A BJT Self-Oscillating Buck-Boost Converter for Battery-Power LED Flashlights

This paper presents a BJT self-oscillating buck-boost converter for a battery-power LED flashlight. As BJT switch is saturated by positive feedback with capacitor charging current, electric energy is stored in inductor from voltage source. While collector current rises to a value that base current cannot afford the saturation condition, the BJT switch is cutoff by the reversed inductor voltage and capacitor discharging current. While BJT switch is cut off, the stored energy in inductor is released to a LED lamp. At the end of inductor current, parasitic capacitance charges the inductor, and hence the next self-oscillating cycle is initiated. The inductor current is inherently discontinuous. Due to low components count and without integrated circuits, the BJT self-oscillating buck-boost circuits reduce the cost and compact the LED driver.