LME49830 with Foldback Current Limit and 2sk1530 - Page 2 - diyAudio
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Old 26th October 2012, 12:13 PM   #11
pergo is offline pergo  Italy
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add 10nF capacitor between base and collector of Q2 and Q3
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Old 26th October 2012, 12:32 PM   #12
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Yes it worked Wow, so fast!!

I didn't have a 10nF so I used 33nF.

Well done, thanks pergo!!
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Old 26th October 2012, 12:40 PM   #13
pergo is offline pergo  Italy
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great! that was a huge oscillation
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Old 26th October 2012, 01:52 PM   #14
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Q2 and Q3 shouldn't be necessary with the LME49830.

Some other stuff -- 1) the gate stopper resistors should be mounted as close as possible to the gates of the MOSFETs. 2)Increasing the value of the compensation capacitor will reduce the slew rate and may be necessary with some devices.
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Old 26th October 2012, 04:23 PM   #15
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Yes I know, it's my own design for short-circuit protected amplifier and it works!!

No I only have to change the values of the protection because it workes too early.
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Old 27th October 2012, 08:50 AM   #16
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DC and very long duration limiting must respect the DC SOA of the devices.

But, transient peaks far exceeding the DC SOA must be allowed to pass unhindered.

You need to modify your limiting to allow medium term and short term and very short term transient demand currents to pass.
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Old 27th October 2012, 09:05 AM   #17
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It's a bit sad that I can't simulate it with this fets.

On the first step I will change R13 and R14 (the current resistors) from 0R22 to 0R10, then the current circuit will limit much later.

In my testcircuit I used 1N4007 for D1 and D2 because I don't have shottky diodes. Would it be better to replace them with shottky diodes? If yes, what will be the advantage?
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Old 27th October 2012, 09:12 AM   #18
AndrewT is offline AndrewT  Scotland
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It would probably be safer to keep the DC current limit low or very low while you experiment with limier component values.

That last thing you want is to blow up your amplifier because the limiter came in a bit late.
Can you arrange in your circuit for the limit to reduce as heatsink temperature rises?
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Old 27th October 2012, 09:18 AM   #19
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Quote:
Originally Posted by AndrewT View Post
It would probably be safer to keep the DC current limit low or very low while you experiment with limier component values.
My DC supply limits the current at 2,5A.

Quote:
That last thing you want is to blow up your amplifier because the limiter came in a bit late.
Yes, that's right!

Quote:
Can you arrange in your circuit for the limit to reduce as heatsink temperature rises?
Sorry I didn't understand this sentence... Does it mean that I should use a ntc in my current limit circuit?
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Old 27th October 2012, 09:22 AM   #20
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Try to add increase R15, R16 to 220-330 ohms. I have never seen an amp with lateral fets having 22 ohm only. You problem can be found if you read this... I'll trace it down for you.
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