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Class E (and D) with LDMOSFETs

PostPosted: Mon Mar 24, 2014 4:26 pm
by RFRUS1
What an interesting forum to have run across. I have a fundamental question that seems to be very hard to answer. Can LDMOS devices be realistically used for class E (or D) at serious power levels, as in several hundred watts at frequencies above 30MHz? My research has shown two fundamental problems with LDMOS in class E. (1) The low drain breakdown voltage means running an LDMOS with ~ 100 Vbrdss (drain to source breakdown) at ~ 24V to ensure the class E 3.56 X Vdd excursion is not crossed, requiring huge amounts of current to generate any reasonable power. (2) The narrow Vbrgss (gate to source breakdown) precludes driving the capacitive gates with drive circuits with significant overshoot and undershoot. Even with the "rugged" LDMOS parts I'm seeing a Vgs range of only -0.5 to +12 (MRF6V2150NR1) which would require a lot of current to avoid overshoot above +12 and undershoot well below -0.5VDC. While I am an amateur radio license holder (WB9LLO), this question has come up in my new job. I'm experienced in LDMOS design from 450MHz and up class AB, C, and Doherty, but my new job is high efficiency design below 175MHz and primarily using VDMOS devices. My question arises as several of our customers are asking about LDMOS in our legacy designs.

Regards,

John

rfrus1@gmail.com

Re: Class E (and D) with LDMOSFETs

PostPosted: Sun Apr 06, 2014 2:27 pm
by Stu
why not use something already tried and proven since this is a commercial undertaking? http://www.microsemi.com/document-portal/doc_download/124244-drf1400-13-56-mhz-class-d-half-bridge-rf-generator