WO2008090022A1

WO2008090022A1 - Circuit arrangement and method for detecting electrical quantities

Info

Publication number: WO2008090022A1
Application number: PCT/EP2008/050196
Authority: WO
Inventors: Thomas Rossmanith; Maximilian Schmidl
Original assignee: Osram Gesellschaft mit beschränkter Haftung
Priority date: 2007-01-22
Filing date: 2008-01-09
Publication date: 2008-07-31
Also published as: TW200839270A; DE102007003145A1

Abstract

The invention relates to a circuit arrangement and to a method for detecting electrical quantities by means of a measuring circuit for measuring voltages and flows. Said measuring circuit comprises a common measuring element wherein the voltage is input into an A/D-converter. Each branch of the measuring circuit comprises a switch element that is only switched on during the measuring time of each branch.

Description

description

Circuit arrangement and method for detecting electrical quantities.

Technical area

The invention relates to circuit arrangements for detecting one or more electrical variables. The invention preferably relates to circuit arrangements for detecting electrical operating variables in electronic control gear for lamps.

State of the art

Electronic control gear is used today for almost all types of bulbs. To mention here would be e.g. Operating equipment for low-voltage halogen lamps, for low-pressure discharge lamps and for high-pressure discharge lamps. Especially electronic control gear for high-pressure discharge lamps can be very complex and there are a variety of electrical variables to measure. Since these operating devices are usually controlled by a microcontroller today, this requires a variety of analog / digital converters (A / D converters) to measure the electrical variables. However, this causes high costs, since microcontrollers with several A / D converters are significantly more expensive than those with only one A / D converter.

In addition, the measuring circuits must be designed in such a way that a certain current flows, which the A / D converter needs to measure properly. This causes not negligible in each measuring circuit Losses that add up considerably with a larger number of measurement circuits.

task

The object of the invention is to improve these disadvantages of the known electronic control gear in order to produce this cheaper, and at the same time to cause less power dissipation in the electronic control gear.

Presentation of the invention

This is inventively achieved in that a micro- rocontroller with only one analog / digital converter, but a plurality of switching outputs or a control logic is used.

Typically, in prior art circuits, voltages are measured with a voltage divider where the voltage to be measured is scaled to an easy-to-handle level. The voltages to be measured in conventional electronic control gear are several tens to a few hundred volts. With operating devices that are operated with 230 Volt mains voltage, the voltage after the mains rectifier is eg 400V. Therefore, voltage dividers are designed to measure these voltages with a division ratio of 1: 100 so that the 400V is represented by a 4V voltage at the microcontroller input. The A / D converter needs an input current of about 0.3-0, 4mA in order to be able to measure correctly. The voltage divider must therefore be designed so that a current of 0.5 lmA flows continuously in order to operate the A / D converter. With a voltage of 400V to be measured, this then causes losses of approximately 200 to 40 ohms per voltage divider.

In order to be able to measure currents, a shunt is used, which is installed directly in the circuit to be measured. The voltage dropping across the shunt is measured, and with knowledge of the resistance value of the shunt, the current flowing there can be deduced.

If several voltages and currents have to be measured, several voltage dividers or shunts are provided, each of which has a tap which is connected in each case to an A / D converter of the microcontroller (FIG. 1).

This is where the invention starts. According to the invention, a switching element is provided in each voltage divider between the resistors, which can open and close the current path of the voltage divider. For measuring, the corresponding switching element is now closed, the measurement carried out and the switching element then opened again. This now happens one after the other with all quantities to be measured. When all values are measured, the cycle starts over. This allows a microcontroller with only one A / D converter can be used, which only needs as many switching outputs as electrical values must be measured.

Short description of the drawing (s)

Fig. 1 circuit arrangement for measuring electrical quantities according to the prior art Fig. 2 inventive circuit arrangement for measuring a voltage

Fig. 3 inventive circuit arrangement for measuring two voltages

4 shows inventive circuit arrangement for measuring a current

5 shows inventive circuit arrangement in which the switching transistor is operated in the linear range in order to measure a voltage.

Fig. 6 Circuit arrangement according to the invention, in which the track resistance of the switching transistor is used to measure a current.

7 shows inventive circuit arrangement in which two currents are measured with an A / D converter input.

Fig. 8 inventive circuit arrangement, in which also two currents can be measured, which is additionally designed as an energy-saving measuring arrangement.

9 shows inventive circuit arrangement in which voltages and currents can be measured with only one A / D converter input.

10 shows inventive circuit arrangement in which the switching element for voltage measurement consists of a MOSFET with driver circuit.

Fig. 11 inventive circuit arrangement in which two currents can be measured, which as energy-saving measuring arrangement is designed, and wherein only one (high-precision) measuring element is used.

Preferred embodiment of the invention

In Fig. 1, a circuit arrangement for measuring electrical quantities according to the prior art is shown. It consists of the voltage dividers 2a, 5a and 2b, 5b, which are switched from a potential to be measured to ground. Between the resistors in each case a voltage (8a, 8b) is tapped, which is entered into the microcontroller. It is then converted to a digital value and multiplied by the divider ratio to regain the original voltage. For each size to be measured, therefore, an A / D converter is required.

Fig. 2 shows a circuit arrangement according to the invention, in which only a voltage is measured. Between the two voltage divider resistors 2 and 5, a switch is inserted, which can switch the current path on and off. The voltage is measured directly at the lower measuring element 5, so that the voltage drop at the switching element is not included in the measurement. The switching element is closed only at the measuring time. As a result, the power loss of the measuring circuit is minimized.

The advantages of the measuring method according to the invention, however, come into their own only at several measuring points. Fig. 3 shows such a measuring circuit with 2 measuring points. The measuring voltage is tapped on the common measuring element 5. After that, the circuit then splits into two or more paths, each having a switching element (3a, 3b) and a measuring element (2a, 2b) connected in series therewith, which in turn is connected to the voltage to be measured. The switching elements are controlled by switching outputs (7a, 7b) from the microcontroller.

4 shows the basic circuit structure of a current measurement. Here, the switching element is connected in parallel to the measuring element 5. The voltage at the measuring element is again measured against ground and connected via a tap 8 to the A / D converter. Here the switch is open during the measurement period and closed during the normal operating time. This is illustrated by an inverter 9, which is arranged in the drive path of the switching element. Thus, the measuring element is bridged and can no longer produce any relevant power loss.

Finally, FIG. 5 shows a further simplification of a voltage measuring circuit in which the upper measuring element is replaced by a switching transistor. The transistor is not only operated here as a switch, but it is operated in the 'state' in the linear range, so that the track resistance of the transistor corresponds to the upper measuring element resistance. As a result, an internal measurement control can be created, so that the measurement gets compensation characteristic. Under certain circumstances, it may be necessary to use a driver circuit for controlling the transistors, in order to ensure that the drive voltage always remains high enough despite the voltage at the measuring element 5. FIG. 6, in turn, represents a current measurement without a separate measuring element. Here, in contrast to the voltage measurement, very low resistances are required, so that the track resistance of the transistor can be used as a measuring resistor in the fully turned-on state. This type of current measurement is mainly used when in the circuit in any case a switching transistor is provided, for example in the DC-DC converter or in the inverter. In such a case, of course, the current measurement must take place when the transistor is just turned on. This then requires an interaction between the control of the switching transistor and the measurement control.

For measuring a plurality of currents, a circuit as shown in FIG. 7 can be used. In this variant, the current always flows through the respective measuring element, and the voltage at the measuring element is switched to the A / D converter input only during the measurement. However, this circuit has the disadvantage that the power loss can not be reduced.

This requires a somewhat more complex circuit, as shown in Fig. 8. Here, in comparison to the circuit in FIG. 7, two further switching elements are arranged parallel to the measuring elements. These switching elements are again inverted driven, since they are open during the measurement and closed during normal operation. This significantly reduces the power loss during normal operation. The non-inverting switching elements in FIGS. 7 and 8 may possibly include a driver circuit, since the reference potential, the voltage across the sensing elements 2c or 2d, and the Switching potential, so the switching outputs 7c or 7d may be very close to each other under certain circumstances.

A circuit in which voltages and currents can be measured is shown in FIG. 9. Here voltages are measured on the rails Ia and Ib, while on the paths Ic and Id the current is measured. The only difference is that in the case of current measurement, the measuring element 5 is parallel to the current measuring elements 2c or 2d. However, since the resistance of the voltage measuring element 5 is at least ten times as large in the resistance as the resistance of the current measuring elements 2c or 2d, the element 5 does not fall into consideration in the current measurement. Normally, the measuring element 5 is larger by a factor of 1000 than the measuring elements 2c or 2d. Thus, the falsification of the measurement by the measuring element 5 is irrelevant. If, in a special case, the measuring element 8 nevertheless causes a falsification of the measurement which can not be neglected, then a switching element can also be arranged between the measuring element 5 and the A / D converter input 8 so that the measuring element 5 switches away during the current measurement.

Finally, Fig. 10 shows a circuit diagram of a preferred embodiment of the invention in which the switching element consists of a switching transistor, in this case a MOSFET with suitable driver circuit. Since the switching outputs of a microcontroller usually can only represent logic voltages against circuit ground, there is, as already mentioned, the problem that the switching voltage of the switching transistor can be too small, since the voltage at the measuring element 5 is also in the range of logic voltage. This problem is solved by another Switching transistor 10 is remedied, which is controlled via the microcontroller, and an existing in the circuit higher voltage, for example, 15V, on the gate of the actual sense transistor 3 switches to turn this safely. The resistance elements 11 and 12 are used only for the calibration of the power consumption and the on and off speed. The voltage divider resistor element 2 was an example here divided into two series-connected resistive elements 2 and 2 _al _a2 so as not to exceed the dielectric strength of the individual resistive elements in the measured high voltage.

FIG. 11 once again shows another variant of an energy-saving current measurement. In contrast to the measurement from FIG. 8, only one measuring element 2 is used here for the measurement. Again there is a switching element for each measuring path which is switched on in normal operation and a switching element which switches the measuring path to the measuring element 2 when a measurement is carried out. The two switching elements each have the complementary function, which is also indicated by the inverting function of switched on in normal operation switching elements. Again, the non-inverting switching elements may require a driver stage, as already explained for FIGS. 7-9.

Thus, the switches are closed one after the other and the assigned electrical values are measured. This method offers the advantage that only one A / D converter is required for several electrical quantities to be measured. The electrical quantities to be measured must relate only to a reference potential. In this case, the measurement can take place in a strict order, so that all measured values are obtained the same number of times, or an asymmetric measurement can also take place in which different cycle times can be realized for the measured values. For example, a timer can be activated for each measured variable, which initiates a new measurement at the end of the process. This has the advantage that the necessary measuring cycles can be technically optimally designed, and measured variables which are subject to a large temporal variation more frequently than sizes which change little.

For many variables to be measured, it may be more appropriate, instead of many switching outputs on the microcontroller, to use an output which outputs a coded digital signal representing the switching states of all the switching elements. An external device can in this case read in the signal and operate the switches according to the content of the signal.

Claims

claims

1. A circuit arrangement for detecting electrical quantities with a measuring circuit for measuring voltages or currents, characterized in that the measuring circuit has a common measuring element (5) whose voltage is input to an A / D converter, and the measuring circuit a plurality of branches (2a , 3a, 2b, 3b), each branch of the measuring circuit including a switching element (3a, 3b) which is switched over only during the measuring time of the respective branch.

2. Circuit arrangement for detecting electrical variables with a measuring circuit for measuring voltages or currents according to claim 1, characterized in that the circuit arrangement includes a microcontroller (4) or an integrated control component, wherein the microcontroller or the integrated control part an A / D Have converters per measurement circuit.

3. A circuit arrangement for detecting electrical quantities with a measuring circuit for measuring voltages or currents according to claim 2, characterized in that the microcontroller (4) or the integrated control component switching outputs (7a-d), the switching elements (3a-d) of Control the measuring circuit branches.

4. Circuitry for detecting electrical quantities with a measuring circuit for measuring voltages or currents according to claim 2, characterized in that the switching elements (3a-d) are integrated in the microcontroller or the integrated control component.

5. A circuit arrangement for detecting electrical quantities with a measuring circuit for measuring voltages or currents according to claim 2, characterized in that the microcontroller (4) or the integrated control component outputs coded signals which are decoded in a further building block and the switching elements of Measuring circuit due to the signal content on and off.

6. A method for operating a measuring circuit for detecting electrical quantities characterized by the following steps:

Switching on a measuring-circuit switching element (3a-d)

- Measuring the electrical size

- set timer for re-measurement and switch-off of the measuring circuit switching element (3a-d)

- wait until the timer for the next consecutive measuring string has expired

7. A method for operating a measurement circuit for detecting electrical quantities, wherein a loop is repeatedly traversed from 1 to the number of branches of the measuring circuit, characterized by the following Steps within the loop:

Switching on a measuring-circuit switching element (3a-d)

- Measuring the electrical size

- Switching off the Meßstrangschaltelementes (3a-d) - Waiting for a predetermined time