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Kevin Weddle
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Posts posted by Kevin Weddle
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Why do voltage regulators require zener diodes? Can't circuits not use them? They can't be very effective with a low impedance load.
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But shouldn't loss, as in the way of resistors be avoided. Of course discrete component circuits use them, but isn't it because of the necessity to complete the design. It's a way of interfacing circuit sections and is a concession in a design.
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230 Vac is very high voltage to charge 12V batteries. Commercial 12V battery charges use 120 Vac and have designs that are too difficult to be redesigned. You might take a 12V battery and create a circuit to charge a 9V battery, so you will know what basic circuits will be required.
You could use simple 230 Vac to 12VDC converters and simple logic devices, but the batteries might overheat, and not last as long without a good charging circuit. -
Lower frequency op-amps are more stable than high frequency op-amps and are cheaper too.
Low frequency opamps are more suitable for low frequencies than high frequency opamps? I'm not so sure because opamps have a bandwidth that extends to 0Hz. A high frequency opamp would maybe incorporate newer technology bipolar transistors, and maybe extra transistor amplifier stages to make up for loss. -
Do IC's employ any passive circuits to reduce base collector capacitance? Why don't all high frequency circuits use base collector capacitance neutralization?
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Inductors produce a magnetic field, just like a magnet. I imagine magnetic based generators are still being used because of their advantages.
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What diode couldn't you use in a DC to DC converter? Designs are mainly based on operating charactersitics. Most common diodes switch fast for many circuits, including DC to DC converters.
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A fast switching diode might not be necessary for a DC to DC power supply. Schotkey diodes have a P region that is just metal, don't quote me. But the diodes you want have the voltage and current specifications that are just adequate. Using high current diodes, or low current diodes at their maximum rating, is not efficient.
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A transistor constant-current-source (or sink) and a transistor current mirror work better and use a very small amount of space.
Nothing I've read describes the drawbacks of not operating transistors under normal biasing conditions. Such as turning a transistor on and off is not the same as a transistor operated linearly. Using transistors to control gain by creating impedance seems not to be good design, although IC's do it all the time. Maybe better circuits would not use an IC, except for it's advantages due to the manufacturing.
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Do low frequency opamps have any advantage over high frequency opamps?
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I was thinking I should have asked that no one give him any hints or the answer -
The max p-p output above 9kHz for a 741 opamp is reduced in level as shown on a graph in its datasheet because its output cannot slew (ramp) fast enough.
I was thinking the loss was due to voltage loss at the base emitter junctions because of capacitance. And that the slew rate specification guarantees low signal distortion. -
Hero99, the post is about roll-off. A 20db/decade roll-off of an opamp approaches the limitation of the device. You extend the bandwidth of an opamp by reducing gain.
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A capcitor fe
And that is why operating the opamp at 100Khz doesn't matter. The external capacitors dictate a 20db/decade roll off. But what if you don't have external capacitors. Operating the opamp beyond the bandwidth doesn't make more distortion?
Hero99 said operating the 741 opamp on a 20db/decade curve is a good idea. I agree. It is only a general purpose device. -
Sine-waves and square-waves become triangle-waves.
above the slew-rate frequency limit the ramps reduce the max output level.
A triangle wave? A sinewave becomes a triangle wave exceeding the slew rate? Any high frequency approaching the slew rate is too high. Slew rate is a characteristic of the performance of the device. It's the same as device frequency limitation. -
I don't understand slew rate. It is a fuction of voltage and time. Better opamps have great slew rates.
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And that is why operating the opamp at 100Khz doesn't matter. The external capacitors dictate a 20db/decade roll off. But what if you don't have external capacitors. Operating the opamp beyond the bandwidth doesn't make more distortion?
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Many integrated cirucuits have either no resistors or a few low value ones. So how much do they offer to designs?
And many IC's have a wide range of operation. Would a small IC, like a voltage regulator, use many different types of transisotrs? -
Inductors have a self resonant frequency because of the winding capacitance. I'm not sure why the self resonant frequency is avoided, but it may be because the winding capacitance is equal to a poorly constructed capacitor.
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You couldn't be right or wrong, either way it's not an acceptable design because the slew rate limits the output voltage to an unacceptably low level at 100kHz, increasing the frequency only makes things worse.
The amplifier circuit should be correctly designed so the gain is reduced using negative feedback rather than the frequency roll-off which is unpredictable.
Filter circuits attenuate the same as an opamp would above it's bandwidth. It's not recommended to allow the opamp to reach it's 40db/decade attenuation because it might oscillate. I'm wanting to know if the distortion is more appreciable above the opamps bandwidth with the attenuation at 20db/decade. In which case two opamps cascaded might be better. -
Is loss in amplifiers any indication of design? Could you design a good amplifier with a lot of loss? A resistor causes loss, but no distortion. Many times I have had to reduce a signal after amplifying it. Is this a design problem?
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Most designs can't account for the linearity difference between bipolar transistors and MOSFETS. But very large designs suffer from linearity problems, component manufacturing, design etc.
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Is utilizing opamp roll-off a good idea? A 741 opamp has a gain of 100 at 100KHz, and the output is stable. External filtering components are most often used, so is opamp roll-off avoided? If I set the gain at 1000 and use a higher frequency to bring the gain to 500, would that be acceptable design?
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The problem with high current inductors is that their XL/R is always inherently low. So the frequency needs to be very high to get good resonant filtering. A series of three inductors would probably still be inadequate. A typical AC to DC power supply doesn't have resonance, and has better perfomance.
Can you give more detail as to the high current and resonance in the DC to DC converter.
zener diodes
in Theory articles
Posted
How would a zener diode be used in a high voltage regulator. Besides not being used to regulate the output, it would only be used in biasing the circuit. Most circuits don't use them much for biasing.