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Old 20th January 2010, 05:02 PM   #1
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Default another protection circuit

a friend of mine designed a turn on delay +protection circuit based on 555 any body has an idea if any drawbacks ????

opinions please

thank you
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File Type: pdf 555 protection.pdf (16.2 KB, 204 views)
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Old 20th January 2010, 05:13 PM   #2
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Hi sakis

That should be ok. Maybe something is missing to discharge the C1 ?
I like the DC protection
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Old 20th January 2010, 05:14 PM   #3
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yes ... i will look in to it thanks Jan
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Old 20th January 2010, 05:17 PM   #4
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I think it might be needed if you quickly turn the amp off and on again......
A simple test can clear that question
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Old 20th January 2010, 05:19 PM   #5
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very similar to what I have used for soft start and for DC detection/protection.

I have not checked the circuit.
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Old 20th January 2010, 05:23 PM   #6
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thanks again i will make this tests update the schematic with any changes ...

hello Andrew !!! happy new year .... nice to see you I hope you are doing fine

Regards sakis
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Old 21st January 2010, 02:30 AM   #7
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Thanks Sakis for bringing protection circuits up. What is the 220k resistor on the trigger of the 555 with a slash through it and the T beside it? It's not a thermistor attached to the heat sink, is it? They have invented some stuff since I got out of school, and wikipedia didn't show this symbol under thermistor. I was looking at the Newark.com catalog Sunday and found a honeywell 140-103LAC-RB1 thermistor with 25 C resistance of 10Kohm and a beta of 3974. I think this means it goes 1070 ohm at 60 deg C, is that about right? I've been disassembling motor drives trying to find the temperature sensor, but I think they are integrated into the thyristor block where I can't play with them, and honeywell doesn't have and ap note online, so I am trying to get a free education. Thanks in advance.
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Old 21st January 2010, 03:48 AM   #8
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Quote:
Originally Posted by indianajo View Post
Thanks Sakis for bringing protection circuits up. What is the 220k resistor on the trigger of the 555 with a slash through it and the T beside it? It's not a thermistor attached to the heat sink, is it? They have invented some stuff since I got out of school, and wikipedia didn't show this symbol under thermistor. I was looking at the Newark.com catalog Sunday and found a honeywell 140-103LAC-RB1 thermistor with 25 C resistance of 10Kohm and a beta of 3974. I think this means it goes 1070 ohm at 60 deg C, is that about right? I've been disassembling motor drives trying to find the temperature sensor, but I think they are integrated into the thyristor block where I can't play with them, and honeywell doesn't have and ap note online, so I am trying to get a free education. Thanks in advance.
It's a pot.

If a PCB is generated from this schematic have a close look around R5.
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Old 21st January 2010, 04:11 AM   #9
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Originally Posted by Greg Erskine View Post
It's a pot.

If a PCB is generated from this schematic have a close look around R5.
Agreed. By the time a positive offset triggers the protection, it will likely have damaged the speakers or simply blown some fuses. I'm not sure you can get a negative offset to even trigger it. I would think a window comparator would do a better job of it but in all my years of working with audio gear, I personally have never run into a amp that put out significant DC without taking out its own fuses and I've never seen speakers damaged by continuous DC.

G
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Old 21st January 2010, 04:40 AM   #10
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I see no problem around R5 except that value of R4 and R5 maybe has to be lowered...

Quote:
I'm not sure you can get a negative offset to even trigger it.
As T2 is used in it's Grounded base configuration it have a very high Current gain. It should work fine
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