DE3402222A1 - Circuit arrangement for limiting overvoltages - Google Patents

Abstract

In order to limit overvoltages on an apparatus having two power supply lines, a controllable switch is provided in one of the two power supply lines, and a comparator, whose output is connected to the control input of the controllable switch, whose first input is connected via a constant voltage source to the output of the controllable switch, and whose second input is connected to the other power supply line. In the event of overvoltages, the switch which is controlled by the comparator isolates the connected apparatus from the operating voltage. If the controllable switch is constructed as a transistor, the switching-on current surge in the event of a high capacitive load resulting from the connected apparatus can additionally be reduced by means of a capacitor, via the control junction of said transistor.

Description

Licentia Patent-Verwaltungs-GmbH PTL-UL / Sar / lh Theodor-Stern-Kai 1 UL 83 / I7I

D-6000 Frankfurt 70 description Circuit arrangement gum limiting overvoltages

The invention relates to a circuit arrangement for limiting overvoltages on a device with two power supply lines.

The operating voltage of direct current on-board networks are sometimes superimposed with voltage peaks in the μβ and ms range. This can lead to the destruction of components of an ange closed device and thus to failure of the device to lead. While stress peaks in the ps range with Zenor or Transzorb diodes can be cut off, are at voltage peaks in the ms range because of their high performance large-volume voltage limiters or thyristor short NO contact required. However, this has because of the high

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Leakage current has the disadvantage that the input fuse is frequently triggered and this results in undesirable interruptions in operation enter.

Another solution to avoid the destruction of the connected device is to remove the device components to be dimensioned for the maximum expected peak voltage, which leads to a considerable increase in the cost of the Device would lead.

The invention is based on the object of a circuit arrangement of the type mentioned to avoid the disadvantages of the prior art. In particular, should a simple and inexpensive solution has been given.

The object is achieved by the invention mentioned in claim 1. By having a controllable switch the voltage peaks are kept from the device, the device can be designed for the nominal operating voltage and thus does not require any expensive or bulky components. Business interruptions due to overvoltage peaks are definitely avoided. Claim 2 gives a simple feasible with bipolar transistors Solution for an advantageous comparator with which a transistor can be controlled as a controllable switch according to claim 3 in a simple manner. By means of a capacitor According to claim 4, a simple limitation of the inrush current can also be achieved.

The invention will now be illustrated with reference to in figures Embodiments explained in more detail. Show it in öinzelj? en:

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FIG. 1 basic circuit

FIG. 2 shows a first embodiment in bipolar technology

FIG. 3 shows a second exemplary embodiment with a MOS power transistor as a controllable switch.

In FIG. 1 is the basic circuit diagram of the circuit arrangement according to the invention for limiting overvoltages on a device with two power supply lines, which are shown in FIG. * labeled 1 and 2 are shown. The input terminals of the limiting circuit are marked with El and E2 and the output terminals with Al and A2. A controllable switch 3 is interposed in the power supply line 1 between the input terminal El and the output terminal A1. The line section thus lying between the input terminal E1 and the input 32 of the controllable switch 3 is denoted by 11. Furthermore, a comparator k is provided, the output 43 of which is connected to the control connection 31 of the controllable switch 3. Furthermore, its first input kl is connected to the output 33 of the controllable switch 3 via a constant voltage source 5 and its second input 42 to the other power supply line 2.

As soon as the voltage between the power supply lines 1 and 2 exceeds the voltage of the constant voltage source 5, the comparator k emits a signal which opens the switch 3. In order to have a voltage-free output voltage at the terminals Al and A2 for the duration of the overvoltages, a capacitor C2 must be connected between the output terminals Al and A2, which, however, is in the

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Usually connected to the output terminals A1 and A2 Device (consumer) is provided.

In FIG. 2 shows a first exemplary embodiment of the circuit according to the invention. As can be seen, the comparator k is made up of two transistors T1 and T2 of different conductivity types, the base of the transistor T1 being the one input kl and the emitter of the transistor T1 being the other input k2 dos {comparators. The collector of the first transistor Tl is connected to the base of the transistor T2 and the emitter of the transistor T2 is connected to the power supply line 11. The collector of the transistor T2 forms the output dot. {"Comparators and controls the controllable switch on its control electrode 31.

As a controllable switch is shown in FIG. 2 a further transistor T3 is provided, the base of which acts as a control electrode 31 to the collector of the second transistor T2 and via a resistor Rl to the power supply line 2 connected is. The emitter of transistor T3 is 4jer Input terminal El and thus also connected to the emitter of the second transistor T2.

A resistor is used as a constant voltage source R2 from the supply line 2 fed Zener diode Zl.

In normal operation, the operating voltage between the terminals El and E2 is below the Zener voltage of the diode Zl. If, however, the sum of the Zener voltage and the base-emitter voltage of the

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Transistor Tl exceeded, the transistor Tl and thus also the transistor T2 is controlled to be conductive. The collector-emitter voltage of the transistor T2 drops in the process below the base-emitter voltage of the transistor T3 which is necessary to keep it conductive. The transistor T3 is blocked and thus separates the output terminal Al from the input terminal El. One between the Output terminals A1 and A2 switched capacitor C2 of the connected device prevents an intermittent Switching the transistor T3.

In the case of high capacitance capacitors normally present at the output terminals A1 and A2, when the circuit shown in FIG. 2 shows a high solenoid current. In order to avoid this, a capacitor C1 is connected between the collector and emitter of the transistor T2. In connection with the resistor Rl, which, connected between the power supply line 2 and the base of the transistor T3, keeps the transistor T3 in the conductive state in Norsia! Operation, the base-emitter stroke of the transistor T3 is only longest when switched on? Opened according to the time constant V = C1 * R1, thereby limiting the inrush current.

In cases in which the output terminal Al from the input terminal El Should remain separate, the can in an advantageous manner Transistor T2 can be replaced by a thyristor or unijunction transistor.

Of course, instead of a single transistor T3 as a controllable switch also a combination of several transistors e.g. a Darlington pair are used.

FIG. 3 shows a further exemplary embodiment of the invention, which essentially corresponds to the exemplary embodiment in FIG. 2 similar The same circuit parts are provided with the same reference numerals. A MOS power transistor T3 is provided here as a controllable switch, the control path of which is advantageously protected by a Zener diode Z2. Furthermore, to limit the base currents of the transistors T1 and T2, resistors R3 and R4 are connected in the respective base line, which are intended to protect the said transistors. This resistance «? R3 and Rk can also be replaced by a single low-resistance resistor R5 in the emitter line of the transistor Tl. The figure also shows the equivalent circuit diagram of the device to be connected to the terminals A1 and A2 with a filter capacitor C .. and the current-consuming part, which is symbolized _{here by a resistor R v.}

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Claims (4)

Licentia Patent-Verwaltungs-GmbH PTL-ÜL / Sar / lh Theodor-Stern-Kai 1 UL 83 / I7I D-6OOO Frankfurt 70 Claims 1,1 Circuit arrangement for limiting overvoltages on a device with two power supply lines (1,2), characterized in that a controllable switch (3) t in the one power supply line (11,1) between is switched, and a comparator (4) are provided, ' its output (43) with the control connection (31) of the controllable switch (3) · its first input (4l) a constant voltage source (5) with the output (33) of the controllable switch (3) and its second input (42) is connected to the other power supply line (2). 2. Arrangement according to claim 1, characterized in that the comparator (4) is constructed from two transistors of different conductivity types, the base of the first transistor (Tl) of the one input (kl) and the - 2 - UL 83/171 The emitter of the first transistor (Tl) is the other input (42) of the comparator, the collector of the first transistor (Tl) with the base of the second transistor (T2) and the emitter of the second transistor with the one Power supply line (11) is connected, and the collector of the two-tone transistor (T2) is the output of the comparator is. 3. Arrangement according to claim 2, characterized in that the controllable switch «is in transistor (T3) whose Base as a control electrode with the collector of the second transistor (T2) and via a resistor (Rl) with the other power supply line (2) and its emitter are connected to the emitter of the second transistor (T2). 4. Arrangement according to claim 3 * characterized in that z / fish collector and emitter of the second transistor (T2) a capacitor (Cl) is connected.