EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: SArepairman on April 14, 2014, 06:54:59 am
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http://www.zen22142.zen.co.uk/Circuits/Power/gyrator.htm (http://www.zen22142.zen.co.uk/Circuits/Power/gyrator.htm)
So I am fascinated by gyrators and capacitance multipliers lately and I found that. It is a neat trick to use a power resistor with a capacitance multiplier.
Has anyone actually seen this used in a product or is it a electronics parlor trick? How about using it with a big capacitor, like the 10000uF beast I have sitting around? Or paralleling them?
I figured this would be used more often... then again power transistors might be just as expensive as power capacitors.
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gyrators are used inside integrated circuits, as creating capacitors is somewhat easier than creating an inductor. The real world application of this circuit is almost 0, as they don't behave good. The main application of gyrators is to mess with EE students.
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gyrators are used inside integrated circuits, as creating capacitors is somewhat easier than creating an inductor. The real world application of this circuit is almost 0, as they don't behave good. The main application of gyrators is to mess with EE students.
indeed I was touched by a gyrator in school. I only have appreciation for them now when the nightmare of tests is over.
years ago I would have never opened this thread, because it said gyrator (and that means D+ at best!)
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I have heard of capacitance multipliers being used in class A audio amplifiers where you want to filter out the 120 Hz ripple but you can't tolerate the worst case power dissipation of a true regulator. In principle I think it could be used for a lot of applications where you needed good filtering of noise but didn't care about the DC value. However, these days I expect that most of those applications are just as well served by a DC-DC converter followed by a LDO.
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Hi,
i just found this and want to share my experiences with capacitance multipliers.
I tend to use them more and more in tube microphone preamplifiers where i want psu to function for a long time. As this is are not true regulators, voltage changes a little bit with input signal, but this is not a problem at all with 100-300V which are normally used to power small signal tubes. Slow start might be advantage here, although i never found need for it. The best part in my opinion is low cost and very little heat. I use 5W zeners to clamp the voltage, bypassed by something like 10u film cap, this goes into base of HV transistor like TIP50. Some people suggest 100u lytics for first filering cap, base and output cap. But i found out i can get away with less than 1mVp-p with 100u filtering cap (LL Epcos for very long life) and cheap 10u polypropylene caps into base and output.
Schematic looks more or less like this:
http://www.electronicsinfoline.com/Projects/Electronics/Audio_Project/Audio_Amplifier/regulated_vacuum_tube_power_supply.shtml (http://www.electronicsinfoline.com/Projects/Electronics/Audio_Project/Audio_Amplifier/regulated_vacuum_tube_power_supply.shtml)
At 300V and 20mA it gets barely warm, so there is no need for heatsinks and Epcos's datasheet shows very, very long life at this condition. I'm not sure if lytic would corrode in this time rather than dry, 7 years old psu like this (i used 150u, 33u, 33u and 33u lytics instead of lytic and two films) is still going strong.
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The circuit shown by the OP is a voltage regulator that basically just clips to the lowest output voltage from the rectifier. It will track the input voltage and is mostly used for reducing hum on an amplifier rail where the variation of voltage with power output is not going to worry you, but the hum will ( so any amplifier with poor PSRR in this case) and you do not want to have a proper regulated rail. It will dissipate slightly less power as the voltage drop will be lower across it than if you use a regulator, but in most cases a regulator is better.
At first thought I was thinking of a typical gyrator that replaces an inductor with a capacitor and an opamp.
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I used a slightly modified version of this to eliminate the need for a large capacitor in safety system on a satellite power supply I built a few year back. Basically the ideal circuit was a 500mF cap in series with a load that had to operate at 36V, but since a cap the a large would be incredibly expensive and take up a large volume I used this trick and was able to replace it with a 10uF cap.
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This circuit could be used the next time one of us wants to build a bench power supply:
1) The output has a slow start, eliminating switch on transients
2) No need to buy a large capacitor to put across the bridge rectifier
Nice!