Slow diodes or handy timing devices?

摘要

MOST DESIGNERS consider slowness in diodes to be an imperfection or a limitation. Why not take a more positive view of the situation? After all, a zener or an avalanche diode is no more than a diode with a limited breakdown voltage, and you can view a varactor as a diode with a large and nonlinear par asitic capacitance. Similarly, could you view the slowness of a diode as a property or even a feature? For example, consider a PIN diode. Few people are aware that the key property of a PIN diode is indeed its slowness; without it, it would generate large amounts of distortion and require a larger control current to function properly. You can put this ability of slow diodes to store large amounts of electrical charge to good use in a variety of other circuits. Figure 1 shows how to generate dead time using such diodes. A PWM sandcastle (stepped) waveform feeds a half-bridge.