I have a device that runs on -5v DC but I only have 120V AC. I need to build a power supply that can convert 120v AC to -5v DC. I need to draw the best power supple and indicate the wave form at each stage.

 

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Brightened, clipped image of the problem:

 

hi M,
Welcome to AAC.
Have you drawn a sketch showing how you would generate the -5V.?
Post a drawing and we can help you.
E

 

Would it be easy if it was +5 volts? In your schooling have you seen any power supply? +24V?

 

Whoever wrote the assignment knows nothing about electricity.
1) -5V and 0V is the same as +5V and 0V since EARTH is not mentioned.
2) No current?

 

Whoever wrote the assignment knows nothing about electricity.
1) -5V and 0V is the same as +5V and 0V since EARTH is not mentioned.
2) No current?

The first is likely a specific point of the assignment.

The second is, by far, the worst offense.

Close on it's heels is no indication of what constitutes "best possible" -- I hate assignments that pull that crap.

I'd be tempted to offer up something that is a 5.1 V zener, a resistor that brings the zener to 5 V at the peak voltage, and a large, low-leakage capacitor. So what if it takes it minutes to build up to -5 V -- the specs say nothing about that. So what if it can only deliver a few microamps of current before the voltage is pulled way off -- the specs say nothing about that.