It is the same method used in computer psu short protection and yes it uses resistance of a wire..you can use a 0.01 ohm resistor..but for me is easier to use a wire,i can not find such small resistors cheap...at 10 A you will have a vdrop of 100mV.For stereo mode use a 0.001 ohm resistor to ground .I wil make a mini schematic soon ...
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The schematic..
The 10mohm resistor can be made easy with a few spirals of 1mm wire.Protection trip level accuracy is usualy +-15%,can be made smaller with better quality components.
An externally hosted image should be here but it was not working when we last tested it.
The 10mohm resistor can be made easy with a few spirals of 1mm wire.Protection trip level accuracy is usualy +-15%,can be made smaller with better quality components.
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CPX!
Have you ever built and measured it?
Let's assume R4 is bigger than R5 by 1%! What will be the output of 1st OPA, if there is no load current, but there is +/-80 V output voltage? -/+80 mV! What will do the 2nd and 3rd OPA? ...
For protection trip level accuracy of 15 %, R4, R5, R6, R7 have to match with 0.01% accuracy.
This can work as long as the fault current goes back on the speaker connector, but generally you can't guarantee that.
BTW: it cannot be connected to SD pin of IR2110 directly.
Have you ever built and measured it?
Let's assume R4 is bigger than R5 by 1%! What will be the output of 1st OPA, if there is no load current, but there is +/-80 V output voltage? -/+80 mV! What will do the 2nd and 3rd OPA? ...
For protection trip level accuracy of 15 %, R4, R5, R6, R7 have to match with 0.01% accuracy.
This can work as long as the fault current goes back on the speaker connector, but generally you can't guarantee that.
BTW: it cannot be connected to SD pin of IR2110 directly.
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Yes..diferential resistors have to be manualy matched/created for minimum error,i have build this kind of protection for lower voltages(+-40) and with 1/4 divider not 1/10 but with pacience it can be done..maybe not with only 120mV drop for +-80 volt but much lower than the proposed 1 volt...given schematic is only an example...
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This is my overcurrent protection with shunt resistor and NE555. On output is relay only for testing. In simulator works good. Its need 1V drop to start protection..
I didnt try in practice yet.. I will use relay to cut AC lin to my other part of protection. When AC line is cut, speakers are off momently.
What do you think!?
I didnt try in practice yet.. I will use relay to cut AC lin to my other part of protection. When AC line is cut, speakers are off momently.
What do you think!?
Attachments
Yes you are corect here...but i have a lot of pacience
..i use multiple resistors in series/parallel conection if needed to obtain as good accuracy as posible...anyway i said +-15% not 15%Output has to go to an optocoupler or level shifter to work with ir2110 .
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Looks ok on fast examination...but have you measured reaction time?..i have a feeling it is too slow..
(relay excluded).Do not use a relay for short protection ..only for dc protection.....the amplifier will burn in the 10ms required for the relay de stop conducting...
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Yes, relays are to slow for short protection.. Now this is idea only for overload protect, while I create something faster. But when I think better, maybe isnt too slow.
I use fast relays 24V 2x16A (Helshun HLS-14-F1) with 8ms release time. Maybe is not too slow
This is calculation for shunt resistor:
Pout = (Ucc-1/sqrt 2)(Ucc/Rload*sqrt 2) (=) W
Uout = (Ucc-1/sqrt 2) (=) V
Iout = (Ucc/Rload*sqrt 2) (=) A
Rsens = 1/(ucc/2Rload * sqrt2) => Rsens = 2Rload*sqrt 2 / Ucc (=) ohms
(2Rload*sqrt 2) - because only one half of output current will pass through one supplay rail
P dispation (Rsens) = 1V*(Ucc/2Rload*sqrt 2) (=) W
I use fast relays 24V 2x16A (Helshun HLS-14-F1) with 8ms release time. Maybe is not too slow
This is calculation for shunt resistor:
Pout = (Ucc-1/sqrt 2)(Ucc/Rload*sqrt 2) (=) W
Uout = (Ucc-1/sqrt 2) (=) V
Iout = (Ucc/Rload*sqrt 2) (=) A
Rsens = 1/(ucc/2Rload * sqrt2) => Rsens = 2Rload*sqrt 2 / Ucc (=) ohms
(2Rload*sqrt 2) - because only one half of output current will pass through one supplay rail
P dispation (Rsens) = 1V*(Ucc/2Rload*sqrt 2) (=) W
Yes, I forgot that.. But something come to my mind.. What if I put protection bettwen main capacitors and amp and when protection starts, BC238 is opened and momentaly make short on main relay, then raley is off and it realise time is 8ms. Now active led is off too because relay is in short, I have complite indication of whole situation..
Relay is 24V on example on +-60V, relay resistor is 1.5K (relay current is 24mA).
When reley is short, current through BC238 will be 40mA and his current raiting is 200mA, it can handle.. For sure maybe is good to put stronger transistor like BD139
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The problem with your aproach is that this will not only save the the transistors in the event of a sudden short(like when the speaker burns)...an efective protection for the transistors must be very fast both in detection and in action.Detector has to be put on output or on the leg of irfp250 after bypass capacitor 470uf but i recomand it on output.
Protector has to stop input signal and/or transistor oscilation ..only the relay will not work..thre is no point in doing just an overload protection and not a complete fast short protection...
Protector has to stop input signal and/or transistor oscilation ..only the relay will not work..thre is no point in doing just an overload protection and not a complete fast short protection...
