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mantabernd 18th October 2012 07:19 AM

LME49830 with Foldback Current Limit and 2sk1530
1 Attachment(s)

I designed a LME49830 with foldback current limit and the popular 2sk1530/2sj201, the circuit is similar to the an1850 from ti.

Unfortunately I can only simulate the circuit in tina-ti because I don't have the LME in lt-spice. BUT I don't have the 2sk1530 mosfets in tina-ti :( So I tried to simulate it with irfp240 and irfp9240 and it nearly worked. The only thing were the low distortions on the takeover point but I think it is because of wrong bias current and the "wrong" mosfets in the simulation. The current limitier worked very well :)

So now, a question to the specialists here in the fomum, will this amp work??

Is it a good idea to take the expensive 2sk1530 / 2sj201 mosfets instead of the cheaper irfp240 / 9240?

Thanks in advance ;-)


AndrewT 18th October 2012 01:17 PM

are the sources inside the LME sufficiently protected such that when the protection triggers, your circuit does not blow up the LME?

mantabernd 18th October 2012 01:26 PM

Hello Andrew,

good Question, I don't know about fues inside the LME. In the datasheet is only a thermal fuse listed.

How can I protect the LME? With extra transistors for driving the mosfets?

mantabernd 19th October 2012 11:02 AM

No one else any suggestions/comments ?

pergo 19th October 2012 11:43 AM

LME's drivers are current limited to 56mA.
Datasheet shows that drivers can be shorted with a 10ohm resistor without problems.

That circuit will work.

mantabernd 19th October 2012 12:17 PM

Oh ok I didn't see this detail. Thanks for this information!!

So that's my first own amplifier design - I'm very excited about building it. I hope it won't fire it up ... Maybe, if I got the time for it I will test it this evening.

AndrewT 19th October 2012 12:23 PM

I think that both Pass and ESP websites shown a method & circuit to allow non destructive testing of current limiting circuits.

mantabernd 19th October 2012 03:29 PM

Sorry for the question but do you have links for the circuits? I didn't find them and I like non destructive solutions ;-)

basitccp 24th October 2012 07:26 AM

Fold back current limiter
i have a regulated bus supply of 28 volts now i want to design foldback current limiter circuit which limits load current when it exceeds above 5 ampere. can any one has any idea..

Thanks in advance..

mantabernd 26th October 2012 12:08 PM

I built it :)
2 Attachment(s)
I finally built that circuit above with only one pair of mosfets and it worked. I had some problems with oscillations at the beginning, it is very important to have only one big gnd point. After I changed this the oscillations were gone :)

So can't say anything about the sound quality because my testspeaker is very bad but I measured it.

The current limiter needs a bit tuning, the negative side seems to limit correctly but the positive side looks very very strange.

I tested it by putting a 2R4 Ohms resistant from output to gnd.

Supply voltage was +/- 60V. The Voltage at the gate of 2sk1530 was 1,758V and on the 2SJ201 it was -1,537. After putting the 2R4 Ohms at the output the voltage at the 2sk1530 was 1,501V and on the 2SJ201 it was -0,499V.

So it doesn't work simultaneously :(

I added two pictures, one of normal operating mode and another with the resistant at the output.

Anyone any suggestion what to change?

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