• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    In order to enable a voltage measurement of the output voltage on the secondary side in a circuit arrangement (8) with a center tap transformer in a simple and reliable manner, it is provided that at least between the two outer terminals (A1, A2) of the secondary side of the transformer (T) two resistors (R3, R4) connected in series are connected in order to form a measuring point (P) between the two resistors (R3, R4), and a voltage measuring unit (V) is provided which corresponds to the output voltage (UA) Voltage (UP) between measuring point (P) and second output pole (13) measures
    公开号:AT516903A1
    申请号:T50186/2015
    申请日:2015-03-09
    公开日:2016-09-15
    发明作者:Christian Magerl；Franz Peter Dipl Ing Musil；Robert Dipl Ing Eberl (Fh)；Friedrich Steinmaurer
    申请人:Fronius Int Gmbh；
    IPC主号:
    专利说明:

    Circuit arrangement with transformer with center tap and measurement of
    output voltage
    The subject invention relates to a circuit arrangement with at least one transformer with center tap, wherein the center of the secondary side of the transformer via a first output line is connected to a first output pole and the two outer terminals of the secondary side of the transformer via a respective electrical switching element are connected and with a second Output line are connected to a second output terminal and with a voltage measurement for measuring the voltage applied between the first and second output pole output voltage of the circuit arrangement.
    In converters, such as DC-DC converters, switching converters, resonant switching converters, etc., are often used transformers with center tap on the secondary side. An example of this is a power converter 1 in the form of a known resonant converter as shown in FIG. 1, in which a resonant circuit is formed by the choke LR, the capacitance CR and the primary side of the transformer T. The resonant converter is excited by a pulse pattern at the input UE to vibrate. The pulse pattern may be e.g. by a known switch arrangement and a PWM control (not shown in Fig. 1) can be realized. This vibration is transmitted via the transformer T and rectified on the secondary side.
    For regulating the output voltage UA of such power converter 1, a measurement of the output voltage UA is generally required. Especially in high power classes, such as to be found in welding power sources, flow on the secondary side high currents. The switching elements on the secondary side of the power converter 1 are usually mounted on a circuit carrier 3, e.g. a circuit board (as in Fig.2), or the like. The circuit elements can also be connected via copper brackets (especially at very high currents or voltages). In order not to have to carry the current-carrying positive output line 2 of the power converter 1 via the circuit substrate 3, which would necessitate a large copper cross-section on the circuit substrate 3, the positive output line 2 is usually led to the outside as a separate line and not one Circuit carrier 3, on which the voltage measurement 4 is implemented for measuring the output voltage UA, as shown in Figure 2. However, this makes it necessary to connect the positive output line 2 to the circuit carrier 3 via an additional connecting line 5. For this purpose, a socket 6 is arranged on the circuit board 3, to which the connecting line 5 is connected. Of course, the additional connection line 5 and the need for a socket 6 on the circuit board 3 also increase the complexity of the electrical assembly. The same applies analogously to the use of copper bars, since according to the state of the art for voltage measurement between the two output terminals, a connection line 5 for connecting the plus output line 2 to the voltage measuring unit is required.
    Apart from this, there may be occurrences that the connection line 5 dissolves with time, or that is completely forgotten in the assembly to connect the connecting line 5 to the circuit carrier 3 or to the plus output line 2. Both usually leads to the failure of the regulated power converter 1, which requires a measured value of the output voltage UA for operation. In particular, if the connecting line 5 is removed, an overvoltage can occur at the diodes D1, D2, which can also destroy them. It is therefore desirable to dispense with this additional connection line 5, which is a source of error.
    Although the problems of the prior art have been described with reference to the concrete example of a converter with a center tap transformer, this is generally true for any circuit having a center tap transformer in which the output voltage on the secondary side is measured. For example, a center tap transformer is also used in center-to-center rectifiers or synchronous rectifiers.
    It is therefore an object of the subject invention to provide a circuit arrangement with a transformer with center tap, which allows a simple and reliable voltage measurement of the output voltage on the secondary side, without increasing the circuit complexity.
    This object is achieved in that between the two outer terminals of the secondary side of the transformer at least two series-connected resistors are connected to form a measuring point between the two resistors, and a voltage measuring unit is provided which corresponds to the output voltage corresponding voltage between the measuring point and second exit pole. By the two resistors connected in series, a measuring point is created, against which a voltage corresponding to the output voltage is applied in relation to the second output pole. Thus, only the two resistors must be arranged in order to be able to measure a voltage corresponding to the output voltage, and thus also the output voltage, in a simple manner. A connecting line between the first output terminal and the circuit carrier or between the first output terminal and the voltage measuring unit is therefore no longer necessary.
    In an advantageous embodiment, the electrical switching elements and the two resistors are arranged on at least one circuit carrier, in particular a circuit board. No provision needs to be made on the circuit carrier, e.g. in the form of a connection socket to connect the first output line to the circuit carrier, which reduces the circuitry complexity.
    If at least one further resistor is connected between the measuring point and the second output pole, the input voltage range of the voltage measuring unit can be reduced on account of the resulting voltage divider. The voltage measuring unit can thus be advantageously designed for a lower measuring voltage.
    The circuit arrangement according to the invention is particularly advantageous in a resonant converter with a resonant circuit, in particular as a welding power source, for use, since there the measurement of the output voltage for controlling the output voltage is important.
    Certain resonant transducers, such as Series-parallel resonant converter, but have the property that the output voltage UA idle (ie without connected load) due to the resonant circuit formed with Cp increased so that a control of the resonant converter with an output side additional circuit 7 (Figure 3) is advantageous , This is the case in particular in welding power sources, where it is desirable to maintain a certain output voltage UA even when idling. For this purpose, the resonant converter is operated in idle pulsed. For this purpose, voltage pulses are applied to the input UE of the resonant converter for a certain period of time. The vibration generated by the resonant converter charges the capacitor C3 on the secondary side via the diode D3. During the time when no voltage pulses are applied, the capacitor C3 discharges via the resistor R1. Therefore, a mean output voltage UA sets at the output of the resonant converter, which can be kept at a desired level by setting the voltage pulses at the input. In normal operation of the resonant converter, this additional circuit 7 has no influence. Nevertheless, the capacitor C3 must be designed for the maximum output voltage UA and a maximum pulse frequency and is therefore to be dimensioned correspondingly large, which requires appropriate space on the circuit substrate 3. Of course, this circuit also requires the connection line 5 in order to connect the plus output line 2 to the circuit carrier 3, on which this additional circuit 7 is arranged. If the connection line 5 drops away, it must nevertheless be ensured that the output voltage UA during idling of the resonant converter can be regulated to a desired voltage level.
    It is therefore a further object of the subject invention to ensure that the output voltage at idle of a resonant converter with the circuit arrangement according to the invention can be controlled or adjusted to a desired value while avoiding the above-mentioned circuit problems with a simple additional circuit.
    This further object is achieved for a resonant converter according to the invention in that in each case a capacitor is connected in parallel to the electrical switching elements on the secondary side. In normal operation (ie with a connected load), the capacitors only have to conduct a half period of current each time and can therefore be dimensioned substantially smaller than in the circuit according to the prior art. Thus, a possible circuit carrier can be made smaller and it can also be dispensed with the previously required connection line between the first output terminal and the circuit board.
    The subject invention will be explained in more detail below with reference to Figures 1 to 7, which show by way of example, schematically and not by way of limitation advantageous embodiments of the invention. It shows
    1 shows a typical resonant converter according to the prior art,
    2 shows the usual in the prior art voltage measurement on the secondary side of a transformer with center tap,
    3 shows the usual in the prior art additional circuit for controlling the output voltage of a series-parallel resonant converter at idle,
    4 shows a circuit arrangement with a transformer with center tap and inventive voltage measurement of the output voltage,
    5 shows a series-parallel resonant converter with a secondary circuit according to the invention for adjusting the open-circuit voltage,
    Figure 6 shows the voltage in the series-parallel resonant converter resulting voltage curves in the idle case and
    7 shows a series-parallel resonant converter with inventive measuring arrangement for voltage measurement and secondary circuit for controlling the output voltage during idling.
    4 shows a circuit arrangement 8 with a transformer T with secondary-side center tap. On the secondary side of the transformer T with center tap at least three ports are present. One terminal for the center M and two terminals at the ends of the secondary-side winding, these terminals being referred to as outer terminals A1, A2.
    In general, however, it is stated that the term "center tap" in the sense of the invention also means the use of two or more transformers in which the secondary-side windings are connected in series (as shown in FIG. 5). An electrical connection between two series-connected secondary windings then corresponds to the center M, to which the first output line 10 can be connected.
    The secondary-side center M is guided via a first output line 10, here a plus output line, as the first output pole 12, here the positive pole, to the outside. However, the first output line 10 is not guided over a circuit carrier 3, such as a circuit board, for example, but is led directly as a line to the outside. The two outer, or non-series-connected, secondary-side terminals A1, A2 of the secondary side of the transformer T are each guided in a known manner to a first terminal of a switching element S1, S2. The respective second terminals of the switching elements S1, S2 are connected to each other and form the second output terminal 13, here the negative terminal, of the rectifier, which is led to the outside with a second output line 11, in this case a minus output line.
    If passive switching elements in the form of diodes are used as electrical switching elements S1, S2, a known center rectifier is obtained. Are as electrical switching elements S1, S2 active switching elements, such as semiconductor switches, e.g. MOSFETs, one obtains a known synchronous rectifier. Since the functions of a center rectifier and a synchronous rectifier are well known, and are irrelevant to the subject invention, will not be discussed in more detail here.
    The switching elements S1, S2 are arranged in a conventional manner on a circuit carrier 3. Of course, the circuit carrier 3 can also be designed to be split. Particularly in the case of active switching elements S1, S2, the power part with the active switching elements S1, S2 is often arranged on a separate circuit carrier 3. In addition, an electrical measuring arrangement 14 according to the invention for measuring the output voltage UA is arranged on the circuit carrier 3 for voltage measurement. The circuit elements of the secondary side can also be connected to each other by copper brackets. A secondary-side circuit arrangement as a combination with circuit carrier 3 and copper bracket is conceivable. By way of example, the measuring arrangement 14 for measuring the output voltage UA could be arranged on a circuit carrier 3 and the remaining circuit elements could be connected by means of copper bars.
    This measuring arrangement 14 for measuring the output voltage UA consists essentially of two resistors R3, R4, which are connected in series between the two outer terminals A1, A2 of the secondary side of the transformer T. As a result, a measuring point P is generated between the two resistors R3, R4, at which, with respect to the second output pole 13, a voltage UP is established, which corresponds to the output voltage Ua present at the center M. This voltage Up at the measuring point P can be measured with any voltage measuring unit V and made available as an analog or digital measured value MW. For example, the voltage measuring unit V can be designed as an amplifier circuit with an operational amplifier, wherein the output of the amplifier circuit is digitized in an analog-to-digital converter and is passed to the outside as a digital measured value MW.
    If the two resistors R3, R4 are equal, then the voltage UP at the measuring point P corresponds to the output voltage UA at the midpoint M, that is to say the voltage at the first output pole 12 in the exemplary embodiment shown. If the resistors R3, R4 are not the same, then the measuring point P is established a voltage corresponding to the ratio of the resistors R3, R4. In both cases, the output voltage UA can thus be measured at the measuring point P by measuring the voltage UP of the measuring point P with respect to the second output pole 13, as indicated in FIG.
    The voltage UP at the measuring point P can be measured directly, but also the measurement via a voltage divider is conceivable. This allows the use of a voltage measuring unit V with a reduced input range, whereby circuit simplifications can be achieved. For this purpose, a voltage divider can be generated between measuring point P and second output pole 13 by means of an additional resistor R2, as indicated in FIG. In this case, the resistor R2 causes in connection with the resistors R3 and R4 at the measuring point P, a corresponding reduction of the voltage UP, which is nevertheless proportional to the output voltage UA. If the voltage measuring unit V requires an even lower input voltage, in a known way the resistor R2 can be divided in an appropriate ratio to two resistors in order to achieve an adaptation to the input voltage range of the voltage measuring unit V.
    Consequently, with this measuring arrangement 14 according to the invention for the voltage measurement of the output voltage UA, it is no longer necessary to feed the first output line 10 via the circuit carrier 3 or the first output line 10, as in the prior art, with the circuit carrier 3, or with the voltage measuring unit V. to connect via an additional connecting line 5.
    5 shows a power converter 1 in the form of a series-parallel resonant converter with a primary-side series resonant circuit of inductor LR, resonant capacitor CR and the primary side of the transformer T, a secondary side parallel resonant circuit of resonant capacitor CP and the secondary side of the transformer T and a center rectifier (ie with Diodes D1, D2 as electrical switching elements S1, S2) on the secondary side. In this case, the primary side is not completely represented; in particular, the electrical circuit known per se is lacking for generating the illustrated input voltage UE. Of course, the primary-side resonant circuit could be known but also designed as a parallel resonant circuit, in which the resonant capacitor CR, for example, is connected in parallel to the primary side of the transformer T. Likewise, the resonant circuit could be known differently or even not formed on the secondary side. Likewise, of course, the diodes D1, D2 could be reversed polarity or be replaced by other electrical switching elements S1, S2.
    In order to keep the output voltage UA at idle at a desired value, parallel to the electrical switching elements S1, S2, here diodes D1, D2, in each case at least one capacitor C1, C2 connected. This results in addition to the effect, with all the associated and explained above advantages that no separate connection between the first output line 10 and circuit substrate 3 is necessary for the secondary circuit 15 for setting the open circuit voltage.
    At idle, a desired output voltage UA is to be maintained at the resonant converter 1. For this purpose, t-ι voltage pulses UE are applied to the primary side of the transformer T for a certain period of time, which excite the resonant circuit on the primary side. The excitation leads to a vibration on the secondary side of the transformer T. During idling, the voltages applied to the capacitors C1, C2 oscillate around the level of the output voltage UA. The capacitors C1, C2 are thereby charged during the excitation on the primary side in the time span t-ι, which also leads to an increase in the no-load voltage at the output UA. Thereafter, the primary-side excitation is interrupted for a second period t2. In this phase, the capacitors C1, C2 discharge. For this purpose, it is also possible to provide discharge resistors R5, R6, as indicated in FIG. Without discharge resistors R5, R6, the capacitors C1, C2 discharge according to their self-discharge characteristics. If the secondary circuit 15 is implemented together with the measuring arrangement 14 for measuring the output voltage UA (as in FIG. 7), then the resistors R2, R3, R4 of the measuring arrangement 14 simultaneously serve as discharge resistors. During the discharge of the capacitors C1, C2, the open-circuit voltage UA drops at the output. This results in the output at idle, a mean output voltage UA. The output voltage UA can thus be kept at a desired value by setting the voltage pulses UE, the pulse frequency and the time periods t-1, t2. In normal operation (with a connected electrical load at the output), this secondary circuit 15 has no influence. The resulting, for example, in a series-parallel resonant converter voltage curves at idle are shown schematically in Fig. 6.
    The two capacitors C1, C2 of the secondary circuit 15 can be dimensioned smaller than the capacitor C3 in the hitherto conventional circuit according to the prior art (Figure 3). This space can be saved on the circuit board 3. Apart from this, so that the thermal load of the circuit substrate 3 can be reduced, which also results in that the circuit substrate 3 can be reduced in size.
    The smaller capacitance values C1, C2, however, also cause the output voltage UA to decrease more rapidly during idling, which is advantageous, in particular, for use in welding current sources, because this more quickly achieves the permitted maximum voltage after the welding has ended.
    Of course, the measuring arrangement 14 for voltage measurement and the secondary circuit 15 for regulating the output voltage UA during idling can also be combined, as shown in FIG. 7 on the basis of a resonant converter 1 with center rectifier. Such a combination is particularly advantageous because then the output voltage UA at idle (open circuit voltage) by measuring the output voltage UA corresponding voltage UP at the measuring point P can be controlled to a desired value, or a desired value of the open circuit voltage can be ensured.
    权利要求:
    Claims (6)
    [1]
    claims
    1. Circuit arrangement with at least one transformer (T) with center tap, wherein the midpoint (M) of the secondary side of the transformer via a first output line (10) having a first output terminal (12) is connected and the two outer terminals (A1, A2) of Secondary side of the transformer (T) via a respective electrical switching element (S1, S2) are connected and connected to a second output line (11) with a second output terminal (13), and with a measuring arrangement (14) for measuring the between the first output terminal ( 12) and second output terminal (13) applied output voltage (UA) of the circuit arrangement (8), characterized in that between the two outer terminals (A1, A2) of the secondary side of the transformer (T) at least two series-connected resistors (R3, R4 ) are connected to form a measuring point (P) between the two resistors (R3, R4), and a voltage measuring unit (V) is provided, the mi t of the output voltage (UA) corresponding voltage (UP) between measuring point (P) and second output pole (13) measures.
    [2]
    2. Circuit arrangement according to claim 1, characterized in that the electrical switching elements (S1, S2) and the two resistors (R3, R4) are arranged on at least one circuit carrier (3), in particular a circuit board.
    [3]
    3. A circuit arrangement according to claim 1, characterized in that the electrical switching elements (S1, S2) and the two resistors (R3, R4) on a common circuit substrate (3), in particular a common circuit board, are arranged.
    [4]
    4. Circuit arrangement according to claim 1, characterized in that between the measuring point (P) and the second output pole (13) at least one further resistor (R2) is connected.
    [5]
    5. resonant converter with a resonant circuit and a circuit arrangement (8) according to one of claims 1 to 4.
    [6]
    6. resonant converter according to claim 5, characterized in that parallel to the electrical switching elements (S1, S2) in each case at least one capacitor (C1, C2) is connected.
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    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
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