hi Wesley1, your assumption that the supply is a 12 VAC supply that supplies 12 VDC is a bit suspicious. A transformer indeed provides AC voltage/current, however, in order to calculate the rectified DC voltage, assuming that it gets rectified in the normal way with diodes, will yield an average DC voltage that is somewhat higher than 12 volts. The resistive loads that you you are showing are all in parallel, which yields a current that is the parallel resistance of all 3 resistors. From your description, there is not enough information to evaluate this circuit and make any conclusions. One thing is for sure, you cannot pull the voltage to zero at the point of the question mark, without either blowing the fuse or simply overloading the supply. The series resistive equivalent, that has been pointed out by several others, will determine whether the current gets high enough to blow the 100 mA fuse. I doubt that the equivalent series resistance is that high, but it is possible.
You also stated that the power supply was fused to 100 mA, which means that the maximum current can only be 100 mA. If you short this system anywhere, the current will quickly blow the small fuse.
This leads me to question whether you have drawn this circuit correctly, as most pulldown resistor configurations would be in series with ground. Perhaps you have misunderstood/misrepresented the circuit?
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On another note, it is always a good idea to state your problem in terms of your goals, rather than asking an open ended question as you did, however, you did that in a later post, somewhat. I also suggest that you study Ohm's law and Thevenin and Norton's theorems, which will quickly show you that your original premise is unlikely.
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