# DC Value of Square Wave

#### crazyengineer

Joined Dec 29, 2010
156
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?

#### MrChips

Joined Oct 2, 2009
24,192
There is no such thing as the DC value of a square wave. You can talk about the mean or average value.

#### crazyengineer

Joined Dec 29, 2010
156
There is no such thing as the DC value of a square wave. You can talk about the mean or average value.
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?

#### MrChips

Joined Oct 2, 2009
24,192
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

#### crazyengineer

Joined Dec 29, 2010
156
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
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?

#### MrChips

Joined Oct 2, 2009
24,192
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).

#### joeyd999

Joined Jun 6, 2011
4,477
There is no such thing as the DC value of a square wave. You can talk about the mean or average value.
Of course, if you look at it in the frequency domain, you could say it has a 'DC component'.

#### MrChips

Joined Oct 2, 2009
24,192
Yes, I did think of that afterwards.

#### Wendy

Joined Mar 24, 2008
22,546