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Old 27th April 2011, 06:36 AM   #1011
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Quote:
Originally Posted by lorylaci View Post
IRF6668 is rated for 80V, so no.
But how can you solder DirectFETs ???
I use relay output protection, so it protects for startup and poweroff transients too.
It's simple just use a hot air blower and solder paste.

Do you have a schematic of the protection?
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Old 27th April 2011, 09:11 AM   #1012
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Ofcourse. This protection basicly is from elector (PA300 amp) but I Add signal indocator and cliping indicator

R1 - 12V drop, 20mA
R2 - Cliping refererence 3V
R3 - opamp inuputs
R4 - 15V drop, 15mA
R5 - relay droper, 24V drop, 24mA (if coil on relay is 1K)
R6 - AC conector, 0.5mA (example +-60V / 0.5mA= 120K)
R7 - same like R4
R8 - same like R4

Example for R1

Resistor (k Ohms) = ( Supply Voltage - 12 ) / 20mA
Power (mW) = ( Supply Voltage - 12 ) ^2 / Resistor (k Ohms)

For a 45 Volt supply, we get ...

Resistor = ( 45 - 12 ) / 20 = 33 / 20 = 1.65k Ohms
Power = (45 - 12 ) ^ 2 / 1.65 = 33 ^2 / 1.65 = 1089 / 1.65 = 660 mW

Example for R2 cliping reference

Current (mA) = Reference Voltage - So a 3V reference requires 3mA
Resistor (k Ohms) = ( ( Supply V - Reference V ) / Current (mA) ) * 2
Power (mW) = Current ^ 2 * Resistor

An example would be an amp with 45V supplies, and requiring a reference voltage of 5V. So ...

Current = 5mA
Resistor = ( ( 45 - 5 ) / 5 ) * 2 = ( 40 / 5 ) * 2 = 16k Ohms
Power = 5 ^ 2 * 16 = 25 * 16 = 400 mW

I posted word document with table of values if some one dont want to calculate values of resistors, schematic to.

Values for R7,R15,R17,R16 on amplifier are from basic scehmatic of amplifier

Regards
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Old 27th April 2011, 10:04 AM   #1013
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Thank you very much dzony, I'll put the pcb files with protections and smd components as soon as I finish it..
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Old 27th April 2011, 10:16 AM   #1014
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Quote:
Originally Posted by ghabrius View Post
Thank you very much dzony, I'll put the pcb files with protections and smd components as soon as I finish it..
I managed to get solder paste. So maybe later I will experiment some with DirectFETs, they would really increase the performance of the amp.

I use a much simpler relay protection. It is not as effective, has higher treshold, but every component fits under the relay in SMD.
Click the image to open in full size.
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Old 27th April 2011, 10:31 AM   #1015
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Quote:
Originally Posted by ghabrius View Post
It's simple just use a hot air blower and solder paste.

Do you have a schematic of the protection?
speaker protection
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Old 27th April 2011, 10:36 AM   #1016
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I'm gonna make separate supply rails for the protection and the IR2110 cause now I'm starting to see that I have too many zeners flying around on the board lol

Last edited by ghabrius; 27th April 2011 at 10:57 AM.
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Old 27th April 2011, 10:47 AM   #1017
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Quote:
Originally Posted by lorylaci View Post
I managed to get solder paste. So maybe later I will experiment some with DirectFETs, they would really increase the performance of the amp.

I use a much simpler relay protection. It is not as effective, has higher treshold, but every component fits under the relay in SMD.
Click the image to open in full size.
nice. Yeah the Direc-fets are way to go, I havent seen such low rdsOn anywhere but be precise when drawing the footprints and carefull when soldering; If you have a homemade pcb cover coppertracks with very thin layer of tin otherwise you will short the drain(the can) with pcb tracks and don't add too much paste, better too little if youre using PbF devices. Also what I've learnt when soldering the critters is that you can temprorarily leave you multimeter wired to the pcb tracks that go to mosfet, dial it to diode test and see if it shorts while your blowing the hot air. If it shorts at some point of soldering you just slightly move it with tweezers till it snaps in place..

Last edited by ghabrius; 27th April 2011 at 10:55 AM.
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Old 27th April 2011, 01:17 PM   #1018
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btw, where do I connect the AC link of the protection?
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Old 27th April 2011, 02:09 PM   #1019
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Quote:
Originally Posted by ghabrius View Post
btw, where do I connect the AC link of the protection?
For my simple one: when powered off, the 12V for relay discharges very fast due to small puffers in my supply, so relay turns off. Turn on is delayed by the cap.
But you can add an optocoupler to make it more reliable.
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Old 27th April 2011, 03:24 PM   #1020
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Iwas asking about the schematic that Dzony gave,there was this AC pin that I have no idea how to use...
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