Soft switching active snubber for semiconductor circuit operated in discontinuous conduction mode

A snubber network for a power conversion circuit operated in discontinuous conduction mode, the power conversion circuit having an input for coupling to a source of power and an output for coupling to a load to which converted power is to be delivered, the power conversion circuit further including a first semiconductor element (S1) having two main current path electrodes and a control electrode for alternate turn-on and turn-off operation thereof in response to a given gating signal at the control electrode, and a second semiconductor element (D1) connected to the first semiconductor element (S1), the second semiconductor element (D1) having an input electrode and an output electrode and operating to turn-on and turn-off in response to a bias voltage thereacross for selective conduction of current through the power conversion circuit, the first semiconductor element (S1) and the second semiconductor element (D1) being connected such that a first one of the two main current path electrodes of the first semiconductor element (S1) is connected to the input electrode of the second semiconductor element (D1), said snubber network comprising:

• a snubber capacitor (C) having a first terminal and a second terminal;
• a snubber inductor (L) having a first terminal and a second terminal, said snubber inductor (L) and said snubber capacitor (C) being serially connected such that said first terminal of said snubber capacitor (C) is connected to said second terminal of said snubber inductor (L);
• a snubber diode (D3) having an input and an output, said input of said snubber diode (D3) being connected to said first terminal of said snubber inductor (L) and said output of said snubber diode (D3) being coupled to the output electrode of the second semiconductor element (D1) of the power conversion circuit, and said second terminal of said snubber capacitor (C) being connected to a second one of the two main current path electrodes of the first semiconductor element (S1) such that said serially connected snubber capacitor (C) and snubber inductor (L) and said snubber diode (D3) are coupled across the connected first semiconductor element (S1) and second semiconductor element (D1) of the power conversion circuit;
• a controllable switch (S2) operable between on and off states and having a first current path electrode connected to the first one of the two main current path electrodes of the first semiconductor element (S1) and a second current path electrode connected to a first junction defined by said first terminal of said snubber inductor (L) connected to said input of said snubber diode (D3), said controllable switch (S2) further including a control electrode through which said controllable switch can be selectively operated between said on and off states;
• and
• an isolation diode (D2) having an input and an output, said input of said isolation diode (D2) being connected to the first one of the two main current path electrodes of the first semiconductor element (S1) and said output of said isolation diode (D2) being connected to said commonly connected second terminal of said snubber inductor (L) and said first terminal of said snubber capacitor (C), whereby said snubber network provides soft switching active snubbing for the first semiconductor element (S1), while the second semiconductor element (D1) provides soft switching for said controllable switch (S2) of said snubber network when said snubber network is connected within the power conversion circuit and the power conversion circuit is operated in discontinuous conduction mode.

A power conversion network comprising:

• a boost converter circuit having an input for coupling to a source of power and an output for coupling to a load to which converted power is to be delivered, said boost converter circuit further having a boost inductor (L.sub.ia . . . ) coupled to a boost diode (D1) and further having a boost switching device (S1) connected to an input of the boost diode (D1), an output of the boost diode (D1) being connected to the output of the boost converter circuit;
• and
• a snubber network coupled across the boost switching device (S1) and the boost diode (D1), and connected to a junction defined by the boost switching device (S1) connected to the boost diode (D1), said snubber network including:
• a snubber capacitor (C) having a first terminal and a second terminal,
• an isolation diode (D2) having an input terminal and an output terminal, said input terminal of said isolation diode (D2) being connected to the junction between the boost switching device (S1) and the boost diode (D1) and said output terminal of said isolation diode (D2) being connected to said first terminal of said snubber capacitor (C) and coupled to the output of the boost diode (D1), said second terminal of said snubber capacitor (C) being connected to the boost switching device (S1) such that upon turn-off of the boost switching device (S1) said snubber capacitor (C) provides a soft-switching characteristic to the boost switching device (S1) by absorbing energy, and
• an active reset circuit (S2, L, D3) responsive to a given reset signal for resetting of the snubber capacitor (C), said active reset circuit being connected to the junction between the boost switching device (S1) and the boost diode (D1), and to a junction defined by said output of the isolation diode (D2) connected to said first terminal of said snubber capacitor (C), and to the output of the boost diode (D1) such that upon receipt of the given reset signal energy held by the snubber capacitor (C) is recovered through the reset circuit, without potential for damage to the boost switching device (S1) of the boost converter circuit, for subsequent transfer to the output of the boost converter circuit with turn-off of the boost switching device (S1) commensurate with delivery of converted power at the output of the boost converter circuit.