Prior work has shown that the commutation loop inductance is critical to switching performance. But for many applications, power transistors with large through-hole packages are used, due to their low junction-to-case thermal impedance and compatibility with heatsinks. The commutation loop will have larger inductance with these devices due to their long leads. The resultant overshoot and ringing is detrimental. In this work, a small surface-mount device is added in parallel to the large through-hole power transistor to improve switching performance. A 250 W, 50 V buck converter is designed, with measured results demonstrating significant improvements in efficiency.
