POWER CONTROL

Abstract: A method and a device for controlling the power supply to a load utilises an FET, whose control electrode is ramp-controlled in a pulse-time-related-manner by means of a voltage signal from a microcomputer with direct negative voltage feedback related to the current through said FET.

Description: POWER CONTROL Field of the Invention The present invention relates generally to the control of the current feed from a voltage source to a load connected thereto with the aid of a controllable semicon- ductor means connected between them. More specifically, the invention relates to such control where the semiconductor means is controlled in a pulse-time-related manner between a non-conducting and a fully conducting state. Background of the Invention In devices for controlling current feed of the above-mentioned kind a switched semiconductor means of the Triac or Thyristor type is normally used. The abrupt switching-on and switching-off courses or sequences of the semiconductor means give rise to a number of inter- fering current components, which in turn give rise to the emission of interfering high-frequency radiation. In order to eliminate such radiation, relatively costly and bulky passive filter components, such as chokes and capacitors, must be provided. In connection with the control of high power supplied to a resistive load (i.e. lamps) it has been suggested (see e.g. EP 0 191 838 Bl) that one actively ramp controls the switching-on sequence of the semiconductor means used, so that interfering current frequency co po- nents will be generated to a lesser extent, whereby passive filter components can be avoided. The actual ramp control, i.e. the ramp slope, has been considered essential and requires extensive control circuits. Furthermore, special current limiting circuits are required to protect the semiconductor means. Control of the kind described here is not suitable for controlling low power or when the load is non-resistive. Object of the Invention The object of the present invention is to provide power control with active elimination of interfering current components, which power control is particularly well suited for controlling low power levels, such as up to a few hundred watts, typically up to about 1/2 kilowatt; provides very good suppression of interference components; can be implemented by means of a very simple and inexpensive circuit solution; enables easy power factor control; and has low sensitivity to operational disturbances in the supply current and the load. Summary of the Invention The above-mentioned objects are achieved by methods and a device exhibiting the features recited in the appended claims. The invention is thus based on the insight that the primary thing is not to carefully control the slope of the control signal ramps, but to control the current sequence provided so that abrupt current changes, such as in connection with a transition from/to the zero current level and the level corresponding to full conduction respectively, are avoided, i.e. so that in that connection the current sequence will be rounded. With respect to the controlled switching-on and switching-off sequences this means that they are advantageously caused to be generally S-shaped and inversely S-shaped respectively. According to the invention, it has been found advantageous to achieve "rounding" as described above by utilising a fast, i.e. direct current-related, negative feedback of the semiconductor means used. Accordingly, a negative feedback voltage generated by the current through the semiconductor means is preferably used, which voltage is applied directly to the control input of the semiconductor means together with the power controlling ramp-edged control signal. It has been found that, in addition to providing the desired rounding of the current curve at the zero level and the level corresponding to a fully conducting semiconductor means, negative feedback of the aforementioned kind per se also constitutes protection against damaging current surges through the semiconductor means, as well as an effective way of preventing changes in the supply voltage and/or load from negatively influencing the power control or the suppression of interfering components. This is particularly advantageous in connection with supply of current from a transient-rich network. In accordance with the invention it has thus been found that it is easy to prevent interfering current components with frequencies above about 150 kHz from being generated to any significant or inconvenient extent. Moreover, it has been found that the above-mentioned conditions enable the utilisation of a single semiconduc- tor means in an extremely simple circuit which, in addition, is well suited to control utilising a pre-program- mable microprocessor, as will be explained more fully hereafter . According to the invention, the semiconductor means is advantageously of the voltage-controlled current-generator type, typically an FET semiconductor element. While the invention can quite easily be utilised in connection with power supply from a d.c. voltage source, its primary use is in connection with supply from an a.c. network, usually the normal a.c. network. However, it has been found that the desired results are achieved by means of the invention also in connection with supply from a source having a considerably higher frequency, such as several kHz. Preferably, according to the invention, when power is supplied from an a.c. source, a pulsating d.c. voltage obtained subsequent to rectification, such as a full-wave rectified voltage, is supplied to the semiconductor means. This highlights the advantage of utilising a single semiconductor means, as mentioned above. As also mentioned above, the present invention is suitable for use in connection with microprocessor-based control. This is particularly true in view of the difficulties which may arise when changing a pre-set, desired power level, particularly when starting up or turning off, as well as in connection with a non-resistive load. A microcomputer included in the control unit employed may thus advantageously be programmed to provide power change and power factor correction in a simple and efficient manner. In connection with a power change, particularly in connection with the starting of the power supply, the microcomputer can thus successively carry out the change by successively providing, during successive control periods (i.e. supply voltage pulses), changed, power- determining switching-on and switching-off times of the semiconductor means. For example, when starting the power supply, this means that the current sequence through the semiconductor means is started very gradually, i.e. it becomes exceptionally smooth. This may be of particular value if the switching-on takes place at the zero value of a supply voltage pulse and a non-resistive load results in the current striving to be 90° ahead of the voltage, i.e. when, normally, the current would initially be unacceptably high. Furthermore, in connection with power factor cor- rection, the microcomputer can change the times of the switching-on and switching-off of the semiconductor means, so that the current during the respective supply voltage pulse is distributed as advantageously as possible in relation to the pulse middle in order for the power factor to be as close to 1 as possible. In order to enable microcomputer-based control as described above, according to a preferred embodiment of the invention, the distribution of the amount of current during a supply voltage pulse with respect to the pulse middle is detected, as well as the total amount of current during the pulse. The current distribution may advantageously be detected by repeatedly sampling the level of the current during the supply voltage pulse, the sampling values being added up in the microcomputer for the respective halves of the supply voltage pulse. A comparison carried out in the microcomputer between the sum values thus obtained provides guidance to the microcomputer in changing the position of the current conduction interval (i.e. the interval between a controlled switching-on and switching-off) during future supply voltage pulses. After one or more such changes, it has been found that, as a rule, the best possible uniform current distribution around the middle of the supply voltage pulse is achieved, so that the power factor approaches 1. In order satisfactorily to detect the power present- ly supplied to the load, it has been found sufficient to determine the amount of current present during a supply voltage pulse, i.e. simply the sum of the two above-mentioned sampled current sum values. The power-related current sum thus obtained can be compared in the microcom- puter to a current sum desired value stored therein corresponding to the pre-set desired power. Depending upon the comparison, the current conduction interval is changed, i.e. it is increased if the power is to increase and it is reduced if the power is to decrease. This control sequence thus means that the voltage across the load, which, of course, together with the current through the load influences the power supplied, need not be especially detected or taken into consideration. As will be appreciated, the power factor correction could affect the supply power level obtained. Advantageously, the two above-mentioned control processes should therefore be combined. In this connection, it has been found suitable to carry out the power factor control at longer time intervals than the actual power control, typically during every tenth supply voltage pulse, while the power control takes place during every supply voltage pulse. The invention will now be described in more detail by way of non-limiting exemplifying embodiments with reference to the accompanying drawings. Brief Description of the Drawings Fig. 1 is a schematic block diagram illustrating a basic embodiment of the present invention. Fig. 2 is a schematic curve diagram illustrating a possible mode of operation of a circuit according to Fig. 1. Fig. 3 is a schematic circuit diagram comprising an embodiment of a device according to the invention. Fig. 4 is schematic curve diagram illustrating the mode of operation of the circuit according to Fig. 3. Fig. 5 is a schematic circuit diagram comprising another embodiment of a device according to the invention. Fig. 6 is schematic curve diagram illustrating the mode of operation of the circuit according to Fig. 5. Fig. 7 is a schematic circuit diagram comprising yet another embodiment of a device according to the invention. Fig. 8 is a schematic circuit diagram comprising a further embodiment of a device according to the invention. Fig. 9 is a schematic flowchart further illustrating the mode of operation of the circuit according to Fig. 7. Fig. 10 is a schematic flowchart illustrating how current sampling can be utilised in connection with a mode of operation according to Fig. 9. Description of Embodiments The circuit shown in Fig. 1, which illustrates a basic embodiment of the invention, comprises a supply voltage source 1 to the output of which a load 3 is connected in series with a power control device 5. The device 5 comprises a field effect transistor (FET) 7, whose one main electrode 8 (drain) is connected to one side of the load 3 and whose other main electrode (source) 9 is connected to the voltage source 1 by the intermediary of a negative feedback resistor 11. A control unit 13 has a control pulse output, whose one connection is connected to the control electrode (gate) 10 of the transistor 7 and whose other connection is connected to the side of the resistor 11 which is connected to the voltage source 1. The control unit has an input 15 for setting the desired power level P de s, i.e. either for receiving a desired value signal or, for example, for manual adjustment of the desired value, such as by means of a potentiometer or the like. Voltage is supplied to the control unit through a lead 17, while at the same time detection in the control unit of zero crossings of the supply voltage (in connection with pulsating supply voltage) is made possible. Control pulses emitted by the control unit are generated across a capacitor 18, which is charged and discharged by the intermediary of a resistor 19. A typical mode of operation of the circuit according to Fig. 1 in accordance with the invention will now be described with reference to Fig. 2 which, by way of example, shows typical curve sequences of the supply voltage U ιn from the voltage source 1, of the current Iχ through the load 3, the transistor 7 and the resistor 11, of the control voltage U c , and of the control voltage U g of the transistor. It is assumed that U ιn is a pulsating supply voltage 20 full-wave rectified from the network and the load 3 is considered to be completely resistive. U r is a periodic square pulse, whose length during a supply vol- tage pulse is related to P des in accordance with a predetermined relationship. The control unit 13 detects each zero crossing of Uι n and triggers a control pulse 21 in connection with each such zero crossing. The control pulse is applied to the capacitor 18 by the intermediary of the resistor 19, whereby the voltage U g across the capacitor begins to increase according to a usual RC charging curve 23. U r and the RC time constant are chosen so that U g strives towards a voltage level 24 such that the level 25 corresponding to full conduction of the transistor 7 is exceeded, although with a leading edge sequence of the curve having clear RC curve 23 characteristics. When the control pulse 21 stops, a corresponding discharge of the capacitor 18 takes place, i.e. U g falls back to zero also in accordance with a usual RC discharge curve. The resulting current sequence is indicated by the curve Ii, where the dashed curve sequence 27 shows the current sequence which would be obtained in the case of a permanently conducting transistor and a resistive load. The actual current begins to flow at the time To, i.e. it begins to increase from the zero current level, but initially it increases very gently, i.e. in a smoothly rounded manner in the region 29 by virtue of the combination of ramp control and fast, direct negative current feedback, the latter being provided by the voltage generated by the current I across the resistor 11. At the time ti, the transistor has been given full conduction and the current I reaches the dashed line. In this region 30, too, a smooth, rounded transition is obtained by virtue of the combination of the special leading edge sequence and the negative feedback. As the skilled person will easily appreciate, the current then follows the dashed curve 27 to the next transition region 31, at which time the current should begin to return to the zero level in order for the desir- ed power to be achieved. At the time t 2 , U r ceases and the capacitor begins to discharge. At the time t 3 , U g passes the level of full conduction and the current begins to drop much faster than according to the curve 27. However, by virtue of the negative current feedback, there is no abrupt current change but, rather, a smooth, rounded current curve sequence occurs here as well. Subsequently, the current drops quickly in order to return to the zero level in the transition region 32. This final part of the current curve also becomes very smoothly rounded by virtue of the combination of the RC curve control and the negative current feedback. Subse- quently, the whole sequence is repeated during the following supply voltage pulse 20, possibly with a change in length of the control pulse 21, if a changed power level is desired. Fig. 2 shows a sinusoidal supply voltage sequence. However, the skilled person will appreciate that this is by no means a requirement for the smoothly rounded current sequence which according to the invention results in a very low level of interfering high frequency components. Specifically, the negative feedback used means that, for example, interference or transients on the supply voltage will not be able to produce disturbing interference in the current sequence, since such interference is immediately counteracted by the fast negative current feedback. Fig. 3 shows in more detail how a simple, manually adjustable power control circuit comprising an embodiment of the invention can be constructed. A full-wave rectifier 35, emitting a pulsating supply voltage U in , connected to an ordinary a.c. network 33 supplies a lamp 37 which is connected in series with an FET 7 with an associated negative feedback resistor 11. As in Fig. 1, a control unit 39 comprises a capacitor 18 and an associated resistor 19. Here, the capacitor is connected to the control electrode 10 of the tran- sistor by the intermediary of a protection resistor 40. On its input side, the resistor 19 is connected to the inverted output of a control-pulse-emitting Schmitt-trig- ger 41, whose input is connected by the intermediary of a diode 42 to the inverted output of a second Schmitt-trigger 43, which is used for detecting voltage zero-crossings and whose input is connected to the supply voltage by the intermediary of a voltage divider consisting of two resistors 44, 45. A capacitor 47 with a parallel- connected adjustable resistor 48 is connected across the input to the Schmitt-trigger 41. A circuit 49 of conventional design is connected to the supply voltage to pro- vide d.c. voltage Vcc to the Schmitt-trigger circuits 41, 43. With reference also to Fig. 4, which illustrates the various voltage sequences and the current sequence in the circuit, the mode of operation of the above-mentioned circuit is as follows. The desired power level is set with the aid of the adjustable resistor 48. The Schmitt- trigger 43 detects the voltage zero-crossings and in connection with each such crossing charges the capacitor 47 with a very short pulse. The voltage Uc across the capa- citor 47 is discharged through the resistor 48 during a time determined by the resistor setting. At the time ti, the capacitor voltage U c is zero, whereupon the Schmitt- trigger 41 is triggered to emit a rectangular control pulse 51 during the remainder of the voltage pulse in question, which in the same way as the pulse 21 in the circuit according to Figs 1 and 2 gives a ramp-edged transistor control pulse U g with an accompanying current pulse having a smoothly rounded curve shape. In the sequence according to Fig. 2, the power con- trol is effected by causing the transistor to conduct from a zero-crossing during a subsequent time interval, which means that the desired power level is obtained, whereupon the transistor is caused to be non-conducting during the remainder of the supply voltage pulse. In Fig. 3 the situation is the reverse, which means that, in principle, in the two cases the current pulses will be inverted in relation to each other. In Fig. 3, the trailing edge sequence of the current pulse will to a large extent follow the sequence of the decreasing supply voltage pulse (since the load is resistive) , which means that the decay of the gate voltage ϋ g will be of lesser importance. However, the built-in negative feedback will ensure that the transition to zero value of the current is smoothly rounded. Fig. 5 illustrates an embodiment of a d.c. voltage- fed manually adjustable power control circuit comprising the present invention. The basic structure is similar to the one in Fig. 3, and consequently only essential differences will be described. Control pulses are supplied to the RC combination 19, 18 from a self-oscillating flip-flop having an adjustable pulse ratio. The flip-flop consists of a Schmitt-trigger 51 with an inverted output, a resistor 52 being parallel-connected across the Schmitt-trigger and a capacitor 53 being connected across the input of the Schmitt-trigger. The operating point of the Schmitt- trigger can be displaced, thereby changing the pulse ratio, by means of a voltage-fed potentiometer 55, whose moving contact 56 is connected to the input of the Schmitt-trigger 51 by the intermediary of a resistor 57. Typically, the operating frequency of the flip-flop can be about a hundred or a few hundred Herz. Fig. 6 schematically illustrates typical curve sequences obtained in the circuit according to Fig. 5. As will be easily appreciated, the power transferred to the load will be directly dependent on the pulse ratio, i.e. the length of the control pulse 59 itself. Fig. 7 schematically illustrates an embodiment of a microcomputer-controlled power control circuit which advantageously can also be used for a non-resistive load, which circuit comprises the present invention. The load 63 is connected to an a.c. voltage source 65 by the intermediary of a series combination of an FET 7 and a negative feedback resistor 11 and utilising four rectify- ing diodes Dl, D2, D3, D4 in such a way that all current flows unidirectionally through the series combination 7, 11 but bidirectionally through the load 63. The control unit comprises a microcomputer 67 having a control signal output 68 for outputting a control pulse, which, as above, feeds an RC combination 19, 18 for the application of a control voltage U g to the control electrode 10 of the transistor 7 by the intermediary of a protection resistor 40. The microcomputer has a voltage-sensing input 69 connected to a voltage divider which consists of two resistors 71, 72 and which is connected to the line voltage. This voltage sensing enables detection in the microcomputer of the zero-crossings of the supply voltage. Furthermore, the microcomputer 67 has an input 73 connected to the connection point between the transistor 7 and the resistor 11, so that a voltage proportional to the current through the transistor and the resistor generated across the resistor can be sensed by the microcomputer, whereby the value of the current can be deter- mined at every moment. As above, a circuit 74 is arranged for supplying voltage Vcc to the microcomputer itself. A suitably designed circuit 75, e.g. a potentiometer-based circuit or a so-called touch-control-based circuit of a type known per se, gives a P des signal on a desired value input of the microcomputer. The pre-programmed microcomputer thus detects the voltage zero-crossings and uses these as a reference phase. Depending upon the desired power value entered, the microcomputer determines a suitable switching-on and switching-off time respectively (in relation to the reference phase detected) of the transistor and outputs a corresponding control pulse on the output 68. In connection with major changes to the desired power, such as when starting from a zero value, the microcomputer can be programmed successively to change the power until it has reached the desired level. In order to determine the existing power level, the microcomputer uses the signal which corresponds to the current which is received on the input 73, which signal is repeatedly sampled for providing a current sum value, which has been found to be usable with high accuracy as a value of the power without also having to be related to the voltage sequence. The current sum value can easily be compared to current sum values stored in the microcomputer which correspond to different power levels. Furthermore, the current sampling means that the microcomputer can easily detect deviations from a desired power factor (usually 1) by determining the distribution of the current in relation to the middle of the present voltage half period, i.e. the present supply voltage pulse. Subsequently, the microcomputer can change the switching-on and switching-off points of the transistor in order thereby to influence the distribution of current in relation to the half period middle so that a more even distribution is obtained, whereby the power factor improves. It will be appreciated that this power factor control cannot be used in the case of full power since, in that case, the transistor will be continuously conducting. Figs 9 and 10 illustrate by means of flowcharts how the program-based power control and power factor control can be carried out in the microcomputer in a simple and advantageous manner. Although these flowcharts essentially speak for themselves, the following short description thereof, with reference first to Fig. 9, may improve the reader's understanding . When a desired power value has been set (block 101), the microcomputer determines initial switching-on and switching-off times of the transistor (block 102) in order to achieve a smooth power change (especially desirable at the initial starting of the power), i.e. for the purpose of achieving a power change carried out in suit- able steps. Subsequently, the control voltage pulse is applied (block 103) , taking into account the pre-set switching-on time, whereby current can begin to flow through the transistor and consequently through the load. For the purpose of power and power factor control, the microcomputer subsequently determines the amount of current (essentially the integrated current value) during the time from the switching-on until the middle of the voltage pulse or of the voltage half-period, i.e. I A (block 105) , as well as during the time subsequent thereto until switching-off, i.e. I B (block 107). In this case too, the switching-off has been initiated by removing the control voltage pulse (block 106) , taking into account the previously determined switching- off time. Next (block 108), the microcomputer decides whether to follow a power control loop (to the left in Fig. 9) or a power factor loop (to the right in Fig. 9) . It has been found suitable to follow the power factor loop periodi- cally every n th power control loop. The magnitude of n may typically be 10. As will be appreciated, in connection with starting, the power control loop will initially be traversed a number of times for the purpose of increasing the power to the desired level. In the following power control loop, the present power value P act is determined on the basis of the sum of I A and I B (block 109) , after which a comparison with P des is carried out (block 110). If equal, the loop returns to block 103, as indicated by the line 111. If the present power is too low (block 112) , the microcomputer changes the switching-on and switching-off times to increase the conductive time interval of the transistor (block 113), i.e. the switching-on time is brought forward and the switching-off time is delayed. Subsequently, the loop returns to block 103, as indicated by the line 114, for the purpose of control pulse application with the changed switching-on and switching- off times. If the present power is too high (block 115) , the microcomputer changes the switching-on and switching-off times in the opposite direction (block 116) , after which the loop returns to block 103, by the lines 117, 114. If the power factor loop is to be traversed (block 108), the microcomputer compares the current amount values I A and I B (block 118). If equal (block 119), the power factor is optimal, and consequently the microcomputer immediately switches over to the power control loop (block 109) . If I A is greater than I B (block 120), it is desirable to displace an amount of current from the first voltage pulse half-period to the second one, which the microcomputer does by delaying the switching-on and switching- off times (block 121) . Subsequently, the loop returns to block 103 by the line 122. If I A is less than I B (block 123) , it is desirable to carry out a current amount displacement in the opposite direction, which the microcomputer does by bringing forward the switching-on and switching-off times (block 124), after which the loop also returns to block 103 by the line 122. Fig. 10 illustrates in more detail how the central part of the flowchart in Fig. 9 can be carried out in a preferred way based on repeated sampling of a continuously sensed analog current value which is input to the microcomputer. In the microcomputer, a digital desired value I des of the current sum value has been pre-set for the power control (block 131) . In principle, the continued processing then follows the description with reference to Fig. 9, and consequently only matters relevant to the digital process will be discussed in the follow- ing. In connection with the repeated sampling (typically 100 times per period) of the analog current value detect- ed during the current-conduction interval of the transistor (blocks 132 and 133) , analog current amplitude values are obtained which are converted from analog to digital by the microcomputer (blocks 134 and 135) . The digital current values obtained can typically have a resolution of 256 bits. As will be readily appreciated, these digital current values can easily be added up by the microcomputer (blocks 136 and 137) for providing the desired current amount values I A and I B and I A + I B respectively (block 138) for comparisons between themselves and with Ides • As the skilled person will readily appreciate, a power-factor-influencing current amount displacement of the kind described above may already be beneficial when the load is completely resistive, i.e. when controlling according to the illustration in Fig. 2. As will be apparent, if no special measure is taken, the resulting amount of current will be concentrated mainly to the first half of the voltage pulse, which means a power fac- tor displacement from 1. A return to a power factor of about 1 can then be achieved by means of a displacement according to the invention of the current pulse, so that it will be distributed as evenly as possible around the voltage pulse middle, i.e. by delaying the times t 0 and t 2 with a concomitant delay of the times ti and t 3 . A common load case with a non-resistive load is an HF-device for a fluorescent tube or the like. In such a case, the current normally leads the voltage in phase. The power factor will be markedly inadequate, particular- ly in connection with low load power, typically below half power. In such a case, it has been found that power factor control according to the invention results in a considerably improved power factor. It will be appreciated that, in these cases, the power factor control will lead to changes in the output power level, making the combined power and power factor control according to the invention particularly advantageous . In connection with control in this context, because the current strives to be out of phase with the voltage, in addition to the initial and final ramp-controlled sequences, the current sequence will in many cases include considerable intermediate changes in the current sequence. However, these will be neutralised to an essential degree by the negative current feedback according to the invention as far as the generation of disadvantageous interference components is concerned. With respect to the distribution of the amount of current for achieving an improved power factor, it should be emphasised that an even distribution in relation to the present voltage pulse can, of course, include division into, for example, two current pulses, one being output at the beginning of the present time interval and the other being output at the end of the time interval. Such control can easily be achieved by virtue of the use of microcomputer control. In the examples described above, the transistor used is ramp-controlled to a state of full conduction, which is advantageous since small losses in the transistor are desirable. However, in some cases it may be suitable to ramp-control the transistor only towards and not all the way up to a state of full conduction. Accordingly, Fig. 8 illustrates yet another embodiment of the device according to the invention, in which further developed microcomputer control is utilised in combination with incomplete ramp-control of the transistor . With respect to its basic structure, the device according to Fig. 8 corresponds to the device in Fig. 7 but, in addition, it has a control loop 81, which, by a lead 83 on an input, receives an input signal corresponding to the voltage across the transistor 7 and which has a control signal output connected to the connection point between the capacitor 18 and the resistor 19. This control circuit 81 is adapted to provide control when the transistor is ramp-controlled to almost full conduction. In this connection, the combination of the resistors 19 and 84 and the capacitor 18 is dimensioned so that the control output signal of the microcomputer 67 provides the desired ramp-control for switching- on and switching-off with a suitable RC time constant and so that the transistor is brought to a state of almost full conduction, i.e. so that a balanced low voltage drop is obtained across the transistor in the conducting state . The control circuit 81 senses the residual voltage across the transistor 7 in the conducting state and applies its control voltage to the control electrode of the transistor to keep said voltage constant. However, the control is relatively slow, which means that operational changes in the supply voltage and/or the load, which normally might give rise to rapid current changes, are counteracted, i.e. such current changes are stopped. This means that bi-directional protection against interference is obtained. The person skilled in the art will appreciate that the circuit according to Fig. 8 will strive to keep the pre-set, present current constant, i.e. the circuit will be comparable in nature to an inductance and can thus replace a bulky coil in many applications. The person skilled in the art will appreciate that the function of the control circuit 81 can also be implemented in the microcomputer 67. It should be readily apparent from the examples provided of devices utilising the present invention that the circuits included comprise only a few, inexpensive compo- nents and that, without exception, these do not take up a great deal of space. As a result, it is possible to make devices comprising the present invention very small and, consequently, they will have a wide variety of applications. The use of- microcomputer-based control also facilitates the provision of additional functions with respect to the power control, e.g. remote control, memo- ry, timer, etc.

Claims: CLAIMS 1. A method for controlling the current feed from a voltage source to a load connected thereto, comprising the steps of connecting a controllable semiconductor means between the voltage source and the load; generating a control signal intended for controlling said semiconductor means depending upon the desired level of the power supplied to the load; supplying the control signal to said semiconductor means for pulse-time-related control of the current therethrough so that the desired power level is obtained, the current being given a ramp-shaped switching-on sequence and preferably also a ramp-shaped switching-off sequence respectively to and from a current value corresponding to current conduction with a rounded sequence at the ramp start and the ramp end respectively, so that interfering current frequency components are at least essentially avoided, the current being given a rounded sequence at the ramp start and the ramp end respectively by means of a direct, current-related negative feedback of said semiconductor means. 2. A method according to claim 1, wherein the switching-on and switching-off sequences are given a general S-shape and inverse S-shape respectively. 3. A method according to claim 1 or 2, wherein the voltage source emits a pulsating direct voltage, prefer- ably a full-wave rectified alternating voltage, comprising the step of detecting during each respective voltage pulse how the current is distributed between the time before and the time after the pulse middle and, depending upon this distribution, controlling the switching-on and the switching-off times of the semiconductor means so that the current is distributed at least essentially uniformly around said pulse middle. 4. A method for controlling the current feed from a voltage source to a load connected thereto, wherein the voltage source emits a pulsating direct voltage, preferably a full-wave rectified alternating voltage, compris- ing the steps of connecting a controllable semiconductor means between the voltage source and the load; generating a control signal intended for controlling said semiconductor means depending upon the desired level of the power supplied to the load; supplying the control signal to said semiconductor means for pulse-time-related control of the current therethrough so that the desired power level is obtained; giving the current a ramp-shaped switching-on sequence and preferably also a ramp-shaped switching-off sequence respectively to and from a current value corresponding to current conduction with a rounded sequence at the ramp start and the ramp end respectively, so that interfering current frequency components are at least essentially avoided; and detecting during each respective voltage pulse how the current is distributed between the time before and the time after the pulse middle and, depending upon this distribution, controlling the switching-on and the switching-off times of the semiconductor means so that the current is distributed at least essentially uniformly around said pulse middle. 5. A method according to claim 4, wherein the current is given a sequence essentially without abrupt current changes by means of a direct, current-related nega- tive feedback of said semiconductor means. 6. A method according to any one of claims 3-5, wherein the distribution of the current is detected by means of sampled integration of the current during the respective pulse halves and by comparing the current values obtained in this connection. 7. A method according to claim 6, wherein the current values obtained are added up to form a current sum value, which is used as a measure of the power supplied to the load and is compared to a pre-set desired value of the power, and wherein the switching-on and switching- off times of the semiconductor means are also controlled depending upon the result of the power comparison for the purpose of providing the desired power level. 8. A method according to claim 7, wherein the control of the switching-on and switching-off times for influencing the current distribution takes place repeti- tively, every time after the control of the switching-on and switching-off times for influencing the power level has been carried out during a number of voltage pulses. 9. A method for reducing the generation of interfering current components in connection with control- pulse-time-related control between a non-conducting and a conducting state of a semiconductor means connected between a voltage source and a load for the purpose of controlling the power supplied to said load, comprising the step of, in connection with sudden current changes particularly at the zero current level and at a current level corresponding to a conducting semiconductor means respectively, giving the current sequence a rounded transition sequence by means of a direct negative feedback of the semiconductor means related to the current through the semiconductor means. 10. A method according to claim 9, wherein a semiconductor means of the voltage-controlled current generator type, such as of the FET type, is used, the negative feedback being achieved by applying to the control electrode of the semiconductor means a current-related negative feedback voltage generated across a resistor connected to a main electrode of the semiconductor means. 11. A method according to claim 10, wherein the negative feedback voltage is combined with a pulse-shaped control voltage having a leading ramp edge and a trailing ramp edge and being applied to said control electrode. 12. A method according to claim 11, wherein the leading ramp edge is caused to follow a capacitor charging curve and the trailing ramp edge is caused to follow a capacitor discharging curve. 13. A method for controlling the current feed from a voltage source to a load connected thereto, comprising the steps of connecting a controllable semiconductor means between the voltage source and the load; generating a control signal intended for controlling said semiconductor means depending upon the desired level of the power supplied to the load; supplying the control signal to said semiconductor means for pulse-time-related control of the current therethrough so that the desired power level is obtained; and giving the control signal and, consequently, the current such a sequence that interfering current frequency components are at least essentially avoided, wherein a semiconductor means is used which acts as a voltage-controlled current generator, said control signal comprises voltage pulses of controllable length and with a controlled leading ramp edge and preferably also a controlled trailing ramp edge, and said control signal is supplemented with a negative feedback voltage, which is directly related to the current through said semiconductor means. 14. A device for connection between a voltage source and a load for controlling the current flowing from the voltage source to the load and thereby the power supplied to the load, comprising a voltage-controlled semiconductor means intended to be connected to the voltage source and the load, so that said current can flow therethrough, the semiconductor means having a control input for receiving a current control voltage, a control unit adapted to emit a pulsating control voltage, depending upon a desired power value pre-set therein, to the control input of said semiconductor means for pulse-time-related control of the current through the semiconductor means, the pulses of the control voltage having a leading ramp edge and preferably also a trailing ramp edge for bringing the semiconductor means from a non-conducting to a conducting state and from a conducting to a non-conducting state respectively, means for generating a negative feedback voltage related to the current through the semiconductor means, and means for directly applying the negative feedback voltage to the control input of the semiconductor means, so that sudden current changes are given a rounded sequence, whereby interfering current frequency components are at least essentially avoided. 15. A device according to claim 14, wherein said means for generating a negative feedback voltage com- prises a negative feedback resistor which is connected to a main electrode of the semiconductor means and which is traversed by the current of the semiconductor means. 16. A device according to claim 15, wherein the control unit has a capacitor adapted to be charged for pro- viding the leading ramp edge of the control voltage pulses and to be discharged for providing the trailing ramp edge of the control voltage pulses, one connection of the capacitor being connected to the control input of the semiconductor means and the other connection of the capacitor being connected to one connection of the negative feedback resistor, the other connection of the negative feedback resistor being connected to said main elec ¬ trode of the semiconductor means. 17. A device according to any one of claims 14-16, wherein the semiconductor means is of the FET type and preferably comprises a single semiconductor element. 18. A device according to any one of claims 14-17, wherein the control unit comprises a microcomputer, which is adapted to control the semiconductor means in connection with pulsating supply voltage from the voltage source so that, with respect to each supply voltage pulse, the resulting load current is distributed with an at least essentially equal amount on each side of the pulse middle. 19. Use of a semiconductor means of the voltage-con- trolled current-generator type provided with direct current-related negative voltage feedback to the control electrode of the semiconductor means for voltage-pulse- time-related control of the power supply from a voltage source to a load by the intermediary of the semiconductor means.

Inventors: CLAUSEN BJOERN, CLAUSEN, BJOERN
Applicants: ARTEKTRON AB, CLAUSEN BJOERN, CLAUSEN, BJOERN
Application year: 1998
Main classification: H03K17
IPC codes: H03K17