1. Field of the Invention
The present invention relates to the field of power regulation. To control the operation of industrial and domestic appliances, semiconductor power components operating in switched mode are often used. So-called conduction angle (or phase angle) controls are thus made, in which a power switch is turned on only for a portion of the duration of each halfwave or of every other halfwave of the supply voltage. Such systems are currently used in the field of domestic lighting to make light dimmers, and in many other applications to form power variators.
2. Discussion of the Related Art
Phase angle power regulation has the well known disadvantage of generating harmonics on the mains due to the fact that the switch closes while a relatively high voltage is present thereacross. These harmonics cause electromagnetic disturbances and are a major problem. Various standards have been developed to require manufacturers to avoid generating such disturbances. A simple way of avoiding the reinjection of harmonics onto the mains is to filter them. However, the addition of a passive filter to a variator is a serious handicap in terms of size, weight and cost. To avoid this filter, it has also been devised to tackle the problem from the base by controlling the current variation speed (di/dt) upon switchings. Unfortunately, neither a thyristor, nor a triac which are ideal components to manufacture a variator due to their robustness, their breakdown voltage, their easy switching and their small on-state dissipated power enable this di/dt control.
It has thus been provided, in the art, to use systems of the type schematically shown in FIG. 1, which include power components 1 and 2 in parallel. Component 1 is a component such that the variation of the main current upon turning-on is linked to the variation of the control voltage, for example, a power MOS transistor or an isolated-gate bipolar transistor (IGBT). Component 2 is a component of thyristor or triac type which has the advantage, once on, of exhibiting a very small on-state current drop and which further has the advantage of automatically turning off when the current flowing therethrough becomes substantially zero. Thus, it has been attempted to make switches such that their closing is caused by a component of the type of component 1 while most of the on phase and the turning-off are ensured by a component of the type of component 2. A control circuit 3 is accordingly provided to turn on the second component, of thyristor type, once the first component, of MOS or IGBT type, has been turned on.
Given that a MOS- or IGBT-type power transistor is a component having a multicell structure, it has generally been tried to associate, with each of the cells of the MOS component, a structure having the thyristor function. The general structure thus is of multicell type.