I'm not even sure what to call the question that I have, but here goes...
I am using a dual output (secondary) transformer (2 x 8v). The two transformer outputs are two independant windings (eg. four output pins, thus no center tap). I want to keep my 5v circuit separate form my 3.3v circuit, so I use one secondary winding to power a 7805 regulator and the other secondary winding to power a 3.3v switching regulator circuit. Each winding first goes through its own diode bridge before going to regulation. In summary - two secondary windings - two diode bridges - two regulators.
Now my processor runs off the 3.3V and it switches transistors which switches relays which run off the 5V. So where do I connect the transistor's emitter? To ground that comes from the 5V's winding or the 3.3V's winding? Does it matter?
Let's say I want to use my processor to interface to a computer's serial port. The MAX232 runs off 5V, but the TX and RX lines come from the processor. Which ground should be connected to the MAX232 GND pin? The one that comes from the 5V's winding?
How does this work?
I am using a dual output (secondary) transformer (2 x 8v). The two transformer outputs are two independant windings (eg. four output pins, thus no center tap). I want to keep my 5v circuit separate form my 3.3v circuit, so I use one secondary winding to power a 7805 regulator and the other secondary winding to power a 3.3v switching regulator circuit. Each winding first goes through its own diode bridge before going to regulation. In summary - two secondary windings - two diode bridges - two regulators.
Now my processor runs off the 3.3V and it switches transistors which switches relays which run off the 5V. So where do I connect the transistor's emitter? To ground that comes from the 5V's winding or the 3.3V's winding? Does it matter?
Let's say I want to use my processor to interface to a computer's serial port. The MAX232 runs off 5V, but the TX and RX lines come from the processor. Which ground should be connected to the MAX232 GND pin? The one that comes from the 5V's winding?
How does this work?