GB1584510A - Switching arrangement - Google Patents

Abstract

A circuit arrangement (T1, T2, R1-R6) for producing a pulse (terminal m0) for setting the electronics of an electronic apparatus when said apparatus is connected to the supply voltage (VUG) for the first time or when, after a failure of the supply voltage (VUG), said supply voltage does not return until the voltage of a battery (B), which is operated in the buffering mode and is used for supplying standby power to the electronics via a DC/DC converter (DC), falls below a predetermined value. <IMAGE>

Description

(54) A SWITCHING ARRANGEMENT (71) We, SIEMENS AKTIENGESELLSCHAFT, a German company, of Berlin and Munich, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a switching arrangement for producing a pulse for setting the electronics of an electronic device when a supply voltage is first applied to the device or when the supply voltage returns after failure and the output voltage of a stand-by electricity storage device which has been bridging the failure has dropped below a pre determined value.

It is known that with electronic devices after a failure of the supply voltage and on the return of the same - as at the first application of the supply voltage -- the electronic switching circuits can occupy a random position. On the return of the supply voltage therefore information can result which is arbitrary and therefore false. Since the failure of the supply voltage is usually very limited in time, it is usually sufficient for the period of time if a battery takes over the power supply of the electronics. Since it is desirable to manage with the smallest possible battery for the longest possible time, all larger current-consuming devices should be disconnected as far as possible, when the voltage failure occurs and only the information stored in the electronics should be kept.

So, for example, in an electronic maximum mechanism or meter in the case of a failure of the supply voltage the device is practically shut-down and limits itself to the maintaining of the information stored in the individual switching circuits. To be able to manage with the smallest possible battery a single-celled battery may be used and the voltage of the battery transformed with the help of a DC/DC-transformer to a level which is sufficient for the supply of the electronic switching circuits.

It can happen that, after a fairly lengthy failure of the supply voltage, by discharging the battery the voltage supply via the DC/DC-transformer is no longer absolutely guaranteed and this can result in false information. In this case a pulse is to be generated on the return of the voltage supply, by which pulse the electronics of the device are brought into a defined starting position. However, no such pulse is to be produced if a short-term failure of the supply voltage is bridged safely by the battery.

According to the invention there is provided a switching arrangement for product ing a pulse for setting the electronics of an electronic device when a supply voltage is first applied to the device or when the supply voltage returns after failure and the output voltage of a stand-by electricity storage device which has been bridging the failure has dropped below a predetermined value, the arrangement comprising a bistable switch- ing circuit which is to be acted upon by said supply voltage and said output voltage and which is arranged to occupy one condition when, during a supply voltage failure or on restoration of supply voltage the voltage acting upon it falls below or exceeds a first threshold value which is lower than the normal output voltage of the stand-by electricity storage device and is equal to said predetermined value, and to occupy another condition when the voltage acting upon it rises above a second threshold value which is higher than the normal output voltage of the stand-by electricity storage device, the bistable switching circuit having an output which is at a first potential while the bistable switching circuit occupies said one condition, and which is connected to pulse producing circuitry arranged to produce a pulse when the bistable switching circuit changes over from said one condition to said other condition.

Preferably, the switching arrangement may generate a pulse only under very definite conditions. For example, a pulse must be generated also when a battery has been put into the device before the first appliance of the supply voltage whether the battery is empty or fully charged, the pulse being generated when the supply voltage exceeds the second threshold value.

For a better understanding of the invention and to show how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawing in which: Figure 1 shows one embodiment of a switching arrangement according to the invention; and Figure 2 shows a voltage diagram.

The power supply of an electronic device which in the case under consideration is supposed to be, by way of example, an electronic maximum mechanism or meter comes in the usual way from an a.c. power supply via a transformer Tr and a rectifier Gl via leads L1 and L2. The lead L1 is at zero potential and lead L2 is connected via a decoupling diode D2 to a terminal VUG. Normally the voltage VUG led directly from the mains voltage amounts to 12 volts. C1 indicates a smoothing condensor.

A battery B contributes to the emergency power supply which is loaded via a resistor RO and de-coupling diode- D1 via parts of a DC/DC direct-voltage converter DC. The direct-voltage converter DC then supplies the voltage VDD for the emergency power supply via a lead L3. The lead L3 is also connected to the lead L2 via a decoupling diode D3 so that in the presence of the supply voltage the voltage VD,D also amounts to 12 volts as does the voltage VUG. However, should the supply voltage fail, the voltage VDD coming from the DC/DC-direct-voltage converter normally amounts to 5--6 volts, corresponding to the state of charge of battery B.

A switching arrangement 0 is acted-on by the voltage VUD. It consists basically of an asymmetrical bistable switching circuit consisting of two transistors T1 and T2 as well as resistors R1 to R6. Output A of the bistable switching circuit is on the one hand connected via a diode D4 connected in the inverse direction to the output mO of the switching arrangement and on the other hand via a resistor R8 and a condensor C2 to the lead L1 carrying the zero potential. The connecting point between resistor R8 and condensor C2 is joined to the base of a transistor T3 which is connected with its collector to output mO and with its emitter to the lead L1. The output mO is furthermore connected to voltage VUG via a resistor R7.

The resistors R1 and R4 are estimated so that the asymmetrically designed bistable switching circuit occupies a preferred position at the first application of the supply voltage VDD, provided it passes the threshold of 3.5V (VDDU in Figure 2), in such a way as to block the transistor T1 and make transistor T2 conductive, as long as the voltage VDD does not exceed a threshold of

In practiceVDDO is approximately 8 volts. When the voltage VDD exceeds the upper control threshold VDDO of the bistable switching circuit 0, the transistor T1 becomes conductive and the transistor T2 blocked.By putting the bistable switching circuit into its second stable position, the output A previously kept at zero-potential is raised to the potential VDD so that the output mO is released via the diode D4. There is then a voltage Vve applied to the output mO via the resistor R7 until the condensor C2 has been charged via the resistor R8 so far that the transistor T3 becomes conductive. In this case the output signal goes back to zero, since zero potential is then connected to the output mO. Through appropriate dimensioning of the RC-component R8 and C2, an output signal mO limited in time as desired can be produced.

This condition of the bistable switching circuit 0 is retained as long as the voltage VDD does not fall below a lower control threshold

In practice VDDU is approximately 3.5 volts. This lower control resolution can only be reached if the mains voltage fails and the battery has been heavily discharged. When VDD, is fallen below, the preferred condition of the bistable switching circuit is regained. Should the battery voltage fall substantially below VDDU, the bistable switching circuit could occupy an indefinite condition. In such a state the return of the supply voltage or the insertion of a fully charged battery will regain the preferred condition of the bistable switching circuit by VD.D rising above VDDIT.

A reloading of a charged battery into the device cannot produce a pulse at the output mO because the upper control resolution of 8 volts is not reached in this manner as is shown in Figure 2. As was previously explained, the voltage Vlg, which is general ted from the battery via the DC/DC-convertor amounts to approximately 5-6 volts.

If VD.D1 is not fallen below, the preferred condition of the bistable switching circuit will be regained only when the supply voltage, exceeding VDvO, is restored.

The circuitry operates with a very small current.

WHAT WE CLAIM IS:- 1. A switching arrangement for producing a pulse for setting the electronics of an electronic device when a supply voltage is first applied to the device or when the supply voltage returns after failure and the output voltage of a stand-by electricity storage device which has been bridging the failure has dropped below a predetermined value, the arrangement comprising a bistable switching circuit which is to be acted upon by said supply voltage and said output voltage and which is arranged to occupy one condition when, during a supply voltage failure or on restoration of supply voltage, the voltage acting upon it falls below or exceeds a first threshold value which is lower than the normal output voltage of the stand-by electricity storage device and is equal to said predetermined value, and to occupy another condition when the voltage acting upon it rises above a second threshold value which is higher than the normal output voltage of the stand-by electricity storage device, the bistable switching circuit having an output which is at a first potential while the bistable switching circuit occupies said one condition, and which is connected to pulse producing circuitry arranged to produce a pulse vrhen the bistable switching circuit changes over from said one condition to said other condition.

2. An arrangement according to claim 1, wherein said pulse producing circuitry has an output connected to the output of the bistable switching circuit, which former output is connected via a transistor to a member at said first potential, the base of said transistor being coupled to a capacitor which, when the bistable switching circuit changes over from said one condition to said other condition, initially allows the output of the pulse producing circuitry to receive a pulse of second potential, this pulse ending when the capacitor has changed to render the transistor conductive and connect the output of the pulse producing circuitry to said member.

3. An arrangement according to claim 1 or 2, wherein said first potential is zero potential and said second potential is a positive potential.

4. An arrangement according to claims 2 and 3 combined, wherein the output of the bistable switching circuitry is connected to the output of the pulse producing circuitry via a diode.

5. An arrangement according to claim 4 or claims 2 and 3 combined, wherein said capacitor is connected between the base of said transistor and said member, and said base is connected to the output of the bistable switching circuit via a resistor.

6. An arrangement according to any one of the preceding claims, wherein the output of the pulse producing circuitry is arranged to receive said supply voltage.

7. An arrangement according to any one of the preceding claims, wherein the bistable switching circuit is an asymmetrical bistable switching circuit.

8. An arrangement according to any one of the preceding claims, wherein said stand-by electricity storage device comprises a DC/DC transformer.

9. A switching arrangement substantially as hereinbefore described with reference to Figure 1 of the accompanying drawing.

10. An arrangement according to any one of the preceding claims, when an electric cell or battery is inserted in said stand-by electricity storage device.

11. An arrangement according to any one of the preceding claims, when connected to an electronic device and a supply voltage therefor.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. as is shown in Figure 2. As was previously explained, the voltage Vlg, which is general ted from the battery via the DC/DC-convertor amounts to approximately 5-6 volts. If VD.D1 is not fallen below, the preferred condition of the bistable switching circuit will be regained only when the supply voltage, exceeding VDvO, is restored. The circuitry operates with a very small current. WHAT WE CLAIM IS:-

1. A switching arrangement for producing a pulse for setting the electronics of an electronic device when a supply voltage is first applied to the device or when the supply voltage returns after failure and the output voltage of a stand-by electricity storage device which has been bridging the failure has dropped below a predetermined value, the arrangement comprising a bistable switching circuit which is to be acted upon by said supply voltage and said output voltage and which is arranged to occupy one condition when, during a supply voltage failure or on restoration of supply voltage, the voltage acting upon it falls below or exceeds a first threshold value which is lower than the normal output voltage of the stand-by electricity storage device and is equal to said predetermined value, and to occupy another condition when the voltage acting upon it rises above a second threshold value which is higher than the normal output voltage of the stand-by electricity storage device, the bistable switching circuit having an output which is at a first potential while the bistable switching circuit occupies said one condition, and which is connected to pulse producing circuitry arranged to produce a pulse vrhen the bistable switching circuit changes over from said one condition to said other condition.

2. An arrangement according to claim 1, wherein said pulse producing circuitry has an output connected to the output of the bistable switching circuit, which former output is connected via a transistor to a member at said first potential, the base of said transistor being coupled to a capacitor which, when the bistable switching circuit changes over from said one condition to said other condition, initially allows the output of the pulse producing circuitry to receive a pulse of second potential, this pulse ending when the capacitor has changed to render the transistor conductive and connect the output of the pulse producing circuitry to said member.

3. An arrangement according to claim 1 or 2, wherein said first potential is zero potential and said second potential is a positive potential.

4. An arrangement according to claims 2 and 3 combined, wherein the output of the bistable switching circuitry is connected to the output of the pulse producing circuitry via a diode.

5. An arrangement according to claim 4 or claims 2 and 3 combined, wherein said capacitor is connected between the base of said transistor and said member, and said base is connected to the output of the bistable switching circuit via a resistor.

6. An arrangement according to any one of the preceding claims, wherein the output of the pulse producing circuitry is arranged to receive said supply voltage.

7. An arrangement according to any one of the preceding claims, wherein the bistable switching circuit is an asymmetrical bistable switching circuit.

8. An arrangement according to any one of the preceding claims, wherein said stand-by electricity storage device comprises a DC/DC transformer.

9. A switching arrangement substantially as hereinbefore described with reference to Figure 1 of the accompanying drawing.

10. An arrangement according to any one of the preceding claims, when an electric cell or battery is inserted in said stand-by electricity storage device.

11. An arrangement according to any one of the preceding claims, when connected to an electronic device and a supply voltage therefor.