Re: irf520 vs irf510

Diver Martin <diver.martin@...>

I think I mentioned it before, but anyone seeking to drop in a Mitsubishi RDMos part should be aware that 

a) They're designed for 12V operation.  You won't want to run them at 18V/etc
b) They have a different pinout, you'll have to solder them in with the leads mangled/crossed.  IRF510/20/30's are Gate-Drain-Source.  The RDMos series are Gate-Source-Drain.  This is a mod I still intend to try at some point, but have other projects on the plate first.
c) They have a different bias voltage.  Turn down the bias voltage before you key up, and then re-bias appropriately. If your IRF510's are biased at something like 4V when the bias voltage for the RDmos's are 2V (I'm making total wild assumptions, it could be the other way around), you'll instantly turn the devices on full-current and potentially blow something up.  
d) The feedback network will want to be different.  These have much more gain at high frequencies.  You may need more negative feedback.
e) You can use an uninsulated grounded heatsink, as the tabs of the these devices is the source and not drain.

I'm looking forward to hearing from someone who's done the mod and tried it out.

On Mon, Jan 15, 2018 at 10:52 AM, Tim Gorman <tgorman2@...> wrote:

Would this be a satisfactory drop-in replacement? I can't find any info
on input or output capacitance to compare it to an irf510.

From the Smith chart on the datasheet I'm guessing the input
capacitance is about 60pf (been a long time since I've used a Smith
Chart) at 30Mhz, much less than the irf510. Would that impact the
negative feedback used on the amp significantly (0.1uf in series with a
220ohm resistor)?

By the same token the output capacitance would appear to be much higher
than the irf510. I suspect that will impact the design of the bandpass
filters but I'm not sure by how much without doing a lot of

I'm just looking for something that would provide more reliability
under adverse conditions (e.g. high swr) than the irf510. Don't really
care if it provides higher output or not - but that might come later

On Sun, 14 Jan 2018 22:51:06 -0800
"Dave Bottom" <ars.kd6az@...> wrote:

> Or the Mitsubishi RF RD16HHF1 MOSFET designed for 2-30MHz RF
> applications. Under $5 each.  Or the RD16HVF1 only pennies more and
> good through 2M.
> With a 12VDC to 24/28VDC DC to DC converters (about $4) and the Mitsu
> parts can be bolted directly to a big heatsink attached to the
> chassis, no insulator required.
> Probably good for 20W through 10M although run off batteries a bit
> shorter battery life.  At real 5W QRP they should be happy forever.
> Dave WI6R
> On Sun, Jan 14, 2018 at 4:33 PM, Tim Gorman <tgorman2@...> wrote:
> > All,
> >
> > Looking to order some spare output finals for the ubitx I have on
> > order.
> >
> > In looking around the IRF520 appears to have higher ratings than the
> > IRF510 with a lower Rds.
> >
> > The 510 does have much lower input and output capacitance.
> >
> > There is hardly any difference in price.
> >
> > Any recommendations on which to order?
> >
> > tim ab0wr
> >
> >
> >
> >

Martin Held - AE7EU
If there aren't any questions, then what is there to learn?

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