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Messages - OgreVorbis

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The RF Workbench / Re: NCP driver sucks
« on: October 15, 2019, 1444 UTC »
I have used the NCP up to 7.290 in the past. Inverting and non-inverting. What keeps them from frying is a few ohms between the driver and the SiC gate.

I thought that was only for protection if the mosfet blows out, so it reduces the current consumption of the driver with no side effect?

The RF Workbench / Re: NCP driver sucks
« on: October 15, 2019, 1112 UTC »
On one side only..

Ok, does it work??


Well, the non-inverted side already works fine (with less than 12V). After reading the truth table again, I don't see why this wouldn't work. Unfortunately, the only way to find out is to send for the PCBs again. I'm just going to go for it. It's only $35 for 6 of them and it's not something I can hack onto my current board because those pins are grounded, so I can't just connect a wire there; I have to get new PCBs. And I shouldn't need pullups or pulldowns because that pin should always be high.

The RF Workbench / Re: NCP driver sucks
« on: October 15, 2019, 0016 UTC »
Drive the '-' I/P on both sides but pull up the '+' I/P on one side and down on the other side.

Sounds more complicated than necessary. Do I need to do it that way?
Alright the modification has been made. I just connected the non-inverted input to 5V and drive the inverted input only.

The RF Workbench / Re: NCP driver sucks
« on: October 14, 2019, 1548 UTC »
Maybe you have to tie the positive input pins high to get the inverter function to work?


Now that I look at it again, yeah, I think you're right.

The RF Workbench / Re: NCP driver sucks
« on: October 14, 2019, 1456 UTC »
The design I use uses the AD9850 PCB's on Ebay and they O/P opposite phases already so I've no need to invert.

I'll have a look at your 'problem'....


OK, tie the O/P's together, ground the I/P you don't want to use, drive the other.

That should give opposing O/P's.


Right, that's what I did and none of the inverted ones are working. They are always low. I checked with a scope right on the output of them.

If I fix this, maybe it will work  :o Even with only one side of the amp firing, I am getting almost exactly 50% efficiency, so I think if I can make the other side work it should be pretty good.
I found that 10V may actually be enough for the drivers. It doesn't seem to lower the output/efficiency until I go to 9V or less.

I don't know if you checked the image of the board, but here it is. You can see the subtle change on the drivers for each side.

Thanks for the help stretchy.

The RF Workbench / Re: NCP driver sucks
« on: October 14, 2019, 1147 UTC »
Thanks for the replies!

The NCP's are fine to beyond 14MHz driving GaN.

The issues arrive from driving Qg and the SiC's I use, C3M0280090D have a Qg of 9.5nC. (GaNs have Qg of 6nC)

Power required to drive FET is QgxfxV, so 9.5e-9x7e6x12 = 800mW so they get a bit warm but are fine.

Apart from one op blowing the sh*t out of the whole Tx by powering it with A.C. I've never had one blow.

Are you using the same SiC FETs?


Yes, that's the one I'm using.

There must be some small difference about my PCB that's making it not work, but it's just too marginal. 800mW in that SOIC-8 seems like a lot. In my situation they are also hand soldered, so the dissipation through the pins is probably not as good as if I had used solder paste.

If I was going to continue this, it wouldn't be hard to make a GaN version of the board because it would just require swapping the drain and source pins. Then the NCPs would run easily with a lot of headroom.

So then the only problem I would have is getting the inverted inputs on them to work.

Stretchy: Have you used the inverting inputs on these? How do you wire it up? I tried connecting the inverted input to the crystal and grounding the non-inverted input, but the output stays low. I have the two OUTH and OUTL tied together, but I think it's wrong. How should it be connected for inverting? Like I said the datasheet is no help and the truth table doesn't make sense. There is no diagram of how to use the inverted input and clearly it's not just a matter of connecting the input to it.

For the record, all these parts are spec'd to 2 MHz...that is all.  In the early days of using power conversion parts, I quickly found that the DIP package parts smoke driving anything over 1 MHz.  I switched to tabbed devices and all my problems went away...sortof.  It did take a bit of fiddling with different parts until I settled on the '614's.  in most applications, you can use the TO-263 version up to about 9 MHz or so, depending on what you are trying to drive.  My fets are about 1000pf each and the 614's will happily drive them to about that, maybe more with decreased performance and more heat.  I'm not sure if there is much of a performance difference between the 4452's and the '614's but the heatsink tab on the latter is tied internally to VSS, which makes layout and thermal management easier.

Fall is here, and 4 MHz historically has worked much better for me than 6 MHz when the leaves start to fall  8)


Eventually some day when I have more time, it's clear to me that the 614s combined with GaN are probably the best, most durable and fool proof way. I love how the tabs are grounded on the 614s and the transphorm GaN. All fets should be that way.

The RF Workbench / NCP driver sucks
« on: October 13, 2019, 1749 UTC »
I'm on my 4th revision of my PCB and the first one was the best. On the first one, I used TC4452 because I didn't know about the IXDD614 at that point. After that I found out about the NCP and thought it would be better than the 614 and so I built my last three PCBs based on it. It was a big mistake and I wasted so much time on it and now if I want to use the 614s, I have to basically start over at square one. So I am giving up for at least a year. It pisses me off because I'm not the type to be able to put something like this down, but it's not worth it to get angry over something like this.

BTW: The waves going in and out of them are square as can be (as square as the crystal source which is connected with very short straight traces).

So what's wrong with them?
1. They get dangerously hot at 12V and above - they may do 15V with a heatsink on top, but they were emitting a smell like they were about to pop (and I did pop several).
2. The datasheet (especially the truth table) is either just really confusing or the design is just wrong. Based on the truth table, there is no way to use the inverting input as the output will always be low. I found this to be the case in practice also.

So yeah, I think it will work with GaN cause they only need about 8V, but if you got it working with SiC at higher voltages, then you must have magical powers.

So for now, I'm just going to use my original design board that works good below 5 MHz. I guess I won't be on the 'fun' band any time soon lol  :)


Here's the datasheet: https://www.onsemi.com/pub/Collateral/NCP81074-D.PDF

Truth table page 5.

The RF Workbench / Re: IXYS-RF better than GaN?
« on: October 07, 2019, 2356 UTC »
That was my suspicion, thanks!

Right now I use C3M0280090D which has 280 mOhm and 150pf

I am looking at GaN:
41mOhm and 1500pf

60mOhm and 1000pf

So they have lower RDS on, but much higher capacitance. So what is more important RDS on or capacitance? Would they be better?

Thanks :)

The RF Workbench / IXYS-RF better than GaN?
« on: October 07, 2019, 2256 UTC »
I just came across these mosfets that are designed specifically for class D or E amplifiers. I knew about SiC and GaN being good options, but I didn't know they made fets for this specific purpose. Do you think they would be better than GaN? The RDS on doesn't look as good as the Gan, but what do you think? Maybe it's just older technology being advertised for this purpose?



They're kind of expensive, but I might try them at some point.

The RF Workbench / Re: Stretchyman 40w GaN TX is sick
« on: October 07, 2019, 1041 UTC »
I have a cheap-o PS I got from amazon. Its really stable and has its own variable fan. Says it can do up to 15A.

I don't understand why so many people buy those unbranded Chinese power supplies. I've seen many of those malfunction.
I could understand if the price was significantly cheaper, but IT IS NOT.

You can get a good quality meanwell of that power level for $30
$19 vs $30 bucks isn't a big deal.


Once you get into the higher wattages, then it makes sense. For those higher powers, eltek flatpacks, and Chinese Velikas are good.

Sorry to get off topic. I'm done.

General Radio Discussion / Are there no radio laws in Greece?
« on: October 06, 2019, 2041 UTC »
There are so many pirate rig builders in Greece. Specifically AM, but I see a lot of HF and FM stuff also.
Does anyone know the details of this?

The RF Workbench / Re: Making a cheap eBay RF Power Amp Sorta Work
« on: October 06, 2019, 2037 UTC »
That too :)

I am really curious about Greece though. Do they not have any radio laws there? There are so many pirates.

The RF Workbench / Re: Class D output match
« on: October 06, 2019, 1841 UTC »
That's interesting. I didn't think you could do CQUAM on a PWM type system. If you don't mind, maybe you could explain it?
There is the Polar Explorer which is able to do class E with SSB.

On the original topic:
I replaced the balun with a coaxial wound one. I found a 1% decrease in efficiency (more or less the same).
I will not give up. I have now sent for revision 4 of my PCB. If this one doesn't work, then I have no clue. The waves were a little rounded on the current one, but this new one has only straight buses and the crystal is hooked up directly.

The RF Workbench / Re: Making a cheap eBay RF Power Amp Sorta Work
« on: October 06, 2019, 1831 UTC »
I'd recommend to always go with Greek gear for MW and HF. There's something about Greece that they seem to be obesesed with these frequencies. There is so much stuff available that's better than the Chinese. They even make custom Class D and E.

Here is a good amp from a vendor I've used for a while:

It might need a pre-amp because I don't know what you're driving with.

Even if you don't need it, I think others might find this guys wares interesting :)

The RF Workbench / Re: Stretchyman 40w GaN TX is sick
« on: October 06, 2019, 0927 UTC »
I'll bet the problem is that one of the NCPs is fried.

My newer transmitter uses those NCPs and I fried a lot of them during the testing process. Yes, it is best to apply the low level voltage first and then the HT after.

But Stretchy knows what he's doing and probably has good symmetry and square waves.

I fried so many of those NCPs when I was designing mine. Just a tiny bit off in symmetry or a slightly rounded wave will make those things bake themselves really fast.

I doubt there is a problem with Stretchy's transmitter as he's been doing this a long time. I just don't like those NCPs very much, they're not any better than the 614s and they can't dissipate heat, so if there is a small problem, you're screwed. Maybe it's better in the long run though because it won't allow you to be sloppy. Even in optimum conditions, you can't apply more than 15V to them.

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