[Amps] Freescale LDMOS devices

[Larry Benko]

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.

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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