Tuesday, February 18, 2014

power supply, 36 volts

power supply
For a 40 meter linear rf amplifier based on irf840 a suitable dc power source was needed.
Transformer is capable to provide 5amp current,  for 24 volt ac. It has 24-0-24  secondary and also 12 volt secondary , so this 12 can be used for the control as well as other receiver chains.

I used the big diodes - 3 amp current capable i.e 1N5408. smoothing capacitor is 4700mfd,50v dc working voltage. Put the fuse of 3 amp and switch.

See, the second foto graph, i have assembled it  in hurry to check whether transformer is working or not. it will need some big cabinets and all the essential ckt i.e voltage regulators, current limiters,  ameter (yes sir ameter ) and also 1n4007 diode bride with capacitor for regulated 12 v dc.etc

But, with this , i can start powering / testing the new homebrew rf amplifers. Beware , 4700mfd is not enough it will require more filtering i.e 4 or 5 more big capacitors and bleeder resistor to discharge these capacitors.
(as of 27jan2015)
Later on I put the transformer on the thick metal plate for heat sink purpose. Used LM7812 for 12vdc and drive a fan to cool the transformer without it was getting very hot. Also put fuse and extra switches. 

When the RF amplifier loaded the supply with 1.6amp current the power rail becomes about 25volts. VU2ORO said its okey. 1.2 is the voltage of secondary... Now a days transformers are not putting that much power like old timers as we are compromising on the laminates now...