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Measuring Initial V(ON) On Power SCR's

IP.com Disclosure Number: IPCOM000076122D
Original Publication Date: 1972-Jan-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 41K

Publishing Venue

IBM

Related People

Lim, HS: AUTHOR

Abstract

This is a simple technique for measuring V(ON) with equipment utilizing a 60Hz AC source and provides a way of monitoring plasma spreading velocities in conventional silicon-controlled rectifiers (SCRs), thereby offering a better understanding of their frequency limitations and transient power dissipation.

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Measuring Initial V(ON) On Power SCR's

This is a simple technique for measuring V(ON) with equipment utilizing a 60Hz AC source and provides a way of monitoring plasma spreading velocities in conventional silicon-controlled rectifiers (SCRs), thereby offering a better understanding of their frequency limitations and transient power dissipation.

By initial V(ON) is meant, the forward voltage across an SCR observed during the first few hundred microseconds after it is triggered into a conducting state at a specified current level with a specified current rise time. The manner in which this voltage decays is an indication of the spreading velocity. A fast decay indicates a fast spreading velocity and a slow decay indicates a slow one. Initial V(ON) also offers a better understanding of the frequency limitations of power SCRs and allows an accurate method to establish the power dissipation within a device, as illustrated in Fig. 1. Fig. 1 shows the current 1 and voltage V characteristics of two different devices as a function of time t. The initial V(ON) is the voltage waveform in the transient state essentially prior to the elapsing of 200 microseconds. From Fig. 1, it is apparent that the device having the voltage characteristic of V1 dissipates more power within 200 microseconds than the device having the voltage characteristics of V2 and it should, therefore, not be used at pulse widths less than 200 microseconds.

Referring to Fig. 2, a 60-cycle AC source is applied through reference transformer T2 to 60-cycle square-wave generator 10. The output of square- wave generator 10 is applied to frequency divider 12, which has an output of approximately 1 cps. This low frequency is required so that the SCR under test (SCR 2) will not heat up. The positive going edge of this 1 cps square wave triggers a variable-width monostable multivibrator, which has two outputs 3 and
4. Output 3 is used as the trigger signal for an oscilloscope us...