The present invention relates to a method of controlling the operation of a light dimmer according to the preamble of patent claim 1.

The invention also relates to a light dimmer according to patent claim .

A method according to the invention relates in particular to serial dimmers, in which AC power to be fed to a load is controlled on the basis of the phase angle. The switch of a light dimmer is hereby controlled synchronously in relation to the current of the AC power or to the phase angle of the electric voltage. Light dimmers presently on the market have a predetermined and limited maximum phase angle, by means of which power may at the most be fed to a lamp load, if a light dimmer is intended for controlling of both halogen and incandescent lamps. The light dimmer, and in particular the control unit thereof, needs energy in order to operate, the energy needed being taken from the voltage acting over the switch of a serial dimmer. By setting a fixed maximum phase angle for a light dimmer, the operation of a light dimmer can be guaranteed under all conditions. As regards to halogen lamps, efficient light intensity and power output will be in some cases achieved by means of a limited maximum phase angle, whereas the light intensity and power output of some halogen lamp loads and in particular incandescent lamp loads will be remarkably weaker than they would ideally be.

An object of the present invention is to eliminate the above- described drawback. Thus, an object of the invention is to effect automatic control cf maximum power in a serial dimmer independently of the load. An object of the invention is in particular to control the maximum phase angle in serial dimmers automatically according to the loads in such a way that the energy supply of a light dimmer is secured all the

time and the available light intensity is at the phase angle used at its maximum all the time.

What is characteristic of a method according to the invention is shown in patent claim 1. What is characteristic of a light dimmer is shown in patent claim 4.

In a method according to the invention, the power needed for controlling the operation of the light dimmer is taken from the AC voltage acting over the light dimmer. In accordance with the invention, the energy available from the AC voltage acting over the light dimmer is monitored, and the maximum phase angle is adjusted accordingly in such a way that the available energy always exceeds the predetermined minimum.

A method according to the invention is based on the realization that the energy becoming available from the voltage acting over the light dimmer is monitored, and on the basis of this, the maximum phase angle of the light dimmer is adjusted accordingly when needed. When it is discovered that the energy falls below the predetermined minimum, the maximum phase angle of the light dimmer will be decreased, and hereby the voltage over the switch and the amount of energy becoming available from it will be increased. Thus, such a control system is provided which guarantees automatic control of the maximum phase angle in relation to the energy needed for the operation of a light dimmer.

An advantage of the invention is that it is possible for a light dimmer to operate in connection with both halogen and incandescent lamps at such a maximum control angle which gives the greatest light intensity possible without the necessity to set a light dimmer separately.

Further, an advantage of the invention is that the apparatus based on a method is of simple construction and easily manufactured, and operates reliably.

The invention is described more in detail below, by way of example, with reference to the accompanying drawings, in which

Fig. 1 illustrates the voltage acting over a light dimmer, the maximum phase angle being constant;

Fig. 2 illustrates the voltage acting over a light dimmer, the maximum phase angle being adjustable;

Fig. 3 illustrates a schematic diagram of a light dimmer, the maximum phase angle of which is controllable;

Fig. 4 illustrates one control unit of the phase angle of a light dimmer;

Figs. 5a, 5b and 5c illustrate voltage curves of a control unit of the phase angle, and

Fig. 5d illustrates a voltage curve of the lamp load of a light dimmer;

Fig. 6 illustrates working characteristics of a light dimmer, the load being a halogen lamp, and the maximum phase angle being controlled; and

Fig. 7 illustrates a light dimmer provided with a control unit of the maximum phase angle.

By means of the light dimmer, the AC power to be fed to the lamp load inserted in an electric network or the like AC source is controlled in such a way that the light intensity of the lamp will change steplessly. The AC power to be fed to the load is controlled according to the phase angle synchronously in relation to the current of the AC power or the phase of the voltage. At least one semiconductor, preferably a field-effect transistor (FET) or the like, is used as a switch in the light dimmer. A serial dimmer is connected in series with the lamp load. The power needed for the control unit of the light

dimmer is hereby taken from the voltage acting over the switch. In order to guarantee the energy supply for the control unit under all conditions, a maximum value is determined for the controllable phase angle. This means that for the power being fed to the lamp load, a maximum power value is set, which is lower than if the power would be fed to the load directly from the AC source past the light dimmer.

The lamp load of the light dimmer affects the voltage acting over the switch of the light dimmer and thus also the energy received by the control unit of the light dimmer. This phenomenon is illustrated in figure 1. Curve a illustrates a voltage U _k over the light dimmer, the load being an incandescent lamp (i.e. substantially a resistive load). Curve b illustrates a voltage U _k over the light dimmer, the load being a halogen lamp, i.e. an electronic halogen transformer

(i.e. substantially a combination of a resistive and a capacitive load) . The energy available at a steady current through the switch of the light dimmer at both loads is in proportion to the shaded areas A and B respectively between the curves a and b and the axis t (time axis) . On the basis of this it can be noted that the maximum phase angle a for a halogen lamp load has to be significantly smaller than when controlling an incandescent lamp load. If the light dimmer is intended for both halogen and incandescent lamps and is provided with a fixed maximum phase angle, an incandescent lamp does not give as much light intensity as required during the use. In practice, this can be seen as significantly dimmer incandescent lamp light at maximum control of the light dimmer compared with especially light intensity which becomes available by means of bypassing of the light dimmer.

In a method according to the invention, energy available from the voltage acting over the light dimmer is monitored. When discovered that the energy falls below the predetermined minimum set value, the phase angle of the voltage being fed to the load will be reduced, and thus the amount of the energy available from the voltage acting over the light dimmer will

be increased until the minimum set value of the energy is achieved. This is illustrated in figure 2. The maximum phase angle of the light dimmer is adjusted in such a way that the energy becoming available for the control unit is constant. Curve C illustrates a voltage U _k over the load, the load being an incandescent lamp, and curve d illustrates a voltage U _t over the load, the load being a halogen lamp, i.e. an electronic halogen transformer. The shaded areas C, D between the curves c, d and axis t are in proportion to the energy available for the control unit at a steady current. The curves c and d in the figure show that maximum phase angles α,, α _: clearly differ from each other in both cases. In particular the power fed to the incandescent lamp is remarkably greater than in previous light dimmers, in which a constant maximum phase angle has been used (cf. Fig. 1) .

A light dimmer 1 according to the invention is illustrated as a schematic diagram in figure 3. The light dimmer l is connected from an input terminal la to an AC network, and a lamp load L is connected to an output terminal lb thereof. The light dimmer 1 is provided with a switch 2 and a control unit

3. The control unit 3, in turn, is provided with a switch controller 4 connected to the switch 2, and with a phase angle regulating unit 5, which is, in turn, connected*into a switch controller 4. The energy needed for the operation of the control unit 3 of the light dimmer 1 is taken from the AC voltage U _k acting over the switch 2. The light dimmer 1 is additionally provided with a maximum phase angle regulating unit 6 and a monitoring unit 7 for observing the voltage acting over the switch 2. The maximum phase angle regulating unit 6 is preferably part of the phase angle regulating unit

4. The monitoring unit 7 is connected to the maximum phase angle regulating unit 6.

In figure 4, the phase angle regulating unit 5 is provided with a comparator 8, a DC voltage regulating unit 9, and a saw tooth generator 10, which is synchronized with the voltage of the AC network (in other words, the output voltage of the unit

10 is set to zero preferably at the zero point of the AC voltage sequence) . A DC voltage regulating unit 9 and the saw tooth generator 10 are connected to the inputs 8a, 8b of the comparator 8. The controllable DC voltage U _r available from the output of the DC voltage regulating unit 9 and the rising saw tooth voltage U, available from the output of the saw tooth generator 7 are compared with each other in the comparator 8. When U _t < U _r in the output 8c of the comparator 8, the voltage is U _p . Otherwise, i.e. when U, > U _r , the output voltage of the comparator 8 differs substantially from the voltage U _r ; it is preferably zero. Thus, from the output 8c of the comparator 8, a voltage control pulse is received, the length of which - i.e. the time sequence t, - depends on the amount of the controllable DC voltage U _r (fig. 5a). A control pulse for the switch controller 4 is hereby received from the output of the comparator 8. In the switch controller 4, the control pulse is amplified and adjusted in order to enable control of the switch 2 so that it may be closed and opened in accordance with the rising edge and with the falling edge of the control pulse respectively (Figs. 5b and 5d) .

In the application of figure 4, the DC voltage regulating unit 9 of the phase angle regulating unit 5 is effected by means of a rheostat 11, such as a potentiometer. The first terminal of the rheostat 11 is connected to the DC voltage U.,- _^ and the second terminal most preferably to the ground. The control terminal of the rheostat 11 and the voltage U _r therein are in turn connected to the first input terminal 8a of the comparator 8.

The saw tooth generator 10 is in the -application of figure 4 provided with a resistor 12 and a capacitor 13, which are switched between the steady voltage ^' ϋ _mΛX and most preferably the ground, and the intermediate terminal of which is connected into a second input 8b of the comparator 8. A controllable switch 14 is arranged beside the capacitor 13 between the input 8b and the ground. Through the rheostat 12, the capacitor 13 is charged during a half cycle of the AC

voltage V, and the voltage U, acting over the capacitor is compared in the comparator 8 with the voltage U _r given by the DC voltage regulating unit 9. At the beginning of the half cycle of the AC voltage V at the zero point, the voltage charge of the capacitor 13 is discharged by connecting it to the ground by the intermediate terminal by means of the switch 14.

The maximum phase angle regulating unit 6 is connected to a DC voltage regulating unit 9. The maximum value U _miX of the controllable DC voltage U _r of the DC voltage regulating unit 9 and, at the same time, the maximum length of the control pulse, i.e. the maximum value t _miX of the time sequence t, corresponding to the maximum phase angle, are controlled by means of this unit.

The maximum phase angle regulating unit 6 is provided with a capacitor 15, a voltage limiter 16, and a charge circuit 17 of the capacitor. The capacitor 15, and the voltage limiter 16, which is preferably a zener diode, are connected in parallel to each other and also parallel to the DC voltage regulating unit 9, such as the rheostat 11. The charge circuit 17 of the capacitor is connected to the terminal 15a of the capacitor 15, the terminal 15a being further connected to the terminal of the maximum voltage V _max of the DC voltage regulating unit 9. The charge circuit 17 of the capacitor is connected to a monitoring unit of the voltage acting over the switch 2, the reference voltage U _v affecting the input of the charge circuit 17. The charge circuit 17 of the capacitor is in this application provided with a forward diode 18 and a resistor

19.

The phase angle regulating unit 5 and the maximum phase angle regulating unit 6 operate in the application of figure 4 as follows. The length of a control pulse of the phase angle regulating unit 5, i.e. the time sequence t,, affects the times when the switch 2 (fig. 3) is open and closed during each voltage phase sequence of the AC voltage. Thus, it also

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affects the voltage U _L over the load, and respectively the voltage U _k over the switch 2, as can be seen in figures 5b, 5c and 5d. Proportional to the voltage U _k over the switch 2, the voltage U _v is fed from the monitoring unit 7 (fig. 3) to the input of the charging circuit 17 of the capacitor of the maximum phase angle regulating unit 6.

In the maximum phase angle regulating unit 6, the capacitor 15 is charged at reference voltage U _v through the diode 18 and the resistor 19 of the charge circuit 17 with a certain charge current I _v . The voltage acting over the capacitor 15 determines the maximum value U- _^ of the DC voltage that affects in the DC voltage regulating unit 9 of the phase angle regulating unit 5 and determines the maximum length of the control pulse, i.e. the maximum value t, _^ of the the time sequence t,. When the charge current I _v of the capacitor 15 is more powerful than the discharge current I _r through the rheostat 11 of the DC voltage regulating unit 9, the voltage limiter 16 operates, by means of which the value of the voltage U-. _^ , is limited to the predetermined level U _z .

When the length t, of the control pulse and the time sequence increases enough, the voltage U _k over the switch 2 and the reference voltage U _v will decrease. Hereby, the charge current I _v of the capacitor 15 will also decrease, and at some value of the charge current, the limiting voltage U _z of the voltage limiter 11 is met, whereby the discharge current I _r substantially corresponds to the charge current I _v . When the rheostat 11 of the DC voltage regulating unit 9 is adjusted to its maximum value or close to the maximum value, the charge current I _v may drop below the discharge current I _r at some form of the voltage U (depending on the load L) , whereby the voltage level of the capacitor 15 and the voltage U-, _^ will drop. When the voltage J _mn , which limits the voltage U _r (0 ≤ U _r ≤ U _na ,,) drops, and the length of the control pulse and the time sequence t, also decreases, since t„, t, _: belongs to the set [0, tea,] . t,, > - ₂ -> U _r (t.]) > U _r (t, ₂ ) . When the time sequence t, decreases, the open state of the switch 2 will increase and

the voltage U _k over the switch 2 and the reference voltage U _v will increase. Hereby, the charge current I _v caused by the reference voltage U _v will increase with respect to its earlier value. When the above-mentioned changes occur, the maximum voltage U _^ of the controllable DC voltage and the maximum length of the control pulse, i.e. the maximum time sequence t _ana .* achieve a stable constant state, in which U _πna- <U ₂ and t.<t.

The above-described control event is schematically illustrated in figure 6. In the figure, control of the value R _ref of the rheostat 11 is effected from zero to the maximum value R _n(πax . When the value R _ref of the rheostat reaches its maximum value ^R _refm«' the regulating arrangements begin to have such an effect as was described above, provided that no energy exceeding the minimum limit is available for the control unit of the light dimmer from the voltage acting over the switch.

Figure 7 shows a light dimmer 20 according to the invention, in which regulating of the maximum phase angle is effected by means of the arrangement shown in figures 3 and 4. In this application, the reference voltage U of the maximum phase angle unit 6 is taken from between the diodes 21, 22 of the voltage regulator belonging to the power feed arrangement of the light dimmer. The diodes 21, 22 are hereby used as a monitoring unit of the voltage acting over the switch 2. In connection with the voltage regulator, there is also a synchronizing unit 23 belonging to the control unit 3. As a switch 2 in the light dimmer there is a pair of FETs 24, 25, which are controlled by means of a switch controller 4. There may also be several pairs of FETs connected in parallel. The operation of the phase angle regulating unit 5 and the maximum phase angle regulating unit 6 connected to it is as described in connection with figures 4 and 5.