Re: IRF510 amplifier failures

William Kimber
 


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?

 


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