Method and control circuit for controlling a thyristor or triac

Abstract

Method for controlling a thyristor or triac (1), wherein the thyristor or triac (1) is triggered by a control circuit (4) by means of a gate current pulse (IP1) after a voltage zero crossing (tN0) of an alternating voltage source (3), comprising: a setting phase (P10) in which the control circuit (4) determines (S120 - S125) a firing pulse duration (TL) of the gate current pulse (IP1) for firing the thyristor or triac (1) so that the current (IR) through the thyristor or triac (1) reaches at least a latching current value (IL) after the end of the gate current pulse (IP1); and an operating phase (P20) in which the control circuit (4) controls the thyristor or triac (1) after a zero voltage crossing (tN0) of the alternating voltage source (3) with a gate current pulse (IP1) with the determined firing pulse duration (TL) (S222, S224) and then monitors a current flow through the thyristor or triac (1) (S241, S242, S246, S247); wherein the control circuit (4) in the setting phase (P10) further determines (S140 - S144) a holding pulse duration (TH) for a further gate current pulse (IP2) before a voltage zero crossing (tN0) of the AC voltage source (3), so that the current (IR) through the thyristor or triac (1) does not fall below a holding current value (IH) before the start of the further gate current pulse (IP2).

Description

[0001] The present invention relates to a method for controlling a thyristor or triac, wherein the thyristor or triac is triggered by a control circuit after a voltage zero crossing of an alternating voltage source by means of a gate current pulse, and to a corresponding control circuit.

[0002] Thyristors and triacs are triggered by a current at the gate electrode, i.e., they are switched on and remain conductive after switching on, even without gate current, until the current flow through the thyristor or triac falls below a so-called holding current. While thyristors can only switch in one direction and thus act like a diode when switched on, triacs functionally represent an anti-parallel circuit of two thyristors and can thus switch alternating current. In principle, it is possible to keep the thyristor or triac permanently switched on by a continuous gate current. On the other hand, the thyristor or triac can also be triggered by gate current pulses after the AC voltage source has crossed zero, which can reduce the power consumption of the control system.

[0003] A method for switching a triac on and off is known from DE 2 325 881 A, wherein the triac is switched on at the zero crossing of the operating alternating voltage and is controlled by means of pulses derived from the zero voltage.

[0004] DE 34 02 793 C1 describes a phase control system in which a triac is triggered by a pulse generator and connected to the mains by the associated switching process, whereby the pulse width of the ignition pulse is a function of the instantaneous value of the mains voltage at which the ignition pulse starts.

[0005] DE 30 37 794 A1 discloses a zero-voltage switch for controlling a triac consisting of two parallel-connected current branches. Each of these branches accepts a direct current supplied by a power source during a half-wave of the alternating voltage. This direct current is coupled out via a third current branch to generate control pulses during the zero-crossing phases of the alternating voltage, when both current branches are blocked. The control pulses for the triac are distributed asymmetrically to the zero crossing between the expiring and newly initiated half-waves of the alternating voltage. This ensures that the triac is reliably switched on without unnecessary power waste in the control circuit until the triac is switched off again.

[0006] A zero-crossing detector circuit for detecting the crossing of two individual threshold values ​​above or below a fixed reference voltage level by an alternating voltage is described in DE 689 07 761 T2.

[0007] From DE 198 50 905 A1 a device for controlling the power of a motor connected to an AC supply network is known, comprising a triac connected in series with the motor and a control device provided with an adjustable capacitance which controls the triac to carry out a phase control.

[0008] An adaptive triac control device is known from US 2013 / 0249604 A1.

[0009] The object of the invention is to provide an improved control of a thyristor or triac with reduced energy consumption and high reliability.

[0010] This object is achieved by the teaching of the independent claims. Particularly advantageous embodiments and further developments of the invention are the subject of the dependent claims.

[0011] According to a first aspect of the invention, the method for controlling a thyristor or triac, wherein the thyristor or triac is triggered by a control circuit after a zero voltage crossing of an AC voltage source by means of a gate current pulse, comprises a setting phase in which the control circuit determines a trigger pulse duration of the gate current pulse for triggering the thyristor or triac so that the current through the thyristor or triac reaches at least a latching current value after the end of the gate current pulse, and an operating phase in which the control circuit controls the thyristor or triac after a zero voltage crossing of the AC voltage source with a gate current pulse with the determined trigger pulse duration and then monitors a current flow through the thyristor or triac.

[0012] By automatically determining a suitable firing pulse duration by the control circuit during the setting phase, the optimum firing pulse duration can be set, resulting in reliable and energy-saving control for firing the thyristor or triac. By monitoring the current flow through the thyristor or triac during the operating phase, correct and energy-saving control for firing the thyristor or triac can be achieved. The monitoring also enables adaptive adjustment of the control of the thyristor or triac to achieve reliable and energy-saving operation. The energy-saving effect is particularly noticeable with thyristors and triacs that require high gate currents for firing. The reduced energy consumption can also reduce the heat generation of the thyristor or triac.

[0013] Preferably, the control circuit adjusts the set firing pulse duration if the monitoring shows that there is no current flow through the thyristor or triac after the end of the gate current pulse.

[0014] The current flow through the thyristor or triac is preferably monitored using a gate voltage between the gate terminal and the cathode terminal of the thyristor or triac. If the gate voltage exceeds a predetermined limit, a current flow occurs through the thyristor or triac.

[0015] In one embodiment of the invention, the control circuit, in the operating phase, controls the thyristor or triac with a further gate current pulse with a holding pulse duration before the AC voltage source crosses zero. In this embodiment, the control circuit, in the setting phase, preferably also determines a holding pulse duration for the further gate current pulse before the AC voltage source crosses zero, so that the current through the thyristor or triac does not fall below a holding current value before the start of the further gate current pulse. Preferably, the control circuit adjusts the set holding pulse duration if the monitoring shows that no current flows through the thyristor or triac before the start of the further gate current pulse.

[0016] In one embodiment of the invention, the thyristor or triac is triggered by a gate current pulse only after a predetermined phase angle following a zero voltage crossing of the AC voltage source. With such a phase-angle control, the control circuit determines the trigger pulse duration in the setting phase as a function of the predetermined phase angle, and in the operating phase, the control circuit triggers the thyristor or triac with a gate current pulse with the determined trigger pulse duration only after the predetermined phase angle following a zero voltage crossing of the AC voltage source.

[0017] In this embodiment, the control circuit preferably determines several different ignition pulse durations for different phase angles in the setting phase.

[0018] In a further embodiment of the invention, the control circuit repeats the adjustment phase regularly. This allows the setting of the firing pulse duration and / or the holding pulse duration to be adapted to potentially changing operating conditions or functional properties of the thyristor or triac.

[0019] According to a second aspect of the invention, the control circuit for driving a thyristor or triac includes a pulse generator for generating a gate current pulse to a gate terminal of the thyristor or triac, a current flow monitoring device for monitoring a current flow through the thyristor or triac, and a controller connected to the pulse generator and the current flow monitoring device, the controller being configured to carry out the above-described method for driving a thyristor or triac according to the invention.

[0020] In one embodiment of the invention, the current flow monitoring device comprises a voltage detection device for detecting a gate voltage between the gate terminal and the cathode terminal of the thyristor or triac.

[0021] Preferably, the control circuit further comprises a memory connected to the controller for storing the determined ignition pulse duration, the adjusted ignition pulse duration, the determined holding pulse duration and the adjusted holding pulse duration.

[0022] The above and other features and advantages of the invention will become more apparent from the following description of preferred, non-limiting embodiments with reference to the accompanying drawings, which show, mostly schematically: Fig. 1 is a circuit diagram of a triac circuit with a control circuit according to the present invention; Fig. 2 is a current-time diagram for explaining the operating principle of a control circuit according to the present invention; Fig. 3 is a flowchart of a method for controlling a triac according to an embodiment of the present invention; Fig. 4 a flow chart of a setting phase for setting the ignition pulse duration for the method of Fig. 3; and Fig. 5 a flow chart of a setting phase for setting the holding pulse duration for the process of Fig. 3.

[0023] Referring to Fig. 1 and Fig. 2, the structure and operation of a triac circuit with a control circuit according to the invention are first explained by way of example.

[0024] The triac circuit contains a series circuit consisting of a triac 1 and a load 2 connected to an AC voltage source 3. The triac 1 is controlled by a control circuit 4.

[0025] The control circuit 4 has a pulse generator 6 for generating gate current pulses IP1, IP2 with a gate current value IG, which are applied to the gate electrode of the triac 1. The pulse generator 6 is operated by a controller 5. To detect the correct times of the gate current pulses IP1, IP2, a phase synchronization 7 with the AC voltage source 3 is provided. The controller 5 is also connected to a memory 8 for storing various parameter values, a timer 9, and a current flow monitoring device for monitoring a current flow through the triac 1. In this exemplary embodiment, the current flow monitoring device has a voltage detection device 10 for detecting a gate voltage UG between the gate electrode and the cathode of the triac 1.

[0026] In the off or blocked state, Triac 1 has a high resistance and corresponds to an open switch, thus blocking the current IR through Triac 1 and thus also through Load 2 (IR = 0). There is no gate current at the gate electrode of Triac 1 (IG = 0). In this operating state, no voltage drops across Load 2 (UR = 0), and the alternating voltage UN drops across Triac 1 (UT = UN). Due to the lack of current flow through the Triac, the gate voltage UG = 0.

[0027] After a zero voltage crossing tN0, triac 1 is triggered with a gate current pulse IP1 with a gate current value IG. In the triggered or switched-on state, triac 1 has a low resistance and corresponds to a closed switch, allowing a current IR through triac 1 and through load 2 equal to the alternating voltage UN. In this operating state, approximately the alternating voltage UN is dropped across load 2 (UR ≈ UN), and no voltage is dropped across triac 1 (UT = 0). Due to the current flow IR through triac 1, a gate voltage UG can be detected that exceeds a limit value UGM.

[0028] The firing pulse duration TL of the gate current pulse IP1 is selected such that the current IR through the triac exceeds a latching current value IL after the end of the gate current pulse IP1, so that the triac 1 remains switched on even without the gate current IG. If the triac 1 is to be prevented from switching off when the current IR through the triac 1 falls below a holding current value IH, a further gate current pulse IP2 is applied to the gate electrode of the triac 1 before the next voltage zero crossing tN0 in order to keep the triac 1 switched on. The holding pulse duration TH of the further gate current pulse IP2 is selected such that the current IR through the triac is still above the holding current value IH at the start of the further gate current pulse IP2. If the phase duration of a voltage half-wave is designated TP, the further gate current pulse IP2 is started at a time tn0 + TP - TH.

[0029] The basic functionality of a triac and its control are well known to those skilled in the art. A more detailed explanation is therefore unnecessary.

[0030] Referring to Fig. 3 to 5, an exemplary embodiment of a control of the triac 1 according to the invention will now be explained in more detail.

[0031] As in Fig. 3 or in the Fig. 3A and Fig. As illustrated in Figure 3B, the method according to the invention for controlling the triac 1 includes a setting phase P10 and an operating phase P20, wherein the operating phase can be divided into an ignition phase P22, a monitoring phase P24 and a holding phase P26.

[0032] In the setting phase P10, the control circuit 4 determines an ignition pulse duration TL for the gate current pulse IP1 after a voltage zero crossing tN0 and a holding pulse duration TH for the further gate current pulse IP2 before a voltage zero crossing tN0, as shown in Fig. 4 or Fig. 5. The setting phase P10 can also be referred to as a learning phase, since the pulse durations TL, TH are not set by a user, but are determined automatically by the control circuit 4.

[0033] As in Fig. 4, the setting of the ignition pulse duration TL in the setting phase P10 by the control circuit 4 comprises steps S120 to S126.

[0034] In the first step S120, the firing pulse duration TL is initially set to a low initial value TL0. Then, the system waits until the voltage zero crossing tN0 (step S121). Upon reaching the voltage zero crossing tN0 ("Y" in S121), in the next step S122, a gate current pulse IP1 with a gate current value IG and the firing pulse duration TL is applied to the gate electrode of Triac 1 to turn on Triac 1. After the firing pulse duration TL has elapsed, the gate current pulse IP1 is terminated (IG = 0) in step S123.

[0035] The controller 5 then checks, with the aid of the voltage detection device 10, whether the gate voltage UG has reached a predetermined limit value UGM in order to determine the presence or absence of a current flow through the triac 1. If a current flow through the triac 1 ("Y" in S124) exists after the end of the gate current pulse IP1, the firing pulse duration TL is long enough for the current IR through the triac to exceed the latching current value IL, and the triac 1 to remain switched on even without the gate current IG. In this case, the current value of the firing pulse duration TL is stored in the memory 8 of the control circuit 4 (step S125) to be used for the gate current pulse IP1 in the firing phase P22 of the operating phase P20.

[0036] If, however, there is no current flow through Triac 1 after the end of the gate current pulse IP1 ("N" in S124), the firing pulse duration TL is too short, so that the current IR through the Triac does not reach the latching current value IL, and Triac 1 switches off without gate current IG. In this case, in step S126, the current value of the firing pulse duration TL is increased by a pulse duration difference dt, and the process from step S122 (or alternatively from step S121) is repeated until the increased firing pulse duration TL is sufficient ("Y" in S124).

[0037] As in Fig. 5, the setting of the holding pulse duration TH in the setting phase P10 by the control circuit 4 comprises steps S140 to S144.

[0038] In the first step S140, the holding pulse duration TH is initially set to an initial value TH0. The initial value can, for example, be the determined ignition pulse duration TL. Then, in step S141, a check is made as to whether current IR is still flowing through Triac 1 at the start of the further gate current pulse IP2, i.e., at time tN0 + TP - TH. If this is not the case (“N” in S141), the holding pulse duration TH must be increased in step S142 so that the further gate current pulse IP2 starts earlier. The increased holding pulse duration TH is then stored in memory 8 (step S143) to be used for the further gate current pulse IP2 in the holding phase P26 of the operating phase P20. If, on the other hand, a current IR is still flowing through Triac 1 at the start of the further gate current pulse IP2 (“Y” in S141), the holding pulse duration TH is shortened by dT in step S144, and the method returns to step S141.

[0039] In an alternative embodiment of the invention, the setting of the holding pulse duration TH by the control circuit 4 can also be omitted. In this case, the holding pulse duration TH is set, for example, to the value of the determined ignition pulse duration TL, so that the further gate current pulse IP2 is reliably long enough for the triac to remain switched on before the next voltage zero crossing tN0.

[0040] After completion of the described setting phase P10, the control circuit 4 goes into the operating phase P20, in which the triac 1 is controlled according to the settings and the correct and energy-saving functioning of the triac 1 is monitored.

[0041] The ignition phase P22 of the operating phase P20 begins at a voltage zero crossing tN0 (step S220). At the voltage zero crossing tN0, the gate current pulse IP1 is started (step S222) and maintained for the determined ignition pulse duration TL (step S224).

[0042] After the firing pulse duration TL ("Y" in S224) has elapsed, the gate current IG is switched off (step S240) and the monitoring phase P24 begins. In step S241, the gate voltage UG is detected by the voltage detection device 10 of the control circuit 4. In step S242, the detected gate voltage UG is compared with a predetermined limit value UGM. If the gate voltage UG reaches the limit value UGM ("Y" in S242), the controller 5 detects a current IR flowing through the triac 1. This means that the firing pulse duration TL is sufficient to fire the triac 1.

[0043] If, however, the gate voltage UG does not reach the limit value UGM (“N” in S242), the controller 5 detects that there is no current flow IR through Triac 1. This means that the firing pulse duration TL was too short to fire Triac 1, and Triac 1 switches off after the gate current pulse IP1 has ended. Therefore, in step S243, the gate current pulse IP1 is immediately reactivated to switch Triac 1 on. The monitoring phase then continues with step S240. Optionally, after the gate current pulse IP1 has been reactivated in step S243, the firing pulse duration TL can also be adjusted. This adjustment is carried out, for example, analogously to the adjustment phase according to Fig. 4.

[0044] If triac 1 remains switched on after the gate current pulse IP1 with the ignition pulse duration TL or the extended gate current pulse IP1 has ended, the system waits until the time tN0 + TP - TH of the planned further gate current pulse IP2. As long as this time has not yet been reached ("N" in S245), the gate voltage UG is detected by the voltage detection device 10 of the control circuit 4 (step S246). In step S247, the detected gate voltage UG is compared with a predetermined limit value UGM. If the gate voltage UG reaches the limit value UGM ("Y" in S247), the controller 5 detects a current flow IR through triac 1. This means that triac 1 is still switched on and the further gate current pulse IP2 correctly did not have to be started yet. Monitoring of the current flow then continues.

[0045] If, however, the gate voltage UG does not reach the limit value UGM (“N” in S247), the controller 5 detects that there is no longer any current flow IR through Triac 1. This means that the holding pulse duration TH is too short and Triac 1 has already switched off before the start of the next gate current pulse IP2. In step S248, a gate current IG is therefore immediately applied to Triac 1 to switch Triac 1 back on. Optionally, after activating the gate current IG in step S248, the holding pulse duration TH can also be adjusted. This adjustment is carried out, for example, analogously to the setting phase according to Fig. 5.

[0046] If, however, Triac 1 remains switched on until the scheduled start time of the additional gate current pulse IP2 ("Y" in S247), the holding phase P26 begins. In step S260, the additional gate current pulse IP2 is then started to maintain the current flow IR through Triac 1, even if the current IR falls below the holding current value ICH. The additional gate current pulse IP2 is then maintained until the next voltage zero crossing tN0 + TP (step S261).

[0047] The operating phase P20 is then continued for the next voltage half-wave with the same steps S220 to S261.

[0048] While the invention above is based on the Fig. 1 to 5 using the example of a triac control without a phase angle, the present invention can also be implemented in conjunction with a so-called phase angle control. With a phase angle control, the gate current pulse IP1 is only started after a certain phase angle W after the voltage zero crossing tN0, as shown in Fig. 2. Likewise, with phase-angle control, the further gate current pulse IP2 can be terminated a certain phase angle before the voltage zero crossing tN0.

[0049] In the case of such a phase control, in the setting phase P10, the control circuit 4 determines different ignition pulse durations TL and, if necessary, also different holding pulse durations TH for different phase angles W. In the operating phase P20, the control 5 then selects the determined pulse durations TL, TH for the respective desired phase angle W in order to carry out the operating phase P20 with these pulse durations TL, TH.

[0050] While the invention above is based on the Fig. 1 to 5 using the example of a triac circuit, the person skilled in the art can also transfer the concept of the present invention to the control of a thyristor. REFERENCE NUMBER LIST 1 Triac 2 Load 3 AC voltage source 4 Control circuit 5 Control 6 Pulse generator 7 Phase synchronization 8 storage 9 timers 10 Voltage detection device I Current IG Gate current (value) IH holding current value IL latching current value IP1 Gate current pulse after voltage zero crossing IP2 Gate current pulse before voltage zero crossing IR current through load or triac t time dT pulse duration difference TH holding pulse duration TH0 initial value holding pulse duration TL ignition pulse duration TL0 Initial value ignition pulse duration tN0 Time of voltage zero crossing TP phase duration voltage half-wave UG gate voltage UGM limit gate voltage UN alternating voltage UR voltage drop across load UT voltage drop across triac W phase angle

Claims

[1] Method for controlling a thyristor or triac (1), wherein the thyristor or triac (1) is triggered by a control circuit (4) after a voltage zero crossing (tN0) of an alternating voltage source (3) by means of a gate current pulse (IP1), comprising: a setting phase (P10) in which the control circuit (4) determines (S120 - S125) a firing pulse duration (TL) of the gate current pulse (IP1) for firing the thyristor or triac (1) so that the current (IR) through the thyristor or triac (1) reaches at least a latching current value (IL) after the end of the gate current pulse (IP1); and an operating phase (P20) in which the control circuit (4) controls the thyristor or triac (1) after a zero voltage crossing (tN0) of the alternating voltage source (3) with a gate current pulse (IP1) with the determined firing pulse duration (TL) (S222, S224) and then monitors a current flow through the thyristor or triac (1) (S241, S242, S246, S247); wherein the control circuit (4) in the setting phase (P10) further determines (S140 - S144) a holding pulse duration (TH) for a further gate current pulse (IP2) before a voltage zero crossing (tN0) of the AC voltage source (3), so that the current (IR) through the thyristor or triac (1) does not fall below a holding current value (IH) before the start of the further gate current pulse (IP2). [2] Method according to claim 1, wherein the control circuit (4) adapts (S244) the ignition pulse duration (TL) if the monitoring (S241, S242) shows that there is no current flow through the thyristor or triac (1) after the end of the gate current pulse (IP1). [3] Method according to claim 1 or 2, wherein the monitoring of the current flow through the thyristor or triac (1) is carried out on the basis of a gate voltage (UG) between the gate terminal and the cathode terminal of the thyristor or triac (1) (S241, S242, S246, S247). [4] Method according to one of the preceding claims, in which the control circuit (4) in the operating phase (P20) before a voltage zero crossing (tN0) of the AC voltage source (3) controls (S260, S262) the thyristor or triac (1) with a further gate current pulse (IP2) with the determined holding pulse duration (TH). [5] Method according to one of claims 1 to 4, in which the control circuit (4) adapts the holding pulse duration (TH) (S249) if the monitoring (S246, S247) shows that there is no current flow through the thyristor or triac (1) before the start of the further gate current pulse (IP2). [6] Method according to one of the preceding claims, in which the thyristor or triac (1) is triggered by means of a gate current pulse (IP1) only after a predetermined phase angle (W) after a voltage zero crossing (tN0) of the alternating voltage source (3); the control circuit (4) determines the ignition pulse duration (TL) in the setting phase (P10) as a function of the predetermined phase angle (W); and the control circuit (4) controls the thyristor or triac (1) in the operating phase (P20) only after the predetermined phase angle (W) after a voltage zero crossing (tN0) of the alternating voltage source (3) with a gate current pulse (IP1) with the determined ignition pulse duration (TL) (S222, S224). [7] Method according to claim 6, wherein the control circuit (4) determines in the setting phase (P10) several different ignition pulse durations (TL) for different phase angles (W). [8] Method according to one of the preceding claims, in which the control circuit (4) regularly repeats the setting phase (P10). [9] Control circuit (4) for controlling a thyristor or triac (1), comprising: a pulse generator (6) for generating a gate current pulse (IP1, IP2) to a gate terminal of the thyristor or triac (1); a current flow monitoring device (10) for monitoring a current flow through the thyristor or triac (1); and a controller (5) connected to the pulse generator (6) and the current flow monitoring device, wherein the controller (5) is designed to carry out a method for controlling a thyristor or triac (1) according to one of claims 1 to 8. [10] Control circuit according to claim 9, wherein the current flow monitoring device comprises a voltage detection device (10) for detecting a gate voltage (UG) between the gate terminal and the cathode terminal of the thyristor or triac (1). [11] Control circuit according to claim 9 or 10, further comprising: a memory (8) connected to the controller (5) for storing the determined ignition pulse duration (TL), the adjusted ignition pulse duration (TL), the determined holding pulse duration (TH) and the adjusted holding pulse duration (TH).

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