Digital Oscilloscope
How do I test the efficiency of a Class A Amplifier circuit?
I need help. I have built a circuit that was already designed and now I have to test it for a class. I can calculate the efficiency, but now I have to demonstrate how to test it using a digital multimeter, an oscilloscope, and a frequency generator. I have no idea how to use the equipment. If someone could fill me in I would greatly appreciate it =]
Testing it for efficiency to determine the class is possible using the maximum undistorted power. Basics: Use the frequency generator to make a sine wave test signal. Connect a load resistor (for example 8 ohms) to the amplifier output, and connect the oscilloscope across this resistor. Drive the amplifier until the sine wave becomes slighly distorted (clipped at the peaks). Determine the maximum power output as just before that occurs. Measure the voltage using the oscilloscope (or a multimeter). Determine the RMS voltage (.707/2 of the peak to peak voltage determined by the oscilloscope). Calculate the output power across the resistor as V*V/R. Now use the multimeter to measure the voltage and the current drawn by the amplifier at maximum output and determine the power supplied (usually to the power output stage only). That is V * I. Determine the ratio of the output power to the power supplied, which is the efficiency as a percentage. Use the efficiency to determine the class. A class A will be something like 40%, a class B something like 70%, a class D perhaps 90% and so on. Look them up. One other point is that the amplifier may overheat, so use a fan if that helps, and keep the time running at maximum power to a minimum, allowing time to cool down between tests.
Personal Digital Oscilloscope APS230
