# Convert 120v AC to -5v DC

#### Makenzi

Joined Nov 21, 2020
1
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.

#### Attachments

• 1.6 MB Views: 11

#### dl324

Joined Mar 30, 2015
17,026
Welcome to AAC!

For homework, you need to show your best effort so we know how to provide guidance.

Thank you for posting in the appropriate forum.

Brightened, clipped image of the problem:

#### ericgibbs

Joined Jan 29, 2010
19,031
hi M,
Welcome to AAC.
Have you drawn a sketch showing how you would generate the -5V.?
E

#### ronsimpson

Joined Oct 7, 2019
3,159
Would it be easy if it was +5 volts? In your schooling have you seen any power supply? +24V?

#### Audioguru again

Joined Oct 21, 2019
6,767
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?

#### WBahn

Joined Mar 31, 2012
30,256
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.