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Ground/earth problems in power amplifier

 
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PostPosted: Mon Feb 07, 2011 11:37 am    Post subject: Ground/earth problems in power amplifier Reply with quote

HI
I have built a prototype high power amplifier and it works fine. I need to put it in a suitable case. My problem is the following:
1. The power ground is the same as the input ground. Is that ok or should I separeate them?
2. should I connect the power ground to the chasis and consider it as earth? of course this earth will be connected to the mains earth?
3. I used some protections against dc output and short circuit. Is any other protection required?
4. Any reference for safety and protection of high power amplifiers?

Regards
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Wed Feb 16, 2011 2:15 pm    Post subject: Reply with quote

1. That depends on what kind of high power amplifier you have built and what its purpose is (i. e. audio amplifier for home use, audio amplifier for large PA systems, DC amplifier for servo systems, RF amplifier etc). If common practice for that kind of amplifiers is to connect all grounds together, then do so. Otherwise, it might be better to make some kind of separation of the input (transformer, isolation amplifier etc).

2. Check with the ordinances and laws regarding electrical safety that are in force where you live. There are different requirements for protective earthing in different parts of the world. If you have built the power supply according to "Class II" (reinforced/double insulation), then the unit should not be connected to protective earth.

3. Possibly. If you use fuses for short circuit protection, you should verify that the short circuit current is enough to blow the fuses within 2 seconds. Otherwise, that depends on what your goal with the protection is. If you only want to safeguard against fire, you can get away with a less elaborate protection than if you want to be sure that a fault within the amplifier or an overload condition cannot cause consequential damage to the amplifier or load. I think it is also prudent to make sure that the input is immune to overvoltages or overcurrents due to varying ground potentials. In case of an audio or DC amplifier with mosfet transistors in the output stage, make sure that it cannot go into latch-up due to transient voltages induced in the load or output cabling. Also, remember RF immunity.

4. I recommend a study of application notes - particularly older ones - from the large semiconductor manufacturers. Also, some IEC standards - for instance the IEC 60950.
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Flash1940



Joined: 26 May 2011
Posts: 3
Location: Paris, Kentucky

PostPosted: Thu May 26, 2011 6:57 pm    Post subject: Reply with quote

If there's a power transformer connected to the 120V line.....you should use a three-line cord to supply the power to the primary of the transformer. The green wire of the cord will be connected to the metal chasis of your amp. The black wire in the cord is considered "hot" and should be fused just as the wire enters the equipment.....the other side of the fuse will go to one side of your off-on switch....then to one side of the primary of your transformer. The cord's white wire will connect directly to the other side of the primary of your transformer. WARNING **** if your amplifier is line operated and has no power transformer.....stop right there.....you have a potentially lethal piece of equipment.....do not take it out in public where someone may get hurt and end up taking you to court !
Remember......safety it a top priority.

Flash
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torbjorn



Joined: 07 Jun 2007
Posts: 370
Location: Sweden

PostPosted: Fri May 27, 2011 8:40 am    Post subject: Reply with quote

Please note that those wiring colors (green for protective eart, black for phase, white for neutral) only are used in old cabling in the USA. Current IEC standards, which are mandatory in most countries and now are accepted also in the USA, prescribe green/yellow for protective earth, brown (formerly also black) for phase and blue for neutral.

Most countries require that the mains switch of homebuilt equipment should be a two-pole switch, as the most common wall outlets are not polarized so you can never be sure which conductor is phase or neutral. Also, some countries (i. e. Norway and some utilities in Spain) have so-called IT power systems where the neutral is not available but the wall outlets connected between two phases.
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