JPS62213092A - Dual-line type low voltage dimmer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application] The present invention relates to a dimming circuit that controls the RMS value of an AC voltage applied to a load. Specifically, the present invention relates to a two-wire dimming circuit for use with reactive loads where destructive DC load currents may be present. The device of the invention comprises correction means for reducing the destructive DC current flowing through the load and 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 compensation 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. On the other hand, the invention also has application in other types of loads, such as fluorescent lighting devices.

[Prior art]

Two-wire dimmer circuits are well known. One conventional type of two-wire dimmer circuit includes a triac and a dual phase shift firing circuit operatively connected to the gate terminal of the triac. The dual phase shift firing circuit consists of a series R-C circuit connected to the triac, and a potentiometer connected to the R-C circuit.
-Use an ignition capacitor connected to the C circuit and connected by a diac to the gate terminal of the triac.

This circuit is designed to control the current flow through a reactive load, such as the primary winding of a low voltage transformer, by adjusting the firing angle of the reactor during selected half-cycles of the AC load voltage waveform in the following manner: Correct for the known destructive DC1iE flow. The DC component appears across the triac, thus across the capacitor known as the "lead capacitor". The lead capacitor is the capacitor of the series RC circuit described above. Since the lead capacitor is connected to the ignition capacitor via a potentiometer, the DC voltage across the lead capacitor is transferred to the ignition capacitor.
The firing angle is changed to reduce the DC current.

Although the two-wire dimmer circuit described above may solve the DC current problem known to exist in reactive loads, it has poor voltage regulation capability. That is, in the case of ACiC power supply voltage fluctuations, the RMS of the AC voltage supplied to the load cannot be maintained substantially constant. It is also known to modify two-wire dimmers of this type to exhibit better voltage regulation capabilities by replacing the lead capacitor with a diac. However, the modified circuit cannot correct the DC current problem after the lead capacitor is removed.

Five-wire dimmer circuits are also well known. In a three-wire dimmer circuit, two of the five wires are connected in direct voltage to the ACIIE source voltage, and the firing angle is determined from the AC source voltage. That is, the firing angle is D, which may flow through the load.
It is also known to integrate voltage regulating diacs into the ignition circuits of 03-wire dimmers that are not operated by C current.

This type of three-wire dimmer exhibits good voltage regulation ability but does not exhibit DC current problems. However, a 3-wire dimmer has 3 wires (AC hot, AC neutral and load)
must be installed up to each wall box, requiring no additional installation.
This is not desirable because it requires 1lI cost.

The present invention provides a two-wire dimmer with a voltage adjustment circuit and a DC1
The disadvantages of the prior art are overcome by combining both IE current correction circuits.

[Summary of the invention]

The dimmer circuit of the present invention for use with a reactive load, such as a low voltage transformer, has a
It has only paired wires. first and second conductivity controllable thyristors are operatively connected to the pair of wires, and a control circuit applies a control signal to the gate terminal of the first thyristor to cause an instantaneous change in the AC voltage across the control circuit. firing the first thyristor at a firing angle governed 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 rendered non-conducting only after the second thyristor is rendered conductive. In the preferred embodiment, the thyristors used are triacs, but anti-parallel connected SCRs or other suitable devices could also be used.

Voltage compensation means are arranged in the circuit, so that the A applied to the load is
Adjust the RMC value of c1 voltage. In the embodiment disclosed, the voltage compensating means is a diac with negative resistance characteristics, and when a fluctuation occurs in the AC power supply voltage, the voltage applied by the diac to the control circuit changes the timing of the control signal and therefore the point of the triac. The arc angle is modified to maintain a substantially constant RMS value of the AC voltage applied to the load. This compensation effect occurs as long as the magnitude of the AC voltage is greater than the breakdown voltage of the diac.

The circuit of the invention also comprises correction means for correcting asymmetries in the waveform of the AC load voltage caused by the DC current flowing through the load. The DC current flowing through the load causes the firing angle to advance 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 waveform of the AC load voltage becomes asymmetric.

The compensation means compensates for the asymmetry by advancing or retracting the firing angle in successive half cycles until the waveform of the AC load voltage is substantially symmetrical, thereby reducing the destructive DC current flowing in 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 DCm current flowing through the load. A feedback loop adds the voltage on the correction capacitor to the voltage on the ignition capacitor operatively connected to the first triac gate. During each subsequent half-cycle of the AC load voltage waveform, the firing angle is advanced or retracted by an amount governed by the magnitude and polarity of the voltage across the correction capacitor (as compared to the preceding half-cycle of opposite polarity). regarding the firing angle).

In other embodiments, the correction capacitor is placed in series with the voltage compensation diac. The correction capacitor is charged by the current flowing in the voltage compensation diac to a voltage level that dictates the magnitude and polarity of the DCi current flowing in the load. The voltage across the correction capacitor is applied in series with the diac to effectively adjust the voltage applied to the firing capacitor, thereby advancing or retracting the firing angle in each subsequent half cycle.

[Explanation of specific examples]

[Embodiments] Preferred embodiments of the present invention will be described below with reference to the drawings. Note that the same reference numerals refer to the same members throughout the drawings.

Referring to the drawings, FIG.
A conventional two-wire low voltage dimmer is shown. The dimmer 10 comprises a two-wire dimmer circuit 12 having only one pair of wires 26 , 28 connected in series with the transformer 23 and the primary winding 20 of the AC power supply 18 . Dimmer circuit 12
includes a triac 16 and a control circuit 14 operatively connected across the triac 16 for providing a control signal to the gate 17 for selectively conducting the triac 16.

As is well known in the art, the timing of the control signals, and therefore the firing angle of the triac, depends on the A supplied to the load.
Controls the RMS value of CII pressure.

The dimmer circuit 12 illustrated in FIG. 1 is shown as controlling a low voltage connected to the secondary winding 22. The dimming circuit 12 illustrated in FIG.

As is well known, the firing angle of the triac 16 is governed by the control circuit 14 and therefore by the voltage across the lines 26 and 28. The firing angle will therefore be influenced by the DC magnetizing current flowing in the primary winding 20 of the transformer 23. The magnitude of this DCIIE stream can be substantial and can cause arm problems as discussed below.

Problematic DC currents can be caused by a number of factors. For example, the secondary winding 2 of the transformer 23
When the lamp 24 or other load connected to 2 is turned off (i.e. becomes an open circuit), the DC flowing through the secondary winding 20
The C magnetizing current magnitude can be substantial compared to the RMS value of the AC current flowing through the -order winding 20. Also, Ac
It can be envisioned that at the point where the t pressure waveform becomes zero or near zero after a positive or negative half cycle, the supply of AC'WL power to circuit 10 may be momentarily interrupted. At the moment when AC power is restored, the AC1 voltage waveform becomes
At or near O of the same half-cycle of polarity that was present when power was removed, the magnetic material in the core in transformer 23 is saturated, causing the transformer to It is possible that the conduction can be made easier than the above. This delays the firing angle of the triac 16 by one half cycle of the AC 1 g pressure waveform (see Figure 9),
Therefore, the transformer 23 is further polarized. The regenerative nature of this development poses a DC current problem.

FIG. 2 shows a block diagram of a three-wire low voltage dimmer 30. The device 30 comprises a three-wire dimmer circuit 32 with two wires 46,48 connected directly to the AC mains voltage. Line 48.50 is connected to the primary winding 40 of the transformer 41 and supplies the lamp 44 with a low voltage by means of the secondary winding 42. The dimming circuit 52 includes a triac 36 and a control circuit 34 that supplies a control signal to the gate 37 of the triac 56. Similar to the control circuit of FIG. 1, the control circuit 34 is connected directly to the AC1[E pressure.

Therefore, the firing angle of the control signal is not affected by the DC current that may flow through the primary winding 40 of the transformer 41. However, the 3-wire dimmer circuit shown in Figure 2 is not only more expensive to manufacture than the 2-wire dimmer circuit shown in Figure 1, it also runs 3 wires to the wall box instead of 2 wires. This increases the cost associated with installing a three-wire dimmer.

FIG. 3 schematically illustrates a known two-wire dimmer circuit. Third
The illustrated circuit 52 utilizes a control circuit of the type known as a two-pawl phase shift firing circuit for generating control signals. The dual phase firing circuit includes a resistor 54 and a lead capacitor 5.
6, potentiometer/trim circuit 58, ignition capacitor and diac 62. The operation of this circuit is well known in the art.

The two-wire dimmer circuit of FIG. 3 does not exhibit the problems previously discussed caused by DC'wL current flowing through the load, provided the characteristics of the triac 64 are selected according to certain criteria. This criterion will be discussed later. When a DC component appears on triac 64, this component also appears on lead capacitor 56. The advance capacitor 56 is
Since it is coupled to the firing capacitor 60 via the potentiometer/trim circuit 58, the DC voltage on the lead capacitor 56 adjusts the firing angle of the F-tear gate 64 during selected half-cycles of the AC load voltage waveform. to correct. The effect of changing the firing angle in this manner and how this corrects the DC current problem will be seen later.

If the characteristics of the triac 64 are properly chosen, it is ensured that the circuit of FIG. 3 does not exhibit the DC11L flow problem described above, but other problems occur. The circuit of FIG. 3 is unable to maintain the RMS value of the AC1 voltage supplied to the load substantially constant with respect to ACgC supply voltage dynamics. 2 wire DC
It is desirable that such voltage adjustment be possible in a compensation dimming device.

Attempts have been made in the past to modify the circuit of FIG. 3 to perform the desired voltage regulation function.

One such variation is to replace the advance capacitor 56 with a diac so that the voltage applied to the potentiometer/trim circuit 58 during the period when the diac conducts changes the firing angle to compensate for variations in the ACt source. This includes changing in such a manner.

This variation results in a two-wire dimmer that regulates the voltage as long as the AC voltage does not vary below the breakdown voltage of the diac. However, since this modification requires the removal of capacitor 56, the resulting dimmer will have less D flowing through the load.
C11E flow cannot be corrected.

The following discussion explains why this is so. In the following discussion, the term "modified circuit" will be used to refer to the circuit of FIG. 3 that has been modified in the manner described above by replacing lead capacitor 56 with a diac.

Referring to the waveforms in Figures 7.8 and 9, the AC power supply voltage (74, 74', 74"), the AC load voltage (76, 76"),
', 76"), AC load current (78, 78', 78")
and the AC voltage applied to the triac (80,80',
80") is illustrated.

As shown in each drawing, the AC load voltage (76, 76/
, 76'') are chopped by a torch 64 in a well-known manner to provide a voltage of the desired RMS value.

As is well known in the art, the firing angle of triac 64 [f
17 yields the corresponding 1M node of the RMS value of the AC voltage supplied to the load.

FIG. 7 shows the ACwtws pressure 74, AC load voltage 76 for a purely resistive load that may be connected to the modified circuit of FIG.
and various waveforms of AC load current 78 are shown. As shown, all waveforms, including waveform 80 representing the AC voltage applied to triac 64, are shown! It is the same phase as ! It is symmetrical. Therefore, the operation of the circuit of FIG. 3 when used with a purely resistive load is acceptable.

FIG. 8 illustrates the same waveforms produced when the modified circuit of FIG. 3 is applied to a load that is mostly resistive and has a slightly inductive component.

As shown, the inducible component is AC1! flow waveform 78
' is slightly out of phase with respect to 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. 3 is also acceptable.

FIG. 9 illustrates that the modified circuit of FIG. 3 is unacceptable for use with loads having substantially both inductive and resistive components, such as transformer loads. A.C.
The phase of the load current 78'' is also the waveform 7 of the AC load voltage.
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, thus reducing the AC load voltage 76' During the period in which the load decreases, the AC load current 7B'' is increased to an abnormally high level, as shown at 84. Since the F-tiac 64 is a current sensing device, the load voltage 76' has been sufficiently reduced to cause the ACm current 7
TRIAC 64 will not become non-conducting until B" is forced below the triac's hold current, rendering it non-conducting as illustrated at rhJ in FIG. 9. The net effect is illustrated in FIG. As shown in FIG. , occurs only during repeating positive or negative half-cycles, rather than over the duration of a full cycle, so waveform 76'' is asymmetric.

Also, as illustrated in FIG. 9, shifting the firing angle during repeated half-cycles causes the AC voltage across triac 64 to be greater in one half-cycle than in the preceding half-cycle of opposite polarity. . Furthermore, it can be seen that the voltage on triac 64 during the positive half cycle is lower than the voltage during the eclipse 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 means that the load voltage is equal to the difference between the supply voltage and the triac voltage, and A
This is because the asymmetric cycles of the C power supply have essentially equal RMSIN, positive values. Transformer to which load voltage is applied -
Since the secondary winding has a higher positive voltage than the negative voltage, the transformer saturates in the direction of positive current in the primary winding. This further increases the magnitude of peak current 84. It can therefore be seen that a slight asymmetry in the load voltage causes a positive feedback effect due to its effect on the dimmer.

This results in a continuous deterioration of any small initial visit until a much larger peak current value 84 occurs. If the peak value 84 of the AC load current 78'' is allowed to increase unchecked, a fuse may blow, a circuit breaker may open, or a fire hazard may also exist if the temperature rises to a sufficient level.

It will be appreciated that although the above article is for illustrative purposes and the DC current problem is described as occurring during the positive half cycle, it can occur just as well during the negative half cycle. In any case, potentially destructive DCm currents can be eliminated if the firing angle can be advanced or retracted as needed during the selected positive or negative half-cycle where the pC current problem is present. . In other words, if the waveform of the ACt pressure applied to the load could be maintained symmetrically, that is, if it could be varied to provide negative feedback rather than the positive feedback described above, the current problem described above would not occur. Dew.

A dimming circuit that achieves this function will be described below.

Referring to FIG. 3, one embodiment of a dimming circuit according to the present invention is shown. As in FIG. 3, the dimmer circuit of FIG. 3 includes an RF1 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 diac 96 and a first
Triac 98 gate terminal and potentiometer/
A control circuit includes an ignition capacitor 94 operatively connected to one terminal of trim circuit 92 . A resistor 101 is connected in series with the triac 98, and a second triac 99 is connected on both sides of the dimming circuit, with its gate terminal connected to the junction of the resistor 101 and the first triac 98. The use of two triacs 9B, 99 rather than a single triac can improve the operation of the dimmer circuit at low load currents, if these triacs are selected in the manner described below.

An RC series connection of resistor 88, potentiometer/trim circuit 92, and capacitor 94 provides a timed signal to the gate of triac 98. As is well known,
The timing of the control signal (and therefore the firing angle) is controlled by circuit 9
2 potentiometer settings.

In addition, the dimmer circuit adjusts the RM of the AC voltage supplied to the load.
Voltage compensation means 90 for maintaining the S value substantially constant
and means 1 for correcting the asymmetry of the waveform of the AC voltage supplied to the load in order to eliminate the DC current problem discussed above.
00, 102 and 104.

As shown, the voltage compensation means 90 comprises a diac operatively connected to the other terminal of the control circuit, particularly the potentiometer/trim circuit 92, and to the resistor 88. diac 9
0 has a breakdown voltage, which is supplied to the control circuit, specifically the potentiometer/trim circuit 92, when the diac is conducting. The control circuit controls the breakdown voltage supplied by the diac 90 and the AC1j! In response to variations in the source voltage, the timing of the control signals and thus the firing angles of triacs 98 and 99 are adjusted to maintain a constant RMS value of the AC voltage supplied to the load. Similar to the modified circuit of FIG.
Adjust load voltage.

In the circuit of FIG. 3, the correction means includes 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 through the load. The voltage on correction capacitor 102 is coupled to the voltage on ignition capacitor 94 by feedback resistor 104. Thus, the voltage across firing capacitor 94 is changed, changing the firing angle of triacs 9B and 990 in the next subsequent half cycle. The process of feeding back the voltage to the ignition capacitor 94 continues until the waveform is substantially symmetrical, i.e. DC
This continues for subsequent half cycles of the AC load voltage waveform until the I current is substantially eliminated.

The dual F RIAC condition illustrated in FIG. 3 overcomes several problems inherent in single TRIAC type dimmer circuits. In a single triac type dimmer circuit, the triac must be sized for maximum load current and therefore has a relatively high hold current. If the load current falls 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. Additionally, the hold currents for forward and reverse currents in the triac are not the same. This asymmetry can cause severe problems in low voltage dimmers where the load has a significant inductive component, such as in low voltage transformers. This is sufficient to activate the positive foot meter mechanism described above inherent in the operation of known two-wire low voltage dimmer circuits.

In the circuit of FIG. 3, a control signal is applied to the gate of the first triax 9B as described above.

Thus, when a control signal is applied to the gate of TRIAC 9 and a sufficient voltage is applied to TRIAC 9, TRIAC 9 becomes conductive. When the current flowing through triac 98 and resistor 101 creates a voltage across resistor 101 sufficient to ignite triac 99, triac 99 becomes conductive. This voltage drop is nominally 1 volt according to the preferred embodiment.

When the triac 99 is completely conductive, the triac 9
The voltage between the anode and gate of 9 becomes essentially zero and the triac 98 no longer has enough current. When the current in the triac 98 drops below the hold current (the liac 98 turns off and the triac 9
9 carries the full load current of the dimming circuit.

If the load current of the triac 9B is low enough, the resistance 10
A voltage drop of 1 is not large enough to trigger triac 99 to conduct in the manner described above. in this case,
TRIAC 9B is not turned off by TRIAC 99 as described above and carries full load current until the load current is large enough to trigger TRIAC 99 into conduction.

As mentioned above, the advantage of using two triacs is that
It is possible to select the characteristics of triacs 98 and 99 independently for low and high ranges of load current. Another advantage is that by choosing an appropriate value for resistor 101, the boundaries between operating ranges can be defined. The main factor that determines the characteristics of TRIAC 99 is the general 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 greatly between different samples of the same type of triac, and also with respect to temperature and current specifications. The following summarizes the considerations that should be taken into account when selecting a triac for use in the circuit of FIG.

The most problematic operating condition for two-wire low voltage dimmers operating transformer loads occurs when the transformer is unloaded. Under this condition, the current flowing through the conducting triac (typically triac 98 in FIG. 3) will be only slightly greater than the hold current for each half cycle of 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 AC load voltage crosses 00. The angle at which the triac stops conducting can be quite different in the positive and negative half-cycles due to the above-mentioned asymmetry in the hold current.

As a result of this different conduction in each half-cycle, the transformer encounters a DC voltage component and may be driven into saturation as a result.

The hold current of a triac is typically about 1/1000 of its maximum current specification. Therefore, for example, a 25 amp rated triac would be expected to have a hold current of about 25 mA.

Even this relatively low hold current can cause severe transformer saturation problems. This is because a small low voltage transformer is only about 40 or 50 mA. If a 0.8A standard triac is used, the hold current will be approximately α8fiA. Or, it is relatively small compared to the magnetizing current. However, the α8A triac cannot sustain the desired loads or transient surges that are common in dimmer applications.

Referring to FIG. 3, if the value of resistor 101 is chosen to be about 50, only triac 98 will be conductive when the peak load current is less than about 20OmA.

That is, 200 mA is required to cause a voltage drop of 1 V across a 5 Ω resistor and to make the triac 99 conductive. Therefore, the triac 98 can be rated for relatively low maximum load currents and very low hold currents as discussed below. If the load current increases above approximately 200 mA, triac 99 will turn on and triac 98 will turn off, as described above. Triac 99 handles full load currents and its relatively high hold current becomes insignificant at these high load currents.

The above example in which triac 98 is rated at 0.8A and triac 99 is rated at 25A is a typical ratio. The value chosen for resistor 101 will depend on the actual current rating, but should generally be spaced to provide a voltage drop of 1 volt at a current level approximately equal to the maximum current rating of triac 98. This ensures that low load currents are conducted only in the triac 98 and only high load currents are conducted in the triac 99.

FIG. 4 shows another implementation circuit according to the invention. Again, the RFI circuit includes a resistor 106, a capacitor 108, and an inductor 116. first triac 124
The control circuit for supplying the control signal to the gate terminal of
Includes resistor 110, potentiometer/trim circuit 118, diac 120 and firing capacitor 122. As previously mentioned, a 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 resistor 127 and triac 124. Triacs 124 and 125 are selected similarly to triacs 98 and 99 described above.

A diac 112 is connected to control circuitry, particularly a potentiometer/trim circuit 118, as shown. A correction capacitor 114 is also connected to one side of the diac 112 and the dimming circuit in the manner shown. resistance 11
3 connects the other side of the dimming circuit to the connection point between the diac 112 and the correction capacitor 114. As previously mentioned, the diac 112, when conducting, provides a compensated breakdown voltage to the control circuit, particularly the potentiometer/) rim circuit 11B. The control circuit adjusts the firing angle of the control signal in response to ACII source voltage variations and breakdown voltages to maintain a substantially constant RMS value of the AC voltage supplied to the load. As previously mentioned, the RMS value of the AC voltage supplied to the load remains substantially constant unless the AC1 voltage varies below the breakdown voltage of the diac. Thus, in the circuit of FIG. 4, diac 112 performs a voltage regulation function.

In the circuit of FIG. 4, the correction means is the capacitor 114.
, resistor 1101, diode 112, and resistor 113. The current flowing through resistor 110, diacs 112 and 113 flows through capacitor 114, and DC'! through the load.
! ! charged to a voltage level that dictates the magnitude and polarity of the flow.
do. The voltage across correction capacitor 114 is provided in series with diac 112, thereby effectively regulating the voltage provided to ignition capacitor 122 via potentiometer/trim circuit 118. Potentiometer/
Ignition capacitor 122 via triac circuit 118
This variation in the voltage supplied to each phase corrects the firing angle in each subsequent half cycle, thereby eliminating asymmetries in the AC voltage waveform and substantially eliminating DC current.

The value of the correction capacitor 102 used in the circuit of FIG.
And the value of capacitor 114 utilized in the circuit of FIG. 4 must be large enough so that only a relatively small AC impedance is present. Preferably, the correction capacitors 102.114 are AC1! The size should be such that it provides a substantial short circuit to the current. Therefore, only a small rip/L' voltage appears across the correction capacitor 102.114.

The embodiment of FIG. 5 is substantially the same as the embodiment of FIG. However, the circuit in Figure lIC5 replaces capacitor 114 with two electrolytic capacitors 138, 140 and 2.
Two diodes 134 and 136 are utilized. This modification minimizes the physical size of the circuit and allows installation in a standard box. Again, the previous discussion on how to select a triac can be applied.

According to another aspect of the invention, the two-wire system does not have voltage compensation means, but has an improved dimming capability at low load currents and an improved resistance to DC currents, as described above. A low voltage dimmer circuit is provided. This circuit uses dual triacs selected according to the criteria described above.

In FIG. 10, a well-known 3#1 dimmer circuit is shown having three wires 160, 162, and 164 for connection to AC power source 146 and load 152.

As shown, load 152 is a low voltage ratio transformer that includes a negative primary winding and a secondary winding 156 connected to an incandescent lamp 158 . Circuit 142 includes a resistor 151 in series with dual F-tiacs 14B, 150 and triac 148 as shown.

The gate of triac 14B receives and receives control signals from control circuit 144. The gate of triac 150 is operatively connected to the junction between resistor 151 and triac 14B. In connection with the structure of the three-wire dimmer circuit 142, a triac 148.150 according to the aforementioned criteria
It is known to select. However, as previously mentioned, a three-wire dimmer circuit of the type illustrated in FIG. 10 is undesirable. This is because three lines must be extended to the can wall box, which increases installation costs.

According to the invention, two selected according to the above discussion
A two-wire low voltage dimmer circuit utilizing a heavy duty triac is provided. Such a circuit is illustrated in FIG. 11 and generally designated 166. Circuit 1166 provides DC correction but is not capable of voltage regulation for the same reasons discussed in connection with circuit 52 illustrated in FIG. The circuit consists of a pair of wires 17 for series connection with the AC source and the load.
Contains only 2.174. 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 ballast F
connected in series with

As previously discussed, circuit 166 includes capacitor 168, resistor 170 and inductor 176 connected as shown.
It includes an RFI filter consisting of: RFI filters do not form part of the invention. Circuit 166 also includes a series RC circuit combination, resistor 170 and capacitor 17B operatively connected to wire 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
In operation, it is connected to the diac 184 in series with the gate of the triac 18B. Further, the capacitor 182 is
In operation, potentiometer/trim circuit 1 as shown
80 and the connection point of capacitor 178 and inductor 176. Triac 6 a day is
In operation, wire pair 172.174 is connected through inductor 176.
It is connected in series with 188 in between. triac 19
0 is operatively connected in series with wire pair 172.174 through inductor 176 as shown, and its gate terminal is operatively connected to the junction of resistor 188 and triac 186.

The triacs 186, 190 are preferably selected as described above and their operation is as described above.

The circuit of FIG. 11 provides DC correction, but performs voltage regulation. However, the circuit of FIG. 11 exhibits improved dimming capability at lower currents for the reasons discussed above. moreover,
The dual triac used in the circuit of FIG. 11 prevents the problems normally caused when the load has a significant inductive component.

The present invention may be embodied in other specific forms without departing from the spirit thereof, and is limited only by the scope of the claims.

Figure 1 is a block diagram of a well-known 2-wire low-voltage dimmer circuit, Figure 2 is a block diagram of a well-known 3-wire low-voltage dimmer circuit, and Figure 3 is a block diagram of a well-known 3-wire low-voltage dimmer circuit.
FIG. 4 is a schematic diagram of one specific example of the two-wire low-voltage dimming circuit according to the present invention, FIG. 4 is a schematic diagram of another specific example of the two-wire low-voltage dimming circuit according to the present invention, and FIG. The figure is a schematic diagram of still another specific example of the two-wire low-voltage dimming circuit according to the present invention, FIG. 3 is a schematic diagram of a conventional two-wire dimming circuit, and FIGS. Exemplary voltage waveform diagrams used in the detailed description of the invention, FIG. 10 is a schematic diagram of a well-known three-wire dual triac dimmer circuit, and FIG. 11 is a voltage compensation circuit according to the present invention. 1 is a schematic diagram of a two-wire low-voltage dual triac dimmer circuit without a

90: Voltage compensation means 98: 1st trial 99: 2nd triac

Claims (1)

[Scope of Claims] 1. Comprising a bidirectional electronic switching means, the electronic switching means is selectively conductive in accordance with the supplied timed repetitive control signal to supply the load. In a two-wire AC dimmer circuit comprising control input means for controlling the RMS value of an AC voltage supplied to a load, the control input means adjusts the RMS value of an AC voltage supplied to a load and is induced by a load having resistive and inductive components. A circuit for reducing destructive DC current flowing through a load includes: (a) first means for providing a signal having a value indicative of the DC current flowing in the load; and (b) responsive to the signal provided by the first means. A supplied to the load
(c) adjusting the timing of the control signal to reduce the DC current flowing in the load during a selected half cycle of the C voltage waveform; 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 means for charging the first capacitor to a DC voltage having a magnitude and polarity indicative of the magnitude and polarity of the DC current flowing in the load; A light control circuit according to claim 1. (3) when said electronic switching means includes thyristor means, the control input means includes a gate terminal of the thyristor means, and the dimmer is operatively coupled to the gate terminal and charged to a predetermined voltage; 3. A dimmer circuit as claimed in claim 2, including a second capacitor for providing a control signal to make the thyristor means conductive. (4) The thyristor means comprises first and second thyristors each having a specific hold current characteristic, and the hold current characteristic of the first thyristor is considerably smaller than the hold current characteristic of the second thyristor. The dimming circuit described in item 3. (5) A resistor connected in series with the main terminal of the first thyristor, the gate of the first thyristor receiving the control signal, and the gate of the second thyristor connecting the resistor and the main terminal of the first thyristor. The second thyristor is made conductive when the voltage across the resistor 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 has a D corresponding to the first capacitor.
4. A dimmer circuit as claimed in claim 3, including a feedback loop for coupling the C voltage to the voltage on the second capacitor to change the voltage across the second capacitor, thereby changing the timing of the control signal. . (7) the third means includes a diac operatively connected to the first capacitor, the diac having a breakdown voltage, and when in its conductive state, at least a portion of the breakdown voltage is applied to the second capacitor; A dimmer circuit according to claim 3 provided in claim 3. (8) the second means for supplying the DC voltage on the first capacitor to the diagonal to effectually modify the voltage supplied to the second capacitor, thereby modifying the timing of the control signal; A dimmer circuit according to claim 7, comprising means. (9) The dimmer circuit according to claim 1, wherein the load is a low voltage transformer. (10) The dimming circuit according to claim 1, wherein the load is a ballast. (11) A dimming circuit according to claim 3, 6, 7 or 8, wherein said thyristor means comprises a triax. (12) The first and second thyristors each have a first
and a second triax.
Or the dimming circuit described in Section 5. (13) In a circuit for controlling the RMS value of an AC voltage supplied to a partially resistive and partially inductive load, (a)
a pair of electrical conductors for connection in series with a load and an AC power supply voltage; and (b) a first bidirectional electronic switch means operatively connected between the pair of electrical conductors; (c) operatively connected to the control input means and responsive to the instantaneous magnitude of the AC voltage appearing between the pair of wires; (d) voltage compensation means for adjusting the RMS value of the AC voltage supplied to the load; , (e) correction means for correcting asymmetry in the waveform of the AC voltage supplied to the load. (14) the voltage compensation means includes a second voltage sensitive bidirectional electronic switch means having a breakdown voltage, the breakdown voltage being supplied to the control circuit means during the conduction period of the second electronic switch means; and the control circuit means control the breakdown voltage and the A
14. The control circuit of claim 13, wherein the control circuit adjusts the firing angle and thereby the RMS value of the AC voltage supplied to the load in response to variations in the AC power supply voltage. 15. A control 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 correction means includes a capacitor operatively coupled to the control circuit means for adjusting the firing angle of the first electronic switch means during successive half-cycles of the waveform of the AC voltage supplied to the load; A control circuit according to claim 13. (17) The first electronic switching 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 one of the pair of conductors. a first resistor operatively connecting a second main terminal of the first thyristor to the other of the pair of conductors, the main terminal of the second thyristor being operatively connected directly between the pair of conductors; The gate terminal of the first thyristor receives a control signal from the control circuit means, and the gate terminal of the second thyristor is operatively connected to the connection point of the first resistor and the second main terminal of the first thyristor. A control circuit according to range item 13. (18) 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. control circuit. (19) The first and second thyristors each have a maximum current specification, and the maximum current specification of the first thyristor is different from that of the second thyristor.
18. The control circuit of claim 17, wherein the current is less than about 1/10 of the maximum current specification of the thyristor. (20) The value of the first resistor is set such that when the first thyristor has a maximum current specification and the flowing current is about 1/10 to 1/2 of the maximum current specification, about 1 volt is present in the first resistance. A control circuit as set forth in claim 17. 21. The control circuit of claim 17, wherein the control circuit includes adjustment control means for manually adjusting the firing angle to change the RMS value of the AC voltage supplied to the load. (22) The adjustment control means includes a potentiometer, and the control circuit means includes a first diac connected in series between a first terminal of the potentiometer and a gate terminal of the first thyristor; 22. A control circuit according to claim 21, comprising a first capacitor operatively connected between a connection point (i) with one terminal and one of the conductor pairs (ii). (23) the voltage compensating means includes a second dielectric having a first terminal operatively connected to a second terminal of the potentiometer and having a breakdown voltage, the breakdown voltage being applied to the potentiometer during the conduction period; the RMS of the AC voltage supplied to the load, and the control circuit adjusts the firing angle in response to breakdown voltage and AC line voltage variations, thereby increasing the RMS of the AC voltage supplied to the load at the value dictated by the potentiometer setting.
23. A control circuit according to claim 22, which adjusts the value. 24. The control circuit of claim 23, wherein said correction means includes a second capacitor operatively connected between the second terminal of the second dielectric and one of the pair of conductors. (25) operatively connected between the connection point (i) between the second capacitor and the second terminal of the second dielectric and one of the pair of conductors (ii), the DC flowing through the load of the second capacitor; A second resistor is provided for charging to a voltage that dictates the magnitude and polarity of the current, so that the voltage on the second capacitor effectively regulates the breakdown voltage of the second dielectric and the waveform of the AC voltage supplied to the load. 25. The control circuit of claim 24, wherein the control circuit changes the firing angle in selected half-cycles 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 conductive wires; and a first capacitor and a first
A feedback loop is provided to the connection point of the diac, where a second capacitor is charged to a voltage that dictates the magnitude and polarity of the DC current flowing through the load, and the second capacitor is normally connected to the first diac by the first capacitor. Changes the supplied voltage and thereby the A supplied to the load
24. The control circuit of claim 23, wherein the control circuit changes the firing angle in selected half cycles of the C voltage waveform to reduce the DC current flowing through the load. (27) Claim 1 in which the load is a low voltage transformer
Control circuit according to item 3. (28) The control circuit according to claim 13, wherein the load is a ballast. (29) A control circuit according to claim 15, wherein said thyristor means comprises a triax. (30) The first and second thyristors each have a first
and a second triax.
7, 18, 19, 20, 21, 22, 23, 24, 25
Or the control circuit according to item 26. (31) In a circuit for regulating the RMS value of an AC voltage supplied to a load and reducing destructive DC currents induced by a load having resistive and inductive components, the circuit comprises: (a) connected in series with the load and the AC supply voltage; (b) a gate terminal and first and second main terminals, the first main terminal being operatively connected to one of the pair of conductors;
(c) a first thyristor having a main terminal operatively connected to the other of the pair of conductors by a resistor; (d) a second thyristor operatively connected between the gate terminal of the first thyristor and the conductor pair and connected in R-C series; 1 capacitor and potentiometer,
a control circuit for selectively firing and conducting the first and second thyristors at firing angles determined at least in part according to the settings of the potentiometers; When passing, the second thyristor is fired and made conductive, and after the second thyristor is made conductive,
The first thyristor is made non-conducting and the AC supplied to the load
the RMS value of the voltage is thereby made variable according to the setting of the potentiometer, and further comprising: (e) a diagonal having a breakdown voltage disposed in the circuit;
superimposing the breakdown voltage on the R-C series connection of the potentiometer and the first capacitor during the period when the diode is conductive, adjusting the firing angle to compensate for fluctuations in the AC supply voltage;
(f) a second diaphragm operatively connected to the circuit for charging a DC voltage that directs the magnitude and polarity of the DC current flowing through the load; a capacitor; and (g) in response to the DC voltage across the second capacitor, changing the firing angle during selected half-cycles of the waveform of the AC voltage supplied to the load so as to cause a DC current to flow through the load. An adjustment/reduction circuit characterized in that it comprises means for reducing. (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 adjustment/reduction circuit according to item 31. (33) means for changing the firing angle in response to the DC voltage across the second capacitor, applying the voltage across the second capacitor to the voltage on the dipper; 32. The regulating and reducing circuit according to claim 31, which changes the voltage across the series connection. (34) Claim 3 in which the load is a low voltage transformer
Adjustment/reduction circuit according to item 1. (35) The adjustment/reduction circuit according to claim 31, wherein the resistor is a ballast. (36) Claims 31, 32, 33 in which the first and second thyristors are comprised of first and second triaxes.
, the adjustment/reduction circuit according to item 34 or 35. (37) comprising a bidirectional electronic switch means for selectively conducting the electronic switch means in accordance with a timed repetitive control signal applied to the control input means to supply the load; A two-wire AC lamp dimmer comprising control input means for controlling the RMS value of the AC voltage supplied to the load, the control input means for controlling the RMS value of the AC voltage supplied to the load, caused by the load having resistive and inductive components. A method for reducing destructive DC current comprising: (a) providing a signal having a value indicative of a DC current flowing through the load; adjusting the time of the control signal during successive half cycles of the voltage waveform to reduce the DC current flowing through the load;
c) A method of regulation and reduction, characterized in that the timing of the control signal is adjusted to compensate for variations in the AC voltage supplied to the dimmer, thereby adjusting the RMS value of the AC voltage supplied to the load. . (38) (a) only one pair of conductors for connection in series between the AC voltage source and the load; and (b) operatively connected in series with a resistor between the pair of conductors for the connection of the AC voltage supplied to the load. RMS
(c) a first thyristor having a gate terminal operatively connected to a control circuit for generating a control signal that adjusts the value;
a second thyristor operatively connected directly between the pair of conductors and having a resistor and a gate operatively connected to the connection point of the first thyristor, while a relatively low load current is flowing through the dimming circuit. , the first thyristor is made conductive, and the second thyristor is made conductive.
characterized in that the first thyristor is substantially non-conducting and the second thyristor is conducting while the thyristor is substantially inactive and a relatively high load current is flowing through the dimming circuit. Low voltage dimmer circuit. (39) Each of the first and second thyristors has respective hold current characteristics, and the hold current characteristics of the first thyristor are considerably smaller than the hold current characteristics of the second thyristor. Voltage dimmer circuit. (40) Each of the first and second thyristors has a maximum current specification, and the maximum current specification of the first thyristor is less than about 1/10 of the maximum current specification of the second thyristor. low voltage dimmer circuit. (41) A patent in which a load current flowing through a first thyristor develops a voltage across a resistor and a second thyristor is made conductive only after such voltage across the resistor exceeds a selected value. A low voltage dimmer circuit according to claim 38. (42) The resistance value is such that when the load current flowing through the resistor is approximately 1/10 to 1/2 of the maximum current rating of the first thyristor, a voltage approximately equal to the selected value is generated across the resistor. A low voltage dimming circuit according to claim 41. (43) the control circuit includes a series R-C circuit connection operatively connected between the pair of conductors and to a potentiometer for adjusting and controlling the period of the control signal, the potentiometer being in series with the gate of the first thyristor; 39. A low voltage dimmer circuit as claimed in claim 38, operatively connected to the dial and to a capacitor operatively connected between the potentiometer and one of the pair of conductors. (44) Claim 3 in which the load is a low voltage transformer
The low voltage dimming circuit according to item 8. (45) The low voltage dimming circuit according to claim 38, wherein the load is a ballast. (46) Claim 38, wherein the first and second thyristors comprise first and second triaxes, respectively;
The low voltage dimming circuit according to item 39, 40, 41, 42, 43, 44 or 45. (47) (a) only one pair of conductors for connection in series between an AC power supply and a resistor; and (b) operatively connected in series with a resistor between said pair of conductors for the AC voltage applied to the load. RMS
a first thyristor having a gate terminal operatively connected to a control circuit for generating a control signal for adjusting the value;
(c) a second thyristor operatively connected directly between the pair of conductors and having a resistor and a gate terminal operatively connected to the connection point of the first thyristor; the first thyristor is rendered conductive and the second thyristor is rendered substantially non-conductive while a relatively high load current flows through the dimmer circuit; a second thyristor is made conductive, the first and second thyristors each having a maximum current rating, the maximum current rating of the first thyristor being less than about 1/10 of the maximum current rating of the second thyristor; The first and second thyristors each have their own hold current characteristics, and the hold current characteristics of the first thyristor are different from those of the second thyristor.
Significantly less than the hold current characteristic of the thyristor, a voltage is developed across the resistor when the load current flows through the first thyristor, and only when the voltage developed across the resistor exceeds a selected value does the second thyristor is made conductive and the resistor value is such that the voltage across the resistor is approximately equal to the selected value when the load current in the resistor is equal to approximately 1/10 to 1/2 of the maximum current rating of the first thyristor. and (d) the control circuit includes a series R-C circuit operatively connected between the pair of conductors and a potentiometer that adjusts and controls the period of the control signal, the potentiometer being a first A low voltage two wire dimmer circuit operatively connected to a dielectric in series with the gate of a thyristor and a capacitor operatively connected between the potentiometer and one of the pair of conductors. (48) A dimming circuit according to claim 47, wherein the first and second thyristors are comprised of first and second triaxes, respectively.