roofingboom said:
I don't know what you consider "simple" (simple is relative), but typically current sensing is done with a low Ohm resistor (milli-ohms) in series with a voltage. The voltage drop across the resistor is sensed across a comparator with a reference. When the current (read as voltage drop across the sense resistor) hits the comparator threshold, the comparator turns on. The comprator then removes power in some way, typically by opening a switch, such as a FET. You can build in a delay so that the unit can attempt to turn back on after some period of time, in this case apparently 20 seconds.
You always want some hysterisis on a comparator, or a short circuit condition would cause oscillation as the comparator ties to turn off and back on instantly.
Are you trying to design your own short circuit protection?
Hope this helps.
Cheers,
bg
yes i am trying to make my own short circuit protection
i had a problem yesterday i was playing music into an unrated speaker and it got too hot causing it to short internally causing my amp to short and poof the power transistors went up in flames
i am wondering what i can do to prevent this
maybe a starting schematic would be nice
i like your explanantion beer guy are there some links to some start schematics possibly?
nate
i had a problem yesterday i was playing music into an unrated speaker and it got too hot causing it to short internally causing my amp to short and poof the power transistors went up in flames
i am wondering what i can do to prevent this
maybe a starting schematic would be nice
i like your explanantion beer guy are there some links to some start schematics possibly?
nate
is a dc protection circuit the same thing as short circuit circuit? same thing different name?
the protection on my sony amp is really nice because it cuts out and trys to turn back on in like 20 secconds
this would save me tons of trouble since i just fried some output transistors due to speaker failure
any information schematics pointers for me would be very useful
thanks
nate
the protection on my sony amp is really nice because it cuts out and trys to turn back on in like 20 secconds
this would save me tons of trouble since i just fried some output transistors due to speaker failure
any information schematics pointers for me would be very useful
thanks
nate
Not really. When a short exists there is no dc across the speaker so a dc detector won't detect anything. You usually get dc when a power transistor fails and the dc ends up frying your speaker. In the case of a short circuit it is your speaker that fries your transistors.
I often use both a "fast" current limiter at the power-transistors themselves and a dc-detector that disconnects the speakers if the dc level exceeds +/- 0.7V. My primary concern is the speaker rather than the amp (new speakers are much more expensive than new transistors).
In theory, what you need to protect the amp is to measure the resistance of the speaker and then disconnect the speaker if it is too low. This can be done with many levels of sophistication. One question to ask yourself is how low can the speaker resistance be before the protection kicks in?
One method might be to put a current sensing resistor in series with the speaker, say between speaker and gnd. Then measure the ratio of voltage at amp output to that at the sensing resistor. If the ratio is too low then cut the speaker off using a relay.
Eg: sensing resitor is 0.5-ohms. Speaker resistance is 8-ohms. Both are in series so if the voltage between amp out and gnd is Vamp, then the voltage across the sense resistor will be Vr = Vamp x 0.5 / (8 + 0.5) = 0.06Vamp. Now, if the speaker is shorted the ratio will be 1. If the speaker is 1-ohm the ratio will be 0.3. You can make an op-amp circuit to measure the ratio and trigger a relay if it is too high.
Another thing you need is to make sure the transistors don't suffer damage while the protection circuit is turning off the relay. There will be a millisecond delay due to the mechanics. You need a fast circuit near each output transistor to limit the peak current to within the specs of the transistors during this delay. This is easy for MOSFETs (often just a zener across gate and source) but more complicated for bipolars (transistor and low-pass filter).
take a look at the protection circuit in the Leach Amp. The output current is sensed at the emitter resistors. Too much voltage and the protection transitors kick in and remove the drive signal. It seems to work well, although I don't think I get mine anywhere near the current limit.
If you don't like the idea of having the protection circuit potentially messing with the signal, use the same scheme to drive a relay with some sort of hold open delay. The transistor could also be used to feed some DC into your dc protection circuit and trip that.
If you don't like the idea of having the protection circuit potentially messing with the signal, use the same scheme to drive a relay with some sort of hold open delay. The transistor could also be used to feed some DC into your dc protection circuit and trip that.
Hi!
In the Sony there must be a thermal shut-down sensing the heat-sink temperature, it is activated after 20 mp, but there must be a current limiter too. The current limiter most of the time is like one in leach. If limiting point is set high enough then it won't iteract with normal signal, but the transistors must have enough dissipation capability. I found that the transistors dissipation rate must be twice as the power output to be safe in all circumstances. (Motorola found that too: they suggest the MJW1302 (Pd=200W) transistor for 100W amplifier.)
I don't speak English well, please correct me, if I write wrong!
Bye!
In the Sony there must be a thermal shut-down sensing the heat-sink temperature, it is activated after 20 mp, but there must be a current limiter too. The current limiter most of the time is like one in leach. If limiting point is set high enough then it won't iteract with normal signal, but the transistors must have enough dissipation capability. I found that the transistors dissipation rate must be twice as the power output to be safe in all circumstances. (Motorola found that too: they suggest the MJW1302 (Pd=200W) transistor for 100W amplifier.)
I don't speak English well, please correct me, if I write wrong!
Bye!
Stone age protection circuit.
Not joking, kidding or something bad!
I do this all the time.
Have a power ammeter.... short for half second or the small time you can an try to read the maximum current when shorted... this is the maximum transistor have to support if something failed.
Now increase your rectifing diodes to hold this shorted current. Put a lot of them in parallell, they will be happy with some companie...some friends together.
Now put transistor pairs, in a quantity that can hold this short... each rail may hold this short!....amplifier will work happy dividing energy to a lot of friends, all them with happy emitter resistors... can increase all emitters resistors values, because they will be in parallel related to audio flux.
And do you know how to test it... put maximum signal, damn distorted!.....open your bass entirely, give more bass, more treble, more mids, turn your volume all up, have sure you put it into the end.....switch amplifier of, to have transient when switch on, and ask God to switch on exactly when AC mains reach its maximum voltage moment, join the output wires..... better to change it to small length and heavy wires... have sure the short you done, both channels are zero ohm resistance.
Then switch on and hear transformer making sound... and feel electrons moving and overheating your unit... and count the time you need to perceive amplifier stop to work, when you are inside the shower, full of soap from up to down, not so big amount of water... the worst condition you can face... nobody at home to help you, house thermall switches too big to protect......and then.... this time will be the one you need to run fast to pull the plug out of outlet!... consider the time you need to dry your hands because you can turn into a barbecue.
And cut your protection inside amplifier.... this one was made to shorten price of unit.... and has damn contacts of relay.... remove this awfull thing and send it to trash!
What you think about one automobile that you put whole people inside.... all 5 passengers automobile, and go to a long an up hill, in a good road, but up hill is 50 degrees, and car heavy, and motor trying to keept on moving, rotation is diminishing, you nervous put you feet on clucth to have more rotations and controlling clutch tried to have better rotation.... and clutch start to smell..... and car moves.... you are going, Yeahhhh!... moving and motor melted!... do you really think this is fair! nobody told you that it melted when you need it hard!!!
why amplifiers, submited to extreme jobs have to switch of or melt?
I am trying to find my wife plug, to switch off this damn Spanish beauty. not kill her, i love her...but talk too much...but she is so pretty......
She talk too much! aaaagh!.... imagine a old disc, the one made of plastic, 33 rpm, now push its outlet plug, keeping amplifier on.... try to imagine the sound reducing frequency when turntable will reducing its speed... till the sound becames very bassy, and stop.... I want to do this with my wife....switch damn beauty off for some moments. where's the outlet!!!
Carlos
Not joking, kidding or something bad!
I do this all the time.
Have a power ammeter.... short for half second or the small time you can an try to read the maximum current when shorted... this is the maximum transistor have to support if something failed.
Now increase your rectifing diodes to hold this shorted current. Put a lot of them in parallell, they will be happy with some companie...some friends together.
Now put transistor pairs, in a quantity that can hold this short... each rail may hold this short!....amplifier will work happy dividing energy to a lot of friends, all them with happy emitter resistors... can increase all emitters resistors values, because they will be in parallel related to audio flux.
And do you know how to test it... put maximum signal, damn distorted!.....open your bass entirely, give more bass, more treble, more mids, turn your volume all up, have sure you put it into the end.....switch amplifier of, to have transient when switch on, and ask God to switch on exactly when AC mains reach its maximum voltage moment, join the output wires..... better to change it to small length and heavy wires... have sure the short you done, both channels are zero ohm resistance.
Then switch on and hear transformer making sound... and feel electrons moving and overheating your unit... and count the time you need to perceive amplifier stop to work, when you are inside the shower, full of soap from up to down, not so big amount of water... the worst condition you can face... nobody at home to help you, house thermall switches too big to protect......and then.... this time will be the one you need to run fast to pull the plug out of outlet!... consider the time you need to dry your hands because you can turn into a barbecue.
And cut your protection inside amplifier.... this one was made to shorten price of unit.... and has damn contacts of relay.... remove this awfull thing and send it to trash!
What you think about one automobile that you put whole people inside.... all 5 passengers automobile, and go to a long an up hill, in a good road, but up hill is 50 degrees, and car heavy, and motor trying to keept on moving, rotation is diminishing, you nervous put you feet on clucth to have more rotations and controlling clutch tried to have better rotation.... and clutch start to smell..... and car moves.... you are going, Yeahhhh!... moving and motor melted!... do you really think this is fair! nobody told you that it melted when you need it hard!!!
why amplifiers, submited to extreme jobs have to switch of or melt?
I am trying to find my wife plug, to switch off this damn Spanish beauty. not kill her, i love her...but talk too much...but she is so pretty......
She talk too much! aaaagh!.... imagine a old disc, the one made of plastic, 33 rpm, now push its outlet plug, keeping amplifier on.... try to imagine the sound reducing frequency when turntable will reducing its speed... till the sound becames very bassy, and stop.... I want to do this with my wife....switch damn beauty off for some moments. where's the outlet!!!
Carlos
Carlos - are you wearing any clothes in that photo? 
Roofingboom, the thing is you need both of the protection approachs that have been mentioned so far.
1) Peak current limiting for the power transistors
2) Average power limiting
The challenge is that the peak current you need is much higher than the average current you need. Peak may be 10A to 30A but it would be very expensive to design something to allow this current continously (as in a short circuit situation).
Suppose your psu is +/- 40V. Your emitter resistors ar 0.1-ohm. With a short the peak current could be up to 400A and peak power 16kW. If you apply current limiting to the transistors at, say 10A, you'll still see 400W peak. If you want to design your amp to work at 400W dissipation in the output stage then ok. Otherwise you need to have a second system to limit the average power - which responds slowly enough to not interfere with normal music peaks.
Roofingboom, the thing is you need both of the protection approachs that have been mentioned so far.
1) Peak current limiting for the power transistors
2) Average power limiting
The challenge is that the peak current you need is much higher than the average current you need. Peak may be 10A to 30A but it would be very expensive to design something to allow this current continously (as in a short circuit situation).
Suppose your psu is +/- 40V. Your emitter resistors ar 0.1-ohm. With a short the peak current could be up to 400A and peak power 16kW. If you apply current limiting to the transistors at, say 10A, you'll still see 400W peak. If you want to design your amp to work at 400W dissipation in the output stage then ok. Otherwise you need to have a second system to limit the average power - which responds slowly enough to not interfere with normal music peaks.
Yes!...No!..more or less!, using shorts!
Whe do not use shirt (that's the name?) inside our houses, in Northeast the weather is unconfortable hot, either for us too.
I have de advantage to be in 16 floor in front of the beach, and wind here flows high speed, around 15 miles an hours almost all day from sea to land, at night, because temperature sucks air from oposite side, from land to sea... smells a lot because of suggar cane factories...making suggar and sending some smelling watter into rivers, and river send it to the strip i have in front of my beach....because we have a reef barrier here... and water from river became separated from sea water...smells from the land, and in the morning somethimes from this strip of sweet water (what a sweet.... non potable...awfull)...but sometimes the sea advance and is beatifull because you see swiming pool there... sometimes a shark is waiting you as a delicious sandwich too.
i was reading when this picture was taken by my small daugther Larissa... she was learning how to take photographs... the old Kodak paper ones. this way, as i am fat, i asked her only to put my face.... and shoulder appear too.... very strong isnt'it..NO!... a mountain of fat i am... strong too.
Good that you made this observation.... i was judged by one Nordish young man as a ironic....because the smile..... it means also ironic... i can agree...but the feeling in the moment my dear larissa take the picture was kind acceptation of she was doing, some proud because so small and so clever, so happy one more step in her life i was seeing, and the best kind small smile i can give to the one i love so much.... and the Nordish Frozzen young boy thougth i was ironic.....maybe because of picture.
Do you think i must change it!...please, tell me real thing.... not helpfull beeing kind this way.
I Agree hundred per cent on you.... but, as my name says, i am a Destroyer.... and X.... extra large,..... extra destroyer.... and sometimes i made a lot of 53 years old foolishes, here is an old beginner man, starting to be grandfather...near to be kid again..... so i need to make those really strongs amplifiers....my friends hate me when they made their amplifiers and say me that can work with 2 ohms..... and i ask them( just to kid with them, because they knows me very well)... can your monster support 5 seconds short in both output same time, without burn stupid fuses or destroy weak rectifiers or melt f... transistors....no?.... send it to trash!!!...i do not really believe that this is the good way to judge....but i put my worst expression, and controlling to not smile, i say that to them seriously!!! (and have a lot of fun with friends).....you!.... trash maintainers...... you!..... loosing money with transistors..... you!!!
But, really... thinking a little more...make some sense, don't you think?
Carlos
Whe do not use shirt (that's the name?) inside our houses, in Northeast the weather is unconfortable hot, either for us too.
I have de advantage to be in 16 floor in front of the beach, and wind here flows high speed, around 15 miles an hours almost all day from sea to land, at night, because temperature sucks air from oposite side, from land to sea... smells a lot because of suggar cane factories...making suggar and sending some smelling watter into rivers, and river send it to the strip i have in front of my beach....because we have a reef barrier here... and water from river became separated from sea water...smells from the land, and in the morning somethimes from this strip of sweet water (what a sweet.... non potable...awfull)...but sometimes the sea advance and is beatifull because you see swiming pool there... sometimes a shark is waiting you as a delicious sandwich too.
i was reading when this picture was taken by my small daugther Larissa... she was learning how to take photographs... the old Kodak paper ones. this way, as i am fat, i asked her only to put my face.... and shoulder appear too.... very strong isnt'it..NO!... a mountain of fat i am... strong too.
Good that you made this observation.... i was judged by one Nordish young man as a ironic....because the smile..... it means also ironic... i can agree...but the feeling in the moment my dear larissa take the picture was kind acceptation of she was doing, some proud because so small and so clever, so happy one more step in her life i was seeing, and the best kind small smile i can give to the one i love so much.... and the Nordish Frozzen young boy thougth i was ironic.....maybe because of picture.
Do you think i must change it!...please, tell me real thing.... not helpfull beeing kind this way.
I Agree hundred per cent on you.... but, as my name says, i am a Destroyer.... and X.... extra large,..... extra destroyer.... and sometimes i made a lot of 53 years old foolishes, here is an old beginner man, starting to be grandfather...near to be kid again..... so i need to make those really strongs amplifiers....my friends hate me when they made their amplifiers and say me that can work with 2 ohms..... and i ask them( just to kid with them, because they knows me very well)... can your monster support 5 seconds short in both output same time, without burn stupid fuses or destroy weak rectifiers or melt f... transistors....no?.... send it to trash!!!...i do not really believe that this is the good way to judge....but i put my worst expression, and controlling to not smile, i say that to them seriously!!! (and have a lot of fun with friends).....you!.... trash maintainers...... you!..... loosing money with transistors..... you!!!
But, really... thinking a little more...make some sense, don't you think?
Carlos
,
and 
-proof!
Thank you traderbahn, cannot scape..
From my own reallity.
I was reading,yesterday, the letter Pero Vaz de Caminha, the one that informs Portugal King the new land discovered (brazil) were spanish Vicente Pinzon had been before him and advise Spanish King, and from Spain the informs gonne to Portugal... they had an agreement in 1500 about how to divide the world.
And i read carefully the letter he sent.... my God, the indians where perfect people related to everything Jesus Crist said!
Peacefull, total friendly, no fear, no agressive, just curious and friendly... and they help portuguese to find water and help them to carry potable watter to the Portuguese Ships.
And then someone put a big cross and have some Catholic meeting there.... indians goes together and made all movements Portuguese did.... friendly and inoccent.... they were killed some year passing...because no Baptized, not a man, they were considered animals, killed as animals.
Wonderfull civilization, the modern one, and who were stupid... the indians?
I am one indian too.... try to help all the time.... a lot of misunderstood me too.
Carlos
From my own reallity.
I was reading,yesterday, the letter Pero Vaz de Caminha, the one that informs Portugal King the new land discovered (brazil) were spanish Vicente Pinzon had been before him and advise Spanish King, and from Spain the informs gonne to Portugal... they had an agreement in 1500 about how to divide the world.
And i read carefully the letter he sent.... my God, the indians where perfect people related to everything Jesus Crist said!
Peacefull, total friendly, no fear, no agressive, just curious and friendly... and they help portuguese to find water and help them to carry potable watter to the Portuguese Ships.
And then someone put a big cross and have some Catholic meeting there.... indians goes together and made all movements Portuguese did.... friendly and inoccent.... they were killed some year passing...because no Baptized, not a man, they were considered animals, killed as animals.
Wonderfull civilization, the modern one, and who were stupid... the indians?
I am one indian too.... try to help all the time.... a lot of misunderstood me too.
Carlos
Yes Carlos, isn't it very sad. I have also read some of those early histories. Like you said, they were perfect Christians, except they were not baptised. So we (Europeans) killed most of them. As I said before, I have no problems with God, but His Customer Service Personnel here on Earth are some of the worst devils I have ever met. Like condemning millions in Africa to die because condoms are wrong. Unbelievable that any sane man can come to such a choice.
Jan Didden
Jan Didden
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