|
Hello Still thinking about IRF510 failures and ways to avoid making smoke..... It seems that there may be two ways to limit current in BITX RF PA stages that use the IRF510 device.? First would be to incorporate a current limiter in the positive voltage supply to the RF PA stage.? Second might be to use current sensing in the RF PA supply line to cause a voltage drop in the MOSFET bias line(s).? In the first instance it should be possible to use another IRF510 or preferably a higher power, MOSFET as a control that limits voltage to the RF PA section if the current exceeds a preset value (usually this would be 2.0 to 3.0 amperes).?
This circuit has not been built or tested by me (too cold in Idaho hamshack in winter). The MOSFET could be an IRF840, or similar.? Option-B? potentially solves another problem, that of low level noise from powered RF PA stage during receive mode.? 
In the second instance we could get by with smaller control devices if we used current sensing in the RF PA power line to turn off bias to the IRF510 device(s).?
This bias control circuit used by .? You could probably do this using 2N3906 transistors.? I like the fact that it includes a warning light/LED.  Arv? K7HKL _._
|
One of those little Hall-effect surface mounts would be perfect for this application…? The SGC mobile amp does this as I recall (maybe not… getting old!)! ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ ? Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois ? Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: Like us on Facebook! ? ? email:? bill@... ?
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From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Arv Evans
Sent: Saturday, January 27, 2018 4:14 PM
To: BITX20@groups.io
Subject: Re: [BITX20] IRF510 amplifier failures? Hello
Still thinking about IRF510 failures and ways to avoid making smoke.....
It seems that there may be two ways to limit current in BITX RF PA stages that use
the IRF510 device.? First would be to incorporate a current limiter in the positive
voltage supply to the RF PA stage.? Second might be to use current sensing in the
RF PA supply line to cause a voltage drop in the MOSFET bias line(s).?
In the first instance it should be possible to use another IRF510 or preferably a higher
power, MOSFET as a control that limits voltage to the RF PA section if the current exceeds
a preset value (usually this would be 2.0 to 3.0 amperes).?
This circuit has not been built or tested by me (too cold in Idaho hamshack in winter).
The MOSFET could be an IRF840, or similar.? Option-B? potentially solves another
problem, that of low level noise from powered RF PA stage during receive mode.?
In the second instance we could get by with smaller control devices if we used
current sensing in the RF PA power line to turn off bias to the IRF510 device(s).?
This bias control circuit used by .? You could
probably do this using 2N3906 transistors.? I like the fact that it includes a warning
light/LED.
Arv? K7HKL
_._
|
It would seem to me that this type of operation is actually AM modulation of final. When you limit the current flow in an FET that is very similar to plate modulation in a vacuum tube. It certainly can't be good for the linearity of the amplifier since the operational curve would no longer be linear but, instead, flat-topped at some value. Why not just fuse the power lead? It would tell you immediately that you have a problem. tim ab0wr On Sat, 27 Jan 2018 12:13:49 -0800 "Arv Evans" <arvid.evans@...> wrote: Hello
Still thinking about IRF510 failures and ways to avoid making
smoke.....
It seems that there may be two ways to limit current in BITX RF PA
stages that use the IRF510 device.? First would be to incorporate a
current limiter in the positive voltage supply to the RF PA stage.
Second might be to use current sensing in the RF PA supply line to
cause a voltage drop in the MOSFET bias line(s).?
In the first instance it should be possible to use another IRF510 or
preferably a higher power, MOSFET as a control that limits voltage to
the RF PA section if the current exceeds a preset value (usually this
would be 2.0 to 3.0 amperes).?
This circuit has not been built or tested by me (too cold in Idaho
hamshack in winter). The MOSFET could be an IRF840, or similar.
Option-B? potentially solves another problem, that of low level noise
from powered RF PA stage during receive mode.?
In the second instance we could get by with smaller control devices
if we used current sensing in the RF PA power line to turn off bias
to the IRF510 device(s).?
This bias control circuit used by AC2CZ in his 50 watt IRF510 linear
( ).? You could probably
do this using 2N3906 transistors.? I like the fact that it includes a
warning light/LED.
Arv? K7HKL
_._
|
Tim AB0WR
No modulation involved.? The operation is as a switch between ON and almost
OFF.? Gain of the two BJTs makes it operate quickly and drop the output voltage
to the point where the current sensing resistor has less than the 0.65 threshold
voltage across its base-emitter junction.
I see where it does look like some of the CB-era AM modulators because it
causes a drop in voltage when current exceeds the base-emitter threshold.? ?
I'm still looking at the current limiter with an eye toward possibly adding another
MOSFET to get both polarity protection and current limiting.? Problem with fuses
for protection is that most do not operate fast enough.? There are specialty
Fast-Acting fuses? and Slow-Blow fuses but most hams do not have a ready stock
of these.
Arv
_._
On Sun, Jan 28, 2018 at 9:59 PM, Tim Gorman <tgorman2@...> wrote: It would seem to me that this type of operation is actually AM
modulation of final. When you limit the current flow in an FET that is
very similar to plate modulation in a vacuum tube. It certainly can't
be good for the linearity of the amplifier since the operational curve
would no longer be linear but, instead, flat-topped at some value.
Why not just fuse the power lead? It would tell you immediately that
you have a problem.
tim ab0wr
On Sat, 27 Jan 2018 12:13:49 -0800
"Arv Evans" <arvid.evans@...> wrote:
> Hello
>
> Still thinking about IRF510 failures and ways to avoid making
> smoke.....
>
> It seems that there may be two ways to limit current in BITX RF PA
> stages that use the IRF510 device.? First would be to incorporate a
> current limiter in the positive voltage supply to the RF PA stage.
> Second might be to use current sensing in the RF PA supply line to
> cause a voltage drop in the MOSFET bias line(s).?
>
> In the first instance it should be possible to use another IRF510 or
> preferably a higher power, MOSFET as a control that limits voltage to
> the RF PA section if the current exceeds a preset value (usually this
> would be 2.0 to 3.0 amperes).?
>
> This circuit has not been built or tested by me (too cold in Idaho
> hamshack in winter). The MOSFET could be an IRF840, or similar.
> Option-B? potentially solves another problem, that of low level noise
> from powered RF PA stage during receive mode.?
>
> In the second instance we could get by with smaller control devices
> if we used current sensing in the RF PA power line to turn off bias
> to the IRF510 device(s).?
>
> This bias control circuit used by AC2CZ in his 50 watt IRF510 linear
> ( ).? You could probably
> do this using 2N3906 transistors.? I like the fact that it includes a
> warning light/LED.
>
> Arv? K7HKL
> _._
|
A current "limiter" which modulates the current, i.e. limiting the current no matter the drive level, is like applying an ALC to the exciter. Improper design can result in compression of the signal which can then generate spurious responses in the output. If the current limiter is of a "drop-out" style which requires resetting then this won't happen, it will just shut down the exciter. In that case, however, it doesn't provide much efficiency over a plain old fuse! tim ab0wr On Fri, 26 Jan 2018 05:32:08 -0800 "n5ib_2" <n5ib@...> wrote: One other possibility to consider to protect against overcurrent
situations is to use a current limiting power supply, or add a
current limiter to an existing power supply or battery.
The current limiter circuit whose link is at this site:
<>
will go up to 2.2 amps, and includes a low-dropout voltage regulator
that also provides reverse polarity protection.
There is a version, in a different package, of that same regulator
chip that has an added "tracking" feature - being able to parallel
multiple chips to increase the available current. Details are on the
datasheet in the document.
Jim, N5IB
|
Maybe part of the point has been missed at several levels.? The proposed current
limiter is not much different from current limiters in many commercial power
supplies.? It is not active until some current value has been reached.? Up to then
there is no current limiting or "modulation" or "compression".? Yes, the in-series
current sensing resistance does allow an output voltage drop until voltage across
this resistance reaches about 0.65 volts to forward bias the sensing transistor.
If your power supply output is not stiff enough to hold a steady voltage this could
add to the sensing resistance and cause voltage droop and in really bad cases
compression of RF output.?
Question...is RF compression all that bad?? It is what most transmit ALC circuits
do.? It would also be possible to make the proposed circuit driven by reflected
power instead of current.? Then we could call it a transmit ALC to protect the
IRF510(s).?
It would be fairly simple to add a latching function to the limiter design so that it
totally shuts down output when Imax has been reached.? This is possible but would
then require a RESET button or power cycling to restore power to the RF PA stage.
It is also possible to change the proposed design to put the current sensing ahead
of the control MOSFET and make that MOSFET into a voltage control circuit.? This
was my initial approach but the component count became just too high to be an
internal modification for transceivers.? It would be more suitable for converting
an unregulated power supply to a regulated one.?
For those who are using modified PC power supplies it is possible to change the
current sensing so that the switching regulator would shut down if Imax of 2 to 3
amperes is exceeded.? This approach would require power cycling to restore
operation.?
Problem with using fuses is that they have a short but measurable heating period
before they go open.? When they do open they spark internally for another short
period.? Both the delay and the spark are potential problems for circuit components.
Poly-fuse? or resettable fuse devices are intended to address a different issue.?
Some are equivalent of FAST-BLOW fuses, and some are just conventional
resettable circuit breakers.
Suggestion here is that "if you can come up with something else that is adequate,
please submit a circuit drawing and explanation of how it works"? We could all
benefit from that.
Arv? K7HKL
_._
On Fri, Jan 26, 2018 at 11:27 AM, Tim Gorman <tgorman2@...> wrote: A current "limiter" which modulates the current, i.e. limiting the
current no matter the drive level, is like applying an ALC to the
exciter. Improper design can result in compression of the signal which
can then generate spurious responses in the output.
If the current limiter is of a "drop-out" style which requires
resetting then this won't happen, it will just shut down the exciter.
In that case, however, it doesn't provide much efficiency over a plain
old fuse!
tim ab0wr
On Fri, 26 Jan 2018 05:32:08 -0800
"n5ib_2" <n5ib@...> wrote:
> One other possibility to consider to protect against overcurrent
> situations is to use a current limiting power supply, or add a
> current limiter to an existing power supply or battery.
>
> The current limiter circuit whose link is at this site:
> <>
> will go up to 2.2 amps, and includes a low-dropout voltage regulator
> that also provides reverse polarity protection.
>
> There is a version, in a different package, of that same regulator
> chip that has an added "tracking" feature - being able to parallel
> multiple chips to increase the available current. Details are on the
> datasheet in the document.
>
> Jim, N5IB
>
>
>
|
This discussion highlights the best and worst parts of this forum.? There are many of us that are quite content to design away to meet a need… and we all have some great designs.? Lots of problems can be solved in more than one way.? We head off down the path of designing our circuits in the forum while others watch and say “what about me…I want one too… but which one?”.? I guess maybe the designers should all (and this has been done quite a bit here already) make YouTube videos of our circuits in operation so that the rest of the guys can choose what works for them (and that includes a look at the board size).? Otherwise it’s a little bit of “Hey, look what I’ve got” going on… ?Of course I am guilty too. ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ ? Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois ? Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: Like us on Facebook! ? ? email:? bill@... ?
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From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Michael Hagen
Sent: Monday, January 29, 2018 1:23 PM
To: BITX20@groups.io
Subject: [SPAM] Re: [SPAM] Re: [SPAM] Re: [SPAM] Re: [SPAM] Re: [BITX20] IRF510 amplifier failures? Yes, but I was talking Thermal was the only thing Raduino could do.? The thermal response would? be slow, so Radino could catch it.? I have made latching current sensors for small currents on HV supplies.?? I used a comparitor with positive Feed Back. Also an OptoIsolator in the high side sensing to get an isolated trigger.? Worked great.?? I like the latching feature, doesn't oscillate, and you can light a Led.? A reset switch is not necessary, just turn off the device, clear the overcurrent, and re-power. My Mega Pro RaduinoXP replacement has plenty of memory and extra ports to do Built in Test.? It is a little larger though. It might be inconvenient in cabinets that have already been designed for Raduino. I have it running my uBit. 73's Mike ? ? On 1/29/2018 9:05 AM, K9HZ wrote: Hardware trip is gonna be way faster than the Raduino… but it still could work if a small safety margin is added.? ? One thing we have not done that I think is imperative for the next Raduino replacement is a set of built in tools… like a 0-5V meter, frequency counter, LCR meter, etc…. like Hans did with his QCX.? It’s a nice touch for those who don’t have all the expensive equipment.? Hans is pretty cool about it and may share some of the algorithm structures to help get it off the ground where needed (even though his MCU is not an Arduino). ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ ? Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois ? Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: Like us on Facebook! ? ? email:? bill@... ? ? QRT or Silent Key!?? ha.. ha Another reason for fast blowing fuses, and not Poly Fuses for reverse protection. And you still may have to change the Mosfet. For over current situation (not blowing the fuse with a diode for reverse polarity protection) a fast fuse still may not work? A fast comparitor (over current detection) and high side P Fet as suggested by Bill is probably the best answer? Thermal protection may be given over to the Raduino to do, if there are enough ports left?? Or, besides thermistors, there are a lot of temperature sensors out there, Microchip makes some cheap ones.? Thirty cents or so. 73's Mike, WA6ISP ? On 1/29/2018 8:22 AM, Mvs Sarma wrote: ?I fear that Thermal shut down would be rather slow and doesn't hel\p. By that time the mosfet etc might gone QRT. ?Current sense and fasrt action only could save from damages like bad SWR etc. Thanks and rtegards ?sarma ?vu3zmv
? On Mon, Jan 29, 2018 at 8:19 PM, K9HZ <bill@...> wrote: After I sent this note, I figured someone would say “is there a board available” so even though I’m on vacation at our villa in the Caribbean I sat down with a piece of paper and started working on something.? So far I have designed a power FET switch to control voltage to the PA and a toggle trip mechanism.? I thought about the what conditions were desirable to trip the switch off and came up with 1. Over current, and 2. Over temperature.? I need to finish the designs to interface those parts and then bread board it.? I’ll design it so that you can implement either or both by just deleting or adding the interface parts, plus leave the trip line available so that you can design you own interface circuits (like high SWR trip too). ? Sheesh I better retire soon… this is getting to be a full time job. ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ ? Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois ? Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: Like us on Facebook! ? ? email:? bill@... ? ? Is there a circuit or, better yet, a board available? It sounds like this could be current limiting as well. Sent from my Verizon, Samsung Galaxy smartphone -------- Original message -------- Date: 1/29/18 08:58 (GMT-05:00) Subject: Re: [SPAM] Re: [SPAM] Re: [BITX20] IRF510 amplifier failures Now with this said… you could measure the current draw to the FET using a small Hall-effect device and use that to make a simple resettable trip circuit.? Very easy to do. ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ ? Owner - Operator Big Signal Ranch – K9ZC Staunton, Illinois ? Owner – Operator Villa Grand Piton – J68HZ Soufriere, St. Lucia W.I. Rent it: Like us on Facebook!
-- Mike Hagen, WA6ISP 10917 Bryant Street Yucaipa, Ca. 92399 (909) 918-0058 PayPal ID? "MotDog@..." Mike@...
|
Why not let
individuals make their decisions from the posts, and other's
feed back.?? That's how we learn?
Most contributors put
a lot of effort in their responses trying to help with
problems.
There is a very wide
group here, which seems great to me.? But maybe its just too
much for some?
I don't think anyone
is on here that "just wants their BitX to work?"? They are
having a good time learning and experimenting.
It is a lot reading
nearly 3000 posts a month!? Wow.
73's
Mike, WA6ISP
On 1/29/2018 9:38 AM, K9HZ wrote:
This
discussion highlights the best and worst parts of this
forum.? There are many of us that are quite content to
design away to meet a need… and we all have some great
designs.? Lots of problems can be solved in more than one
way.? We head off down the path of designing our circuits in
the forum while others watch and say “what about me…I want
one too… but which one?”.? I guess maybe the designers
should all (and this has been done quite a bit here already)
make YouTube videos of our circuits in operation so that the
rest of the guys can choose what works for them (and that
includes a look at the board size).? Otherwise it’s a little
bit of “Hey, look what I’ve got” going on… ?Of course I am
guilty too.
?
?
Dr.
William
J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ
PJ2/K9HZ
?
Owner
- Operator
Big
Signal Ranch – K9ZC
Staunton,
Illinois
?
Owner –
Operator
Villa
Grand Piton – J68HZ
Soufriere,
St. Lucia W.I.
Rent it:
Like us on Facebook!
?
?
email:?
bill@...
?
?
Yes, but I was talking Thermal was the only thing
Raduino could do.? The thermal response would? be slow, so
Radino could catch it.? I have made latching current sensors
for small currents on HV supplies.?? I used a comparitor
with positive Feed Back.
Also an OptoIsolator in the high side sensing to
get an isolated trigger.? Worked great.?? I like the
latching feature, doesn't oscillate, and you can light a
Led.? A reset switch is not necessary, just turn off the
device, clear the overcurrent, and re-power.
My Mega Pro RaduinoXP replacement has plenty of
memory and extra ports to do Built in Test.? It is a little
larger though.
It might be inconvenient in cabinets that have
already been designed for Raduino.
I have it running my uBit.
73's
Mike
?
?
On 1/29/2018 9:05 AM, K9HZ wrote:
Hardware
trip is gonna be way faster than the Raduino… but it still
could work if a small safety margin is added.?
?
One
thing we have not done that I think is imperative for the
next Raduino replacement is a set of built in tools… like
a 0-5V meter, frequency counter, LCR meter, etc…. like
Hans did with his QCX.? It’s a nice touch for those who
don’t have all the expensive equipment.? Hans is pretty
cool about it and may share some of the algorithm
structures to help get it off the ground where needed
(even though his MCU is not an Arduino).
?
?
Dr.
William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ
VP5/K9HZ PJ2/K9HZ
?
Owner
- Operator
Big
Signal Ranch – K9ZC
Staunton,
Illinois
?
Owner –
Operator
Villa
Grand Piton – J68HZ
Soufriere,
St. Lucia W.I.
Rent
it:
Like us on
Facebook!
?
?
email:?
bill@...
?
?
QRT or Silent Key!?? ha.. ha
Another reason for fast blowing fuses, and not Poly Fuses
for reverse protection.
And you still may have to change the Mosfet.
For over current situation (not blowing the fuse with a
diode for reverse polarity protection) a fast fuse still may
not work?
A fast comparitor (over current detection) and high side P
Fet as suggested by Bill is probably the best answer?
Thermal protection may be given over to the Raduino to do,
if there are enough ports left??
Or, besides thermistors, there are a lot of temperature
sensors out there, Microchip makes some cheap ones.? Thirty
cents or so.
73's
Mike, WA6ISP
?
On 1/29/2018 8:22 AM, Mvs Sarma wrote:
?I fear that Thermal shut
down would be rather slow and doesn't hel\p.
By that time the mosfet etc might gone QRT.
?Current sense and fasrt
action only could save from damages like bad SWR
etc.
Thanks
and rtegards
?sarma
?vu3zmv
?
On Mon, Jan 29, 2018 at 8:19 PM,
K9HZ <bill@...>
wrote:
After
I sent this note, I figured someone would say
“is there a board available” so even though
I’m on vacation at our villa in the Caribbean
I sat down with a piece of paper and started
working on something.? So far I have designed
a power FET switch to control voltage to the
PA and a toggle trip mechanism.? I thought
about the what conditions were desirable to
trip the switch off and came up with 1. Over
current, and 2. Over temperature.? I need to
finish the designs to interface those parts
and then bread board it.? I’ll design it so
that you can implement either or both by just
deleting or adding the interface parts, plus
leave the trip line available so that you can
design you own interface circuits (like high
SWR trip too).
?
Sheesh
I better retire soon… this is getting to be a
full time job.
?
?
Dr.
William J. Schmidt - K9HZ J68HZ 8P6HK
ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ
?
Owner -
Operator
Big
Signal Ranch – K9ZC
Staunton,
Illinois
?
Owner – Operator
Villa Grand Piton –
J68HZ
Soufriere, St. Lucia
W.I.
Rent it:
Like us
on Facebook!
?
?
email:? bill@...
?
?
Is
there a circuit or, better yet, a board
available? It sounds like this could be
current limiting as well.
Sent
from my Verizon, Samsung Galaxy smartphone
--------
Original message --------
Date:
1/29/18 08:58 (GMT-05:00)
Subject:
Re: [SPAM] Re: [SPAM] Re: [BITX20] IRF510
amplifier failures
Now
with this said… you could measure the
current draw to the FET using a small
Hall-effect device and use that to make a
simple resettable trip circuit.? Very easy
to do.
?
?
Dr.
William J. Schmidt - K9HZ J68HZ 8P6HK
ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ
?
Owner -
Operator
Big
Signal Ranch – K9ZC
Staunton,
Illinois
?
Owner – Operator
Villa Grand Piton –
J68HZ
Soufriere, St. Lucia
W.I.
Rent it:
Like us
on Facebook!
--
Mike Hagen, WA6ISP
10917 Bryant Street
Yucaipa, Ca. 92399
(909) 918-0058
PayPal ID? "MotDog@..."
Mike@...
--
Mike Hagen, WA6ISP
10917 Bryant Street
Yucaipa, Ca. 92399
(909) 918-0058
PayPal ID "MotDog@..."
Mike@...
|
I have not received my uBitx yet. I’ve been? reading this forum for about two weeks. Looks like PA failures is a huge problem. Are the two main causes reverse DC power and high SWR? For the DC polarity problem how about a full wave rectifier at the DC input? Two diode voltage drop a problem with this approach? What would be the best way to limit PA? power out to a very small value to allow a manual tuner to be used for the SWR issue? ? Tnx John WA8US ? ?
|
John I also have been on here for a couple of weeks and I see a couple of people have had issues. It is the discussion about it that has gotten huge. I use an HF Packer amp that uses the IRF510s and have not experienced any failures. Out of the box the uBitx will work but by our nature as hams we like to tinker and adjust to see what improvements we can get out of our equipment. With out proper test equipment these adjustments are difficult at best. One of the ham having problems appears to lack enough test equipment (an Oscope and RF probe) to see the RF flow through the TX chain. Plus as pointed out many times the IRF510 is a switch after all and needs some kind of dc load inline between the supply and ground otherwise puff out comes the magic smoke.
Skip Davis, NC9O
Sent from my iPad
|
I have? 3 bitx sets I have never adjusted the bias for the FETs or checked it left it set by the maker and so far never blown one up and I have run poor swr when portable mine run at 8 watts out and sets run with 13v from lith po4 chris
On 30 Jan 2018 14:03, "Skip Davis via Groups.Io" <skipnc9o= yahoo.com@groups.io> wrote: John I also have been on here for a couple of weeks and I see a couple of people have had issues. It is the discussion about it that has gotten huge. I use an HF Packer amp that uses the IRF510s and have not experienced any failures. Out of the box the uBitx will work but by our nature as hams we like to tinker and adjust to see what improvements we can get out of our equipment. With out proper test equipment these adjustments are difficult at best. One of the ham having problems appears to lack enough test equipment (an Oscope and RF probe) to see the RF flow through the TX chain. Plus as pointed out many times the IRF510 is a switch after all and needs some kind of dc load inline between the supply and ground otherwise puff out comes the magic smoke.
Skip Davis, NC9O
Sent from my iPad
|
Same here have a bitx40 that's run all mode pretty much stock on the PA side never even adjusted the bias. I have messed with the gain a bit, that is about it still stock heatsink too.
The things to keep in mind: It's qrp don't push it and for digi modes 1/2 the power to be safe and not stress the IRF510. I have worked the world on digi modes under 5w.
I also run a WA2EBY with 2 510's other than some heat they run just fine.
I have not seen to many under "normal" operation blow unless its part failure from a manufacture defect or operator error.
At QRP levels (5-10w) the 510 can take the heat its when you push them north of 40-50W where SWR and heat become something to pay attention to.
--
David
?N8DAH
|
We have thousands of uBitx's and Bitx40's out there now, an occasional post to the forum about? a blown IRF510 is inevitable My opinion is that SWR is not what blows the IRF510's, especially when operating from 12v. Biggest issue is that the heatsink is quite small, especially if operating continuous duty in some digital mode and/or feeding the IRF510's more than 12v to get higher power. Also, be aware that the gate bias adjustments are backwards (clockwise is minimum), and get very touchy as you approach the transition region, so once the drain current starts going up it is not much of a turn? to go from the optimal 100ma to a very hot IRF510 with 3A of drain current. And be aware that the heatsinks as shipped are not insulated from the IRF510 tab (connected to the drain). I'd guess most failures are due to overheating and messing up when adjusting for 100ma of drain current. A temp sensor and foldback current limiting would avoid these troubles if you want a safety net. Other failures due to screwdrivers in the works or flying leads touching the wrong spot and other such snafus. Reverse DC is not a problem for the IRF510.? It has an intrinsic reverse diode from source to drain, will blow the traces or coils between it and the power supply.? Or, with some foresight, the fuse you put into that power supply lead.? Where you need reverse protection is going into the remainder of the board, be it Bitx40 or uBitx.? A 1n4148 diode would suffice, a 1n400x would not get quite so hot, but there is no problem with running all that stuff at 0.7 volts less.?? Having a full wave rectifier in line with the power supply to the IRF510's would reduce the voltage there by 1.4 volts.? And have a significant hit on output power available. In post 22597, KB1GMX reports:
My experience with IRF510s is extensive and much different. ?I rarely kill one even during experimenting.? I use them for RF power though 6M. ?How much 8 in a parallel 4x4 push-pull at 6M running 225W! ?My favorite is two in a push pull amp (K500r/wa2eby design) with 28V running about 55W on 40m and 37W at 10M and after 6 years of wrong antenna and all sorts of usual havoc its still running with the same pair.?
So the IRF510 is capable of being worked very hard, and still surviving when driving a high SWR. Testing an antenna system with no more than 12v into the IRF510 should be fairly bulletproof. If you want to reduce power further, reduce the drive level to the final using R136 on the Bitx40, RV1 on the uBitx. Again, note that these pots work backwards, fully clockwise is minimum drive. Jerry, KE7ER
On Tue, Jan 30, 2018 at 04:54 am, John Brock wrote:
I have not received my uBitx yet. I’ve been? reading this forum for about two weeks. Looks like PA failures is a huge problem.
Are the two main causes reverse DC power and high SWR?
For the DC polarity problem how about a full wave rectifier at the DC input? Two diode voltage drop a problem with this approach?
What would be the best way to limit PA? power out to a very small value to allow a manual tuner to be used for the SWR issue?
?
|
Respectfully, current limiting in the final amp is exactly how high-level plate modulation in an old AM transmitter works. Your audio amplifier, which is required to generate a significant amount of power, is transformer coupled into the plate lead of your final amplifier. This allows the audio to vary the voltage and current in the final amplifier turning it into a mixer. That's how you get the audio sidebands plus the carrier that is a high level generated AM signal. Flat-topping in a linear amplifier is actually nothing more than a form of current limiting and it too generates spurious responses by making the amplifier non-linear. Before you do anything to modulate the current and voltage being fed into a linear amplifier you should have a two-tone audio generator and a spectrum analyzer of some kind to monitor your signal. tim On Mon, 29 Jan 2018 09:49:00 -0700 "Arv Evans" <arvid.evans@...> wrote: Maybe part of the point has been missed at several levels. The
proposed current
limiter is not much different from current limiters in many commercial
power
supplies. It is not active until some current value has been
reached. Up to then
there is no current limiting or "modulation" or "compression". Yes,
the in-series
current sensing resistance does allow an output voltage drop until
voltage across
this resistance reaches about 0.65 volts to forward bias the sensing
transistor.
If your power supply output is not stiff enough to hold a steady
voltage this could
add to the sensing resistance and cause voltage droop and in really
bad cases
compression of RF output.
Question...is RF compression all that bad? It is what most transmit
ALC circuits
do. It would also be possible to make the proposed circuit driven by
reflected
power instead of current. Then we could call it a transmit ALC to
protect the
IRF510(s).
It would be fairly simple to add a latching function to the limiter
design so that it
totally shuts down output when Imax has been reached. This is
possible but would
then require a RESET button or power cycling to restore power to the
RF PA stage.
It is also possible to change the proposed design to put the current
sensing ahead
of the control MOSFET and make that MOSFET into a voltage control
circuit. This
was my initial approach but the component count became just too high
to be an
internal modification for transceivers. It would be more suitable for
converting
an unregulated power supply to a regulated one.
For those who are using modified PC power supplies it is possible to
change the
current sensing so that the switching regulator would shut down if
Imax of 2 to 3
amperes is exceeded. This approach would require power cycling to
restore operation.
Problem with using fuses is that they have a short but measurable
heating period
before they go open. When they do open they spark internally for
another short
period. Both the delay and the spark are potential problems for
circuit components.
Poly-fuse or resettable fuse devices are intended to address a
different issue.
Some are equivalent of FAST-BLOW fuses, and some are just conventional
resettable circuit breakers.
Suggestion here is that "
*if you can come up with something else that is adequate, *
*please submit a circuit drawing and explanation of how it works*" We
could all
benefit from that.
Arv K7HKL
_._
On Fri, Jan 26, 2018 at 11:27 AM, Tim Gorman <tgorman2@...> wrote:
A current "limiter" which modulates the current, i.e. limiting the
current no matter the drive level, is like applying an ALC to the
exciter. Improper design can result in compression of the signal
which can then generate spurious responses in the output.
If the current limiter is of a "drop-out" style which requires
resetting then this won't happen, it will just shut down the
exciter. In that case, however, it doesn't provide much efficiency
over a plain old fuse!
tim ab0wr
On Fri, 26 Jan 2018 05:32:08 -0800
"n5ib_2" <n5ib@...> wrote:
One other possibility to consider to protect against overcurrent
situations is to use a current limiting power supply, or add a
current limiter to an existing power supply or battery.
The current limiter circuit whose link is at this site:
<>
will go up to 2.2 amps, and includes a low-dropout voltage
regulator that also provides reverse polarity protection.
There is a version, in a different package, of that same regulator
chip that has an added "tracking" feature - being able to parallel
multiple chips to increase the available current. Details are on
the datasheet in the document.
Jim, N5IB
|
I give up!? Maybe this IRF510 failure thing is a non-problem.
Someone recently suggested adding a 1K resistor across the
antenna connection to limit really high SWR situations.? That
sounds interesting.
Arv? K7HKL
_._
On Tue, Jan 30, 2018 at 11:08 AM, Tim Gorman <tgorman2@...> wrote: Respectfully, current limiting in the final amp is exactly how
high-level plate modulation in an old AM transmitter works. Your audio
amplifier, which is required to generate a significant amount of power,
is transformer coupled into the plate lead of your final amplifier.
This allows the audio to vary the voltage and current in the final
amplifier turning it into a mixer. That's how you get the audio
sidebands plus the carrier that is a high level generated AM signal.
Flat-topping in a linear amplifier is actually nothing more than a form
of current limiting and it too generates spurious responses by making
the amplifier non-linear.
Before you do anything to modulate the current and voltage being fed
into a linear amplifier you should have a two-tone audio generator and
a spectrum analyzer of some kind to monitor your signal.
tim
On Mon, 29 Jan 2018 09:49:00 -0700
"Arv Evans" <arvid.evans@...> wrote:
> Maybe part of the point has been missed at several levels.? The
> proposed current
> limiter is not much different from current limiters in many commercial
> power
> supplies.? It is not active until some current value has been
> reached.? Up to then
> there is no current limiting or "modulation" or "compression".? Yes,
> the in-series
> current sensing resistance does allow an output voltage drop until
> voltage across
> this resistance reaches about 0.65 volts to forward bias the sensing
> transistor.
> If your power supply output is not stiff enough to hold a steady
> voltage this could
> add to the sensing resistance and cause voltage droop and in really
> bad cases
> compression of RF output.
>
> Question...is RF compression all that bad?? It is what most transmit
> ALC circuits
> do.? It would also be possible to make the proposed circuit driven by
> reflected
> power instead of current.? Then we could call it a transmit ALC to
> protect the
> IRF510(s).
>
> It would be fairly simple to add a latching function to the limiter
> design so that it
> totally shuts down output when Imax has been reached.? This is
> possible but would
> then require a RESET button or power cycling to restore power to the
> RF PA stage.
>
> It is also possible to change the proposed design to put the current
> sensing ahead
> of the control MOSFET and make that MOSFET into a voltage control
> circuit. This
> was my initial approach but the component count became just too high
> to be an
> internal modification for transceivers.? It would be more suitable for
> converting
> an unregulated power supply to a regulated one.
>
> For those who are using modified PC power supplies it is possible to
> change the
> current sensing so that the switching regulator would shut down if
> Imax of 2 to 3
> amperes is exceeded.? This approach would require power cycling to
> restore operation.
>
> Problem with using fuses is that they have a short but measurable
> heating period
> before they go open.? When they do open they spark internally for
> another short
> period.? Both the delay and the spark are potential problems for
> circuit components.
> Poly-fuse? or resettable fuse devices are intended to address a
> different issue.
> Some are equivalent of FAST-BLOW fuses, and some are just conventional
> resettable circuit breakers.
>
> Suggestion here is that "
> *if you can come up with something else that is adequate, *
> *please submit a circuit drawing and explanation of how it works*"? We
> could all
> benefit from that.
>
> Arv? K7HKL
> _._
>
>
> On Fri, Jan 26, 2018 at 11:27 AM, Tim Gorman <tgorman2@...> wrote:
>
> > A current "limiter" which modulates the current, i.e. limiting the
> > current no matter the drive level, is like applying an ALC to the
> > exciter. Improper design can result in compression of the signal
> > which can then generate spurious responses in the output.
> >
> > If the current limiter is of a "drop-out" style which requires
> > resetting then this won't happen, it will just shut down the
> > exciter. In that case, however, it doesn't provide much efficiency
> > over a plain old fuse!
> >
> > tim ab0wr
> >
> > On Fri, 26 Jan 2018 05:32:08 -0800
> > "n5ib_2" <n5ib@...> wrote:
> >
> > > One other possibility to consider to protect against overcurrent
> > > situations is to use a current limiting power supply, or add a
> > > current limiter to an existing power supply or battery.
> > >
> > > The current limiter circuit whose link is at this site:
> > > <>
> > > will go up to 2.2 amps, and includes a low-dropout voltage
> > > regulator that also provides reverse polarity protection.
> > >
> > > There is a version, in a different package, of that same regulator
> > > chip that has an added "tracking" feature - being able to parallel
> > > multiple chips to increase the available current. Details are on
> > > the datasheet in the document.
> > >
> > > Jim, N5IB
> > >
> > >
> > >
> >
> >
> >
> >
> >
|
What many people fail to realise when using a diode bridge for
reverse polarity protection is it means neither of the power wires
are at ground potential.? If used in vehicle with battery having
one terminal grounded the grounds are not at same potential.? So
your metal case and vehicle body have a diode drop difference.
Cheers,
Will
ZL1TAO
On 31/01/18 06:05, Jerry Gaffke via
Groups.Io wrote:
<SNIP>
Reverse DC is not a problem for the IRF510.? It has an intrinsic
reverse diode from source to drain,
will blow the traces or coils between it and the power supply.?
Or, with some foresight, the fuse
you put into that power supply lead.? Where you need reverse
protection is going into the remainder
of the board, be it Bitx40 or uBitx.? A 1n4148 diode would
suffice, a 1n400x would not get quite so hot,
but there is no problem with running all that stuff at 0.7 volts
less.??
Having a full wave rectifier in line with the power supply to the
IRF510's would reduce the voltage
there by 1.4 volts.? And have a significant hit on output power
available.
<SNIP>
On Tue, Jan 30,
2018 at 04:54 am, John Brock wrote:
I have not
received my uBitx yet. I’ve been? reading this forum for about
two weeks. Looks like PA failures is a huge problem.
Are the two
main causes reverse DC power and high SWR?
For the DC
polarity problem how about a full wave rectifier at the DC
input? Two diode voltage drop a problem with this approach?
What would be
the best way to limit PA? power out to a very small value to
allow a manual tuner to be used for the SWR issue?
?
|
I agree, I blew a 510 by
messing with the bias adjustment. My meter was
not reading the 100 ma, so I cranked up all the way full CCW.
Out of the box
it worked! My uBitX works with over 5 watts out, I'm leaving it
alone. If
it works, leave the power alone and skip to fix the other
problems (pop,
agc etc.) Mic that came with unit works well without
amplification.
Stay QRP and look for us Sunday 7178 7278.
Ed W0OIC
On 1/30/2018 11:05 AM, Jerry Gaffke via
Groups.Io wrote:
toggle quoted message
Show quoted text
We have thousands
of uBitx's and Bitx40's out there now, an occasional post to the
forum about?
a blown IRF510 is inevitable
My opinion is that SWR is not what blows the IRF510's, especially
when operating from 12v.
Biggest issue is that the heatsink is quite small, especially if
operating continuous duty in some digital mode
and/or feeding the IRF510's more than 12v to get higher power.
Also, be aware that the gate bias adjustments are backwards
(clockwise is minimum), and get very touchy
as you approach the transition region, so once the drain current
starts going up it is not much of a turn?
to go from the optimal 100ma to a very hot IRF510 with 3A of drain
current.
And be aware that the heatsinks as shipped are not insulated from
the IRF510 tab (connected to the drain).
I'd guess most failures are due to overheating and messing up when
adjusting for 100ma of drain current.
A temp sensor and foldback current limiting would avoid these
troubles if you want a safety net.
Other failures due to screwdrivers in the works or flying leads
touching the wrong spot and other such snafus.
Reverse DC is not a problem for the IRF510.? It has an intrinsic
reverse diode from source to drain,
will blow the traces or coils between it and the power supply.?
Or, with some foresight, the fuse
you put into that power supply lead.? Where you need reverse
protection is going into the remainder
of the board, be it Bitx40 or uBitx.? A 1n4148 diode would
suffice, a 1n400x would not get quite so hot,
but there is no problem with running all that stuff at 0.7 volts
less.??
Having a full wave rectifier in line with the power supply to the
IRF510's would reduce the voltage
there by 1.4 volts.? And have a significant hit on output power
available.
In post 22597, KB1GMX reports:
My experience with IRF510s is extensive and much different. ?I
rarely kill one even during experimenting.? I use them for RF
power though 6M. ?How much 8 in a parallel 4x4 push-pull at 6M
running 225W! ?My favorite is two in a push pull amp
(K500r/wa2eby design) with 28V running about 55W on 40m and 37W
at 10M and after 6 years of wrong antenna and all sorts of usual
havoc its still running with the same pair.?
So the IRF510 is capable of being worked very hard, and still
surviving when driving a high SWR.
Testing an antenna system with no more than 12v into the IRF510
should be fairly bulletproof.
If you want to reduce power further, reduce the drive level to the
final using R136 on the Bitx40, RV1 on the uBitx.
Again, note that these pots work backwards, fully clockwise is
minimum drive.
Jerry, KE7ER
On Tue, Jan 30, 2018 at 04:54 am, John Brock wrote:
I have not
received my uBitx yet. I’ve been? reading this forum for about
two weeks. Looks like PA failures is a huge problem.
Are the two
main causes reverse DC power and high SWR?
For the DC
polarity problem how about a full wave rectifier at the DC
input? Two diode voltage drop a problem with this approach?
What would be
the best way to limit PA? power out to a very small value to
allow a manual tuner to be used for the SWR issue?
?
|
Ok, So my next mods for the uBITX is to install a voltage boost for the PA.
LARGE heatsink + ALU case mount the 510, even a thermostatically controlled fan...
The boost converter can go up to 30v. I understand that the electro caps C98 and C99 will need to be upgraded too?
Any other thoughts?
Why? well becuase its fun, and I like playing... and I have a packet of 20 spare 510s... and the priceless look on the XYLs face when one does go off will be hillarious.
73, Nick, VK4PLN
|
K9HZ
Skip Davis
N8DAH
ekelley
Nick VK4PP