Circuit for the control of a triac without galvanic isolation

1. A circuit for controlling a bidirectional switch referenced to a first ground connection by a control circuit supplied by a first voltage and referenced to a second ground connection, wherein the supply voltage of the control circuit is connected by a diode to a coupling circuit comprising a node, this node being connected:

via a first impedance, to the collector of an NPN transistor having its emitter connected to the second ground connection and having its base receiving the output of the control circuit,

to a first terminal of a capacitor having its second terminal connected to the first ground connection, and

to the emitter of a PNP transistor having its base connected to the collector of the NPN transistor via a second impedance, and having its collector connected to the control terminal of the bidirectional switch,

wherein the first ground connection is independent from the second ground connection.

2. The circuit of claim 1 , wherein the collector of the PNP transistor is connected to the control terminal of the bidirectional switch via a control current limiting resistor.

3. A circuit for controlling an electromagnetic relay of control of a load with an A.C. voltage, comprising a transformer which supplies, on the one hand, a control coil in series with a current-controlled bidirectional switch and, on the other hand, via a rectifier, a circuit for controlling said switch, using a control circuit according to claim 1 .