An n-type transistor and a p-type transistor are connected in series such that, when the two transistors are turned on, current flows from the collector of the n-type transistor to the collector of the p-type transistor. A positive-feedback capacitor is connected between the collector of one transistor and the base of the other transistor. The two transistors turn on together when the base voltage of the n-type transistor exceeds the base voltage of the p-type transistor by at least the sum of the turn-on threshold voltages of the two transistors and (i) the two transistors turn off together when the base voltage of the n-type transistor fails to exceed the base voltage of the p-type transistor by at least that sum. The positive-feedback capacitor ensures that the two transistors turn fully on and off together. In certain embodiments, the circuitry can be controlled to operate as a current pulse generator.