[Amps] Freescale LDMOS devices

[Carl]

----- Original Message ----- 
From: "Larry Benko" <xxw0qe at comcast.net>
To: <amps at contesting.com>
Sent: Friday, March 08, 2013 6:02 PM
Subject: Re: [Amps] Freescale LDMOS devices


> There are 2 type of power factor calculations.
>
> For linear loads PF = true power / apparent power = cos(theta) where theta 
> is the angle between the voltage and current entering the device.  Think 
> "motor" here for an example.  This power factor CAN be corrected by a 
> shunt capacitor across the line.
>
> For non-linear loads (like ALL power supplies linear or switching) the 
> calculation is considerably harder BUT after more math than anyone here is 
> interested in we get PF = cos(theta) * ( 1 / sqrt( 1 + THD^2) ) where 
> theta is the angle between the fundamental (60Hz or 50Hz) voltage and the 
> the fundamental current.  The other term accounts for all the harmonics 
> that are generated and THD is the total power in all the harmonics as a 
> fraction of the total power. This case can NOT be fixed by a shunt 
> capacitor.  Looking at any capacitor input filter shows the  fundamental 
> voltage and current are very close to being exactly in phase unless the 
> power xfmr has a lot of leakage inductance.  If I remember correctly even 
> with an inductor input filter where the inductor current never falls to 
> zero you can not totally fix the PF issue especially since most chokes 
> used for this purpose are swinging chokes which are non-linear.  In the 
> case of a high frequency switching power supply the harmonic issues can be 
> filtered out restoring good PF but for linear power supplies removing the 
> 120 and 180 etc. Hz harmonics while passing the 60Hz is not easy to do.


** Henry and others did it with a tuned choke and it worked well until the 
cap started getting leaky and the C changed.  BANG!

Carl
KM1H


>
> In this country we pay for real power and not reactive power.  The 
> electric meters I have played with (20 years ago) did a very good job of 
> only responding to real power.  I loaded some down with large capacitive 
> loads which did not appreciably change the measured power consumption.
>
> Larry, W0QE
>
>
> On 3/8/2013 2:51 PM, Carl wrote:
>> So install a power factor correction cap at the mains panel.
>>
>> Carl
>> KM1H
>>
>>
>>
>>
>> ----- Original Message ----- From: "Roger" <sub1 at rogerhalstead.com>
>> To: <amps at contesting.com>
>> Sent: Friday, March 08, 2013 11:23 AM
>> Subject: Re: [Amps] Freescale LDMOS devices
>>
>>
>>>
>>> Curiosity, as this is something most hams are unaware of, or concerned 
>>> about power factor.
>>>
>>> In practical terms just what does that mean to a QRO operator? Yes, I 
>>> know it makes the load appear larger than it actually is and if you draw 
>>> enough load it can be noticed by the power company.  Still, no one here 
>>> in the states complains whether you draw 1 KW, or 15 with your station.
>>>
>>> I've never heard of a commercial ham amp with power factor correction. 
>>> Do they exist?
>>> So other than a bit of unneeded increase in your bill, what is the 
>>> problem where the single station is concerned "here in the states"?
>>>
>>> 73
>>>
>>> Roger  (K8RI)
>>>
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>>>
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>
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