diyAudio

diyAudio (http://www.diyaudio.com/forums/)
-   Chip Amps (http://www.diyaudio.com/forums/chip-amps/)
-   -   Pushing the limit of supply voltage (http://www.diyaudio.com/forums/chip-amps/84799-pushing-limit-supply-voltage.html)

enzedone 15th August 2006 11:08 PM

Pushing the limit of supply voltage
 
I have a tranny that'll give me 42.4VDC (+/-) unloaded. I think this is right on the limit for a LM3785?

But I got the thing free out of an old amp.

Sherman 15th August 2006 11:13 PM

The spec sheet says 84 volts max so you are .8 V over the limit. :D

However since the 42.4 is unloaded you can count on a few volts dropping when you connect it to your amp. You will be under the limit.

Build it! :smash:

enzedone 16th August 2006 12:00 AM

Build and check
 
Yeah, I'll build the power supply up and then check again, just to make sure it's not too far out.

pinkmouse 16th August 2006 12:07 AM

You will need big heatsinks though...;)

enzedone 16th August 2006 12:13 AM

Heatsink
 
Well, I have a 3 metre length of heatsink sitting in the garage, so I think that should cover it

;) :hot:


Brett

pwan 16th August 2006 05:27 AM

Quote:

Originally posted by Sherman
The spec sheet says 84 volts max so you are .8 V over the limit. :D

However since the 42.4 is unloaded you can count on a few volts dropping when you connect it to your amp. You will be under the limit.

Build it! :smash:

just wonder if using resistor ( one or more "1 Ohm 10 W" per rial) in series will help more voltage dropping and a bit lower ripple?

DigitalJunkie 16th August 2006 05:53 AM

Or perhaps some chokes with a bit of DCR?

AndrewT 16th August 2006 08:02 AM

Hi,
using the higher supply voltages has the consequence of demanding you use the higher load impedances as well.

Effectively 4 to 8ohm and 6ohm speakers are out the window.
Some demanding 8ohm may also overstress the chips.

12ohm or 16ohm speakers become your ideal match. Headphones?

macboy 16th August 2006 01:16 PM

The LM3886 will tolerate extreme supply voltages better than the LM3875. The LM3875 doesn't have a lot of wiggle room (its safe operating area is more limited than the LM3886).

If you parallel two LM3875s and drive no less than 8 ohms, you may get decent results.

You could also try lowering the voltage using a capacitor multiplier or a regulator. Either one will help clean up the power supply in addition to lowering the voltage to a more ideal point.

rabbitz 16th August 2006 04:17 PM

Throwing a larger heatsink at it will work to a certain limit and you can forget about it for a TF package but the TA package is on the limit with a 6R load.

Reducing the voltage is a better way to go and have a look around for the Overture Design Guide spreadsheet at National Semi Conductor. That will give you a guide at what you can and can't do.


All times are GMT. The time now is 09:20 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio


Content Relevant URLs by vBSEO 3.3.2