Australian Amateur Radio Station
( -ve Voltage and Voltage Boost Generator)
Negative Volt and Volt Boost Generator:
In dealing with 28 V SMA relays and various Bias circuits that require -volts, I found the
following circuit invaluable as the "back bone" of a lot of DC supply issues for Microwave

A search on the web finds a plethora of techniques and devices to accomplish these
This is just another one that works nicely!

The circuit will easily deliver several hundred mA of current.  It can be followed with a -ve
regulator such as an 7905 to provide the negative volts that a lot of FET devices require,  or
it can be used as an SMA relay driver either by using the 2@ Volt in  OUTPUT  or using the
negative output and the positive input to drive the relay.

A word of caution.......MOST SMA relays I have used will pull in without any problems with
20-22V.  However I have come across some relays that have a higher requirement ( closer to
+28V)  to pull in reliably.  I found this out the hard way with some "Teldyne" surplus relays.  
All I suggest is check on the test bench first.  "Relays aint relays!"

I must thank David, VK3QM (VK3XLD)  for this circuit which has worked              
admirably in numerous applications!