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.