WO2005029671A1

WO2005029671A1 - Electronic circuit for provision of a supply voltage for an electronic user

Info

Publication number: WO2005029671A1
Application number: PCT/DE2004/002032
Authority: WO
Inventors: Werner Bumen; Christian Gern; Gerhard Haaga
Original assignee: Robert Bosch Gmbh
Priority date: 2003-09-16
Filing date: 2004-09-09
Publication date: 2005-03-31
Also published as: DE10342719A1

Abstract

The invention relates to an electronic circuit, for provision of a supply voltage for an electronic user. According to the invention, the supply voltage can be generated from both a voltage (Vex) applied externally to the electronic circuit, as well as from an internal voltage source (120), provided within said electronic circuit, whereby a series circuit arranged in parallel with the internal voltage source, comprising a diode (D1) and an impedance device (R1) with one end thereof connected to the cathode of the first diode (D1), is provided. The plus pole (+Vex) of the external voltage source is connected to the cathode of the first diode (D1) and the minus pole (0V) of the external voltage source is connected to the minus pole of the internal voltage source. The supply voltage is tapped from the impedance device and generated from the external voltage source when the external voltage is greater than the internal voltage generated from the internal voltage plus the through voltage of the first diode.

Description

Electronic circuit for providing a supply voltage for an electronic consumer

State of the art

The invention relates to an electronic circuit for providing a supply voltage for an electronic consumer, in particular a current measuring circuit of a current clamp. In addition, the invention relates to a current clamp with such an electronic circuit.

Current clamp meters are basically known in the prior art. They are used to detect, in particular, the size or the amount of a current flowing through an electrical conductor. For this purpose, they typically comprise a current measuring circuit with a Hall element for detecting a magnet lde induced by the current flowing through the conductor, the strength of which is proportional to the strength of the flowing current sought.

Various types of clamp meters are currently on the market. In particular, current clamps for Muitimeter or handheld devices are typically with their own internal voltage source in the form of a battery or an accumulator equipped to provide a suitable supply voltage for the current measuring circuit. In addition, wire-bound current clamps for stationary devices, such as the MOT 250 motor diagnostic device from Robert Bosch GmbH, are available on the market. These line-bound current clamps do not usually have their own internal voltage source, but instead are supplied with a supply voltage for their current measuring circuits from an external voltage source in the stationary device.

Although these two types of current clamps basically serve the same purpose and function in the same way, they are not compatible with one another due to their different intended supply voltage. The operator of a workshop, which will be in both handheld devices and stationary devices used with current clamps is therefore disadvantageously been forced ^'to buy for each device each associated clamp meter with. There are sometimes several current clamps in a workshop, which is an unnecessary cost factor.

Starting from this prior art, it is therefore the object of the invention to provide an electronic circuit which provides a suitable supply voltage for an electronic consumer, regardless of whether the electronic circuit itself is supplied from an external or an internal voltage source.

This object is achieved by the subject-matter claimed in claim 1. Accordingly, the electronic circuit according to the invention is characterized by an internal voltage source for providing an internal voltage; a series circuit connected in parallel with the internal voltage source, comprising at least a first diode, an impedance device connected at one end to the cathode of the first diode, and a first electrical connection for connecting the other end of the impedance device to the negative pole of the internal voltage source; a second electrical connection between the positive pole of an optionally connectable external voltage source and the cathode of the first diode, the external voltage provided by the external voltage source between its positive pole and negative pole being greater than the internal voltage plus the forward voltage of the first diode; and a third electrical connection between the negative pole of the external voltage source and the first electrical connection, the supply voltage for the consumer being available for tapping via the impedance device.

Advantages of the invention

A prerequisite for the proper functioning of the claimed electronic circuit is that, as also described in the claim, the external voltage is greater than the internal voltage plus the forward voltage from the first diode. If so, the claimed electronic circuit advantageously automatically recognizes whether the external voltage is present or not. If he determines that the external voltage is present, then he uses only this and not the existing internal voltage source to provide the supply voltage for the consumer. On the other hand, if it detects that no external voltage source is connected to it, it generates the Supply voltage for the consumer from the internal voltage. The claimed electronic circuit simultaneously ensures that the external and internal voltage sources are decoupled from one another and do not influence one another when both voltage sources are connected.

According to an advantageous embodiment of the electronic circuit, the series circuit has an electronic switching device. This enables at

Battery operation, i.e. when the supply voltage is provided from the internal voltage source and not from the external voltage source, an optional switching on and off of the internal voltage source and thus the supply voltage for the consumer.

Advantageously, the claimed electronic circuit can either be for connecting a two-pole external voltage source with plus and minus potential or for connecting a three-pole external

Voltage source must be designed with plus, gauze and minus potential. If the electronic circuit is designed to connect a two-pole external voltage source, it is advantageous if its second and / or third electrical connection is designed as a protective diode to prevent current flow from the cathode of the first diode to the positive pole of the external voltage source. There is a risk that such a current flow will occur in particular if, for example, an external voltage is accidentally connected to the electronic circuit which is less than the internal voltage plus the forward voltage of the first diode.

In the event that when only one two-pole external voltage source to the electronic circuit of the consumer must still be supplied with a three-pole symmetrical supply voltage, it is recommended to install a suitable circuit element parallel to the impedance device to generate a negative potential of the supply voltage for the consumer. ^:

The specific design of the electronic switching trip in the event that it is designed to connect a three-pole external supply voltage is the subject of one of the subclaims.

The above-mentioned object of the invention is finally also achieved by a current clamp for measuring the current flowing through an electrical conductor with the electronic circuit claimed above. The advantages of this clamp meter essentially correspond to the advantages mentioned above with regard to the electronic circuit. In addition, the

Current clamps, however, have the advantage of universal availability. This means that, thanks to the built-in electronic circuit, it can be operated independently, that is, independently of an external voltage source, but also connected to one.

For workshops which work both with handheld devices and with stationary devices, this has the advantage that the current clamp meter according to the invention can be used equally without hesitation for connection to both types of device. So you no longer need different ones

Current clamps with individual suitability for one of the devices. This results in cost savings on the user side. Simultaneously, the current clamps according to the invention follows from the universal availability, the ability to manufacture and ^■ Set of higher numbers of universal electricity essays compared to several different versions.

A total of four figures are attached to the description

drawings

1 shows a first exemplary embodiment of the electronic circuit according to the invention;

FIG. 2 shows a second exemplary embodiment of the electronic circuit according to the invention;

FIG. 3 shows a third exemplary embodiment of the electronic circuit according to the invention;

Figure 4 is a current clamp according to the invention; and

Figure 5 shows a fourth exemplary embodiment of the electronic circuit according to the invention.

shows .

Description of the exemplary embodiments

The invention is described in detail below using various exemplary embodiments with reference to FIGS. 1 to 5.

FIG. 1 shows a first exemplary embodiment of the electronic circuit 100 according to the invention. This is used to provide a supply voltage V +, 0V for an electronic consumer 200. The electronic circuit 100 has an internal voltage source 120 to provide an internal equilibrium voltage 0 _5c The internal voltage source 120 is typically a battery or a ^ k '- ^ um _^ lator. A series circuit is connected in parallel with the internal voltage source 120, which in the first exemplary embodiment shown in FIG. 1 shows a first diode Di, an impedance device m-shaped with one end connected to the cathode of the first diode D1, in the form of the resistor R1, and a first electrical connection L1 to connect the other end of the impedance device R1 with the

Has negative pole of the internal voltage source 120. In the first exemplary embodiment, the first electrical connection L1 is designed as a normal electrical line. The plus pole + Vex of an external voltage source (not shown here) is connected to the cathode of the first diode D1 via a second electrical connection L2. A third electrical connection L3 connects the mirror pole OVe ^ of the external voltage source to the first electrical connection L1 and to the other end of the impedance device R1. The supply voltage V ⁴ -, 0V can then be tapped via the impedance device R1.

The mode of operation of the electronic circuit shown in FIG. 1 is explained in more detail below

As long as no external voltage source is connected to the electronic circuit and therefore no external voltage U = is available, the supply voltage V- ¹ -, 0V is provided for the user 200 from the internal voltage source 120. The first

Diode Dl is then switched in the forward direction and the supply voltage is tapped via the impedance Rl. Such operation is also referred to below as battery operation. After all, an external voltage source with the positive pole + Vex and the negative pole OV is connected to the electronic circuit 100 via the second and third connections L2, L3, as shown in FIG. 1, and the voltage provided by the external voltage source is greater than the internal voltage U _3a t plus the forward voltage of the first diode D1, this connection is automatically recognized by the electronic circuit and it provides the supply voltage V +, 0V for the consumer 200 from this external voltage. The diode D1 serves as a detection element. In the case described last, it prevents a negative current from flowing through the internal voltage source 120 and the latter being discharged. Due to the diode Dl, the internal voltage source 120 and the external

The voltage source, although connected to the electronic circuit at the same time, is decoupled from one another, so that they would not have a negative effect, for example, in the form of a discharge of the internal voltage source 120.

FIG. 2 shows a second exemplary embodiment of the electronic circuit shown in FIG. 1. In both figures, the same components are provided with the same reference symbols; the way it works is basically the same.

However, for example in FIG. 2 a electronic switching device S is provided between the positive pole of the internal voltage source 120 and the anode of the first diode D1. This switching device enables in

Battery operation advantageously switching the internal voltage source on and off by the consumer 200. On the other hand, if the supply voltage is generated from the external voltage, then the switching device S has no function. To connect _< a two-pole external voltage source with a positive pole + Vex and a negative pole OV and a provided external voltage U _e; , _: which is smaller than the sum of the internal voltage U _Ba - and the

Forward voltage of the first diode is to prevent an undesired current flow from the cathode of the first diode Dl to the positive pole + Vex of the external voltage source, the second and / or the third electrical connection L2, L3 is advantageously designed as a protective diode Ds.

If the second electrical connection L2 is designed as a protective diode Ds, the anode of this diode Ds must be connected to the positive pole + Vex of the external voltage source. If, as an alternative or in addition, the third electrical connection L3 is designed as a protective diode, not shown in FIG. 2, the cathode of these protective diodes must be connected to the negative pole of the external voltage source.

In contrast to the exemplary embodiment shown in FIG. 1, the consumer 200 needs a three-pole

Supply voltage comprising a plus potential V +, 0V and V-, the still missing negative potential V- of the supply voltage for the consumer can be generated by providing a switching element 130 connected in parallel with the resistor R1.

All modifications of the electronic circuit according to the invention shown in FIG. 2 and just described, that is to say in particular the switching element S, the protective diodes Ds and the circuit element 130, can be provided individually in the electronic circuit 100 independently of one another or in any combination with one another. If the consumer requires a symmetrical supply voltage V +, OV, V- ₍ for its operation, it is advisable not to use a two-pole electronic circuit, as shown in FIGS. 1 and 2, but, as shown in FIG. 3, with a The impedance device in the embodiment shown in Figure 3 is designed as a series connection of two resistors R1 and R2, and at the same time the first electrical connection L1 is in the form of a second diode D2, which has its cathode connected to the negative pole of the internal voltage source 120. The third connection L3 now connects the negative pole -Vex, that is the negative pole of the external voltage source to the anode of the diode D2, and the entire supply voltage between the positive pole V + and the negative pole V- is now connected in series via Rl and R2 tapped A center tap M between the preferably equally sized W. The resistors R1 and R2 are used via a driver device 140 connected to them to provide a zero potential OV for the three-pole symmetrical supply voltage. This gauze potential is connected to the zero potential of the external voltage source and then overall represents the zero potential of the electronic circuit.

A lamp 150 is advantageously connected in parallel with the impedance devices R1 and R2, which basically lights up when the electronic circuit is in operation; this applies regardless of whether the supply voltage V +, 0V, V- from the internal

Voltage source 120 or is generated by the external voltage source. FIG. 4 shows a preferred application for the electronic circuit 100 according to the invention in the form of a current clamp 300. This is used to measure an electrical current flowing through an electrical conductor 400. This flowing current induces a magnetic field in the measuring clamp 300, which is detected by a Hall element and evaluated by a current measuring circuit. The registered in ^'this way, the magnetic field strength is a measure of the strength of the current flowing through the conductor 400 electric current. Said current measuring circuit is a consumer 200 in the sense of the present invention. If only a positive or only a negative current is to be measured with this current measuring circuit, it is sufficient if the current measuring circuit is only supplied with a two-pole supply voltage V +, 0V or 0V, V-. If, on the other hand, both current and negative current components are to be measured with this current measuring circuit, the current measuring circuit requires a symmetrical supply voltage V +, 0V, V-. In any case, the current measuring circuit 200 generates an output measuring voltage U _üu t, as is indicated in FIG. 1, which represents the amount of the current flowing through the conductor 400. In its standard version, the current clamp meter 300 according to the invention includes the electronic circuit 100 according to the invention a cable 310 and a six-pin connector 320, via which it can be connected to an external voltage source. In addition to three connections for the external voltage source + Vex, 0V, -Vex, the six-pole connector plug 320 comprises two pins for outputting the measurement signal U _u - and a coding pin which outputs an information signal with which measurement unit the measurement signal is to be interpreted. The latter depends on the type of clamp meter used depending on whether it is designed for the detection of currents up to 20 A or for the detection of currents up to 1000 A.

On the other hand, if the current clamp meter according to the invention is not to be operated on a stationary device with an external voltage source, but on a mobile multimeter or on a handheld device, an adapter 322 which can be plugged onto the six-pole plug 320 is provided for this purpose, which in addition to the two pins for the

_Measuring signal U _0u t _isolates all other pins of the six-pole plug and only provides the two pins for outputting the measuring signal via two banana plugs 32 for insertion into the multimeter or handheld device.

Figure 5 shows a fourth embodiment of the electronic circuit according to the invention. It aims at the problem of a gauze adjustment of the measurement signal U _0u t provided by the current clamp 300. In addition, it should be noted that the current clamp 300 typically has an internal device 310 for realizing a zero adjustment of the measurement signal U _0u t in order to have effects internal to the current clamp, such as temperature - or to prevent aging effects which cause an undesirable voltage offset in the measurement signal Uo _u t which is superimposed on the measurement signal and falsifies it.

When the current clamp is operated via the external voltage source + Vex, OVex, -Vex, however, the cable 310, which is generally several meters long, forms an additional one

Source for such unwanted offset voltages. Such an undesired offset voltage arises when a current flows through this cable 310, as a result of which a voltage drop in the form of the undesired offset drops across this cable 310. Depending on the cable used and Size of the flowing current, this offset can be a few millivolts.

The fourth exemplary embodiment shown in FIG. 5 shows a solution of how this undesirable voltage drop across the cable 310 can be avoided. The fourth embodiment is essentially based on the first embodiment shown in FIG. 1; Identical electronic components are identified by the same reference symbols. In contrast to FIG. 1, however, FIG. 5 clearly illustrates the operation of the current clamp meter via the external voltage source (not shown) with the potentials + Vext, -Vext, preferably built into a motor test device 500. In addition, the motor test device 400 receives the measured current I representing output voltage Uou in order to process it electronically and. display to a user. It can be seen that this output voltage U _0u t is _measured against the mass of the current _clamp , that is to say against the potential of the neutral conductor L3.

In the case of an asymmetrical voltage supply, as is provided in the first and second exemplary embodiments of the electronic circuit according to the invention shown in FIGS. 1 and 2, the supply voltage + Vex, 0V provided by the external voltage source would result in a current flow l _h -2, I 3 through the Effect conductor L2 via current measuring circuit 200 and conductor L3, 310 back into the external voltage source or motor test device 500. This supply current I _b3 would, however, on the long usually several meters connection line L3, 310 several between the current measurement circuit 200 to the taps for the output voltage Uout and the measurement input AB of the engine test apparatus 500 has a not insignificant voltage drop of typically Effect millivolts. This voltage drop or this offset voltage would undesirably overlap at the measuring input AB of the motor test device 500 with the output voltage U _0u t representing the actual measured variable and in this way lead to incorrect measurement results. In other words, even if the output voltage U _0u t was adjusted to 0 V with the aid of an internal clamp device 350, there would be a voltage drop not equal to 0 V at the measurement input AB of the motor test device 400 in the amount of the voltage drop across the connecting line L3.

In order to prevent such an undesirable voltage drop, it is proposed according to the invention to make the current through the conductor L3 zero when the current clamp is supplied via the external voltage source. According to the invention, as illustrated in FIG. 5, this is achieved by providing a line L4 between the connection for the negative potential -Vex of the voltage source and the ground conductor L3, a suitably dimensioned balancing resistor being built into this line L4. The

The symmetry resistor R _sym is to be dimensioned such that it represents the total resistance as it results without taking the symmetry resistance into account when moving from the external voltage source into the. the connected circuit is looked into. For the circuit shown in FIG. 1, the balancing resistor R-sm would have to be dimensioned such that it represents the parallel connection from the resistor Rl and the impedance of the current measuring circuit 200. The circuit arrangement shown in FIG. 5 then ensures that the same amount of current flows via the external feed lines L2 and L4 and that none flows via the gauze conductor L3, 310 Supply current flows. No undesired offset voltage can then drop across the conductor L3.

Finally, it should be noted that in all exemplary embodiments of the electronic circuit according to the invention, the diode D1 can also be implemented electronically, for example with the aid of a field effect transistor.

Claims

Expectations

1. Electronic circuit (100) for providing a supply voltage (V +, OV, V-) for an electronic consumer (2.00), in particular a current measuring circuit of a current clamp (300); characterized by: an internal voltage source (120) for providing an internal voltage (Ußat); a series circuit connected in parallel with the internal voltage source (120) comprising at least a first diode (Dl), an impedance device (Rl, Rl, + R2) connected at one end to the cathode of the first diode (Dl) and a first electrical connection ( Ll) for connecting the other end of the impedance device (R1) to the negative pole of the internal voltage source (120);

a second electrical connection (L2) between the positive pole (+ Vex) of an optionally connectable external voltage source and the cathode of the first diode (Dl), the external voltage (UV _.; ) provided by the external voltage source between its positive and negative pole being greater than the internal voltage {plus plus the forward voltage from the first diode (Dl) must be; and

a third electrical connection (L3) between the negative pole (OVex, -Vex) of the external voltage sources (U _e:. _:) and the first electrical connection (Ll); the supply voltage (V +, OV, V-) for the consumer (110) across the impedance device (Rl, Rl, + R2) is ready for tapping.

2. Electronic circuit (100) according to claim 1, characterized in that the series circuit further comprises an electronic switching device (S) for switching the internal voltage source (120) on and off.

3. Electronic circuit (100) according to claim 1 or 2, characterized in that the second and / or the third electrical connection (L2, L3) are at least substantially designed as a protective diode (Ds) for preventing a current flow from the cathode the first

Diode (Dl) to the positive pole (+ Vex) of the external voltage source.

4. Electronic circuit (100) according to any one of the preceding claims, characterized by a circuit element (130) connected in parallel with the first impedance device (R1) for generating a negative potential (V-) for the supply voltage.

5. Electronic circuit (100) according to claim 1 or 2, characterized in that

the impedance device (Rl + R2) has a series connection of two preferably equally large opposites (Rl, P.2); the first electrical connection (Ll) at least t im

It is essentially designed as a second diode (D2), which has its cathode connected to the negative pole of the internal 13

Voltage source (120) and with its anode connected to the impedance device (R1 + R2) and the third electrical connection; a driver device (140) is provided between a center tap (M) between the two resistors (R1, R2) and ground potential; and the gauze potential of the external supply voltage source (0V) is conductively connected to the ground potential.

6. A current clamp (300) for measuring the electrical current flowing through an electrical conductor (400), comprising:

a current measuring circuit (200) for detecting the amount of the flowing current by evaluating a magnetic field induced by the current in the current clamp, preferably with the aid of a Hall probe;

marked by

the electronic circuit (100) according to one of claims 1 to 5 for providing a supply voltage (V +, 0V, V-) for the current measuring circuit (200) as an electrical consumer.