DE3310242A1 - Circuit arrangement for surge-voltage protection, with an automatic reset - Google Patents

Abstract

The invention relates to a circuit arrangement for automatic resetting of a surge-voltage protection device once it has tripped and is characterised in that a two-pole network, assuming two resistance values, is connected in parallel with the surge-voltage protection device, which two-pole network has such a low resistance after triggering of the surge-voltage protection device that the current through the latter falls below the value of its short-circuit latching current so that the surge-voltage protection device is extinguished, and in that, subsequently, the two-pole network is changed back to its high-resistance state. As a result of this uncomplicated arrangement, which just has to be connected in parallel in a simple manner, the blocking of a surge-voltage protection device is automatically cancelled, as a result of which long failures of unmanned stations, especially after thunderstorms and switching processes can be avoided.

Description

AEG-TELEFUNKEN ■ Κ1 E7 / call / sch

Nachrichtenentechnik GmbH BK 82/67

Gerberstrasse 33

D-7150 Backnang

Circuit arrangement for overvoltage protection with automatic reset

The invention relates to a circuit arrangement for overvoltage protection with automatic reset according to the preamble of claim 1.

Overvoltage protection circuits are usually blocked after the overvoltage protection has been triggered and are then blocked reset to the operating state by switching off and then on again.

Such manually reset overvoltage protection devices require the use of personnel, even if they are occupied Stations is annoying. Unoccupied stations can be out of service for a very long time, for example after a thunderstorm, High-current or high-voltage switching operations, etc., without a real device defect being present.

DE-PS 25 69 260 provides a protective device that automatically switches off and on again for a power supply device

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became known that switches off when an overcurrent occurs and automatically switches on again after such a short time that the temporary malfunction as such hardly occurs is registered. This protective device contains a set of reed contacts near the air gap of a charging choke, whose In the event of an overcurrent, the increased magnetic field can influence the reed contact set connected in series with the charging throttle in such a way that that he opens.

The object of the present invention was to provide an inexpensive one Circuit arrangement for the overvoltage protection with automatic reset of the above type with purely electronic Specify switching means that are connected in a simple manner to the overvoltage protection device or to the terminals of the supply voltage will.

The solution takes place with those specified in the characterizing part of the main claim Means.

The circuit arrangement according to the invention has the advantages that it automatically blocks the in an inexpensive manner Overvoltage protection cancels the same again after it has been triggered, purely electronic switching means being used and this additional device is connected in a simple manner in parallel to the overvoltage protection device. the The overvoltage protection device is reset after a fixed, adjustable time, the dimensioning of which is based on, for example the mean duration of the overvoltage peaks. In principle, this time can even be set very short, which has the consequence that short voltage dips are almost done are not perceived and that in the case of a longer overvoltage period, a second blockage after the first reset has taken place followed by a second reset or, if necessary, several times until the overvoltage peak is finished. Optimal configurations result from the subclaims.

■ - ·, -, -pi O

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The invention will now be described with reference to the figure. The figure shows the circuit diagram for an embodiment of the Invention. A thyristor Th of a power supply device can be seen on the right. the operating voltage at its output terminals U. is present 'and to which the left-side extending two-pole is connected. The three capacitors Cl, C2 and C3 are charged to approximately the operating voltage U. via decoupling rectifier sections Gr2, Gr3 and Gr5, respectively. It is a first electronic switch (TsD, a field effect transistor recognizable, at its gate via a resistor R2 and a third electronic switch Ts2, the positive pole of the second capacitor C2, whose negative pole can be switched on Can be connected to the positive pole of the first capacitor Cl via a fourth electronic switch Ts3, and the negative pole of the first capacitor C1 is connected to the source terminal of the field effect transistor Ts1. The first electronic Switch Ts1 is located with its drain and source connections' parallel to the plus or minus pole of the operating voltage U .. The minus poles of the three capacitors C1, C2 and C3 are common at the negative pole of the operating voltage U., while the positive pole of the capacitors are each decoupled from the positive pole of the operating voltage U. The third ■ electronic switch Ts2 is over at its base a voltage divider R3, R4 connected between the positive poles of the first two capacitors C1 and C2 is switched on, controllable. The fourth electronic switch Ts3 is on his Basis also via a voltage divider R7> R9, which between the positive pole of the first capacitor C1 and the collector of the second electronic switch Ts5 is controllable. A discharge resistor RIl is located parallel to the third rectifier Gr5. The emitter of the second electronic capacitor C3, and its base is via a voltage divider R8, RIO, which is connected between the positive pole of the first capacitor C1 and the common negative pole is controllable. The positive pole of the third capacitor C3 is across a resistor R12 and a fifth electronic switch Ts4 with the common

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Negative pole connectable, with the base of the latter having a. Voltage divider R5, R6, which is between the collector of the fourth electronic switch Ts3 (is at the same time on the negative pole of the second capacitor C2) and the common negative pole is connected, can be controlled.

The circuit works as follows:

If the operating voltage U. is established, the capacitors are charged C1 to C3 to a voltage value of almost U, and all transistors are blocked. In the event of overvoltage the thyristor Th of the power supply ignited, and the output voltage U. breaks very quickly to the forward voltage of the Thyristor of about 1 volt together. While the first two capacitors C1 and C2 continue to store the output voltage the third capacitor C3 discharges through the resistor R11. If now the voltage of the third capacitor C3 to a Value of the voltage applied to resistor R10 reduced by the base-emitter voltage of the second electronic switch Ts5 has dropped, the latter begins to become conductive. The second electronic switch Ts5 the fourth electronic switch Ts3 is activated, which in turn controls the fifth electronic switch Ts4 to be conductive. The third capacitor C3 is quickly discharged through the latter, which causes feedback when the transistors become conductive Ts3, Ts4 and Ts5 result. After the fourth electronic switch Ts3 becomes conductive, the third electronic switch Ts2 conductive, its collector potential is then approximately the sum of the charging voltages of the first and second capacitor, that's about two times U ..

This voltage doubling of the control pulse for the first electronic switch Ts1 is necessary even at a low output voltage of, for example, 5 volts to have a gate control voltage of about 10 volts available for the power MOS-FET Ts1, so that this field effect transistor can be controlled completely conductive. The duration of the control pulse of the

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the latter is mainly determined by the values of the second capacitor C2 and the resistor R3. The conductive transistor Ts1 has a forward voltage U _DS which is lower than the forward voltage of the thyristor Th, so that the thyristor is almost de-energized and thus extinguished. When the second capacitor C2 is now discharged, the third electronic switch Ts2 and thus also the first Ts1 are blocked. This removes the short circuit and the output voltage can be set again, provided that there is no longer any overvoltage. If the overvoltage is still present, the overvoltage protection thyristor ignites again and is extinguished again after a certain time, which depends on the value of the third capacitor C3 and that of the resistor RIl, as described above. If necessary, further such extinctions and ignitions can follow periodically.

Of course, the circuit arrangement according to the invention is not limited to the exemplary embodiment of the figure. 20th

Claims (1)

Claims 1.! Circuit arrangement for the overvoltage protection with automatic resetting or blocking of the overvoltage protection device after ignition or triggering of the overvoltage protection device, characterized in that a two-pole connection is connected in parallel to the overvoltage protection device, which can assume two states assumes a high-resistance state and which becomes so low-resistance after the overvoltage protection device has been ignited that the current through the overvoltage protection device falls below the value of its short-circuit holding current, so that the overvoltage protection device is extinguished and the two-terminal device is then returned to its high-resistance state. Circuit arrangement according to Claim 1, characterized in that the overvoltage protection element is a thyristor. - 2 - BK 82/67 3- Circuit arrangement according to Claim 1 or 2, characterized in that the overvoltage protection element is contained in a power supply device. 4. Circuit arrangement according to one of the preceding claims, characterized in that the two-pole contains a memory for the operating voltage in the nominal value range, that a comparator is also provided for comparing the current operating voltage values with the stored value, that a first electronic switch (Ts1) is provided , which short-circuits the two two-pole terminals (+, -) when the operating voltage (U _A ) falls below the nominal value threshold, and that a first timer is provided which cancels the short circuit again after a certain time. 5. Circuit arrangement according to claim 4, characterized in that the memory contains first, second and third capacitors (C1, C2 and C3) which are charged by the operating voltage via decoupling first, second and third diode sections (Gr 2, 3 and 5) . 6. Circuit arrangement according to claim 5, characterized in that a discharge resistor (R 11) is connected in parallel with the third decoupling diode path (Gr 3). 25th 7- Circuit arrangement according to claim 4 or 5, characterized in that the comparator contains a second electronic switch (Ts 5) which, after falling below the charging voltage of the third capacitor (C 3), is below one derived from the charging voltage of the first capacitor (C 1) Value becomes conductive and controls the first electronic switch (Ts 1) conductive. - 3 - BK 82/67 8. Circuit arrangement according to claim 7, characterized in that the voltage value is derived from the charging voltage of the first capacitor (C1) by means of a voltage divider (R8 / R1O) and is, for example, approximately half the nominal voltage. 9. Circuit arrangement according to one of the preceding claims, characterized in that the first timing element is an RC element made up of a second capacitor (C2) and a discharge resistor (R3), the charging voltage of which is a third electronic switch (Ts2) via a fourth electronic switch (Ts3 ) controlled, which latter is controlled conductive by the second electronic, conductive switch (Ts5). 10.Schaltung arrangement according to claim 9, characterized in that a fifth electronic switch (Ts4) is provided which is controlled to be conductive by the conductive fourth electronic switch (Ts3) and which via a further discharge resistor (R 12) the third capacitor (C3) discharges quickly.