KR19980040228A - Transient protection circuit - Google Patents

Abstract

The present invention relates to a transient voltage protection circuit for effectively blocking or mitigating a suddenly generated DC input voltage such as lightning and static electricity.

The protection circuit includes a coaxial cable, a first and a second diode having a cathode end and an anode end respectively connected in parallel to the coaxial cable, and the cathode end connected to an anode end of a first diode connected to the coaxial cable to charge a transient voltage. A first capacitor for supplying an output voltage of the second capacitor, the second diode and the second capacitor to charge the transient voltage by connecting the anode terminal in parallel to the output terminal of the cathode terminal of the second diode connected to the coaxial cable And a voltage rectifier IC supplying the set constant voltage to the home appliance.

Description

Transient protection circuit

1 is a conventional transient voltage protection circuit diagram,

2 is a transient voltage protection circuit diagram according to the present invention,

3 is a waveform diagram according to an embodiment of FIG.

4 is a reference diagram for describing an exemplary embodiment of FIG. 2.

* Explanation of symbols for main parts of the drawings

10: coaxial cable, 20: constant voltage rectifier IC, 30: internal circuit, D1, D2: diode, C1-C2: capacitor, R1: resistor

The present invention relates to a transient voltage protection circuit, and more particularly, to a transient voltage protection circuit that can safely protect an internal circuit of an electronic product by blocking or mitigating an accidental transient voltage such as a lightning strike.

In general, the LNB for satellite broadcasting reception installed outdoors is provided with a device for protecting an internal electronic circuit from a transient voltage caused by lightning static electricity.

1 is a conventional transient voltage protection circuit diagram. Referring to FIG. 1, the conventional transient voltage protection circuit diagram is connected to the output terminal of the coaxial cable 1 in parallel with the transient voltage protection element 2, and the constant voltage generator 3 connected in series with the coaxial cable 1 is connected. It supplies a certain level of direct current (mostly 9V). The constant voltage generator is mainly used as a constant voltage rectifier IC.

If high voltage flows from the coaxial cable 1 due to lightning or static electricity, the whole sub rectifier IC is destroyed, so that the transient voltage protection device is placed in front of the voltage rectifier IC to block the transient voltage below a certain power. In this device, two zener diodes are connected in opposite directions.

However, in the conventional circuit, when a transient voltage greater than the breakdown voltage of the zener diodes in which the transient protection ICs are connected in opposite directions is input, the zener diode is turned on to cut off the overcurrent delivered to the voltage rectifier IC. However, the power that a zener diode can handle in semiconductor technology is limited, and in order to withstand transient voltages of more than 1.5KV, the size of a semiconductor IC must be very large, resulting in high manufacturing cost and practicality. In general, increasing the maximum allowable power of a zener diode requires increasing its size. SUMMARY OF THE INVENTION The present invention is directed to a circuit arrangement that can effectively cut off transient voltages of at least 2000 volts with a combination of several commonly used rectifier diodes and electrolytic capacitors.

It is an object of the present invention to provide a transient voltage protection circuit capable of blocking or mitigating a transient voltage of at least 2000 volts by using a rectifier diode, an electrolytic capacitor, and a resistor, which are generally widely used.

In order to achieve the above object, the present invention provides a power input means, first and second diodes having a cathode and an anode connected to the power input means in parallel, and a cathode of the first diode connected to the power input means. A first capacitor connected to an anode terminal for charging the transient voltage, a second capacitor connected to the output terminal of the cathode terminal of the second diode connected to the power input means in parallel to charge the transient voltage, and the second capacitor And a voltage rectifying means for receiving the output voltage of the diode and the second capacitor and supplying a predetermined constant voltage to the internal circuit.

Hereinafter, with reference to the accompanying drawings will be described in detail the configuration, operation and effects of the present invention.

2 is a transient voltage protection circuit diagram according to the present invention.

Referring to FIG. 2, the transient voltage protection circuit according to the present invention includes two diodes D1 and D2 connected in parallel to the coaxial cable 10 for inputting power, and the cathode ends of the coaxial cable 10. A capacitor C1 connected to the anode terminal of the diode D1 connected to the resistor, a resistor R1 connected in parallel to the capacitor C1, and an output terminal of the cathode terminal of the diode D2 connected to the coaxial cable 10 with the anode terminal connected to the coaxial cable 10. An internal circuit diagram of receiving a set level of direct current from a constant voltage rectifier IC 20 commonly connected to a capacitor C2, a diode D2, and a capacitor C2 connected in parallel.

Operation of the transient voltage protection circuit of the present invention having the configuration as described above in the normal state in which the transient voltage is not applied is as follows.

DC power is supplied from the coaxial cable 10, usually a voltage of + 12- + 18V. Since this voltage is a positive polarity, diode D1 is always off, so that capacitor C1 and resistor R have no effect, while diode D2 is on and the input of constant voltage rectifying IC 20 is turned on. The DC power supplied from A is transferred to terminal B. The constant voltage rectifier IC 20 receives the supply voltage and outputs the voltage at a constant level to supply the internal circuit 30, and usually has a voltage value between 7-9V. (For example, 8V output IC will always output 8V.)

Current from A to B through C is usually 80-150μA. On the other hand, there are two cases where transient voltage is applied. First, when a coaxial cable 10 enters the A terminal from a transient voltage having a positive polarity, the diode D1 is turned off and the diode D2 is turned on. The input terminal B of the constant voltage rectifying IC 20 is turned on. Due to the effect of the connected electrolytic capacitor C2 (usually about 470 μF is appropriate), the voltage at B gradually increases with time as in the third degree.

That is, as shown in FIG. 3A, even when the transient input voltage rises momentarily to a peak value of 2 KV or more within a short time, the voltage at the input terminal B of the constant voltage current IC 20 is equal to that of the capacitor C2. because the charging time is also 4 to gradually rise as shown in the curve (B) is transmitted to only the relatively low voltage of about V _ICmax. At this time, if the product of the driving current of the constant voltage rectifying IC 20 and V _ICmax , that is, the power is within the maximum power rating of the constant voltage rectifying IC 20, the constant voltage rectifying IC 20 is not destroyed and maintains a normal operating state. The main _factor determining V _ICmax is directly related to the capacitance value of capacitor C2 since the voltage rising rate, that is, charging time, is shown in the curve of FIG.

In FIG. 4, if the switch is turned on at t = 0, the voltage across the capacitor C becomes Vc = V [1-exp (-t / RC)], where (t is the time) the source resistance Rs and the capacitor ( It can be seen that the capacitance value of C) is a factor influencing the slope of voltage rise.

In the present invention, the source resistor Rs may be viewed as an equivalent resistance when viewed from the B terminal toward the coaxial cable 10 and the constant voltage rectifying IC 20, and the capacitor C corresponds to the capacitor C2. The resistance (R) is usually about tens of ohms, and in this case, the capacitor (C2) satisfies the transient voltage condition applied to a communication device having a 160 μsec, 1.5KV peak value using a capacitance value of about 470 μF. Proven through

After the voltage at point B reaches V _ICmax , the transient voltage charged in the capacitor C2 gradually discharges and falls.

In addition, when a transient voltage having a negative polarity is input, the diode D1 is turned on and the diode D2 is turned off, so that the transient voltage is charged in the capacitor C1.

That is, since the transient voltage is charged in the capacitor C1 and is not transmitted to the constant voltage rectifying IC 20 and the internal circuit 30 at all, the constant voltage rectifying IC 20 and the internal circuit 30 are automatically protected and the input transient voltage is increased. After reaching the peak, the capacitor C1 discharges again toward the parallel resistor R1.

Even in this case, the maximum voltage applied to the capacitor C1 can be adjusted by appropriately adjusting the capacitance value of the capacitor C1. The larger the capacitance value of the capacitor C1, as in the case of a positive transient voltage, the more the capacitor C1 is applied to the capacitor C1. As the rising speed of the applied voltage is delayed, the maximum voltage value becomes small. The value of the capacitor C1 is set so that the maximum voltage is lower than the maximum rated voltage of the electrolytic capacitor C1 (typically about 20-30V).

According to the present invention as described above, it is possible to prevent the destruction of the internal electronic circuit due to a sudden increase in the DC input voltage in the event of lightning or static electricity, and much higher voltage than the transient voltage cut off in the conventional protection circuit ( 2KV or more) can be blocked, as well as improve the reliability and safety of the product to which the present invention is applied, and has the advantage that can be implemented at a low price.

Claims (2)

Power input means, the first and second diodes in which a cathode terminal and an anode terminal are connected in parallel to the power input means, respectively, the cathode terminal is connected to the anode terminal of the first diode connected to the power input means for charging a transient voltage A first capacitor, the anode terminal is connected in parallel to the output terminal of the cathode terminal of the second diode connected to the power input means to provide an output voltage of the second capacitor, the second diode and the second capacitor for charging the transient voltage And a voltage rectifying means for supplying a predetermined constant voltage to an internal circuit. 2. The transient voltage protection circuit according to claim 1, wherein a discharge path of the second capacitor is formed by connecting a resistor in parallel with the first capacitor.