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Author Topic: C2M0280120D SiC FETs at different freqs  (Read 3363 times)
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VE3ELQ
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« on: April 16, 2015, 01:57:24 PM »

Today I conducted some basic frequency range tests on my 6 FET C2M0280120D RF amp deck. It is configured with 1 IXDD614 TO-220 driver for 3 parallel FETs per side running at 15 Volts regulated but works just as well at 12 volts. The signal source was a UDB 1308S 8mhz dual channel DDS function generator from China set for 40% duty cycle. Following is the drive current results:
Freq(Mhz)       Current(MA@15V)
2                150
3                220
4                290
5                330
6                380
7                440
7.5              460
8                500
The deck was run at 50 volts 200 watts with the OP direct to a 50 Ohm resistive dummy load from the secondaries in series, no tuning or filter. The OP transformers have been optimized for 80 meters with 8 turns bifilar on 2 T200-2 cores. At 4 mhz the OP waveform is like a peaky sign wave, at 2 Mhz it is very peaky with big gaps between the plus and minus peaks and at about 5 mHz starts to merge to near sign wave with a drop in OP power which decreases with frequency and at 8 mhz power was down to 125 watts. It shows all the signs of needing more primary inductance for 2 mhz and much less at 8 mhz. Since I did not have any spare cores no attempt was made to optimize the OP transformers for each band of interest. Also the drain snubber capacitors were not optimized for each frequency.
The deck ran cool at all freqs. The FEts were switching well as they should at 8 mhz which is as high as my signal source will go. I think a drive current of 1/2 amp for 6 FETs at 8 mhz is pretty amazing. I have no doubt these FETs will make a great 40 meter RF deck with the right OP transformer inductance and drain capacitors. Its definitely on my bucket list.

73s  Nigel
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« Reply #1 on: April 16, 2015, 03:17:38 PM »



Nigel,

   I like where this is going. Thanks for taking the time to do those experiments.

Looks like the SIC stuff is coming out of the woodwork's. I am not sure if the Monolith parts are available, but they are developing a line of their own:

900vds,  0.05 ohm rds on
http://www.monolithsemi.com/GLBC/GLBC-Datasheets.html

Jim
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ka1tdq
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« Reply #2 on: April 16, 2015, 05:44:21 PM »

Will the UDB 1308S do square waves in opposite phases?  If so, gotta have one!

Jon
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VE3ELQ
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« Reply #3 on: April 16, 2015, 06:12:05 PM »

Will the UDB 1308S do square waves in opposite phases?  If so, gotta have one!

Jon
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Yes it will do co-phase with adjustable duty cycle from .01hz to 8mhz. It does all the audio waveforms also, great for testing. Check the spec write up.
Many online places sell it, prices vary about $55 US.  Here is but one:
http://cleanenergy-npt.en.alibaba.com/product/1304663168-218407933/UDB1308S_8MHz_dual_channel_audio_signal_generator.html
Check on shipping times, mine took 6 weeks but you can get it quicker or overnight if you pay extra.
73s  Nigel

Edit:
Here is a better listing.
http://www.ebay.com/itm/UDB1308S-Dual-DDS-Source-TTL-Signal-Generator-60MHz-Sweep-Frequency-Counter/111379851180?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D29980%26meid%3Dd74b6ff7fae54dcb860abd0dbcb09381%26pid%3D100005%26rk%3D4%26rkt%3D6%26sd%3D111198045477&rt=nc
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« Reply #4 on: April 19, 2015, 01:29:12 PM »

Interesting testing !!!!

I've been looking at 40 meters also.

The 280120D (the device used in this experiment) has a gate internal resistance of 11.4 ohms, and the capacitive reactance of the 259pF of input capacitance at 7.3 mHz is 84 ohms.  So, the internal gate resistance at the fundamental frequency is approximately 1/7th of the total input impedance.

There will be more loss at the leading and falling edges because they contain more high frequency components.  It may be necessary to provide a slightly higher driving voltage to overcome the gate resistance and turn the device on hard.  I use 15V for my 75 meter transmitter - looking at the curves for the device, the R D-S on drops as the gate voltage increases.  It may be that 18V might be a good choice on 40 meters.

All of the devices in the family have a internal gate resistances which are in approximately the same proportions (internal gate resistance V/S input capacitive reactance).

These devices show much promise for 40 meters.  If they came out with a metalized gate version (similar to what IXYS does with standard MOSFETs today), the maximum frequency of operation could be quite a bit higher than it is currently.

Good stuff!
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VE3ELQ
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« Reply #5 on: April 23, 2015, 07:59:12 AM »



All of the devices in the family have a internal gate resistances which are in approximately the same proportions (internal gate resistance V/S input capacitive reactance).

These devices show much promise for 40 meters.  If they came out with a metalized gate version (similar to what IXYS does with standard MOSFETs today), the maximum frequency of operation could be quite a bit higher than it is currentl


Steve thanks for the analysis. I agree completely.  I should have saved a frame grab of the gate waveforms at 8 mhz but as I remember they were pretty good looking with fast leading and trailing edges at 15 volts. And this was 1 driver for 3 FETs.  I have some C2M0160120D 1200V 19A 160mohm FETs on order and plan to build a 4 FET deck.  Will start with 40 meters and see how that works out with everything optimized.
73s  Nigel
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