Calculating Power Output with PWM and 1ohm Load

In summary, the conversation discusses using PWM for power calculations and the importance of taking an RMS average. The speaker explains that using a 50% duty cycle does not result in half the power output due to the averaging of current and voltage. The correct method is to use an RMS average for accurate results. The speaker also clarifies that RMS is not only used for sine waves but for any arbitrary function. The conversation ends with gratitude for the helpful explanations.
  • #1
GlynnHeeswijk
20
1
Hi
I have a question to do with using PWM
If for example I had a 1ohm load and a voltage supply of 4JC-1, I would get a power draw of 16JS-1, now if I had a duty cycle of say 50% I should get an average power output of 8JS-1. However if i thought of it as having an average current of 2CS-1 and a average voltage of 2JC-1 then the power output comes out to be 4JS-1, which is 4 times less and not half. If it should be the half what does the actual voltage and current average out to?

Thank you very much.
 
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  • #2
(4V)^2/1 Ohm = 16W continuous = 4A * 4V

50% duty cycle

8W = 4A * 4V * 0.5

You can't average both the current and voltage, without taking an RMS average. RMS averages give you the right answer -- can you see why?
 
  • #3
I can see that it does seem work. However I thought that RMS using route 2 was for sine waves? Am i missing something?

Thank you
 
  • #4
GlynnHeeswijk said:
I can see that it does seem work. However I thought that RMS using route 2 was for sine waves? Am i missing something?

Thank you

No, it's used quite generally for power calculations. You can calculate the RMS value of an arbitrary function:

http://en.wikipedia.org/wiki/Root_mean_square

.
 
  • #5
Be sure to keep in mind that .707 * Vpeak is the RMS equivalent for sine waves only. But real actual RMS doesn't care what the waveform is.
 
  • #6
Thank you both very much for your help. I understand it a lot better now.
 

1. How do I calculate the power output with PWM and 1ohm load?

The power output can be calculated using the formula P = V^2/R, where V is the voltage and R is the resistance. In this case, the voltage is determined by the PWM duty cycle and the input voltage, and the resistance is 1ohm. So, the power output can be calculated by substituting the values into the formula.

2. What is the importance of calculating power output with PWM and 1ohm load?

Calculating power output is important because it helps determine the efficiency and performance of a circuit. It also allows for proper sizing of components and can help identify any potential issues or limitations.

3. Can the power output be increased by using a different load instead of 1ohm?

Yes, the power output can be increased by using a different load with a lower resistance. This is because a lower resistance allows for more current to flow, resulting in a higher power output.

4. How does PWM affect the power output?

PWM (Pulse Width Modulation) is a method of controlling the average power delivered to a load by quickly switching a power source on and off. The duty cycle of the PWM signal determines the amount of time the power source is on, which in turn affects the average power output. A higher duty cycle results in a higher average power output.

5. Are there any limitations to using PWM for power output calculations?

There are a few limitations to keep in mind when using PWM for power output calculations. The accuracy of the calculated power output may be affected by factors such as the switching frequency and the load's response time. Additionally, PWM may not be suitable for high-power applications due to potential heat dissipation and other factors.

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