Kevin Weddle

Indulis, do commercial power supplies utilize switch mode? Most operate directly from the power outlet, and even the cheapest AC to DC adaptors are used to power laptop computers.

Saturated biploar transistors do have a lot of base current, but the power dissipation is the same as a MOSFET. A bipolar transistor can be put into cutoff or saturation by 1V. A MOSFET reguires a high VGS difference between saturation and cutoff, maybe 5V. But I know that biploar transistors require biasing resistors all of the time, where as the biasing for a MOSFET might save power depending on the biasing resistors. Is there a major guideline in choosing between a MOSFET and a biploar transistor for low frequency applications? And I've read that MOSFET linearity is better, or is it marginally better?

MOSFETS tend to have a high VGS requirement. I see them used a lot in power supplies. But the real benefits in using a MOSFET over a biploar junction transistor, although not immediately noticeable from a schematic, don't appear to be utilized. Might it be better not to use MOSFETS at all? Or are they just a good option because of availability?

I'm surpised at the results. I know that mismatching impedances can cause standing waves, and it may depend on where you probe on the transmission line. But I think there would still be enough signal loss, and it would seem hard to get that good of a measurement to make a comparison.

A pi filter can be used to match loads? Most impedance matching that I've seen match the source and load impedance. Although depending on the application, pi filters can play a role in impedance matching.

That transistor is also used to create the DC bias for the MOSFET. To bias the MOSFET with only a 555 timer creates a lower impedance and higher current for the 555 timer. It's common to buffer IC's with higher current transistor's with high current loads, and in this case the load is the MOSFET biasing.

I'm not good with battery technology, but small batteries that are contantly being used might benefit from an intelligent recharging system. Slow charging, I've always heard, is more desireable than fast charging.

Simple circuits such as the 555 IC are still being used. Microprocessors use a variety of simple circuits so as not to introduce unnecessary problems. So why do so many electronics products have so many components?

A diode in parallel with an inductor, like many protection diodes, prevents adverse voltages generated from the inductor from shortening the life of the connected devices.

One MOSFET is a better idea. Puting MOSFETS in parallel that all do the same thing only serves one good purpose and might be marginally beneficial. Replacing the transistor with one that is not designed for may work if it's close.

My mistake audioguru, I misread the posting.

Is it somewhere in between a 0 volt power supply and a 30V power supply? You need to be more specific on the voltage requirements of the circuit. Your talking about designing a very expensive power supply. I would use a variable voltage regulator for most applications. If you have a general power supply, you can add variable voltage regulators to get the voltage you need.

I don't see how the term "negative feedback" can be applied to an emitter resistor.

I've seen some circuits that use a capacitor in parallel with an emitter resistor. The RC time constant needs to be short compared to the period of the input, or signal distortion will occur. Is this a real consideration of circuit design, or does it not really matter in most circumstaces?

You might try using negative feedback instead of positive feedback if you don't need that high of gain. Opamps can latch up and the switch point voltages can be hard to control. Even at a low gain, getting the bias you want is sometimes difficult.

C7 also prevents DC loading of the amplfier and doesn't affect the impedance. It might be added to help prevent high frequency oscillation, and it may allow for a more constant impedance between the high and low frequencies.

Power inverters, which are sold in stores, are more reliable and won't damage the mixer. You might want to have the circuit designed and funtioning before testing it out on the mixer.

An LC filter uses larger value components than what is concerned with impedance matching. It would be the main filtering section and the impedance matching done to help eliminate problems caused by a transmission line or requirements of the devices connected to it.

An inductor can produce a different result depending on the waveform you apply to it. Sometimes waveforms are not constant and may have periods of DC, AC, or pulsating DC. A diode in parallel with an inductor is sometimes used.

It might depend on the the size of the battery. I'm not familiar with a microcontroller based battery charger, but it sounds complicated. I think the concept is very good. But even battery chargers you buy from a store I doubt use microcontrollers. Probably because the cost/benefit does't isn't good.

The rise time is proportional to the time of the square wave and is made by amplifying the sinewave using high gain. So it's dependent on gain and the time of the sine wave. However, the time of the square wave is the biggest factor when comparing the rise time of let's say a 1KHz square wave to a 1MHz square wave. And I believe overshoot, undershoot, and ringing are caused by resonance.

According to your post, you added internal resistance to the 1Kohm for 1900ohm. But you said if it's less than 10K you subtract internal resistance. It's not subtracted.

Interesting point, if less than 10Kohm subtract the internal resistance. The impedance does look too low for MOS. But nothing I design lasts more than 3 hours, so it looks like a plausable design to me.

Maybe the resistor value in the RC common network is a factor. If someone uses 47Kohm and 100nF for the RC, then uses a 1Kohm resistor in the RC common network, then the time constant will be affected. So a small resistor like 10 Ohms might be more accurate if you used a 47Kohm and 100nF.

A strong base signal could be developed at the base, bringing the base in phase with the emitter, which is the case of a common emitter or common collector.