I have some IRF630 Fets and am wondering if they would be suitable for replacement for the 510?

I think they are a higher Voltage and Current device TO220 package.

So If I was to use said device? would the specs be close enough or are they not sutable.

Cheers Mark

I ran across an IRF-614 in an old TV the other day, was wondering the same thing :)

--
Ryan Flowers W7RLF

?

?<-- Learn how to go digital on the BITX40

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Probably compare Gate to Source input Capacitance.? The lower the better.

Mike, WA6ISP

I have some IRF630 Fets and am wondering if they would be suitable for replacement for the 510?

I think they are a higher Voltage and Current device TO220 package.

So If I was to use said device? would the specs be close enough or are they not sutable.

Cheers Mark

-- 
Mike Hagen, WA6ISP
10917 Bryant Street
Yucaipa, Ca. 92399
(909) 918-0058
PayPal ID  "MotDog@..."
Mike@...

The gate capacitance is different, so you would need to adjust the input coupling to them to start with.

There also may not be enough drive power, so an extra drive stage might be needed.

Terry VK5TM

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?one of the two proposed has 800 pf of gate capacitance (like 5 times that of the irf510) -- which at 20 meters would have a capacitive reactance of 14 ohms.....so a feed with an impedance of 100 ohms won't do so well.....? ?

if you tuned that with a parallel inductor of course this would change a lot......

but that is more complicated.

Gate to drain capacitance is the more significant.
As the gate voltage rises by perhaps 1 volt, the drain voltage might fall by 10v or more
due to the gain of the FET. ?This effectively multiplies the effect of the gate-to-drain
capacitance by a factor of 10. ?This effect is called the miller capacitance.

Switching FETs have a spec called Total Gate Charge, in nano-Coulombs.
That is perhaps the best spec to determine the amount of drive that will be required

A direct replacement for the IRF510 is the IF610. Except for drain voltage tolerance,
they are very similar.

Other types can be used, but pay close attention to the specs. If they are too far off,
especially gate capacitance, don't use them, or modify the circuit accordingly.

The IRF630 is not a good substitute for the IRF510. The IRF614 is an odd MOSFET, and may work.
Check the data sheet.

john
AD5YE

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Thank you for explaining the miller effect.? I keep learning here!

This article discuses high power high efficiency MOSFET amplifier design at just about 20 meters:

?

Interestingly, the GATE INDUCTANCE is an issue for this designer and they literally designed a circuit to resonate with that.? ?The voltage that Ryan Flowers measured at the gate terminal.....isn't actually what drives the device....it is what makes it to the gate capacitance after traversing the gate inductance....

So here we have yet another low pass filter problem that can lower the gain of a simple amplifier at higher frequencies.? ?The BITX40 does not have a tuned gate drive circuit, just a tranformer (?auto transformer?) from Q14....? ?So the actual drive voltage to the die may well decline with frequency......

I went and looked at my bitx40 and the source is soldered right to the ground plane on the bottom of the board, and the top has a trace that goes out a ways and then thru a via to the bottom as well, both attempts to reduce the source lead inductance I believe.? ?So that part looked optimized to me.? ?

the combination of the device's inherent gate low pass filter and the source inherent inductance in the bond wires both tend to reduce the "apparent" gain at higher frequencies...

gordon

800 pf of gate capacitance (like 5 times that of the irf510) -- which at 20 meters would have a capacitive reactance of 14 ohms....

if you tuned that with a parallel inductor of course this would change a lot......

---

From: [email protected] <[email protected]> on behalf of augustinetez <vk5tm@...>
Sent: Wednesday, November 15, 2017 8:31 PM
To: [email protected]
Subject: Re: [BITX20] IRF630 Fets #parts

?

The gate capacitance is different, so you would need to adjust the input coupling to them to start with.

There also may not be enough drive power, so an extra drive stage might be needed.

Terry VK5TM

--
{ mailed mobile }

The IRF510 has a typical drain voltage rating of 70v. That is why the DC voltage maximum
is typically 48v. This allows a signal excursion of about 96v with only an occasional peak
of 96v. There is some distortion but it is hardly noticeable.

The typical drain voltage of the IRF610 is about 100v. Hence one can use a little higher
DC and signal voltage. Probably about 20% or so. That means about 30-40% more power
output. Even at 48v, the power output would be a it cleaner.

john
AD5YE

That total gate charge has to be BOTH charged and discharged with your CW to maintain low phase and harmonic distortion. Thus your max. frequency? then gives you an idea of the amount of gate drive needed to achieve this.
--
AncelB, MIT EE6002

Vds max for the IRF610 is 200v, vs 100v for the IRF510.
So yes, the IRF610 can survive a higher voltage power supply

However Rds-on (resistance from drain to source with transistor fully turned on)
goes up from 0.54 ohms on the IRF510 to 1.5 ohms on the IRF610.
So the IRF610 may not be a complete win. ?
The devices have exactly the same thermal characteristics, so at DC the IRF510
could handle 3x the current that the IRF610 can. ?Power dissipation is all in Rds-on for DC.
At RF we spend significant time in the transition region, so not obvious just how much Rds-on
will affect performance.?

Mouser prices the IRF610 about 25% cheaper than the IRF510, so cost is not an issue.
Well worth trying.

The output transformer at T7 in the Bitx40v3 is currently a 1 to 4 impedance transformer,
the windings may need to be adjusted to give the FET a higher impedance load when?
running with higher supply voltages. ?Caps for the low pass filter should be rated
for several hundred volts as power levels increase.

Jerry, KE7ER

Wow thanks for all the replies, this group rocks.

And ahh I never considered to imput capacitance, yeah a lot higher than the 510, looks like more work than needed.

And there was me thinking higher Voiltage higher power output LOL

see thats why I asked as I didnt know what I was looking for in these FET thingy ma jigs lol

Dont think I will bother with them IRF510 stays put.
Cheers Mark

Clark Martin
KK6ISP

On Nov 16, 2017, at 11:23 AM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:

Vds max for the IRF610 is 200v, vs 100v for the IRF510.
So yes, the IRF610 can survive a higher voltage power supply

However Rds-on (resistance from drain to source with transistor fully turned on)
goes up from 0.54 ohms on the IRF510 to 1.5 ohms on the IRF610.
So the IRF610 may not be a complete win.
The devices have exactly the same thermal characteristics, so at DC the IRF510
could handle 3x the current that the IRF610 can. Power dissipation is all in Rds-on for DC.
At RF we spend significant time in the transition region, so not obvious just how much Rds-on
will affect performance.

But the transistor is not being fully turned on so Rds doesn’t matter. It’s operating in the linear region where there is always going to be power dissipation.

Power dissipation is a matter Ic * Vce and is a function of output power.

Yup, you're right.
Jerry

Yeah, Clark:

That's what I was going to say, but you beat me to it.

Rds(on) applies mostly to very low frequencies (15 KHz)
in switching power supplies. We are working in the small linear
region which is never "full-on" operation. Rds(on) is incidental
for RF applications. In fact, it applies in the "avalanche" condition.

However, Jerry is right in a way. The IRF610 would allow only 1/3 the instantaneous
current amount as the IRF510...but it still is enough to destroy the part if it
lasts longer than a few microseconds. Hi.

Which means that current limiting is a very good idea. The IRF610 is a
touchy beast also. Probably the gate voltage should not be more than
about 3v. with these as the PA, the same as the IRF510.

I have has some for a few years but have not gotten around to using them
yet. It seems to me they would be a very good match to the WA2EBY amp,
but the output transformer would probably have to be changed a bit.

john
AD5YE

I'll agree that Rds-on is mostly lost in the noise here.
But for the sake of starting a good argument,
concede that it represents the inherent resistance of the FET's silicon.?

If we have 25 watts of clean fundamental RF going into a 12.5 ohm load from the FET's drain
the RF current is 1.414 rms, and power lost due to 1.5 ohms of Rds-on is 3 Watts.

The FET is typically under 50% efficient in generating those 25 Watts,
I'm not really sure how that plays out with respect to Rds-on,
but suspect it adds another ~12% hit there as well.

These IRF parts have limited thermal transfer from die to tab.
I suspect if the gate voltage is high enough to put it into this avalanche condition,
it will already be smoking due to the heat anyway. ? So just keep that drain current in check.

Jerry, KE7ER