# DC Value of Square Wave

Discussion in 'Physics' started by crazyengineer, Jan 18, 2012.

1. ### crazyengineer Thread Starter Member

Dec 29, 2010
156
2
Okay, so this is one concept I keep trying to understand after my Signals and Systems class. Is there a generalized formula for finding the DC value of a square wave. Here's a very poor picture example.

Also, let say I conceptually connect a DC motor to a voltage source that's emitting the square wave in the above picture. Do that mean the motor will see this DC value?

2. ### MrChips Moderator

Oct 2, 2009
12,648
3,458
There is no such thing as the DC value of a square wave. You can talk about the mean or average value.

3. ### crazyengineer Thread Starter Member

Dec 29, 2010
156
2
Sorry for the stupid mistake, I meant average value.

So if I wanted to find the average value, would I just do (2ms/4ms)*5-2.5?

4. ### MrChips Moderator

Oct 2, 2009
12,648
3,458
The average value is the area under the curve for a full cycle divided by the time period of the cycle

average = ( (5V x 1ms) + (0V x 1ms) ) / 2ms = 2.5V

crazyengineer likes this.
5. ### crazyengineer Thread Starter Member

Dec 29, 2010
156
2
I see. One more question: if I connected a motor to the square wave in the above picture, then will it see this average value?

6. ### MrChips Moderator

Oct 2, 2009
12,648
3,458
A lot depends on the motor, the size, weight, inertia, load, power requirements, frequency of the pulses.

Yes, chances are the motor will see the average value. This is what is know as PWM drive (Pulse Width Modulation).

7. ### joeyd999 AAC Fanatic!

Jun 6, 2011
2,758
2,937
Of course, if you look at it in the frequency domain, you could say it has a 'DC component'.

8. ### MrChips Moderator

Oct 2, 2009
12,648
3,458
Yes, I did think of that afterwards.

Mar 24, 2008
20,772
2,540