Measurement structure and method for measuring a current
Patent Information
- Application Number
- EP2023772176
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-10-05
- Filing Date
- 2023-09-14
- Publication Date
- 2025-08-13
AI Technical Summary
Existing measurement setups for current from a center tap between two transistors of a half bridge fail to protect against higher-frequency interference due to discontinuous signal curves, leading to interference modulation and incorrect signal interpretation.
A measurement setup with separate channels for each transistor, equipped with low-pass filters and analog-digital converters, where signals from both channels are added to create a continuous signal curve, allowing effective filtering and interference protection.
This configuration converts discontinuous signal curves into continuous ones, enabling effective filtering and preventing interference modulation, thus accurately measuring currents from the center tap between transistors.
Smart Images
Figure 1.1
Abstract
Description
[0001] Description
[0002] Measurement setup and method for measuring a current
[0003] The invention relates to a measuring setup for measuring a current from a center tap between two transistors of a half-bridge through a load according to the preamble of claim 1 and to a method for measuring a current from a center tap between two transistors of a half-bridge through a load according to the preamble of claim 5.
[0004] To protect measurement channels in electronic circuits against interference, low-pass filters (LPFs) are commonly used, usually designed as first-order or higher-order RC elements as shown in Figure 1. The low-pass filter (LPF) is connected in parallel to a shunt (SH).
[0005] The prerequisite for the measurement setup shown in Figure 1 is that the signal to be measured has a continuous waveform. This is the case for the current I from the center tap of a half-bridge consisting of two transistors T1, T2 through the shunt SH, which in this example allows the current I to be measured using a voltmeter V. Thus, the voltmeter V can be protected against higher-frequency interference by a low-pass filter TPF. The measurement configuration in Figure 2 does not meet this requirement.
[0006] In the example in Figure 2, the voltage drop across a channel resistance of a respective conductive transistor T1, T2 of the half-bridge is measured and again evaluated using a voltmeter. In Figure 2, this combination is shown in simplified form as an ammeter A. Consequently, the current I can only be measured as long as the respective transistor T1, T2 is conductive. This results in two partial current measurements, which are shown in Figures 3 and 4. Figure 3 shows a curve of the current I through the upper transistor T1 over time t, and Figure 4 shows a curve of the current I through the lower transistor T2. Since a low-pass filter TPF only displays the mean value of the measurement signal above about ten times the cut-off frequency, it cannot be used to protect the ammeter A against interference at the measurement input. As a result, the analog-to-digital converter ADC1, ADC2 usually used to record the measurement signal is not protected, and the result is the occurrence of beats.In other words, noise signals in the higher frequency range, such as signal jumps, are modulated into the functional range due to the violation of the Nyquist-Shannon theorem and interpreted as a measurement signal.
[0007] The invention is based on the object of specifying a novel measuring setup and a novel method for measuring a current from a center tap between two transistors of a half-bridge through a consumer.
[0008] The object is achieved according to the invention by a measuring setup having the features of claim 1 and by a method having the features of claim 5.
[0009] Advantageous embodiments of the invention are the subject of the subclaims.
[0010] According to the invention, a measuring setup for measuring a current from a center tap between two transistors of a half-bridge through a load is proposed, wherein the measuring setup is configured to measure a voltage across a channel resistance of the transistor in each of the two transistors in separate measuring channels when the respective transistor is conductive. According to the invention, each of the measuring channels has an adder, a low-pass filter, and an analog-to-digital converter, so that in each measuring channel, signals of the respective voltage drop can be fed to the analog-to-digital converter via the adder and the low-pass filter, wherein the adder of each of the measuring channels is configured to additively add the signals of the respective other measuring channel to the signals of the respective measuring channel.
[0011] In this way, the discontinuous signal waveform in each of the measurement channels is converted into a continuous signal waveform, thus enabling filterability. In one embodiment, the low-pass filter is a first-order or higher-order low-pass filter.
[0012] According to one aspect of the present invention, a device is proposed comprising a measuring setup as described above and a half-bridge comprising two transistors, as well as a load fed from a center tap between the two transistors.
[0013] In one embodiment, the transistors are designed as field-effect transistors, with the source of the upper transistor connected to the drain of the lower transistor.
[0014] According to one aspect of the present invention, a method for measuring a current from a center tap between two transistors of a half-bridge through a load is proposed, wherein in each of the two transistors, a voltage is measured across a channel resistance of the transistor in separate measuring channels when the respective transistor is conductive. According to the invention, in each measuring channel, signals of the respective voltage drop are fed to an analog-to-digital converter via an adder and a low-pass filter, wherein in the adder of each of the measuring channels, the signals of the respective other measuring channel are additively added to the signals of the respective measuring channel. In this way, the discontinuous signal waveform in each of the measuring channels is converted into a continuous signal waveform, thus enabling filterability.
[0015] Embodiments of the invention are explained in more detail below with reference to drawings.
[0016] Figure 1 shows a schematic view of a half-bridge with a measuring setup for measuring a current from the half-bridge through a consumer according to the prior art,
[0017] Figure 2 is a schematic view of a half-bridge with a further measuring setup for measuring the current from the half-bridge through a consumer according to the prior art,
[0018] Figure 3 shows a current profile through an upper transistor of the measurement setup according to the prior art,
[0019] Figure 4 shows a current profile through a lower transistor of the measurement setup according to the prior art,
[0020] Figure 5 is a schematic view of a measuring setup according to the invention for measuring the current from the half-bridge through a consumer,
[0021] Figure 6 is a schematic diagram of a current profile in a lower measuring channel of the measuring setup according to Figure 5,
[0022] Figure 7 is a further schematic view of the measurement setup according to Figure 5, and
[0023] Figure 8 is a schematic diagram of a current profile in an upper measuring channel of the measuring setup according to Figures 5 and 7.
[0024] Corresponding parts are provided with the same reference numerals in all figures.
[0025] Figure 1 is a schematic view of a half-bridge HB, comprising two transistors T1, T2, in particular field-effect transistors, wherein source S of the upper transistor T1 is connected to drain D of the lower transistor T2. In order to measure a current I flowing from a center tap M between the two transistors T1, T2 through a load L, a measuring setup is provided which has a shunt SH between the load L and the center tap M. By measuring the voltage drop across the shunt SH using a voltmeter V, and knowing the resistance of the shunt SH, the current I can be determined. In order to protect measuring channels in electronic circuits against the coupling of interference, low-pass filters (TLFs) are usually used, usually designed as first-order or higher-order RC elements.The low-pass filter LPF shown as an example comprises a series circuit of a resistor R and a capacitor C connected in parallel to the shunt SH, to which the voltmeter V is connected in parallel.
[0026] The signal to be measured should have a continuous waveform. This is the case for the current I from the center tap M of the half-bridge HB consisting of two
[0027] Transistors T1 and T2 are separated by the shunt SH, which in this example allows the current I to be measured using a voltmeter V. Thus, the voltmeter V can be protected against high-frequency interference by the low-pass filter LPF.
[0028] Figure 2 is a schematic view of a half-bridge HB, comprising two transistors T1, T2, in particular field-effect transistors, wherein source S of the upper transistor T1 is connected to drain D of the lower transistor T2. In order to measure a current I flowing from a center tap M between the two transistors T1, T2 through a load L, an alternative measuring setup is provided in which the voltage drop across a channel resistance of a respectively conductive transistor T1, T2 of the half-bridge is measured and in turn evaluated using a voltmeter V. In Figure 2, this combination is shown as an ammeter A. Consequently, the current I can only be measured as long as the respective transistor T1, T2 is conductive, for example when the gates G of the transistors T1, T2 are controlled with pulse-width modulated signals. This results in two partial current measurements, which are shown in Figures 3 and 4.Figure 3 shows the current I through the upper transistor T1 over time t, and Figure 4 shows the current I through the lower transistor T2. Since a low-pass filter TPF only displays the mean value of the measurement signal above approximately ten times the cut-off frequency, it cannot be used to protect against interference at the measurement input in the measurement setup shown in Figure 2. This means that an analog-to-digital converter ADC1, ADC2, which is usually used to record the measurement signal, is not protected, and the result is the occurrence of beats. In other words, interference signals in the higher frequency range, for example signal jumps, are modulated into the functional range and interpreted as a measurement signal due to a violation of the Nyquist-Shannon theorem.
[0029] Figure 5 is a schematic view of a measurement setup 1 with an upper measurement channel OMK for signals SO of the voltage drop across the channel resistance of the upper transistor T1 according to Figure 2 and with a lower measurement channel UMK for signals SU of the voltage drop across the channel resistance of the lower transistor T2 according to Figure 2. In each of the measurement channels OMK, UMK, the signals SO, SU of the respective voltage drop are fed to an analog-to-digital converter ADC1, ADC2 via an addition element AG and a low-pass filter TPF.
[0030] In Figure 5, the signals SO from the upper measurement channel OMK are added to the lower measurement channel UMK via the summing element AG. Taking the channel resistance into account, this results in a current I curve before the low-pass filter TPF as shown schematically in Figure 6.
[0031] Figure 7 shows a schematic view of the measurement setup 1 according to Figure 5, wherein the signals SU of the lower measurement channel UMK are added additively to the upper measurement channel OMK via the summing element AG. Taking the channel resistance into account, this results in a current I curve before the low-pass filter TPF as shown schematically in Figure 8.
[0032] Figures 6 and 8 clearly show that signal jumps are avoided by this addition. Therefore, filtering using the low-pass filter (LPF) is possible in the measurement setup shown in Figures 6 and 8. If measurements are continued only in the active time window, i.e., while the respective transistor T1, T2 is conducting, then other desired information, such as current thresholds, can be evaluated as before.
[0033] List of reference symbols
[0034] 1 Measurement setup
[0035] A ammeter
[0036] ADC1 , ADC2 analog-to-digital converter
[0037] AG Addition element
[0038] C capacitor
[0039] D Drain
[0040] G Gate
[0041] HB Halbbrücke
[0042] I Current
[0043] L Consumer
[0044] M center tap
[0045] OMK upper measuring channel
[0046] R resistance
[0047] S Source
[0048] SH shunt
[0049] SO, SU signals t time
[0050] T1 , T2 transistors
[0051] LPF low-pass filter
[0052] UMK lower measuring channel
[0053] V Voltmeter
Claims
Patent claims 1. A measuring setup for measuring a current (I) from a center tap (M) between two transistors (T1, T2) of a half-bridge (HB) through a load (L), wherein the measuring setup is configured to measure a voltage across a channel resistance of the transistor (T1, T2) in each of the two transistors (T1, T2) in separate measuring channels (OMK, UMK) when the respective transistor (T1, T2) is conductive, characterized in that each of the measuring channels (OMK, UMK) has an adder (AG), a low-pass filter (TPF) and an analog-digital converter (ADC1, ADC2), so that in each measuring channel (OMK, UMK) signals (SO, SU) of the respective voltage drop can be fed to the analog-digital converter (ADC1, ADC2) via the adder (AG) and the low-pass filter (TPF), wherein the Addition element (AG) of each of the measuring channels (OMK, UMK) is configured to add to the signals (SO, SU) of the respective measuring channel (OMK, UMK) the signals (SO, SU) of the other measuring channel (OMK,UMK) additively.
2. Measurement setup according to claim 1, characterized in that the low-pass filter (LPF) is a first-order or higher-order low-pass filter (LPF).
3. Device comprising a measuring setup according to claim 1 or 2, characterized in that the device further comprises a half-bridge (HB) comprising two transistors (T1, T2), and a load (L) fed from a center tap (M) between the two transistors (T1, T2).
4. Device according to claim 3, characterized in that the transistors (T1, T2) are designed as field-effect transistors, the source (S) of the upper transistor (T1) being connected to the drain (D) of the lower transistor (T2).
5. Method for measuring a current (I) from a center tap (M) between two transistors (T1, T2) of a half-bridge (HB) through a load (L), wherein in each case a voltage across a channel resistance of the transistor (T1, T2) is measured in separate measuring channels (OMK, UMK) of both transistors (T1, T2) when the respective transistor (T1, T2) is conductive, characterized in that in each measuring channel (OMK, UMK) signals (SO, SU) of the respective voltage drop are fed to an analog-digital converter (ADC1, ADC2) via an addition element (AG) and a low-pass filter (TPF), wherein in the addition element (AG) each of the Measuring channels (OMK, UMK) the signals (SO, SU) of the other measuring channel (OMK, UMK) are added additively to the signals (SO, SU) of the respective measuring channel (OMK, UMK).