JPH0658825B2 - Two-wire dimming circuit and dimming method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a dimming circuit that controls the RMS value of an AC voltage applied to a load. In particular, the present invention relates to a two wire dimming circuit for use with reactive loads in which destructive DC load currents may be present. The device of the invention comprises a correction means for reducing the breakdown DC current flowing through the load and a voltage compensation means for adjusting the RMS value of the AC voltage applied to the load. A two wire low voltage dimming circuit is also provided that does not include voltage compensating means, but has improved dimming capability at low load currents.

The invention has particular application in low voltage dimmers where the load is a low voltage transformer. Meanwhile, the present invention has application to other types of loads such as fluorescent lighting devices.

[Prior art]

Two-wire dimming circuits are well known. One conventional type of two wire dimmer circuit comprises a triac and a dual phase shift firing circuit operably connected to the gate terminal of the triac. The dual phase shift ignition circuit is a series RC circuit connected to a triac and a potentiometer for R
Using an ignition capacitor connected to the -C circuit and connected by a diak to the gate terminal of the triac.
The circuit finds that it can flow in a reactive load, such as the primary winding of a low voltage transformer, by adjusting the firing angle of the triac in selected half-cycles of the AC load voltage waveform in the following manner. Compensating for destructive DC current. The DC component appears across the triac, and thus across the capacitor known as the "leading capacitor". The lead capacitor is the capacitor of the series RC circuit described above. Since the lead capacitor is connected to the ignition capacitor through the potentiometer, the DC voltage applied to the lead capacitor is added to the voltage applied to the ignition capacitor, and the ignition angle reduces the DC current. To be changed.

Although the two-wire dimming circuit described above can solve the DC current problem known to exist in reactive loads, it lacks voltage regulation capability. That is, when the AC power supply voltage fluctuates, the RMS of the AC voltage supplied to the load cannot be maintained substantially constant. It is also known to modify a two-wire dimmer of this kind so that the lead capacitor is replaced by a diak to exhibit good voltage regulation capability. However, the modified circuit cannot correct the DC current problem after the lead capacitor is removed.

A 3-wire dimming circuit is also known. In a three-wire dimmer circuit, two of the three wires are connected in series with the AC power supply voltage, and the firing angle is determined from the AC power supply voltage.
That is, the firing angle is not acted upon by the DC current that may flow through the load. It is also known to integrate a voltage adjustment dial into the ignition circuit of a three-wire dimmer. This type of three-wire dimmer has good voltage regulation capability,
It does not exhibit DC current problems. However, a three-wire dimmer is undesirable because it requires three wires (AC hot, AC neutral and load) to be laid down to each wall box, which requires additional equipment costs.

The present invention overcomes the deficiencies of the prior art by incorporating both a voltage adjustment circuit and a DC current correction circuit in a two-wire dimmer.

[Outline of Invention]

The dimming circuit of the present invention for use with a reactive load such as a low voltage transformer is designed for connecting in series with a load and an AC power source.
It only has a pair of lines. A first and a second conductively controllable thyristor are operatively connected to the pair of wires, the control circuit applying a control signal to the gate terminal of the first thyristor to provide an instantaneous AC voltage to the control circuit. The first thyristor is ignited at an ignition angle dominated by the target size. The second thyristor is made conductive only after the load current in the first thyristor exceeds a selected magnitude. The first thyristor is turned off only after the second thyristor is turned on. In the preferred embodiment, the thyristor used is a triac, but an anti-parallel SCR or other suitable device could also be used.

The circuit is equipped with voltage compensation means,
Adjust the RMS value of the C voltage. In the disclosed embodiment, the voltage compensating means is a diamond having a negative resistance characteristic, and when the AC power supply voltage fluctuates, the voltage applied to the control circuit by the diamond causes the timing of the control signal, and thus the triac. Of the AC voltage applied to the load.
Keep the MS value substantially constant. The effect of this compensation is
It occurs as long as the magnitude of the AC voltage is greater than the breakdown voltage of the diac.

The circuit of the present invention also comprises correction means for correcting the asymmetry of the AC load voltage waveform caused by the DC current flowing through the load. The DC current flowing through the load causes the firing angle to lead or lag in the positive or negative half cycle of the AC load voltage waveform, depending on the magnitude and polarity of the DC current. Thus, the AC load voltage waveform is asymmetric. The corrector corrects the asymmetry by advancing or retracting the firing angle of successive half cycles until the waveform of the AC load voltage is substantially symmetrical, thereby reducing the destructive DC current flowing through the load. .

In the disclosed embodiment, the correction means includes a series connected resistor and a correction capacitor connected across the dimming circuit. The correction capacitor charges to a voltage level that dictates the magnitude and polarity of the DC current flowing through the load. The feedback loop adds the voltage across the compensation capacitor to the voltage across the ignition capacitor operatively connected to the first triac gate. In each successive half cycle of the waveform of the AC load voltage, the firing angle is advanced or retracted by an amount governed by the magnitude and polarity of the voltage across the compensation capacitor (of the preceding half cycle of opposite polarity). Regarding the firing angle).

In another embodiment, the correction capacitor is placed in series with the voltage compensation diamond. The correction capacitor is charged by the current flowing in the voltage compensation dia to a voltage level which dictates the magnitude and polarity of the DC current flowing in the load. The voltage across the compensation capacitor is provided in series with the diac to effectively regulate the voltage applied to the firing capacitor, thereby advancing or retracting the firing angle in each successive half cycle.

〔Example〕

The present invention will be described below with reference to the accompanying drawings. The same reference numerals refer to the same members throughout the drawings.

Referring to the drawings, FIG.
A conventional two-wire low-voltage dimming device is indicated by. The dimmer 10 comprises a two-wire dimmer circuit 12 having only a pair of wires 26, 28 connected in series with a transformer 23 and a primary winding 20 of an AC power supply 18. Light control circuit 12
Is provided with a triac 16 and a control circuit 14 which is operatively connected to both ends of the triac 16 and supplies a control signal to a gate 17 for selectively conducting the triac 16. As is well known in the art, the timing of the control signal, and thus the firing angle of the triac, governs the RMS value of the AC voltage supplied to the load. The dimming circuit 12 illustrated in FIG. 1 is shown as controlling a low voltage connected to the secondary winding 22.

As is well known, the firing angle of triac 16 is dominated by the instantaneous voltage across control circuit 14, and thus between lines 26 and 28. Therefore, the firing angle will be affected by the DC magnetizing current flowing in the primary winding 20 of the transformer 23. The magnitude of this DC current can be considerable,
It can cause the problems described below.

The DC current in question can be caused by multiple factors. For example, the secondary winding 2 of the transformer 23
When the lamp 24 or other load connected to 2 is disconnected (that is, it becomes an open circuit), DC flowing through the primary winding 20
The magnitude of the magnetizing current may be significant compared to the RMS value of the AC current flowing in the primary winding 20. Also, AC
It can be envisioned that the supply of AC power to the circuit 10 may be momentarily interrupted when the voltage waveform is at or near 0 after a positive or negative half cycle. If, at the moment AC power is restored, the AC voltage waveform is at or near zero of a half cycle of the same polarity that existed when the power was removed, the magnetic material in the core in transformer 23 Can be saturated and cause the transformer to conduct more easily in one direction than in the other. This delays the firing angle of the triac 16 in one half cycle of the AC voltage waveform (see FIG. 9), which causes the transformer 23 to become more polarized. The regenerative nature of this development causes DC current problems.

FIG. 2 shows a block diagram of the three-wire low-voltage light control device 30. The device 30 comprises a three-wire dimming circuit 32 with the two wires 46, 48 directly connected to the AC power supply voltage 38. The lines 48, 50 are connected to the primary winding 40 of the transformer 41 and provide a low voltage to the lamp 44 by the secondary winding 42. The dimming circuit 32 includes a triac 36 and a control circuit 34 which supplies a control signal to a gate 37 of the triac 36. Similar to the control circuit of FIG. 1, the control circuit 34 is directly connected to the AC voltage. Therefore, the firing angle of the control signal is not affected by the DC current that may flow in the primary winding 40 of the transformer 41. However, the 3-wire dimming circuit of FIG. 2 is not only more expensive to manufacture than the 2-wire dimming circuit of FIG. 1, but it also runs 3 instead of 2 wires to the box on the wall. This also increases the costs associated with installing the 3-wire dimmer.

FIG. 6 schematically shows a known two-wire dimmer circuit. Sixth
The circuit 52 illustrated in the figure utilizes a control circuit of the type known as a dual phase shift firing circuit which produces control signals. The dual phase ignition circuit has a resistor 54 and a lead capacitor 5
6, potentiometer / trim circuit 58, firing capacitor and dial 64. The operation of this circuit is well known in the art.

The two-wire dimmer circuit of FIG. 6 does not exhibit the problems discussed above caused by the DC current flowing through the load if the characteristics of triac 64 are selected according to certain criteria. This criterion will be discussed later. When the DC component appears on triac 64, this component also appears on capacitor 56. Since the lead capacitor 56 is coupled to the ignition capacitor 60 via the potentiometer / trim circuit 58, the DC voltage across the lead capacitor 56 will be triaced during a selected half cycle of the AC load voltage waveform. Correct the firing angle of 64. The effect of changing the firing angle in this manner, and how it corrects the DC current problem, will be made clear later.

Proper selection of the characteristics of triac 64 ensures that the circuit of FIG. 6 does not exhibit the DC current problem described above, but other problems do occur. The circuit of FIG. 6 cannot maintain the RMS value of the AC voltage supplied to the load substantially constant with respect to variations in the AC power supply voltage. It is desirable that such a voltage adjustment be possible in the two-wire DC compensation light control device.

Previous attempts have been made to modify the circuit of FIG. 6 to perform the desired voltage regulation function. One such variation is to replace the lead capacitor 56 with a diac, and the voltage across the potentiometer / trim circuit 58 during the diac's conduction changes the firing angle to cause variations in the AC power supply. Including changing in a compensating manner. This modification results in a two-wire dimmer that regulates the voltage unless the AC voltage varies below the breakdown voltage of the diac. However, the resulting dimmer is unable to correct the DC current flowing through the load, as this change proceeds and requires removal of the capacitor 56. The following discussion explains why this is the case. In the discussion below,
The term "modification circuit" refers to the sixth modification modified in the manner described above by replacing the lead capacitor 56 with a diac.
Used to refer to the circuit in the figure.

Referring to the waveforms of FIGS. 7, 8 and 9, AC power supply voltage (74, 74 ′, 74 ″), AC load voltage (76, 7).
6 ′, 76 ″), AC load current (78, 78 ′, 7)
8 ") and AC voltage (80, 8) across the triac
0 ', 80 "). As shown in the figures, the AC load voltage (76, 76', 76") is
It is chipped by the triac 64 in a known manner to provide the desired RMS voltage value. As is known in the art, adjusting the firing angle of triac 64 results in a corresponding adjustment of the RMS value of the AC voltage supplied to the load.

FIG. 7 shows various waveforms of AC power supply voltage 74, AC load voltage 76 and AC load current 78 for a purely resistive load that may be connected to the modified circuit of FIG. As shown, all waveforms are in A
Including the waveform 80 representing the C voltage, it is largely in-phase and generally symmetrical. Therefore, the operation of the circuit of FIG. 6 when used with a purely resistive load is acceptable.

FIG. 8 illustrates the same waveform that results when the modified circuit of FIG. 6 is applied to a load that has an almost resistive but slightly inductive component. As shown,
The inductive component causes the AC current waveform 78 'to be slightly out of phase with the AC load voltage waveform 76'. However, all waveforms are symmetrical. Therefore, if the inductive component of the load is small, the modified circuit of FIG. 6 may be acceptable.

FIG. 9 illustrates that the modified circuit of FIG. 6 is unacceptable for use with loads having both substantially inductive and resistive components, such as transformer loads. AC
The phase of the load current 78 ″ is also the waveform 7 of the AC load voltage.
Slightly out of phase with respect to 6 ". If there is saturation in the magnetic material of the load (transformer), the load may conduct current more easily in one direction than in the other and thus the AC load voltage 76". During a period of time, the AC load current 78 "is increased to an abnormally high level as shown at 84. Since the triac 64 is a current sensitive device, the load voltage 76" is sufficiently reduced to reduce the AC current 7 ".
Triac 64 does not become non-conductive until 8 ″ is forced below the triac hold current to make it non-conductive as illustrated in FIG. 9a. The net effect, as illustrated in FIG. 9, is that the DC current shifts the firing angle of the triac 64 considerably during repeated positive or negative half-cycles, causing the magnitude of the AC load current to rise to an abnormal level. Is to increase. This phenomenon occurs only during repetitive positive or negative half-cycles, not over the entire cycle, so the waveform 76 ″ is asymmetric.

Also, as illustrated in FIG. 9, the shift in firing angle during the repeating half cycles causes the AC voltage on the triac 64 to be greater in one half cycle than in the preceding half cycle of opposite polarity. . Further, it can be seen that the voltage on triac 64 during the positive half cycle is lower than the voltage during the negative half cycle. This means that the voltage supplied to the load is higher during the positive half cycle than during the negative half cycle. This is because the load voltage is equal to the difference between the supply voltage and the triac voltage,
This is because both half cycles of the AC power supply have essentially equal RMS voltage values. Since the transformer primary winding to which the load voltage is applied has a positive voltage higher than the negative voltage, the transformer is saturated in the direction of positive current in the primary winding. This further increases the magnitude of peak current 84. Therefore, it can be seen that some asymmetry of the load voltage causes a positive feedback effect due to its effect on the dimmer. This causes any small initial disturbances to become progressively worse until a large peak current value 84 occurs. If the peak value 84 of the AC load current 78 "is increased uncontrolled, there may be a fire hazard if the phase blows, the circuit breaker opens, or the temperature rises to a sufficient level.

Although the above paper is for illustrative purposes and the DC current problem was described as occurring during the positive half-cycle, it will be appreciated that it could occur just as well during the negative half-cycle. In any event, potentially destructive DC currents can be eliminated if the firing angle can be advanced or retracted as needed during selected positive or negative half-cycles where DC current problems exist. . In other words, if the waveform of the AC voltage applied to the load can be maintained symmetrically, i.e. it can be changed to give a negative feedback back instead of the above-mentioned positive one, the above current problem does not occur. Let's do it. A dimmer circuit that achieves this function will be described below.

Referring to FIG. 3, one embodiment of the dimming circuit according to the present invention is shown. As in FIG. 6, the dimmer circuit of FIG. 3 comprises an RFI circuit including a resistor 84, a capacitor 86 and an inductor 87. This RFI circuit does not form part of the present invention. The dimming circuit also includes a potentiometer / trim circuit 92, a dial 96 and a first
Triac 98 gate terminal and potentiometer /
A control circuit is provided that includes an ignition capacitor 94 operatively connected to one terminal of the trim circuit 92. The resistor 101 is connected in series with the triac 98, and the second triac 99 is connected to both sides of the dimming circuit, and its gate terminal is connected to the connection point between the resistor 101 and the first triac 98. The use of two triacs 98, 99 rather than a single triac can improve the operation of the dimming circuit at low load currents if these triacs are selected in the manner described below.

The RC series connection of resistor 88, potentiometer / trim circuit 92 and capacitor 94 provides a timed signal to the gate of triac 98. As we all know,
The timing of the control signal (hence the firing angle) is determined by the circuit 9
It is at least partially dominated by the potentiometer setting of 2. In addition, the dimming circuit supplies A to the load.
Voltage compensating means 90 for maintaining the RMS value of the C voltage substantially constant, and means 100 for correcting the asymmetry of the waveform of the AC voltage supplied to the load to eliminate the DC current problem discussed above. , 102 and 104.

As shown, the voltage compensating means 90 comprises a control circuit, specifically a diac operably connected to the other terminal of the potentiometer / trim circuit 92 and the resistor 88. Diamond 9
0 has a breakdown voltage which is supplied to the control circuit, and in particular the potentiometer / trim circuit 92, when the diac is conducting. The control circuit responds to variations in the breakdown voltage and the AC power supply voltage provided by the diac 90 to adjust the firing angles of the triacs 98 and 99 in accordance with the timing of the control signal to control the AC voltage supplied to the load. Keep the RMS value approximately constant. Similar to the modified circuit of FIG. 6, this circuit regulates the AC load voltage unless the AC voltage varies below the breakdown voltage of the diac 90.

In the circuit of FIG. 3, the correction means comprises a series connection of a resistor 100 and a correction capacitor 102 connected on both sides of the dimming circuit as shown. The correction capacitor 102 is
Charge to a voltage level that dictates the magnitude and polarity of the DC current flowing in the load. The voltage across the compensation capacitor 102 is coupled to the voltage on the ignition capacitor 94 by the feedback resistor 104. Thus, the voltage across firing capacitor 94 is changed, changing the firing angle of triacs 98 and 99 in the next subsequent half cycle. The process of feeding back the voltage to the firing capacitor 94 is done until the waveform is substantially symmetrical, ie D
Continue for the next half cycle of the AC load voltage waveform until the C current is substantially eliminated.

The dual triac state illustrated in FIG. 3 overcomes several problems inherent in a single triac type dimmer circuit. In a single triac type dimming circuit, the triac must be sized for maximum load current and therefore has a relatively high hold current. If the load current drops below the hold current, the triac stops conducting and power is removed from the load. Therefore, dimming cannot be performed for load currents below the hold current. Moreover, the hold currents for the triac forward and reverse currents are not the same.
This asymmetry can cause serious problems in low voltage dimmers where the load has a significant inductive component, such as in low voltage transformers. This is because it is sufficient to activate the above-described positive feedback mechanism inherent in the operation of known two-wire low voltage dimming circuits.

In the circuit of FIG. 3, the control signal is supplied to the gate of the first triac 98 as described above. Thus, if a control signal is applied to the gate of triac 98, and triac 98 has sufficient voltage, triac 98 will conduct. The current flowing through the triac 98 and the resistor 101 is applied to the triac 99 across the resistor 101.
Triac 99 is rendered conductive when a sufficient voltage is generated to ignite. This voltage drop is nominally 1 volt according to the preferred embodiment. Triac 9
When 9 is fully conducting, the voltage across the anode and gate of triac 99 is essentially zero and triac 98 no longer has sufficient current. Triac 98
When the current inside falls below the hold current, triac 98 turns off, allowing the full load current of triac 99 dimming circuit to flow.

If the load current of the triac 98 is low enough, the resistance 10
The voltage drop of 1 is not large enough to trigger the triac 99 to conduct in the manner described above. in this case,
The triac 98 is not turned off by the triac 99, as previously described, but allows the full load current to flow until the load current is large enough to trigger the triac 99 into conduction.

As mentioned above, the advantages of using two triacs are:
The ability to independently select the characteristics of triacs 98 and 99 for low and high range load currents. Another advantage is that the boundaries between operating ranges can be limited by choosing an appropriate value for resistor 101. The main factor that determines the characteristics of the triac 99 is the maximum load current standard of the dimming circuit. That is, the triac 99 must be able to faithfully carry the maximum load current. Another characteristic that must be selected is the hold current of each triac. The hold current of a triac varies significantly between different samples of the same type of triac, and also with respect to temperature and current specifications. The following is a summary of the items to be taken into consideration when selecting a triac for use in the circuit of FIG.

The most problematic operating condition of a two wire low voltage dimmer operating a transformer load occurs when the transformer is unloaded. Under these conditions, conducting triacs (usually third
The current flowing through the illustrated triac 98) will be only slightly greater than the hold current for each half cycle of the AC load current. In this case, if the load current begins to decrease, such as towards the end of each half cycle, the triac may stop conducting before the zero crossing of the AC load voltage. The angle at which the triac stops conducting can vary considerably in the positive and negative half cycles due to the above-mentioned asymmetry of the hold current. As a result of this different conduction in each half-cycle, the transformer may encounter a DC voltage component and consequently be driven into saturation.

The triac hold current is typically about 1/1000 of its maximum current specification. Therefore, for example, a 25 amp standard triac would be expected to have a hold current of about 25 mA. Even this relatively low hold current can cause serious transformer saturation problems. Because a small low-voltage transformer is only about 4
This is because it is 0 or 50 mA. Hold current is about 0.8m when using 0.8A standard triac.
Will be A. Alternatively, it is relatively smaller than the magnetizing current. However, 0.8A triacs cannot sustain the desired load or transient surges that are common in dimmer applications.

Referring to FIG. 3, when the value of the resistor 101 is selected to be about 5Ω, only the triac 98 conducts when the peak load current is about 200 mA or less. That is, 200 mA is required to make the triac 99 conductive by causing a voltage drop of 1 V in the resistance of 5Ω. therefore,
The triac 98 can be a standard for a relatively low maximum load current and have a very low hold current as described below. If the load current increases above about 200 mA, triac 99 turns on and triac 98 turns off as described above. The triac 99 handles full load currents and its relatively high hold current becomes insignificant at these high load currents.

The above example where the triac 98 is rated at 0.8A and the triac 99 is rated at 25A is a typical ratio. The value chosen for resistor 101 depends on the actual current rating, but is generally chosen to produce a 1V voltage drop at a current level of about 1/10 to 1/2 of the maximum current rating of triac 98. Should be. This ensures that low load currents are conducted only in triac 98 and only high load currents are conducted in triac 99.

FIG. 4 shows another implementation circuit according to the present invention. Again, the RFI circuit includes resistor 106, capacitor 108 and inductor 116. The first triat 124
The control circuit for supplying the control signal to the gate terminal of
Includes resistor 110, potentiometer / trim circuit 118, dial 120 and ignition capacitor 122. As mentioned above, the resistor 127 is connected in series with the first triac 124. A second triac 125 is connected to both sides of the dimming circuit, and its gate terminal is
It is connected to the connection point of the resistor 127 and the triac 124. Triacs 124 and 125 are selected similarly to triacs 98 and 99 described above.

The dial 112 is connected to a control circuit, specifically a potentiometer / trim circuit 118, as shown. A correction capacitor 114 is connected between the dial 112 and one side of the dimming circuit in the illustrated manner. Resistance 11
3 connects the other side of the dimming circuit to the connection point between the diamond 112 and the correction capacitor 114. As mentioned above, the diamond 112, when in the conductive state, provides a compensated breakdown voltage to the control circuitry, and in particular the potentiometer / trim circuitry 118. The control circuit adjusts the firing angle of the control signal in response to fluctuations in the AC power supply voltage and breakdown voltage to maintain the RMS value of the AC voltage supplied to the load substantially constant. As mentioned above, the RMS value of the AC voltage supplied to the load remains substantially constant unless the AC voltage varies due to the breakdown voltage of the diac. Thus, in the circuit of FIG. 4, the diamond 112 performs the voltage adjusting function.

In the circuit of FIG. 4, the correction means is the capacitor 11
4, resistor 110, diamond 112 and resistor 113. The current flowing through resistor 110, diacs 112 and 113 charges capacitor 114 to a voltage level that dictates the magnitude and polarity of the DC current flowing through the load. The voltage across the correction capacitor 114 is provided in series with the dial 112, thereby effectively adjusting the voltage provided to the firing capacitor 122 via the potentiometer / trim circuit 118. This variation in the voltage supplied to the firing capacitor 122 via the potentiometer / triac circuit 118 corrects the firing angle in each successive half cycle, thereby eliminating the asymmetry of the AC voltage waveform and the DC Substantially eliminate current.

The value of the correction capacitor 102 used in the circuit of FIG.
And the value of the capacitor 114 utilized in the circuit of FIG. 4 must be large enough so that there is only a relatively small AC impedance. Preferably, the correction capacitors 102, 114 should be sized to provide a substantial short circuit for AC current. Therefore, only a small ripple voltage appears across the correction capacitors 102 and 114.

The embodiment of FIG. 5 is substantially the same as the embodiment of FIG. However, the circuit of FIG. 5 utilizes two electrolytic capacitors 138, 140 and two diodes 134, 136 instead of the capacitor 114. This variant minimizes the physical size of the circuit and allows installation in standard wall boxes. Again, the previous discussion on how to choose a triac applies.

According to another aspect of the invention, a two wire system having no voltage compensation means, but having improved dimming capability at low load currents and improved resistance to DC current, as described above. A low voltage dimming circuit is provided. This circuit uses a dual triac selected according to the criteria mentioned above.

FIG. 10 shows a well known three wire dimmer circuit having three wires 160, 162, 164 for connection to an AC power source 146 and a load 152. As shown, the load 152 is a low voltage transformer that includes a primary winding and a secondary winding 156 connected to an incandescent lamp 158. Circuit 14
2 is a double triac 148, 15 as shown.
0 and a resistor 151 in series with triac 148. The gate of triac 148 receives control signals from control circuit 144. The gate of triac 150 is operatively connected to the connection point between resistor 151 and triac 148. In connection with the structure of the three-wire type dimming circuit 142, according to the above criteria, the triac 148,
It is known to select 150. However,
As mentioned above, a 3-wire dimmer circuit of the type illustrated in FIG. 10 is undesirable. This is because the three lines must be extended to the box on each wall, which increases the cost of laying.

In accordance with the present invention, the two selected according to the above discussion
A two wire low voltage dimming circuit utilizing a heavy triac is provided. Such a circuit is illustrated in FIG. 11 and is generally labeled 166. Circuit 1166 is D
A C correction is made, but the voltage adjustment is not possible for the same reasons as described in connection with the circuit 52 illustrated in FIG. The circuit includes a pair of wires 17 for series connection with AC power and load.
Only 2,174 included. As mentioned above, the load may be a low voltage transformer. In addition, circuit 16 with some changes
6 can be used as a fluorescent lamp dimmer and is connected in series with the ballast.

As previously mentioned, the circuit 166 includes a capacitor 168, a resistor 170 and an inductor 176 connected as shown.
It includes an RFI filter consisting of The RFI filter does not form part of the present invention. Circuit 166 also includes a series RC circuit combination, namely, resistor 170 and capacitor 178 operably connected to line pair 172, 174 via inductor 176. The junction of resistor 170 and capacitor 178 is operatively connected to one side 179 of potentiometer / trim circuit 180. The other side 181 of the potentiometer / trim circuit 180 is operatively connected to the dial 184 in series with the gate of the triac 186. Also, the capacitor 182 is
A potentiometer / trim circuit 180 as shown,
It is connected between the connection point of the capacitor 178 and the inductor 176. The triac 186 is
18 between the line pair 172, 174 via the inductor 176.
8 is connected in series. The triac 190 is operatively coupled to the wire pair 17 via the inductor 176 as shown.
2 and 174 are connected in series, and their gate terminals are operatively connected to the connection point of the resistor 188 and the triac 186. The triacs 186 and 190 are
The selection is preferably made as described above, and the operation is also as described above.

The circuit of FIG. 11 provides DC correction but not voltage regulation. However, the circuit of FIG. 11 exhibits improved dimming capability at low currents for the reasons mentioned above. Furthermore, the double triac used in the circuit of FIG.
It avoids the problems usually caused when the load has a considerable inductive component.

The present invention can be embodied in other specific forms without departing from the technical idea of the present invention, and is limited only by the scope of the claims.

[Brief description of drawings]

FIG. 1 is a block diagram of a well-known 2-wire low-voltage dimming circuit, and FIG. 2 is a block diagram of a well-known 3-wire low-voltage dimming circuit.
FIG. 4 is a schematic diagram of a specific example of a two-wire low voltage dimming circuit according to the present invention, and FIG. 4 is a schematic diagram of another specific example of a two-wire low voltage dimming circuit according to the present invention. FIG. 6 is a schematic diagram of still another specific example of the two-wire type low voltage dimming circuit according to the present invention, FIG. 6 is a schematic diagram of a conventional two-wire type dimming circuit, and FIGS. An exemplary voltage waveform diagram used to describe the operation of the invention, FIG. 10 is a schematic diagram of a known three-wire dual triac dimmer circuit, and FIG. 11 is a voltage compensation circuit according to the present invention. FIG. 3 is a schematic diagram of a two-wire low-voltage double triac dimming circuit without a light source. 84: Resistor (RFI circuit) 86: Capacitor (RFI circuit) 87: Inductor (RFI circuit) 88: Resistor (control circuit) 92: Potentiometer / trim circuit (control circuit) 94: Firing capacitor (control circuit) 96 : Diac (control circuit) 90: Voltage compensating means 98: First triac 99: Second triac 100: Resistance (correction means) 102: Correction capacitor (correction means) 104: Feedback resistance (correction means)

Claims (48)

[Claims] 1. A bidirectional electronic switching means comprising a type of AC voltage applied to a load which selectively conducts the electronic switching means in response to a timed repetitive control signal applied. In a two-wire dimming circuit equipped with control input means for controlling the RMS value, the RMS value of the AC voltage supplied to the load is adjusted so that a destructive DC current caused by the load having a resistance and an inductive component is generated. A reducing circuit is provided to the load in response to the signal provided by (a) a signal having a value indicative of a DC current flowing through the load; and (b) a signal provided by the first means. A
Second means for adjusting the timing of the control signal to reduce the DC current flowing through the load during the selected half cycle of the waveform of the C voltage, and (c) adjusting the timing of the control signal to the dimming circuit. And a third means for compensating for variations in the supplied AC voltage and thereby adjusting the RMS value of the AC voltage supplied to the load. 2. The first means comprises: a first capacitor; and a means for charging the first capacitor to a DC voltage having a magnitude and polarity indicating the magnitude and polarity of the DC current flowing through the load. The light control circuit according to claim 1, further comprising: 3. The electronic switching means includes thyristor means, the control input means includes a gate terminal of the thyristor means, and the dimming circuit is operatively coupled to the gate terminal and charged to a predetermined voltage. The dimming circuit according to claim 2, further comprising a second capacitor that supplies a control signal to turn on the thyristor means when the circuit is turned on. 4. The thyristor means comprises first and second thyristors each having a particular hold current characteristic, the hold current characteristic of the first thyristor being considerably smaller than the hold current characteristic of the second thyristor. The light control circuit according to the third section. 5. A resistor connected in series with the main terminal of the first thyristor, wherein the gate of the first thyristor receives the control signal, and the gate of the second thyristor has the resistor and the main terminal of the first thyristor. A second thyristor is made conductive when the voltage applied to the resistance exceeds a selected value, and the first thyristor is made non-conductive after the second thyristor is made conductive. The light control circuit according to item 4. 6. The second means couples the DC voltage applied to the first capacitor to the voltage of the second capacitor to obtain a second voltage.
4. A dimming circuit as claimed in claim 3 including a feedback loop which alters the voltage across the capacitor and thereby alters the timing of the control signal. 7. The third means includes a diac operably connected to the first capacitor, the diac having a breakdown voltage such that at least a portion of the breakdown voltage is in a conductive state when in its conducting state. The dimmer circuit according to claim 3, which is supplied to two capacitors. 8. The second means for supplying the DC voltage applied to the first capacitor to the diac to effectively change the voltage supplied to the second capacitor, thereby changing the timing of the control signal. A dimmer circuit according to claim 7 including means. 9. The dimming circuit according to claim 1, wherein the load is a low-voltage transformer. 10. The dimmer circuit according to claim 1, wherein the load is a ballast. 11. A light control circuit according to claim 3, 6, 7 or 8 wherein said thyristor means comprises a triac. 12. A dimmer circuit according to claim 4 or 5, wherein said first and second thyristors comprise first and second triacs, respectively. 13. A circuit having a circuit for controlling the RMS value of an AC voltage supplied to a partially resistive and partially inductive load.
In a line dimming circuit, (a) a pair of conductors for connecting in series with a load and an AC voltage source voltage; and (b) a first bidirectional electronically connected between the conductor pairs. Control means for selectively operating the switch means and the first electronic switch means to supply an AC voltage to the load; and (c)
Repetitively activating the first electronic switching means at a selected time period defining an ignition angle in response to the instantaneous magnitude of the AC voltage operatively connected to the control input means and appearing between the pair of lines. Control circuit means for conducting, (d) voltage compensation means for adjusting the RMS value of the AC voltage supplied to the load, and (e) correction means for correcting the asymmetry of the waveform of the AC voltage supplied to the load. A two-wire dimming circuit characterized by comprising. 14. The voltage compensating means includes a second voltage sensitive bidirectional electronic switching means having a breakdown voltage, the breakdown voltage being provided to the control means during conduction of the second electronic switching means. And the control circuit means adjusts the firing angle in response to variations in the breakdown voltage and the AC power supply voltage.
14. The dimming circuit according to claim 13, thereby adjusting the RMS value of the AC voltage supplied to the load. 15. The dimmer circuit according to claim 14, wherein said first electronic switching means comprises thyristor means and said second electronic switching means comprises a diac. 16. The compensating means is operatively coupled to the control circuit means and includes a capacitor for adjusting the firing angle of the first electronic switching means during successive half cycles of the waveform of the AC voltage supplied to the load. 14. A dimmer circuit according to claim 13 including. 17. The first electronic switch means comprises first and second thyristors each having a gate terminal and first and second main terminals, the first main terminal of the first thyristor being a wire pair. Operatively connected to one of the first thyristors, the first resistor operatively connects the second main terminal of the first thyristor to the other of the pair of conductors, and the main terminal of the second thyristor is operatively directly connected between the pair of conductors. And a gate terminal of the first thyristor receives a control signal from the control circuit means and a gate terminal of the second thyristor is operatively connected to a connection point between the first resistor and the second main terminal of the first thyristor. The light control circuit according to claim 13. 18. The method according to claim 17, wherein the first and second thyristors each have a specific hold current characteristic, and the hold current characteristic of the first thyristor is considerably smaller than the hold characteristic of the second thyristor. The dimmer circuit according to the item. 19. The first and second thyristors each have a maximum current standard, and the maximum current standard of the first thyristor is less than about 1/10 of the maximum current standard of the second thyristor. The light control circuit according to item 17. 20. The first thyristor has a maximum current rating, and when the flowing current is about 1/10 to 1/2 of the maximum current rating, there is about 1 volt of the first resistance so that there is about 1 volt of the first resistance. The dimmer circuit according to claim 17, wherein a value is set. 21. The control circuit supplies AC to a load.
18. The dimming circuit according to claim 17, further comprising adjustment control means for manually adjusting the firing angle so as to change the RMS value of the voltage. 22. The adjustment control means includes a potentiometer, and the control circuit means includes a first potentiometer.
A first diac connected in series between the terminal and the gate terminal of the first thyristor, a connection point (i) between the first diac and the first terminal of the potentiometer, and one of the conductive wire pairs (ii). 22. The dimming circuit according to claim 21, comprising a first capacitor operatively connected. 23. The voltage compensating means comprises a second diac having a first terminal operatively connected to a second terminal of the potentiometer and having a breakdown voltage, the breakdown voltage being in the conducting state during the conducting period. Supplied to the potentiometer,
A control circuit adjusting the firing angle in response to variations in the breakdown voltage and the AC supply voltage, thereby adjusting the RMS value of the AC voltage supplied to the load at the value indicated by the potentiometer setting. The light control circuit according to item 22. 24. The correction means includes a second diak of the second diac.
24. The dimmer circuit of claim 23 including a second capacitor operably connected between the terminal and one of the pair of conductors. 25. A second capacitor is operatively connected between a connection point (i) between the second capacitor and the second terminal of the second diac and one of the wire pairs (ii), and An AC voltage supplied to the load, which is provided with a second resistor for charging to a voltage indicating the magnitude and polarity of the flowing DC current, and effectively adjusts the breakdown voltage of the second DIAC with the voltage of the second capacitor. 25. The dimmer circuit of claim 24, wherein the firing angle is changed in selected half-cycles of the waveform to reduce the DC current flowing through the load. 26. A series-connected second resistor and a second capacitor operatively connected between the pair of conductors, and a connection point between the second capacitor and the second resistor to connect the first capacitor and the first diac. A feedback loop to the point is provided, and the second capacitor is charged to a voltage indicating the magnitude and polarity of the DC current flowing to the load,
A capacitor changes the voltage normally supplied to the first diac by the first capacitor, thereby changing the firing angle at selected half-cycles of the waveform of the AC voltage supplied to the load, thereby flowing DC through the load. 24. The dimmer circuit according to claim 23, wherein the current is reduced. 27. The dimmer circuit according to claim 13, wherein the load is a low voltage transformer. 28. The dimmer circuit according to claim 13, wherein the load is a ballast. 29. A light control circuit according to claim 15, wherein said thyristor means comprises a triac. 30. Claims 17, 18, 19, 20, 21, 22, 23, 2 wherein said first and second thyristors comprise first and second triacs, respectively.
The dimming circuit according to item 4, 25, or 26. 31. A two-wire dimming circuit having a circuit for adjusting the RMS value of an AC voltage supplied to a load and reducing a destructive DC current caused by a load having a resistance and an inductive component. ) Having only one pair of lines for series connection with the load and the AC power supply voltage, and (b) having a gate terminal and first and second main terminals, the first main terminal being connected to one of the conductor pairs. The first thyristor, which is operatively connected and whose second main terminal is operatively connected to the other of the pair of conductors by resistance, and (c) the pair of main terminals are operatively directly connected between the pair of conductors, and the gate terminal is , A second thyristor operatively connected to a connection point between the resistor and the second terminal of the first thyristor, and (d) operably connected between the gate terminal and the wire pair of the first thyristor, R-
C is provided with a first capacitor and a potentiometer connected in series, the first or second at an ignition angle determined at least in part according to the setting of the potentiometer.
And a control circuit for selectively igniting and conducting the thyristor, when the voltage value applied to the resistance exceeds the selected value, the second thyristor is called and conducted, and the second thyristor is conducted. The first thyristor is made non-conductive,
The RMS value of the AC voltage supplied to the load is thereby made variable according to the set value of the potentiometer, and (e) is a diac having a breakdown voltage arranged in the circuit, the period during which the diac is conducting. The breakdown voltage is superimposed on the R-C series connection of the middle potentiometer and the first capacitor, the firing angle is adjusted to compensate the fluctuation of the AC voltage, and thereby the RM of the AC voltage supplied to the load.
A diac for adjusting the S value, (f) a second capacitor operatively connected to the circuit for charging to a DC voltage indicating the magnitude and polarity of the DC current flowing through the load, (g)
Responsive to a DC voltage across the second capacitor, means for altering a selected half-cycle mid-firing angle of the waveform of the AC voltage supplied to the load to reduce the DC current flowing through the load. 2 wire type dimming circuit. 32. The means for changing the firing angle in response to the DC voltage across the second capacitor comprises a feedback loop that adds the voltage across the second capacitor to the voltage across the first capacitor. The light control circuit according to item 31. 33. Means for changing the firing angle in response to a DC voltage across the second capacitor adds the voltage across the second capacitor to the voltage of the diac, and an RC series connection of the potentiometer and the first capacitor. The light control circuit according to claim 31, wherein the voltage applied to the light source is changed. 34. The dimming circuit according to claim 31, wherein the load is a low voltage transformer. 35. The light control circuit according to claim 31, wherein the resistor is a ballast. 36. Claims 31 and 3 in which the first and second thyristors comprise first and second triacs.
The dimming circuit according to the item 2, 33, 34, or 35. 37. A form having a bidirectional electronic switching means, selectively conducting the electronic switching means according to a timed repetitive control signal supplied to the control input means to supply the load. In a two-wire dimmer including control input means for controlling the RMS value of the AC voltage,
Destructive DC caused by a load having a resistance and an inductive component by adjusting the RMS value of the AC voltage supplied to the load
In a dimming method comprising reducing current, (a) providing a signal having a value indicative of a DC current flowing in a load, and (b) responding to the signal provided in step (a),
Adjust the time of the control signal during the successive half cycles of the waveform of the AC voltage supplied to the load to reduce the DC current flowing through the load, and (c) adjust the timing of the control signal and supply it to the dimming circuit. A method of dimming, characterized in that it guarantees a fluctuation in the AC voltage supplied to the load, thereby adjusting the RMS value of the AC voltage supplied to the load. 38. (a) a single pair of conductors for connecting in series between an AC voltage source and a load; and (b) an AC operatively connected in series with a resistor between the pair of conductors to supply the load. Voltage R
A first thyristor having a gate terminal operatively connected to a control circuit for generating a control signal for adjusting the MS value;
(c) A second thyristor having a gate voltage operatively connected to a resistor and a connection point of the first thyristor, which is connected between the pair of operationally operating wires, and which has a relatively low load current flowing through the dimming circuit. The first thyristor is made conductive while
The second thyristor is substantially deactivated and the first thyristor is substantially non-conducting and the second thyristor is conducting while a relatively high load current is flowing in the dimming circuit. A two-wire dimming circuit for low voltage. 39. The scope of claim 38, wherein each of the first and second thyristors has its own hold current characteristic, and the hold current characteristic of the first thyristor is considerably smaller than the hold current characteristic of the second thyristor. Dimming circuit. 40. A method according to claim 38, wherein each of the first and second thyristors has a maximum current standard, and the maximum current standard of the first thyristor is less than about 1/10 of the maximum current standard of the second thyristor. The dimmer circuit according to the item. 41. A load current flowing through the first thyristor,
39. A dimmer circuit according to claim 38, wherein a voltage is developed across the resistor and the second thyristor is rendered conductive only after the voltage across the resistor exceeds a selected value. 42. A resistor such that when the load current flowing through the resistor is about 1/10 to 1/2 of the maximum current rating of the first thyristor, a voltage is produced across the resistor that is approximately equal to the selected value. The dimmer circuit according to claim 41, wherein a value is set. 43. The control circuit includes a series RC circuit connection operatively connected to the potentiometer for regulating and controlling the period of the control signal between the pair of conductors, the potentiometer comprising a gate of the first thyristor. 39. The dimming circuit of claim 38 operatively connected to a diac in series with a capacitor operably connected between the potentiometer and one of the pair of conductors. 44. The dimming circuit according to claim 38, wherein the load is a low voltage transformer. 45. The light control circuit according to claim 38, wherein the load is a ballast. 46. A claim 38, 39, 40, 41, 42, 43, 44 or 4 in which the first and second thyristors comprise first and second (2) triacs, respectively.
The light control circuit according to item 5. 47. (a) Only one pair of conductors for connecting in series between an AC power source and a resistor; and (b) AC operatively connected in series with a resistor between the pair of conductors and applied to a load. RM of voltage
A first thyristor having a gate terminal operatively connected to a control circuit for generating a control signal for adjusting the S value; and (c) a resistor and a first thyristor directly operatively connected between the pair of conductors. A second thyristor having a gate terminal operatively connected to the connection point of the first thyristor while the relatively low load current flows in the dimming circuit circuit, the first thyristor is made conductive, and the second thyristor is substantially non-conductive. It is turned on, and while the relatively high load current is flowing in the dimming circuit, the first
Of thyristors are made substantially non-conductive, the second thyristor is made conductive, the first and second thyristors each have a maximum current standard, and the maximum current standard of the first thyristor is the maximum current of the second thyristor. Smaller than about 1/10 of the standard, the first and second thyristors have respective hold current characteristics, the hold current characteristic of the first thyristor is considerably smaller than the hold current characteristic of the second thyristor, and the load current is A voltage is developed across the resistor as it flows through the first thyristor, and the second thyristor is rendered conductive only when the voltage across the resistor exceeds a selected value and the load current in the resistor is The resistance is set so that the voltage across the resistor is approximately equal to the selected value when it is equal to about 1/10 to 1/2 of the maximum current specification of one thyristor, and ( d) the control circuit comprises a series RC circuit operatively connected between the pair of conductors and a potentiometer for adjusting and controlling the period of the control signal, the potentiometer being in series with the gate of the first thyristor. And a low-voltage two-wire dimming circuit, which is operatively connected to a capacitor operably connected between the potentiometer and one of the pair of conductors. 48. The claim of claim 4 wherein the first and second thyristors comprise first and second triacs, respectively.
The light control circuit according to item 7.