Kevin Weddle

How much change in transistor current should there be for best signal quality? I'm using a 741 opamp input 100mVpp. I think it's DC biased at 100nA. Should I use a smaller input signal or is 100mVpp a good size?

Are photodiodes really diodes? The architecture is different and light is such a weak source of power. Photocouplers are integrated into a single device so that the light source is right next to the light receiver which can be a photodiode or phototransistor.

In all circumstances an AC to DC power supply is better than a battery? What about a battery with a voltage regulator?

[quote A Butterworth 2nd-order (two poles) active lowpass filter uses positive feedback to boost the cutoff frequency so it is down only -3dB and so that the respose is flat to about 1/4 the cutoff frequency.

Does anybody have an explaination as to why the 5th harmonic in the 120Vac 60 Hz home outlet is so high? And is a battery voltage supply better than a conventional AC to DC power supply?

That amount of distortion must be due to the large output voltage swing. An opamp circuit is also capable of high distortion, but has very low distortion when operated within it's recommended but very narrow limits. Many amplfiers share some common design, but they are tailored for different applications. I've seen designs which utilize single transistor amplifers cascaded together. But I think their main purpose was for filtering and not so much for amplification.

Since an LC filter can only produce 40db/decade attenuation, it can be replaced with a two pole RC or LC filter. A simple low pass filter will always attenuate a higher frequency. A tuned filter might attenuate a higher or lower frequency within the fundamental frequency bandwidth depending on conditions. Resonance is often avoided in circuit design, but is also chosen to reduce signal loss.

A simple resistor and transistor signal amplifier produces maybe a gain of 50 or 100. An opamp provides high gain, high input impedance, and lower output impedance given the design. A single transistor with good voltage regulation has to be advantageous.

An active filter doesn't require positive feedback. Designing simple LR filters and RC filters in a cascade arrangement along with amplifiers might create less harmonics and varying harmonic frequencies.

I don't believe that the design of an opamp provides for that low of distortion. But it might. Maybe two or three transistors would not provide the gain, impedance, or current capabilities, but it should produce better results because of simplicity.

Some active filters are designed at resonance and some are not. It would seem that resonace would cause more problems in circuits. Doesn't a high pass filter followed by a low pass filter and an amplifier produce the same result without the added harmonics?

Loading of a device means lowering the resistance of the load. But if the transistor circuit is designed with low value resistors, then a medium resistor load will not affect it much.

Analog IC's vary in design depending on their function. Different IC's can be used in circuits and provide the same function. You might use a simpler transistor circuit over an opamp for example. Although it's easier to just connect complicated IC's together, it still guess work.

For instance, two different IC amplifers that produce the same result, but have different specifications that overlap. Using a more modern opamp would have lower noise, but operating it near the end of it's specification creates more distortion. Frequency response is the only indicator of performance near the end of a devices specifications.

So the filtering of a 120vac power supply doesn't benefit by resonant filtering?

The saturation voltage increases unless the base current increases? What about transistor transfer charcteristics? I've read that FET'S have different transfer characteristics than bipolar transisitors.

Are power supplies designed at resonant frequency? I've used many that weren't and I've never seen the circuits that show it.

IC devices have a low amount of noise according to data sheets. But is it a good indicator of signal distortion? Transfer characteristics show to be different depending on the transistor. So does this mean that transfer charateristics are negligible, even though they do operate on small areas of the transfer curve?

An opamp at the function generator ouput will provide high impedance during switching. The PWM device can be used to control the opamp output.

Are ferrite core transfomers used for power supply applications? Have you ever made a transformer? I have seen ferrite core inductors that provide a high value of inductance, and iron core transformers used for power supplies.

Also, power supplies that are not integrated into a single product are somewhat general purpose. Whether they waste too much power is not as important as their purpose.

So there isn't really much difference between using a MOSFET and a bipolar transistor. That is what I expected, however a good design needs to utilize one or the other based on component charateristics and circuit requirements.

A biploar transistor OR gate uses an input transistor with two emiiters. I have never seen these used elsewhere and am surprised to see it used for OR gate design. Are unusual devices not seen so much because of cost, availability, or design difficulty?

Designing circuits for reliability is different than designing circuits for performance. But your saying that all it takes is staying within component specification. If I need to power a 100W load, then it's fine to use a device that's rated to deliver 105W?

When building a circuit from initial design, a lot of components fail prematurely. Is it due to electrically stressing the components temporarily, or powering the circuit on and off? Most commercially bought products are rigorously tested, but I have some simply designed circuits that would probably fail rigorous testing. Are circuits designed around reliability problems like these?