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Uncle Bulgaria · 28th Jul 2019, 12:09 pm

This morning's reading has been on BJT switches, though the accepted circuits I've found have the emitter grounded.

I'm guessing that the biasing on T10 is meaning the switch is not turning off properly. The current on the base means it is not biased into cut-off when the switch is open.

Does this mean the S1002 acts to allow current to flow between the 9.5V rail on the collector, through the 2.2K R79 which should turn the switch on?

In which case, should I be increasing the values of R81 and R79 to decrease base current, even though the Zener diode is holding the base to 5.6V?

28th Jul 2019, 12:09 pm	#53
Uncle Bulgaria Nonode Join Date: May 2016 Location: Cornwall, UK. Posts: 2,339	Re: Uher CR240 Troubleshooting Best Practice This morning's reading has been on BJT switches, though the accepted circuits I've found have the emitter grounded. I'm guessing that the biasing on T10 is meaning the switch is not turning off properly. The current on the base means it is not biased into cut-off when the switch is open. Does this mean the S1002 acts to allow current to flow between the 9.5V rail on the collector, through the 2.2K R79 which should turn the switch on? In which case, should I be increasing the values of R81 and R79 to decrease base current, even though the Zener diode is holding the base to 5.6V?