An adaptable, low-power drive circuit for transistor switches requiring
control input current is disclosed. In one embodiment of the invention, a
current source output replaces the prior art voltage drive circuits and
associated external current-limiting resistor. The current-source drive
circuit provides both a high impedance as well as variability. The high
impedance of the current-source drive circuit enables a reduction in the
value of the resistance-bypass capacitor employed in the prior art. The
variability in the output current provided by the current-source circuit
allows the drive circuits to optimize the control current flowing into
the switch device as the characteristics of the switch device change with
operating temperature. The drive circuit is capable of providing as
output either a desired current, at a high output impedance, or a desired
voltage, at a low output impedance, employing a shared amplifier and
output transistor. The drive circuit also derives current from the much
lower output voltage of the buck conversion system that the invention is
used in. This minimizes the static power dissipated in driving the
switch, and also minimizes the energy expenditure incurred in increasing
the output current to modulate the power switch resistance that increases
with increasing temperature.