The invention generally relates to switch mode power
converters (SMPCs). and methods for providing supplementary base drive to a bipolar
transistor of an SMPC, and more particularly to a switching
control circuit for a SMPC, a said SMPC having an inductive component coupled to receive power from an input to the SMPC, a bipolar
transistor coupled to control current flow in the inductive component, an auxiliary power rail, a charge store for supplying power via the auxiliary rail to a switching
control circuit for driving the bipolar
transistor, and a bootstrap circuit for bleeding current from the input to the bipolar transistor to thereby provide an amplified current to the charge store, the switching
control circuit comprising: a base current line for
coupling to a base terminal of a said bipolar transistor, an emitter current line for
coupling to an emitter terminal of a said bipolar transistor, an auxiliary line for
coupling to a said auxiliary power rail, and at least one
reference line for coupling to a reference
voltage; a base
current switch configured to controllably couple a base
current source to the base current line; an emitter
current switch configured to controllably couple the emitter current line to a said
reference line; a bootstrap element for bleeding current from the emitter current line to the auxiliary line, the bootstrap element further operable to block a said current according to a current or
voltage bias; a base
discharge switch configured to controllably bleed current from the base current line to a said
reference line; and a supplementary base drive line for coupling to a series circuit comprising a supplementary base drive
resistor and current control element coupled in series, a said series circuit for bleeding current from a said input to a said base terminal, a said current control element for blocking current flow from a said bootstrap circuit to a said supplementary base drive
resistor.