ON Semiconductor AN122 Diode Turn-On Time Application Note

About this manual

The document addresses the potential failure of switching regulator ICs caused by transient voltage overshoot resulting from finite diode turn-on times. It explains that while historically ignored due to short durations, this factor becomes critical at clock speeds beyond 1MHz and requires careful qualification testing to ensure reliability.

A detailed measurement scheme is proposed to characterize diode turn-on time under realistic operating conditions. The text specifies the necessary equipment, including a sub-nanosecond rise time pulse generator, a high-current amplifier, and a 1GHz oscilloscope, along with specific circuit configurations for accurate testing.

What's inside

• Diode Turn-On Time Perspectives
• Diode Turn-On Time Induced Failures
• Detailed Measurement Scheme
• Pulse Amplifier Configuration
• Complete Diode Forward Turn-On Time Measurement Arrangement
• Diode Testing and Interpreting Results

Specifications

Frequently asked questions

Why is diode turn-on time important in switching regulators?

Finite turn-on time allows transient excursions above the nominal clamp voltage, potentially exceeding the IC's breakdown limit and causing failure.

What is the typical current used to test diode turn-on time in the conceptual method?

The test is performed at 1A.

How long does Diode Number 1 overshoot its steady state forward voltage?

It overshoots for approximately 3.6ns.

What is the peak voltage error for Diode Number 3 above its nominal forward voltage?

It peaks 1V above the nominal 400mV V FWD.