I have read that electrolytic capacitors age within 3 to 30 years, depending on quality. After that they gradually dry out; their capacitance is reduced and their resistance is increased, making them useless. Can't we substitute electrolytic caps with something else if we want a long-lasting circuit?
Forgive me for raising this topic from the dead... :-\
What is the voltage difference between the Ground pin of the LM and the ground of the power socket on my wall?
What is the voltage difference between the ground output of bridge-rectified AC and the ground of the power socket on my wall?
What is the difference between Neutral and Ground? (generally speaking, not related to LMs)
Thank you very much.
What is the voltage difference between the Ground pin of the LM and the ground of the power socket on my wall?
What is the voltage difference between the ground output of bridge-rectified AC and the ground of the power socket on my wall?
What is the difference between Neutral and Ground? (generally speaking, not related to LMs)
Thank you very much.
audioguru2
- Apr 6, 2004
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Hi Autir,
This topic is never dead! ;D
The power transformer isolates your LM78xx and LM79xx circuit from the ground of your mains power socket. Same for a rectifier bridge.
With the isolating transformer, the circuits have their ground terminal grounded if you wire the circuit ground to the ground wire of the mains power plug, and the mains power socket is wired correctly. Or if you wire the circuit ground to an external ground. Or if the circuit is grounded through cables that connect it to something that is grounded.
The live and neutral wires supply power to the load. The ground wire is for safety so that metal enclosures are grounded and cause a fuse or breaker to blow if the live wire shorts to the enclosure.
The neutral and ground are connected together at the fuse/breaker panel.
This topic is never dead! ;D
The power transformer isolates your LM78xx and LM79xx circuit from the ground of your mains power socket. Same for a rectifier bridge.
With the isolating transformer, the circuits have their ground terminal grounded if you wire the circuit ground to the ground wire of the mains power plug, and the mains power socket is wired correctly. Or if you wire the circuit ground to an external ground. Or if the circuit is grounded through cables that connect it to something that is grounded.
The live and neutral wires supply power to the load. The ground wire is for safety so that metal enclosures are grounded and cause a fuse or breaker to blow if the live wire shorts to the enclosure.
The neutral and ground are connected together at the fuse/breaker panel.
Kevin Weddle
- Feb 23, 2004
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I believe the capacitor on the output is simply a low pass filter. It always help to filter a little bit on the output of a regulator because the signal it is regulating against is present at the output circuit of the regulator. Therefore it is like the frequency already exists in circuit. But we can low pass filter and remove that rate of change a little. Too much filtering and the rate of change of output of the regulator does not produce enough error voltage and the regulator does not regulate. So you need the signal there in order for the output of the regulator to correct the voltage.
audioguru2
- Apr 6, 2004
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No Kevin,
The datasheets say that the regulator's output capacitor is used to improve its transient response.
1) If a load is suddenly applied to a regulator, its output voltage would drop suddenly because its high-gain amplifier is slow to react. The output capacitor supplies current to the load until the regulator catches-up. The opposite happens when a regulator's load is suddenly removed.
2) The same quick output voltage spikes occur in a regulator circuit without a small output cap if the regulator's input voltage suddenly drops or rises.
The sudden voltage drop and rise of the regulator's output are short-duration high frequency spikes without a small output capacitor.
The slow reaction time of a regulator shows that it is poor at smoothing high frequency variations in load current or input voltage. A small output capacitor smooths the high frequencies.
The datasheets state and show that too much output filtering of a regulator doesn't make much difference and is a waste of capacitance. The regulator has such a high gain that its output impedance is much lower than a huge capacitor and therefore regulates just as well with or without it. They say that a ceramic disc output capacitor of 0.1uF is fine but that "values more than 10uF will merely improve the loop stability".
The datasheets say that the regulator's output capacitor is used to improve its transient response.
1) If a load is suddenly applied to a regulator, its output voltage would drop suddenly because its high-gain amplifier is slow to react. The output capacitor supplies current to the load until the regulator catches-up. The opposite happens when a regulator's load is suddenly removed.
2) The same quick output voltage spikes occur in a regulator circuit without a small output cap if the regulator's input voltage suddenly drops or rises.
The sudden voltage drop and rise of the regulator's output are short-duration high frequency spikes without a small output capacitor.
The slow reaction time of a regulator shows that it is poor at smoothing high frequency variations in load current or input voltage. A small output capacitor smooths the high frequencies.
The datasheets state and show that too much output filtering of a regulator doesn't make much difference and is a waste of capacitance. The regulator has such a high gain that its output impedance is much lower than a huge capacitor and therefore regulates just as well with or without it. They say that a ceramic disc output capacitor of 0.1uF is fine but that "values more than 10uF will merely improve the loop stability".
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audioguru2
- Apr 6, 2004
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audioguru said:
No. The transformer isolates the circuit ground from the mains ground.
No. The transformer isolates the circuit ground from the mains ground.
If your mains power socket was wired by a drunk electrician, I wouldn't trust it to be wired correctly. Turn off the mains power, take off its cover and look at how it is wired.
My home's mains is connected to ground through a heavy wire connected to the cold water pipe entering my home. Mains in your counrty or in your home might be different.
No. You need live, neutral and ground wires at every mains power socket.
I think so. But I am not a certified electrician, and I didn't take apart my mains breaker box to look and see. Maybe they are joined at the transformer box down my street.
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