Booster

I tried the booster circuit from yesterday:

https://wb9kzy.blogspot.com/2025/06/giving-circuit-boost.html 

Bottom line: it seems to work below 9 volts, so that is good.

What wasn't good was that I spent a lot of time looking for the Seiko (now ABLIC) 1.5 volt regulator IC but no luck so far.  So I tried the circuit with an LM2931 3 volt LDO regulator with the same pinout as the old friend, the 78L05.

Here is that boost circuit from the Onsemi LM2931 datasheet:

With a 300 mA load the voltage only decreased about 2 mV from no load.  The circuit consisted of a 2n3906 PNP transistor (the complementary version of the 2n3904 NPN).  I also added a couple of .1 uF caps by the LM2931, decreased the input cap to 4.7 uF and increased the output cap to 47 uF.  Finally the 10k ohm resistor was reduced to 130 ohms (the LM2931 has a quiescent current much higher than the Seiko regulator I couldn't find).  After a while the 2n3906 became hot with an input voltage of 9V, so I decreased the input to 4.5 V (the dropout voltage of the LM2931 plus the Vbe of the 2n3906 is roughly 1.5 volts) and the circuit worked fine.  But the heatup of the 2n3906 shows that it was taking most of the current, the LM2931 can only provide 100 mA.

And there was another lesson learned: don't use these cheap breadboards:

When I first tried the circuit it was no-go - then I switched over to a 3M breadboard and it worked fine - when will I ever learn ?  :)

Now to find that silly 1.5 volt Seiko regulator !

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm