Kevin Weddle

A 555 timer is a simple circuit that includes voltage divider resistors, two opamp comparators, a transistor, and a flipflop or SR latch. The disadvantage of this circuit is the extra components that are not used in some applications. I am not sure what particular function involves the use of all these devices. Anybody know?

I underatand what you are saying, but a FET gives you the same result. A change in voltage divided by the change in current gives you the impedance. The question is , how much change in voltage will give you the change in current. With a FET, it's dependent on the gm. Maybe the gm could be any value, but I bet the gm is always high because of the biasing. This means a small change in voltage will give you a large change in current. A small gm would be ideal. Just like a reduced beta would be ideal. But a reduced beta is found with high current transistors which makes the two base resistors even lower.

EMI can be generated when an inductor comes into close contact with another inductor. I have always suspected that for this reason a coil can't be located too close to a capacitors plates. I think I have even seen where this is a problem, but I'm not certain.

Can anybody see the problem with analyzing this circuit. There is a peculiarity that exists. The first ciruit. What makes the output of the first inverter go low when it's high? I think it may be the high to low transition of the second inverter. This means the low has to go through D1 and the resistor. Which is okay, but doesn't the resistor value need to be on the low end. I have seen another peculiarity in another oscillator circuit. The transistion causes the input to change opposite of the transition because the capacitor passes the signal caused by the transition.

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Any collector resistor contributes to gain. Most of the time, the capacitor will contribute to voltage reduction instead of gain because the parallel elements make the capacitor independent of gain. When you go to the series circuit, you can't make anything independent so you are left with voltage reduction.

I would just stick it into a beta tester but I don't think it work. You know that it will be a function that has linear properties.

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Could someone explain this circuit in terms of the overall design. Why do they use a low current source and a high current sink? Why do they use the totem pole, which has an emitter follower and a common emitter. The idea I have is that logic is designed to handle the 0 to 5volts. This is a good voltage spread. The second idea is that the gain must be high to give a good transition. So what is the intention of the overall design?

I would be talking about diacs or triacs when I say a 5 layer device. The anode of the zener would be the base. The anode of the diode would be the base. The cathode of the zener would be the collector and the cathode of the diode would be the emitter.

Pulse width modulation involves a capacitor and associated logic. When logic is applied, the capacitor is allowed to charge at one rate. When logic is applied, the capacitor is allowed to discharge at one rate. I suppose you could use a 555 timer, but isn't there an even simpler circuit if someone could post it.

I don' know. Do you have the idea that this will work to a certain extent. It becomes a little tricky when you get away from the transistor model, add a 5 layer device it's even more complicated. Maybe as far as the hfe goes, it would depend on the zener conducting heavily with a small change in base voltage. The diode would have to conduct heavily too or else the base current would be too high. You need current to flow from collector to emitter.

The high impedance, but able to pass the signal. You will find that the two base resistors have to be low value in order to get the base current. This makes the emitter impedance low. I needed a higher impedance for the purpose of gain.

You know that when they post a circuit with a constant current source they don't mean the inclusion of an opamp. I tend to think that the opamp configuration for a constant current source is there as an example of how one could do it if the current you need is high enough. A circuit diagram with a constant current source is probably just a transistor with a constant base voltage set up to source.

The reason I thought of this is because I wanted to operate a transistor backwords in a circuit. I wanted the collector to act like an emitter. The nice thing about the collector is high impedance. The nice thing about the emitter is the ability to change the current and pass the signal. You will find that the emitter impedance is typically low because the base current. In other words the two resistors at the base are of small value because the base get's it's current through these two resistors. As far as the characteristics, I would guess the zener would have to conduct quite a bit when the voltage at the base changes. The zener, under normal conditions, conducts more when the voltage across it exceeds the rated voltage.

I think it could be used to replace the transistor in some cases. The transistor will not change it's current with a changing collector voltage, but maybe a zener with a diode will. This is certainly a legitmate use that may act similarly to a transistor if the zener and diode were chosen properly. I have no doubt that there exists a circuit which has this combination. The question is, how well will it mimick the transistor. Does anybody follow this assertaion?

The amperage part is going to be difficult to know. Just guess by the size of the transformer. It's interesting how high the current can be. The rated amperage is the average current and not the peak current. You will notice that a fuse is very small for the rated current, this is because it deals with peak current.

A square wave applied to a transistor with a capacitor to ground on the collector will produce a charge ramp as well as a discharge ramp.

I like the representation of a transistor that would use a zener and a diode. This seems more suitable. Does anybody like this idea?

The capacitor filters the wave, thus changing it. The peak of the input allows for DC charging of the capacitor, then input voltage drops and you are left with the DC charge that will not drop because of the rate of change. What I had in mind is a full wave rectified sine wave whose average is less than what is produced after filtering.

http://www.ee.washington.edu/stores/DataSheets/74ls/74ls04.pdf

Keep in mind that the capacitors have a specific impedance and could be replaced for resistors at the frequency you want to keep. They look like they attenuate the lower frequencies. Look at the high gain of T3. It's amazing that this is typically done with IC's when we know how unstable it is to not have emitter bias. To answer your question about the gain and the capacitors. The gain and reduction of the signal tends to act against each other, but one will overcome the other with a net result. I would say that the capacitors contribute to voltage reduction while playing a smaller part in gain.

It does not give you the average. It gives you the peak of the voltage with ripple, which can be used for determining the average. The ripple contains the information about what happened to the filtered part. For instance, a reduced ripple would indicate a greater average.

The first thing you should do is determine the exact amount of current you will need. Use a transistor with double this current. Make a regulator with feedback. This involves a reasonable amount of circuit design. I would use a low current transistor whose emitter goes to the base of the high current transistor and whose collector shares the same input voltage. This is a darlington arrangement which allows a small current change to control the large current of the high current transistor. The input to the low current transistor is the control. You could use a transistor whose collector goes to the control and shares the same input voltage but with resistors so that that it's collector voltage will be able to change. Do you understand so far?

It is my opinion that we should find a way to measure waveforms without relying on an A/D process. You have to remember that even an unknown waveform can be electronically deciphered using a circuit. For instance, a full wave rectified sine wave can be filtered to give you a ripple which can be used to determine the average. How could one determine the average using the ripple?