MBRB3030CTLG, NRVBB3030CTLG

http://onsemi.com

5

Modeling Reverse Energy Characteristics

of Power Rectifiers

ABSTRACT

Power semiconductor rectifiers are used in a variety of

applications where the reverse energy requirements often

vary dramatically based on the operating conditions of the

application circuit. A characterization method was devised

using the Unclamped Inductive Surge (UIS) test technique.

By testing at only a few different operating conditions

(i.e. different inductor sizes) a safe operating range can be

established for a device. A relationship between peak

avalanche current and inductor discharge time was

established. Using this relationship and circuit parameters,

the part applicability can be determined. This technique

offers a power supply designer the total operating conditions

for a device as opposed to the present single−data−point

approach.

INTRODUCTION

In today’s modern power supplies, converters and other

switching circuitry, large voltage spikes due to parasitic

inductance can propagate throughout the circuit, resulting in

catastrophic device failures. Concurrent with this, in an

effort to provide low−loss power rectifiers, i.e., devices with

lower forward voltage drops, Schottky technology is being

applied to devices used in this switching power circuitry.

This technology lends itself to lower reverse breakdown

voltages. This combination of high voltage spikes and low

reverse breakdown voltage devices can lead to reverse

energy destruction of power rectifiers in their applications.

This phenomena, however, is not limited to just Schottky

technology.

In order to meet the challenges of these situations, power

semiconductor manufacturers attempt to characterize their

devices with respect to reverse energy robustness. The

typical reverse energy specification, if provided at all, is

usually given as energy−to−failure (mJ) with a particular

inductor specified for the UIS test circuit. Sometimes the

peak reverse test current is also specified. Practically all

reverse energy characterizations are performed using the

UIS test circuit shown in Figure 10. Typical UIS voltage and

current waveforms are shown in Figure 11.

In order to provide the designer with a more extensive

characterization than the above mentioned one−point

approach, a more comprehensive method for characterizing

these devices was developed. A designer can use the given

information to determine the appropriateness and safe

operating area (SOA) of the selected device.

Figure 10. Simplified UIS Test Circuit

HIGH SPEED SWITCH

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