I'm trying to build a small power supply for general experimentation. The plan is to have a fixed 5v output and a +/- supply that can be switched to 5, 12 or 15v. I picked up a transformer at a car boot sale that has isolated 8v (1A) and 14-0-14v (150mA) outputs. I've simulated the circuit in LTspice and the 5v side works fine.
I was expecting to be able to draw up to 100mA from either side of the dual supply and stay within 150mA maximum input current per winding, however this seems to require ~193mA. The maximum output current I can draw while staying within the transformers limits seems to be 75mA (using 250 ohm dummy loads as in the simulation). I've not included the regulator section in the simulation as LTspice doesn't have the required 3 terminal regulators but they should have a negligible effect on current.
My reasoning for expecting a 100mA max output is that if the output voltage increases by √2 (peak voltage) the available current should decrease by the same ratio.
Is my reasoning wrong here or am I doing something wrong in my circuit?
Also attached is the LTspice file.
I was expecting to be able to draw up to 100mA from either side of the dual supply and stay within 150mA maximum input current per winding, however this seems to require ~193mA. The maximum output current I can draw while staying within the transformers limits seems to be 75mA (using 250 ohm dummy loads as in the simulation). I've not included the regulator section in the simulation as LTspice doesn't have the required 3 terminal regulators but they should have a negligible effect on current.
My reasoning for expecting a 100mA max output is that if the output voltage increases by √2 (peak voltage) the available current should decrease by the same ratio.
Is my reasoning wrong here or am I doing something wrong in my circuit?
Also attached is the LTspice file.
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