Patent ID: 8286406

Claim:
An induction sealing device for use to produce pourable food product packages from a tube of heat-seal sheet packaging material, said induction sealing device comprising: a signal source configured to generate an alternating power signal; an inductor connected to said signal source to receive said alternating power signal, and operable to induce an electric current in said sheet packaging material to heat seal the sheet packaging material; and an impedance matching circuit connected between said signal source and said inductor; said impedance matching circuit comprising: a pair of input terminals configured to receive, in use, said alternating power signal; a first line and a second line connected respectively to said input terminals of said impedance matching circuit; a variable-capacitance stage comprising at least one capacitive module connected between said first and second line and comprising a capacitive element and a controlled switch series-connected to each other; said controlled switch being selectively operable to connect said capacitive element between said first and second line; and a control stage configured to control an operating status of said controlled switch; wherein said controlled switch comprises: a pair of input terminals configured to receive, in use, a control signal from said control stage; one of said input terminals being connected to said second line; and a single two-way controlled switching element having a first current-conducting terminal connected to said first line via said capacitive element; a second current-conducting terminal connected to said second line; and a control terminal connected to said input terminals of said controlled switch to receive said control signal from said control stage.