I'm building a bench power supply and would like to switch between several outputs. I have a combination volt/ammeter that I would like to use to monitor the selected output while still being able to use the other outputs. The idea was to use a pair of 2N3055 transitors in parallel (one with a logical inverter on the input) to switch the outputs between direct access to ground and access to ground through the ammeter. The problem came when I made the circuit in LTSpice and the results were not what I expected. In order to troubleshoot the circuit I reduced it to the bare minimum that still returns the same results and this is what I ended up with (the graph shows the voltage and amperage at the collector):
As you can see, the load is only dropping ~3.5V while the transistor is dropping the rest. I chose the load size to simulate the max amperage that I would allow through this circuit. The datasheet for the 2N3055 says VCEO=60VDC and IC=15A. Is there a mistake with the Spice model, or am I missing something here?
As you can see, the load is only dropping ~3.5V while the transistor is dropping the rest. I chose the load size to simulate the max amperage that I would allow through this circuit. The datasheet for the 2N3055 says VCEO=60VDC and IC=15A. Is there a mistake with the Spice model, or am I missing something here?