Decoupling Device for Small Commutation Loop and Improved Switching Performance with Large Power Transistors

Prior work has shown that a power converter's commutation loop inductance is critical to switching performance. For designs with surface-mount components, this inductance may be minimized through the use of clever layout techniques. 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, both of which allow for high power handling capability. In this work, a small surface mount GaN transistor is added in parallel to the large through-hole Silicon power transistor to improve switching performance. Together with a low-side anti-parallel diode and decoupling capacitor, it forms a smaller commutation loop such that the switching transition can be fast with low overlap loss. A simple method is introduced to control both the power and decoupling devices with a single gate driver. A 250 W, 50 V buck converter is designed, with measured results demonstrating significant improvements in efficiency.