[JMS] Power supply design concerns...wait a minute...

Fri, 20 Feb 2004 19:41:45 GMT

Hi again Brian:

Uh, I just rechecked the work. I don't think this solution will work. In order to make 55 watts drive from the 90831, you will need at least 204 mA now. 1/3 of that will be 68 mA. Doing the math, we see an added 23 mA. Brings it to 243 mA. I suspect it won't hurt the choke but I decided to use the extra iron to keep things slightly independent and easier to control. Cal, N6KYR. 

>>>This ain't rocket science.  The solution is simple.  Keep the 600V 
transformer in the design.  Make the filter a choke input by moving the 
input capacitor to the output to reduce the voltage to .9 x 300 = 270VDC. 
270 x 100 ma = 27 Watts DC input.  At 66% efficiency you'll have 17 Watts 
output (perfect).  And, your modulator current is not going to be 140 mA 
all the time. If it peaks at 140 mA, the average will be around 1/3 that, 
or 45 mA.  45+100+40+35 = 220 mA.  Your choke will be fine.  If you don't 
believe me, lash the system up with clip leads to prove it works before 
you start drilling holes.  Having said that, it is always better to have 
separate power supplies for the RF Amp and the Modulator so if you have 
the extra transformer then use it.

Brian K. Harris, Account Manager

Philips Semiconductors 
2140 Lake Park Blvd. Suite 200
Richardson, Texas 75080 USA 

Office:     972-705-2484 (Use This First)
Fax:         972-705-2450
Mobile:    214-763-5977
EMAIL [email protected]

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