenomena in the electronic circuit. Fuses or resistors were also inserted into these to protect against overcurrent.

In these methods, the power consumption of the diode is large compared to that of an electronic circuit.For example, the power supply voltage is 3V, whereas the voltage drop of the most commonly used silicon diode is 0.2 to 0. 8V, the efficiency of the power supply is poor, and the temperature characteristics of the diode are also poor, so depending on the usage conditions, the function of the electronic circuit may be impaired by the diode.

In addition, overcurrent protection measures using fuses can cause the fuse to melt and open the circuit if an abnormal overcurrent flows through the circuit.
It protects electronic circuits from overcurrents, but it takes some time for the fuse to blow after the overcurrent begins to flow, but the electronic circuits may be damaged during this time, and the circuits opened by the fuse may be damaged. Replacement of fuses must be carried out by humans, and in installations where it is difficult to reset, such as on light buoys, or in electronic circuits with extremely complex circuit configurations, it can be very tedious and time-consuming. At times, it was a difficult task that required a lot of effort.

Therefore, even if an abnormal phenomenon occurs in the circuit, such as overcurrent flowing, the circuit is automatically suppressed and protected until the abnormal phenomenon disappears, without interrupting the circuit. In addition, if a protective device were developed that could prevent reverse voltage phenomena, for example, even if a power supply battery is accidentally loaded with the polarity reversed, the circuit would not be damaged and the circuit voltage could always be maintained constant. This will lead to dramatic improvements in maintaining the functionality of electronic circuits and in maintenance work.

The present invention provides an electronic circuit protection device that achieves the above object.

The contents of the present invention will be explained in detail below with reference to the drawings.

Figures 1A and B show the principle configuration of the present invention, and Figures 2A and B
, C shows the characteristic curve of the FET which occupies the main part of the present invention,
3A and 3B show the structure of the present invention.

Further, as described above, FIGS. 4A to 4C show the circuit configuration of a conventional protection device, and FIGS. 5A and 5B show the circuit configuration and current waveform curve when an AC power source is used.

In the figure, 1 is a FET, 2 is an electronic circuit, 3゜31 is a diode, 4 is a constant voltage diode, 5゜5' is a resistor, 6
7 is a fuse, 7 is a DC power supply, 7' is an AC power supply, and 8 is a rectifier.

Now, FET1, its gate G and source S are shown in Figure 1A.
As shown in the figure, the voltage VG between the gate G and the source S is
When S is brought to zero potential and inserted into the power supply 7 and the circuit of the electronic circuit 2, the drain current D flowing between the drain D and the source S is as shown in Fig. 2 A and C. , is suppressed to a constant value determined by the characteristics of the FET 1, and remains constant even if the voltage VDS between the drain D and the source S increases.

Therefore, by selecting the FET 1 having characteristics suitable for the load current value flowing through the electronic circuit 2, the current in the electronic circuit can always be kept constant.

In addition, as shown in FIG. 1B, when the polarity of the power source 7 is opposite to that in case A, the gate G and drain D of FET 1 are short-circuited to bring the voltage VGD between the gate and drain to zero potential. If you insert this into the ←) circuit of power supply 7, F
The characteristics of ET1 are shown in Figure 2 B and C, and ■G
It is suppressed to a constant ■D current value that flows when D is O,
The circuit current is kept at a constant value.

The case in Figure 1B can be considered to be the case when an abnormal phenomenon occurs in case A or when a negative potential is applied when connected to an AC power supply, and the reverse current in this case flows into the electronic circuit 2. In order to prevent this, if the diode 3 is connected in parallel to the electronic circuit 2 as shown, the electronic circuit 2 can be more effectively protected.

In general, batteries are often used to power electronic circuits, and when loading these batteries, the polarity is often reversed and a reverse voltage is applied to the electronic circuit, damaging circuit elements. The circuit configuration shown in FIG. 1B is also extremely necessary for protecting electronic circuits.

Therefore, for the protection of electronic circuits, it is desirable to combine both formulas A and B in Figure 1 above into one, or simply combining them would short-circuit FET1 and provide no protective function. Not born.

The present invention solves this problem and provides a protection device that satisfies the above requirements.

As shown in FIG. 3A, the present invention connects the FETI in series to the side power supply circuit of the electronic circuit 2, and
A diode 3 is connected between the gate G and source S of 1 in such a state that the voltage VGS between the gate G and source S becomes zero potential.
On the other hand, when a reverse voltage is applied to the circuit between the gate G and drain D, the gate G and drain D are A diode 31 is connected between them, and if an overcurrent flows in the electronic circuit 2, VGS is kept at zero potential as described above, so the As shown by the D curve, ■■ when Gs=O, regardless of the rise in VDS.

is constant, so overcurrent is suppressed.

Even when a reverse voltage is applied, as shown in FIGS. 2B and 2C, the current does not flow beyond the ■D current value determined when ■GD is 0.

Furthermore, when the constant voltage diode 4 is connected in parallel to the electronic circuit 2 as shown in the figure, it prevents reverse current from flowing into the electronic circuit 2 and keeps it safe.

Since the constant voltage diode also has the effect of stabilizing the circuit voltage, the electronic circuit 2 also has the same effect as if it were equipped with a constant voltage power supply.

As described above, according to the present invention, abnormal phenomena such as overcurrent, reverse voltage, or overvoltage can be continuously and automatically dealt with without interrupting the circuit, suppressing the abnormal phenomena, and shutting down the electronic circuit. can be protected.

As shown in Figure 3B, if a resistor 5 is inserted between the source S of FET 1, the anode of diode 3, and the connection point of the electronic circuit, VGS can be changed to -1 or -2 in Figure 2C. Since it is possible to obtain drain current characteristics for potentials below the O potential of VGS as shown in the ■D curve shown, by selecting the value of resistor 5, FET1 can be an easily available FET, and resistor 5 can be By combining them, it is possible to match the circuit characteristics required by the electronic circuit 2, facilitating the selection of FETs, and having the effect of increasing economic efficiency.

In addition, a resistor 51 is also added to the drain circuit as shown in FIG. 3B.
By inserting , it is possible to suppress the circuit current value even with respect to reverse current.

Appropriate values for the resistors 5 and 51 may be selected in consideration of the circuit conditions and the mode of protection at the time of forward and reverse voltages.

FIG. 5A shows an example in which an AC power source 7' is used as the power source; in this case, it is preferable to connect a rectifier base to the output side of the protection device of the present invention.

The ID current in this case becomes an alternating current obtained by slicing the top of the alternating current waveform as shown by the solid line in FIG. 5B.

As described above, according to the present invention, when an abnormal phenomenon such as overcurrent, reverse voltage, or overvoltage occurs, it is possible to suppress it very naturally and protect the electronic circuit in a stable and safe state at all times. Moreover, since it does not interrupt the circuit like a fuse, there is no need to reset it.

Therefore, there is no need for maintenance and it can be used as a protection device for complex electronic circuits such as LSI.
It is possible to provide a protection device that is suitable as a protection device for a lighting circuit of a light buoy and has excellent features such as long life, stable performance, and high cost efficiency.

[Brief explanation of drawings]

1A and 1B are circuit diagrams of the principle of the present invention, and FIG. 2A is a circuit diagram of the principle of the present invention. B and C are characteristic diagrams of PET, FIGS. 3A and B are circuit diagrams showing the configuration of the present invention, and FIGS. 4A, B, and C are circuit diagrams of the conventional system. FIGS. 5A and 5B show a circuit diagram and a drain current curve of the protection device of the present invention using an AC power supply. 1 is FET, 2 is electronic circuit, 3 and 31 are diodes, 4
is a constant voltage diode, 5.5' is a resistor, and 7゜71 is a power supply.

Claims (1)

[Claims] 1. In an electronic circuit using a DC or AC power source,
A field effect transistor (hereinafter abbreviated as FET) is connected in series to an electronic circuit, and the gate of the FET is
An electronic circuit protection device configured by connecting diodes with forward directions between sources and between gates and drains. 2. The electronic circuit protection device according to claim 1, wherein a resistor is inserted and connected between the source terminal of the FET, the anode terminal of the diode, and the connection point of the electronic circuit. 3. The electronic circuit protection device according to claim 1, wherein a resistor is inserted and connected between the drain terminal of the FET, the anode terminal of the diode, and a power source.