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diyAudio Member

Join Date: May 2002
Location: The great city of Turnhout, BE
Blog Entries: 8
Quote:
 Originally Posted by magman Some photos of my build. It is dual sided home made pcb Anyone know how much current I can go without heatsink on pass transistor? I will power with dual supply 6 op-amps I fink about ad797B.
Dissipation is current through pass device * voltage across the pass device.
How much current is 6 * AD797? Is in the data sheet, supply current.

How much voltage across the pass device? Vout = 6V, what is the input voltage?

You can do the sums. Once you know the dissipation, we can see if a heatsink is required or not.

(And please you guys out there who want to promote your favorite heatsink: I am trying to help him find it himself. Please don't spoil it).

Jan
__________________
Music is dither to the brain; lets me think below the usual chaos - me
Linear Audio Vol 13 is out! Check out my Autoranger and SilentSwitcher

diyAudio Member

Join Date: Nov 2011
Location: Kaunas
Quote:
 Originally Posted by jan.didden Dissipation is current through pass device * voltage across the pass device. How much current is 6 * AD797? Is in the data sheet, supply current. How much voltage across the pass device? Vout = 6V, what is the input voltage? You can do the sums. Once you know the dissipation, we can see if a heatsink is required or not. (And please you guys out there who want to promote your favorite heatsink: I am trying to help him find it himself. Please don't spoil it). Jan
ad797 Quiescent Current 8.2-10.5mA (so I fink it will be about 5mA over positive ant 5mA over negative rail?) So for 6xAD797 it will be 30ma or 60mA on positive side? Input voltage will be about 25V output 12v. Now with 60mA at output where is no heating.

diyAudio Member

Join Date: May 2002
Location: The great city of Turnhout, BE
Blog Entries: 8
Quote:
 Originally Posted by magman ad797 Quiescent Current 8.2-10.5mA (so I fink it will be about 5mA over positive ant 5mA over negative rail?) So for 6xAD797 it will be 30ma or 60mA on positive side? Input voltage will be about 25V output 12v. Now with 60mA at output where is no heating.
If the data sheet says 10mA it is the current from the V+ through the device out of the V-, so each supply needs to give 10mA.

So for both the pos and the neg you are faced with 60mA current or 0.06A.

Now you say Vin = 25 and Vout = 12V. (Before you said 6V). So the pass device sees 25 - 12 = 13V.

So the dissipation is 0.06 * 13 in Watt. The pass device, if it is TO-220, should be able to survive that with a screw-on heatsink, no need for a large PCB-mounted heatsink.

Your Vin of 25V is quite high for 12V out. It will work of course, but if you can lower the 25V down to say 18V or even 15V, the dissipation would drop a lot and there will be even less heat.

BTW You are hiding your profile, so don't know whether English is your native language, but it is 'I think' not 'I fink'.

Jan
__________________
Music is dither to the brain; lets me think below the usual chaos - me
Linear Audio Vol 13 is out! Check out my Autoranger and SilentSwitcher

Last edited by jan.didden; 19th June 2017 at 02:44 PM.

diyAudio Member

Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Quote:
 Originally Posted by jan.didden I BTW You are hiding your profile, so don't know whether English is your native language, but it is 'I think' not 'I fink'. Jan
Fink can be used as a noun or verb.

diyAudio Member

Join Date: May 2002
Location: The great city of Turnhout, BE
Blog Entries: 8
Quote:
 Originally Posted by jackinnj Fink can be used as a noun or verb.
I am aware of the colloquial meaning

Jan
__________________
Music is dither to the brain; lets me think below the usual chaos - me
Linear Audio Vol 13 is out! Check out my Autoranger and SilentSwitcher

 19th June 2017, 05:55 PM #1296 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders __________________ regards Andrew T. Sent from my desktop computer using a keyboard
diyAudio Member

Join Date: Nov 2011
Location: Kaunas
Quote:
 Originally Posted by jan.didden If the data sheet says 10mA it is the current from the V+ through the device out of the V-, so each supply needs to give 10mA. So for both the pos and the neg you are faced with 60mA current or 0.06A. Now you say Vin = 25 and Vout = 12V. (Before you said 6V). So the pass device sees 25 - 12 = 13V. So the dissipation is 0.06 * 13 in Watt. The pass device, if it is TO-220, should be able to survive that with a screw-on heatsink, no need for a large PCB-mounted heatsink. Your Vin of 25V is quite high for 12V out. It will work of course, but if you can lower the 25V down to say 18V or even 15V, the dissipation would drop a lot and there will be even less heat. BTW You are hiding your profile, so don't know whether English is your native language, but it is 'I think' not 'I fink'. Jan
Sorry I can't find where I say that my Vout is 6V.

Main problem is that my pass device is DPAK CASE 396C, so it is only possible to add heat sink with double sided thermal tape

I already lowered my raw dc supply from 30Vdc (made mistake with psud2 with transformer parameters and think that my talema 2x18vac transformer will be ok) to 22.5Vdc with diodes in secondary and series diodes after bridge. And now added 10ohm series resistor to secondary and now have 20vdc with 50mA load. so it will be something like this: 20-15=5 0.06*5=0.3w so heat-sink of 25K/W will rise temperature about only 8 degree Celsius over ambient. and without heat-sink it will be 25 degree Celsius over ambient if 71.4 C/W as datasheet says junction to ambient thermal resistance.
I need to check my other op-amps to see if they all are capable of +/-15vdc power supply, so I can use 15v instead of 12v, because I will want to roll some op-amps and choose best sounding for me.

It is good that I measure 7.1Vdc on op-amp 2 and 3 pin? you said that it should be no more than 7V

Sorry for my English, I am not native speaker and make mistake

Edit. Adjusted to 15Vdc, current goes to 63mA. Vin drop to 19.6. No heating on pass device. I think I will try without heat-sink, and if I will have heating issues just add one :-)

Last edited by magman; 19th June 2017 at 06:38 PM.

diyAudio Member

Join Date: Nov 2011
Location: Kaunas
Quote:
 Originally Posted by magman Sorry I can't find where I say that my Vout is 6V. Main problem is that my pass device is DPAK CASE 396C, so it is only possible to add heat sink with double sided thermal tape I already lowered my raw dc supply from 30Vdc (made mistake with psud2 with transformer parameters and think that my talema 2x18vac transformer will be ok) to 22.5Vdc with diodes in secondary and series diodes after bridge. And now added 10ohm series resistor to secondary and now have 20vdc with 50mA load. so it will be something like this: 20-15=5 0.06*5=0.3w so heat-sink of 25K/W will rise temperature about only 8 degree Celsius over ambient. and without heat-sink it will be 25 degree Celsius over ambient if 71.4 C/W as datasheet says junction to ambient thermal resistance. I need to check my other op-amps to see if they all are capable of +/-15vdc power supply, so I can use 15v instead of 12v, because I will want to roll some op-amps and choose best sounding for me. It is good that I measure 7.1Vdc on op-amp 2 and 3 pin? you said that it should be no more than 7V Sorry for my English, I am not native speaker and make mistake Edit. Adjusted to 15Vdc, current goes to 63mA. Vin drop to 19.6. No heating on pass device. I think I will try without heat-sink, and if I will have heating issues just add one :-)
Checked my op-amps and I am limited only on AD8610 to +/-13V if I decide to use them.

diyAudio Member

Join Date: May 2002
Location: The great city of Turnhout, BE
Blog Entries: 8
Quote:
 Originally Posted by magman Sorry I can't find where I say that my Vout is 6V. Main problem is that my pass device is DPAK CASE 396C, so it is only possible to add heat sink with double sided thermal tape I already lowered my raw dc supply from 30Vdc (made mistake with psud2 with transformer parameters and think that my talema 2x18vac transformer will be ok) to 22.5Vdc with diodes in secondary and series diodes after bridge. And now added 10ohm series resistor to secondary and now have 20vdc with 50mA load. so it will be something like this: 20-15=5 0.06*5=0.3w so heat-sink of 25K/W will rise temperature about only 8 degree Celsius over ambient. and without heat-sink it will be 25 degree Celsius over ambient if 71.4 C/W as datasheet says junction to ambient thermal resistance. I need to check my other op-amps to see if they all are capable of +/-15vdc power supply, so I can use 15v instead of 12v, because I will want to roll some op-amps and choose best sounding for me. It is good that I measure 7.1Vdc on op-amp 2 and 3 pin? you said that it should be no more than 7V Sorry for my English, I am not native speaker and make mistake Edit. Adjusted to 15Vdc, current goes to 63mA. Vin drop to 19.6. No heating on pass device. I think I will try without heat-sink, and if I will have heating issues just add one :-)
I think you are OK with that set-up.

The nominal voltage on the LM329 is 6.9V. Depending on temperature, and how good your meter is, I always say 'about 7V'. Not important, 7.1V is perfectly OK.

It doesn't matter a whole lot whether the Vout is 14.8 or 15 or 15.3V.

Jan

PS It is always nice to give some info about your situation, like country and occupation. Makes it easier for people to relate to you. But of course, up to you.
__________________
Music is dither to the brain; lets me think below the usual chaos - me
Linear Audio Vol 13 is out! Check out my Autoranger and SilentSwitcher

diyAudio Member

Join Date: Nov 2011
Location: Kaunas
Quote:
 Originally Posted by jan.didden I think you are OK with that set-up. The nominal voltage on the LM329 is 6.9V. Depending on temperature, and how good your meter is, I always say 'about 7V'. Not important, 7.1V is perfectly OK. It doesn't matter a whole lot whether the Vout is 14.8 or 15 or 15.3V. Jan PS It is always nice to give some info about your situation, like country and occupation. Makes it easier for people to relate to you. But of course, up to you.
Thank you for your help and all information I will update my profile, because I never payed attention to it

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