Wayne's 40M H-Bridge

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w9jsw:
This Class E forum needs some new activity!

Now that I have a working board layout for Rod's PWM, I am going to give this circuit a go.

I have a few questions -

1. I am going to drive it with a 2-phase board that has a pair of IXDD614 drivers. So don't need the input inductors to create a phase difference. Is it still wise to keep them in the design?
2. Can this design be tweaked to be able to go 160/80/40? Or should I plan to go like the super senior and have separate 160/80 and 80/40 implementations?
3. Will try those 150V MosFETS. Target voltage is 96V with a carrier of around 48V. This is based on an already existing supply I have on hand. Will I be able to achieve 200W or better? Will I blow the FETs? I am also going to try some 16N50s that I have on hand.
4. When tying this together will I have to sequence the PWM with the driver board? i.e bring up the pwm, then bring up the driver and do the reverse when going back to rx, or can the drive and pwm be brought up together. Reason is I have a 2 stage sequencer/TR board (already in hand) for the antenna and the boards. Having to sequence the driver with the pwm will require a new 3 step sequencer.

My schematic is what I have come up with so far. I previously used those SiC devices and got 375W of carrier with 96Vcarrier at 89% efficient. Impedance was 20.6R which is too high for the PWM, I fear. Also, it would not do 40M.

John

w9jsw:
Got an answer on the sequencing. A 2 stage sequencer process will work.

RX -> PTT -> ANT relay/Drive enable -> wait -> MOD enable = TX

TX -> drop PTT -> drop Mod -> wait for RF to drain off -> drop drive and ANT Relay (will take a few ms to settle) = RX

vk3alk:
Hi John...

Will try to answer your questions.
I am not an engineer and the only qualifications I have is an Amateur Radio licence like you...  :)

1.   Your change in design using IXDDs will not work...
      If you look at the design using transformers you notice 2 things .... there is a transformer across the gate source of each
      FET...and how they are arranged enables the middle of the bridge to float in respect to ground....
      You could use IXDDs but would need 4 of them and the circuit would be far more complicated and is just not worth it...
      Transformer drive is simple ...low cost and there are no adjustments etc: although the drive requires a duty cycle of 50:50..

2.   The circuit will work 160/80/40 as a multibander but only with the FETs in the design...
      Can I leave this for the moment as will promise to post later with this build...

3.    Only use the FETs as detailed...there is another one but would stick to the IPPs.
       Ok on your Power Supply of appox 96 volts....
       Best to use the standard Mark to Space ratio of 60:40 so using appox 100 volts on the Modulator the carrier voltage would
       be 40 volts...
       You need headroom for your positive peaks  :)

4.     No sequencing is needed....just one relay enabling the pulse trains in the PWM and TX and others like Antenna relay muting
        etc:

40M is a little more involved so maybe starting on 160/80M would be a better way to go....
I myself would build up one of those PWMs and test them hard before giving them to anyone as all problems would maybe come back to you... ::)
Build one TX module for say 80M and makeup a little transmitter....with only 40 volts though expect no more than 150 watts at most....
Post your progress on the Forum....


Wayne

w9jsw:
Thanks Wayne,

I am anxious to know more about your multibander.

I have a few ideas on how to tweak my current prototype output transformer as well. After being immersed in transformer math, I have come up with a 7T:19T on a T225-2B as my next try. Hope to get the current up higher at a lower voltage to get the output impedance below 10 ohms. We shall see.

John

w9jsw:
I see that Nigel ran his PWM to drive the PA at 13 ohms of source impedance. That is not far off of what I have now. I was going to run this at 93V carrier and 180V unmodulated. With what I have learned, 75V and 180V are better goals.

I am going to target 13 ohms as that is what Nigel's schematic shows with inductor values already determined for the PWM filter.

Now I am getting 90% efficiency with 93V to get 375W out. I am using a 10T:13T on a T225-2 core shunted by 1200pf.

Going to try 2 different cores next. For one I will use a T225-2B core with a 7T:14T which with an impedance ratio of 3.84 should give me the proper source impedance of 13 ohms. The other try will be the current single core T225-2 using the same 10T on the primary and 19T on the secondary. Hopefully the need for shunt capacitance will go away when I get the proper impedance ratio on the OT.

We shall see.

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