Kevin Weddle Posted March 24, 2005 Report Share Posted March 24, 2005 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. Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 24, 2005 Report Share Posted March 24, 2005 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". Quote Link to comment Share on other sites More sharing options...
autir Posted August 31, 2005 Author Report Share Posted August 31, 2005 Hi Autir,This topic is never dead! Quote Link to comment Share on other sites More sharing options...
autir Posted September 3, 2005 Author Report Share Posted September 3, 2005 Guys? ::) Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 4, 2005 Report Share Posted September 4, 2005 The power transformer isolates your LM78xx and LM79xx circuit from the ground of your mains power socket. Same for a rectifier bridge.-> If we use a center-tapped / linear transformer and rectify it with two diodes etc., the output's neutral cable will be at the same voltage with the mains' ground. Guaranteed. Correct?No. The transformer isolates the circuit ground from the mains ground.-> If we use a non-linear (two output cables) non-center tapped transformer and a four-diode bridge, will the output's neutral cable be at the same voltage with the main's ground? I have build a similar circuit and measured it to be so.No. The transformer isolates the circuit ground from the mains ground.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.What do you mean "correctly"? How can I determine whether my mains power socket is wired properly?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.The external ground you mentioned should be somehow connected to the mains? Or could it be, e.g. a big metal box?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.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.Can I bypass neutral and use ground everywhere?No. You need live, neutral and ground wires at every mains power socket.The neutral and ground are connected together at the fuse/breaker panel.How? Example?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. Quote Link to comment Share on other sites More sharing options...
autir Posted September 4, 2005 Author Report Share Posted September 4, 2005 Thank you for your answers. :) Quote Link to comment Share on other sites More sharing options...
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