DE2743636A1 - Circuit preventing wrong poling of DC load - has polarised and bistable relay winding in series with capacitor across input terminals - Google Patents

Abstract

The protection circuit prevents a load, e.g. a teleprinter, being incorrectly poled on connection to a d.c. supply. A polarised and bistable relay (K) is connected with its coil in series with a capacitor (C) across the d.c. supply poles (1, 2). The relay's contacts (k) are connected in series with one pole and the load (R) and are shunted by a diode (V). The contacts are only closed if the load, i.e. the protection circuit plus load, has been connected with the correct polarity to the supply.

Description

Circuit arrangement for the protection of electrical

Consumers against reverse polarity of the DC operating voltage The invention relates to a circuit arrangement for protecting electrical loads against Incorrect polarity of the DC operating voltage, with one in the consumer circuit Contact can be switched on by a relay winding which can be connected to the mains terminals.

Circuits are known in which protection against polarity reversal is achieved by a diode in series with the device to be protected. However, this measure leads to higher power devices and low operating voltages to a power loss that is no longer acceptable.

So the losses in a converter power supply for almost double a teleprinter that runs on a 24-volt battery.

There is also already known a circuit in which in parallel with the A switch is located in series diodes, which is connected to the mains terminals via a Relay is closed. However, to ensure that this relay is only correct Polarity of the mains terminals responds, there are additional measures, for example another parallel diode to the relay winding is provided. It also consumes too the relay winding during operation is small but still noticeable Power dissipation.

The object of the invention is to provide a circuit arrangement of the initially mentioned To improve the type mentioned so that a protection against reverse polarity is guaranteed without any power loss occurring during operation. According to the invention this object is achieved in that a bistable and polarized relay is used and is connected in series to the input terminals with a capacitor in such a way that that the contact is only closed if the polarity of the operating voltage is correct.

The circuit arrangement according to the invention achieves that when applying the operating voltage to the input terminals of the capacitor via the Relay winding is charged. If the voltage is polarized correctly, it switches bistable relay in the position in which the device circuit has the contact is closed. Thereafter, there is no power in the relay during the entire operation consumed. When the operating voltage is switched off, the capacitor discharges, and the relay switches to the other stable position, so that the protection against reverse polarity is also given the next time it is switched on. That way you will be safer Reverse polarity protection with extremely little effort and above all without power loss reached during operation.

To the contact in the consumer circuit, a Diode be connected in parallel so that the Consumer at right Polarity of the operating voltage can be switched on via the diode. The diode takes over in this case the inrush current. This means that devices with a large capacitance can also be used Input resistor must be connected, and the contact will with this inrush current not burdened. The contact of the bistable takes over the continuous operating current in any case polarized relay.

The series connection of relay winding and capacitor can be done directly are on the mains terminals. If a series diode is provided, this can be connected in series also be connected behind the diode in parallel to the consumer.

Two exemplary embodiments of the invention are illustrated below the drawing explained in more detail.

1 shows a circuit arrangement with directly at the input terminals lying relay circuit, Fig. 2 shows a modification of Fig.1 with one in series relay circuit connected to a diode.

The Fig.l shows a circuit arrangement with a consumer R, which can be connected to the DC operating voltage via terminals 1 and 2. In the consumer circuit there is a contact k, which can be switched on by a bistable polarized relay K.

This relay K is connected in series with a capacitor C directly to the Input terminals. As soon as the mains terminals 1 and 2 are connected to a DC operating voltage the capacitor C charges through the relay winding. Is the tension if the polarity is correct, the relay K switches to the position in which the contact k is closed. The operating voltage is thus switched on to the consumer R. The protective circuit of the relay K does not consume any further power loss during operation.

When the operating voltage is switched off, the capacitor discharges C via the relay K and switches this to the other position so that the contact k is opened. This protects against reverse polarity even when the device is switched on again guaranteed again.

A diode V can be provided parallel to the contact k, which at Correct polarity of the DC operating voltage immediately flows current to the consumer leaves and thus takes over the inrush current. This diode V is then through the Contact k bridged.

FIG. 2 shows a modification of FIG. Here is in any case a diode V is provided in the consumer circuit.

The series connection of relay K and capacitor C is in this Fall behind the diode V, i.e. parallel to the consumer R.

When the DC operating voltage is switched on, it only flows when the voltage is correct Polarity of the current through the diode V to the consumer R and to the capacitor C through the winding of relay K. This closes contact k and bridges diode V.

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Claims (4)

Claims: Circuit arrangement for protecting electrical consumers against incorrect polarity of the DC operating voltage, with one in the consumer circuit Horizontal contact can be switched on by a relay winding that can be connected to the mains terminals is that a bistable and polarized one Relay (K) used and connected to the input terminals with a capacitor (C) in series (1,2) is switched on, that the contact (k) only with correct polarity of the operating voltage is closed. 2. Circuit arrangement according to claim 1, characterized in that to the contact (k) a diode (V) is connected in parallel in such a way that the consumer (R) can be switched on via the diode (V) if the polarity of the operating voltage is correct. 3. Circuit arrangement according to claim 2, characterized in that the series connection of relay winding (K) and capacitor (C) behind the diode (V) is parallel to the consumer (R). 4. Circuit arrangement according to claim 1 or 2, characterized in that that the series connection of relay winding (K) and capacitor (C) parallel to the Mains terminals (1,2) is switched.