| 摘要 |
The supply circuit with semiconductor bridge (Tr1, Tr2) for producing an AC voltage from a DC voltage source comprises means for protecting the switching elements from heating up due to the current of self-inductive origin during switching, which consist of capacitors (C1, C2) connected in parallel with the switching elements (Tr1, Tr2) and means introducing a delay of the opening of the switching elements so as to allow the charging of the capacitor by the current of self-inductive origin, as well as its discharging, these means consisting, for example, of a saturable choke (B) mounted in the diagonal of a control circuit consisting of a transistor bridge (Tr3, Tr4, Tr5, Tr6). An additional choke (L) is furthermore mounted in series or in parallel with the load on each phase. The delay can be introduced by means for servocontrolling the unblocking of the transistors to the voltage across the terminals of each of the capacitors. These servocontrol means consist of a comparator or of a device for measuring the current in the diodes (D1, D2). This circuit makes it possible to prevent any dissipation across the transistors when turning on and to suppress any thermal dissipation in the resistors. It is used in frequency converters e.g. for the supply of induction motors. <IMAGE>
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