Silicon controlled rectifier operation in continuous current mode

Abstract

The invention discloses silicon controlled rectifier operation in a continuous current mode. A method of operating a silicon controlled rectifier (SCR) is provided. The method may include coupling the SCR to receive an AC voltage signal between an anode and a cathode of the SCR. The method may also include applying a gate current between a gate and a cathode of the SCR when the AC voltage signal has a first phase angle corresponding to the first voltage polarity, where the SCR switches from an OFF state to an ON state. The method may also include turning off a gate current between the gate and the cathode at a second phase angle of the AC voltage signal corresponding to a zero voltage cross of the AC voltage signal or corresponding to a second voltage polarity.

Description

Technical Field

[0001] This embodiment relates to the field of power switches and, more particularly, to thyristor-type devices. Background Art

[0002] Thyristors, silicon controlled rectifiers, and related devices (such as TRIACs) are widely used in alternating current (AC) power control applications. Thyristors (such as SCRs and TRIACs) can operate as electrical power switches. More particularly, thyristors are characterized by the ability to quickly switch from a non-conducting current state to a conducting state. In operation, the thyristor is turned on by applying a voltage between the gate and the cathode and causing current to flow from the gate to the cathode, switching from a high impedance state to a low impedance state. Applications of SCRs for regulating current from an alternating current (AC) source are well known. An SCR is a four-layer device formed by alternating P-type and N-type layers. The gate electrode is coupled to the inner layer (layer 2) of the four-layer SCR device, which is beneath the outer layer (layer 1) that forms the cathode. The anode is formed in layer four, where the resulting SCR device presents three P / N junctions at the interfaces of layer 1 / layer 2, layer 2 / layer 3, and layer 3 / layer 4. In operation, the SCR can be triggered from the blocking mode (OFF state) to the forward conducting state by increasing the voltage between the anode and the cathode to exceed the characteristic breakover voltage, or by applying a positive pulse to the gate. Once the SCR starts to conduct, no more gate voltage is required to keep the SCR in the ON state. The minimum current required to keep the SCR in the ON state after removing the gate voltage is called the latching current. On the other hand, the SCR can be turned off by reducing the current flowing through the SCR to a value called the holding current, or by turning off the gate and providing an instantaneous short circuit between the anode and the cathode.

[0003] In known applications, such as in AC applications, when the anode current is below the IH (holding current) of the SCR, such as when a low conduction angle is required in a phase control application (such as a lighting dimmer), the SCR turns off. However, a disadvantage of such control is that after dropping below the holding current, the turn-off of the SCR will interrupt the smooth operation of the load, resulting in problems such as light flickering.

[0004] In view of these and other considerations, the present disclosure is provided. Summary of the Invention

[0005] In one embodiment, a method of operating a silicon-controlled rectifier (SCR) is provided. The method may include coupling the SCR to receive an AC voltage signal between the anode and cathode of the SCR. The method may further include applying a gate current between the gate and cathode of the SCR when the AC voltage signal has a first phase angle corresponding to a first voltage polarity, wherein the SCR switches from an OFF state to an ON state. The method may further include turning off the gate current between the gate and cathode at a second phase angle corresponding to a zero voltage crossing of the AC voltage signal or a second voltage polarity of the AC voltage signal.

[0006] In another embodiment, a method of operating a thyristor is provided. The method may include disposing the thyristor in a thyristor die, the thyristor die being coupled to a load in a circuit supplied by an AC source. The method may further include transmitting a first control signal at a first moment during a positive half-cycle of an AC voltage signal received from the AC source to generate a current pulse between the gate and cathode of the thyristor. Thus, at a second moment during the positive half-cycle of the AC voltage signal, the anode-to-cathode voltage may drop below a determined value corresponding to the turn-on voltage, such that the thyristor turns off while the current pulse is present between the gate and cathode. The method may further include generating a second control signal at a third moment, at or after the time of the zero crossing of the AC voltage signal between the positive half-cycle and the subsequent negative half-cycle of the AC voltage signal, to terminate the current pulse between the gate and cathode of the thyristor. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1A A circuit arrangement in accordance with an embodiment of the present disclosure is presented;

[0008] Figure 1B A composite diagram of signals showing a current control method in accordance with an embodiment of the present disclosure is presented;

[0009] Figure 1C An experimental test signal of a current control method in accordance with an embodiment of the present disclosure is presented;

[0010] Figure 1D Presents Figure 1C a closer view of the test signal;

[0011] Figure 1E An experimental test signal of a current control method according to a known method is presented;

[0012] Figure 1F Presents Figure 1E a closer view of the test signal; and

[0013] Figure 2 An exemplary process flow is depicted. DETAILED DESCRIPTION

[0014] The present embodiment will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. The embodiments should not be construed as limited to the embodiments set forth herein. On the contrary, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey their scope to those skilled in the art. In the drawings, like reference numerals always refer to like elements.

[0015] In the following description and / or claims, the terms "on", "covering", "disposed on", and "above" may be used in the following description and claims. "On", "covering", "disposed on", and "above" may be used to indicate that two or more elements are in direct physical contact with each other. In addition, the terms "on", "covering", "disposed on", and "above" may mean that two or more elements are not in direct contact with each other. For example, "above" may mean that one element is above another element without contacting each other, and there may be another or more elements between the two elements. In addition, the term "and / or" may mean "and", which may mean "or", which may mean "exclusive or", which may mean "one", which may mean "some but not all", which may mean "neither", and / or which may mean "both", although the scope of the claimed subject matter is not limited in this regard.

[0016] Figure 1A A circuit arrangement according to an embodiment of the present disclosure is presented. Circuit 100 may be used to control the current / voltage in a circuit coupled to a load 101, such as a light source, including an LED. In Figure 1A the example, for illustrative purposes, the AC source 103 may output a voltage with a 220V RMS value. According to some non-limiting embodiments, the frequency of the AC source 103 may be in the range of 50 Hz to 60 Hz.

[0017] Circuit 100 includes a control circuit 102, and the control circuit 102 includes a thyristor 106, a switch 104, and a voltage source 110, and the voltage source 110 may be a DC voltage source. The control circuit 102 may regulate the power or current delivered through the load 101, where the current is represented by I A In an implementation as a dimmer circuit, the control circuit 102 may regulate the duration of the current I A flowing through the circuit 100 in any given cycle of the AC voltage delivered from the AC source 103, as discussed in more detail below.

[0018] According to various embodiments, the thyristor 106 can be a silicon controlled rectifier or a similar semiconductor device, in which four semiconductor layers are arranged electrically in series with each other. The turn-on of the thyristor 106 can be controlled by applying a forward voltage between the anode and the cathode and by supplying a gate current. In a simple SCR device, the current flowing through the thyristor 106 can be regulated to flow in exactly one direction, which means flowing during exactly the half-cycle of the AC voltage from the AC source 103. In operation, when the AC voltage signal propagates through the circuit 100, the voltage amplitude across the thyristor 106 will also vary. This voltage can be denoted as V AK , meaning the voltage between the anode and the cathode of the thyristor. When the value of V AK (meaning the anode is forward-biased with respect to the cathode) increases above the breakdown voltage of the thyristor 106, conduction will occur and the thyristor will enter the ON state. If a positive potential V G is applied to the gate of the thyristor 106, the breakdown and conduction of the thyristor will occur at a lower voltage.

[0019] Now turning to Figure 1B , where the top curve shown (curve 120) represents the voltage V AK . As shown, the magnitude of this voltage will typically vary according to the AC voltage signal generated from the AC source 103. The bottom curve (curve 124) represents a train of current pulses generated by the control circuit 102, representing the gate-to-cathode current. According to embodiments of the present disclosure, the control circuit 102 can be set to generate current pulses that represent the gate voltage applied between the gate and the cathode of the thyristor 106. This current pulse can be set to be a regular train of pulses generated on a specific portion of each of the periods 130 of the AC voltage delivered from the AC source 103. As shown, a given pulse, shown as pulse 126, is generated during the positive half-cycle 130A of the AC voltage. When pulse 126 starts, the current I A is triggered to flow, shown as curve 122. At this time, as Figure 1B shown, the voltage V AK drops to the value of the turn-on voltage V T .

[0020] According to embodiments of the present disclosure, the duration D of pulse 126 is set such that pulse 126 extends at least to the zero-crossing point of the voltage signal, as represented by curve 120. Then, the value of the current I A gradually decreases during the remainder of the positive half-cycle 130A, and reaches zero at the point where the value of V AK drops below the turn-on voltage V T , such that the thyristor 106 turns to the OFF state. Subsequently, the voltage V AKTrack the sinusoidal variation of the line voltage generated by the AC source 103 until the thyristor 106 is triggered into the ON state in the subsequent positive half-cycle 130A.

[0021] According to an embodiment of the present disclosure, the switch 104 can be a MOSFET device (see device 104A in Figure 1A ), which is triggered to turn on or off based on a control signal sent by the controller 108. When ON, the switch 104 will supply sufficient gate current to trigger the thyristor 106 into the ON state. Thus, the controller 108 can set the duration of the pulse 126 to extend to or beyond the zero-crossing point 125 from positive voltage to negative voltage in the curve 120, such that the pulse 126 can extend into the negative half-cycle 130B.

[0022] To illustrate the principle of the control method of this embodiment, Figure 1C an experimental test signal of the current control method according to an embodiment of the present disclosure is presented, while Figure 1D a closer view of the test signal of Figure 1C is presented. In the experiment depicted in Figure 1C , a constant gate current I GK is applied. The AC voltage is used to drive the thyristor 106. Since I GK is always on, for the exemplary thyristor used, when the voltage amplitude exceeds about 0.6V, the thyristor 106 will also be in the ON state for most of the positive half-cycle. Note that in various non-limiting embodiments, the range of this V T can be between approximately 0.5V and 1V. Given an AC voltage source of, for example, 220V, the thyristor 106 will thus remain in the ON state for most of the positive half-cycle. Therefore, and as Figure 1B shows, the voltage V AK between the anode and the cathode will remain at a relatively low voltage (corresponding to the on-voltage value of the thyristor) for most of the positive voltage cycle, as shown.

[0023] As Figure 1C and Figure 1D further show, I A will vary smoothly during the positive half-cycle, first increasing and then decreasing smoothly and monotonically to ~ zero mA current at the point where V AK drops below 0.6V.

[0024] As outlined in Figures 1A - 1D , one advantage of this method is that by supplying gate current up to or beyond the voltage zero-crossing moment of the applied AC voltage, the load current can be reduced to a very low value, close to zero, and voltage spiking within the thyristor can be avoided.

[0025] To further illustrate the above advantages of this embodiment, Figure 1E the relevant signals of a scenario using current control according to a known method are shown. In this conventional method, during the positive half-cycle of the AC voltage source connected to the thyristor, the thyristor is triggered ON using short current pulses. During Figure 1E , it is shown by I A , I GK and V AK , whose meaning is the same as that defined above for Figures 1A - 1D . In this conventional method, I GK is supplied as a series of short pulses with a duration of about 2 ms, where one pulse is provided during each positive half-cycle of the AC voltage signal. When the pulse starts at time T P , the current I A is triggered to flow, as shown in the middle curve. Also at T Figure 1B as shown in P , the voltage V AK drops to the value of the turn-on voltage V T .

[0026] As the positive half-cycle progresses, the current I A starts to decrease, and at a given phase angle represented by the time T H , the value of I A drops below the holding current I H of the thyristor under discussion. Once I A drops below I H , the thyristor will turn into the OFF state. In the example shown, the value of this holding current is about 150 mA. As further shown in Figure 1D , at this example point, the voltage value V AK returns to the value of the applied AC voltage signal, and this return may cause a voltage jump as shown in the figure. In an example where the conventional method shown in Figure 1E and and 1F is applied to dimmer control, the behavior shown will interrupt the smooth operation of the load, resulting in problems such as light flickering.

[0027] On the other hand, this embodiment delays the turn-off of the thyristor until after the point where I A drops below the thyristor I H . Instead, the thyristor does not switch to the OFF state until V AK reaches a certain value (such as 0.6 V) near the zero voltage crossing of the external AC voltage. When V AK reaches 0.6 V, the anode current I A has already approached the zero mA value. The subsequent turn-off of the thyristor will not cause V AKThe jump of the value, because the value returns to the line voltage value, thus avoiding problems such as flickering.

[0028] Table I provides a summary comparing various aspects of known current control methods and the method according to this embodiment. As summarized in Table I, using the known method with short IGK pulses, no current remains when the applied AC voltage crosses zero. Additionally, there is a significant load current (shown as anode current I A ) at the turn-off of the thyristor (SCR), which is the thyristor holding current I H . As a result, at the turn-off of the SCR, a significant jump in the value of V AK may occur, from the values of V T and I H to any line voltage at turn-off.

[0029] On the other hand, in this embodiment, since IGK is supplied at least at the moment of zero crossing, the thyristor remains in the ON state until the anode current approaches zero. At turn-off, the value of V AK is small and there is no voltage spike.

[0030] One of the other advantages stemming from this embodiment is the ability to provide improved performance, such as in the case of a light-emitting diode dimmer. For example, this method can achieve the same control as that provided in a dimmer circuit controlled by a MOSFET. For the same rated current or rated power, using a thyristor (SCR) in the circuit of this embodiment is much cheaper than using MOSFET control. Additionally, the thyristor will withstand higher overcurrents and / or overvoltages than a comparable MOSFET.

[0031] Table I

[0032]

[0033] Figure 2 Illustrates an exemplary process flow 200 according to an embodiment of the present disclosure. At block 202, the thyristor die is set to be electrically in series with the load in the circuit supplied by the AC source. In some non-limiting embodiments, the AC source may output an AC voltage signal, where the voltage has a 220V RMS value and a frequency in the range of 50Hz to 60Hz.

[0034] At block 204, at a first moment during the positive half-cycle of the AC voltage signal, a first control signal is generated to send a current pulse between the gate and cathode of the thyristor.

[0035] At block 206, at a second moment during the positive half-cycle of the AC voltage signal, the anode-to-cathode voltage drops below a determined value and the thyristor turns off while a current pulse exists between the gate and cathode.

[0036] At block 208, at the third moment, at the time of the zero crossing of the AC voltage signal between the positive half cycle and the subsequent negative half cycle, a second control signal is generated to terminate the current pulse between the gate and the cathode of the thyristor.

[0037] Although the present embodiment has been disclosed with reference to certain embodiments, many modifications, changes, and alterations to the described embodiments are possible without departing from the scope and range of the present disclosure, as defined in the appended claims. Accordingly, the present embodiment is not limited to the described embodiments and may have the full scope defined by the language of the following claims and their equivalents.

Claims

1. A method of operating a silicon controlled rectifier (SCR), comprising: coupling the SCR to receive an AC voltage signal between an anode and a cathode of the SCR; applying a gate current between a gate and a cathode of the SCR when the AC voltage signal has a first phase angle corresponding to a first voltage polarity, wherein the SCR switches from an OFF state to an ON state; and The gate current between the gate and the cathode is switched off at a second phase angle of the AC voltage signal corresponding to a zero voltage crossing of the AC voltage signal or corresponding to a second voltage polarity.

2. The method according to claim 1, wherein: The second phase angle corresponds to the zero voltage crossing.

3. The method according to claim 1, wherein: The first phase angle corresponds to 90 degrees relative to the zero crossing.

4. The method according to claim 1, wherein: The gate current is triggered from a DC voltage source.

5. The method according to claim 4, wherein: The gate current is supplied to the gate from a field effect transistor that is triggered ON from the DC voltage source.

6. A method of operating a thyristor, comprising: providing the thyristor in a thyristor die coupled to a load in a circuit supplied by an AC source; sending a first control signal at a first moment during a positive half cycle of an AC voltage signal received from the AC source to generate a current pulse between a gate and a cathode of the thyristor, wherein, at a second time during the positive half cycle of the AC voltage signal, the anode-to-cathode voltage drops below a determined value corresponding to a turn-on voltage, causing the thyristor to turn off while the current pulse exists between the gate and the cathode; and At a third time, at or after a zero crossing of the AC voltage signal between the positive half cycle and a subsequent negative half cycle of the AC voltage signal, a second control signal is generated to terminate a current pulse between the gate and cathode of the thyristor.

7. The method according to claim 6, wherein: The determined value is between 0.5V and 1.0V.

8. The method according to claim 6, wherein: The third instant occurs during the subsequent negative half cycle of the AC voltage signal.

9. The method according to claim 6, wherein: The gate current is triggered from a DC voltage source.

10. The method according to claim 9, wherein: The gate current is supplied to the gate from a field effect transistor that is triggered ON from the DC voltage source.

11. The method according to claim 6, wherein: The AC voltage signal comprises a plurality of AC cycles, wherein the current pulse is part of a pulse train comprising a plurality of current pulses, wherein a given current pulse of the plurality of current pulses is applied during a given positive half-cycle of a given AC cycle of the plurality of AC cycles.

12. The method according to claim 11, wherein: The given current pulse terminates during a given negative half cycle immediately following a given positive half cycle of the given AC cycle.

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