Hello everyone!
I am working on a project and need to generate a 2Hz 120v square wave from 120V DC. The current i need is very small, the smaller the better actually and i don't know where to start!

Any advice would be helpful thank you!

 

So your square wave will have a 2 Hz frequency with a pulse width of 1 second. One second On and One second Off is how I read it. I would think you could just use a high voltage MOSFET to switch the 120 VDC ON and Off. Do you have a source for the frequency or do you need to generate that?

Ron

 

Sorry Ron,
I think you mean 250 mS on, 250 mS off.

Les.

 

Is rise and fall time very important? Anything else we should know about your application?

 

One of idea may be to use a NE555 plus high voltage boost mosfet halfbridge.
Generator: https://i.stack.imgur.com/qZJSz.png
Booster: https://upload.wikimedia.org/wikipedia/commons/thumb/7/7f/Pushpull_(English).png/220px-Pushpull_(English).png

P.S. Some mosfets are even very fast, thus the front steepness there is not a question at all.

 

Sorry Ron,
I think you mean 250 mS on, 250 mS off.

Les.

Thanks Les. No clue why I did that. 1 / 2 = .5 and .5 / 2 = .250 makes more sense in the morning.

Thanks Again
Ron

 

Is the wanted square wave uni-polar, i.e. switching between 0V and 120V?

 

What is the load that the 120 V square wave is driving?

Clearly the circuit has to pull the output up to 120 Vdc. BUT, then what? Does the circuit have to pull the output back down to GND with an active device, or can the output be pulled down by a resistor, or can it just release the output and let the load pull it down. These are three variations of the same circuit, each is less complex than the one before it.

Also, is there a low voltage DC source to power the circuit, or must that be derived from the main 120 Vdc source?


ak

 

I have done the same sort of thing myself but realised before I typed anything. I did make a similar error in another recent thread. I was thinking about the time of half a cycle of a sine wave and went on to give an answer using that time for a full cycle.

Les.

 

Hello everyone!
I am working on a project and need to generate a 2Hz 120v square wave from 120V DC. The current i need is very small, the smaller the better actually and i don't know where to start!

Any advice would be helpful thank you!

An "H bridge" scheme would work if you can rectify the AC line for the power source. The bridge can be either big FET devices or bipolar transistors. Using opto-isolators will make driving the bridge easier. The result would be a decent square wave at 2 Hz.
Really, at that frequency you could also use 4 fast solid state relays to do the switching.