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Old 28th November 2005, 04:03 AM   #1
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Default Power supply for LM4702

I recently ordered the LM4702 audio driver from National; it has a maximum supply voltage of +/-75V.


My current power supply will put out +/-80V. Is there any way I can drop about 10V for the 4702 in an efficient and cheap way?
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Old 28th November 2005, 08:00 AM   #2
Tweeker is offline Tweeker  United States
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Cheapest way is a couple strings of diodes, not necessarily the best way.
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Old 20th December 2005, 12:51 PM   #3
alexcd is offline alexcd  United States
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A resistor and zener diode will hold it at 75V... of course they would need to eat up dV*I = MASSIVE POWER.
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Old 21st December 2005, 03:41 AM   #4
AJT is offline AJT  Philippines
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Default Re: Power supply for LM4702

Quote:
Originally posted by rtarbell
I recently ordered the LM4702 audio driver from National; it has a maximum supply voltage of +/-75V.


My current power supply will put out +/-80V. Is there any way I can drop about 10V for the 4702 in an efficient and cheap way?

depends on the power transformer you'll be using, and the final config of your lm4702 amps, could be that the +/-80volt rails will sag to 75volt levels once your amps is powered up and idling!
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Old 21st December 2005, 12:17 PM   #5
alexcd is offline alexcd  United States
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Not to doubt you Tony but it would be pretty unwise to design anything around where the power supply may be in a sag. It doesn't take much time at all to kill an IC with high voltage. Be safe and either find a way to unwind your trans or buy another one. Sorry.
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Old 30th December 2005, 03:07 AM   #6
amp_cy is offline amp_cy  Cyprus
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If your power supply consists of a toroid transformer, you could add several more turns on the transformer core and connect these to the primary windings. The wire should be of the same thickness as the primary. You should then insulate these turns with some insulation tap.

This is a non distructive alteration which will change the transformer turns ratio. NOTE make sure the new windings are in phase with with the primary.
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Old 25th June 2006, 07:18 PM   #7
ahrsix is offline ahrsix  United Kingdom
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Default Power Supply for LM4702

Have a peek at the LM338K 5amp regulator data sheet, there not cheap but I'v used them on PSUs for over 20yrs never regretted it. There are circuits on the forums, a good amps worth it.
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Old 14th February 2016, 06:15 AM   #8
lcd950 is offline lcd950  Sri Lanka
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Red face lm4702 amplifier circuit

Which resister should I use for red circled place on the attached image

As I have 35VAC transformer , is this transformer suitable for this amp
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File Type: gif (YMYA)600W AUDIO AMP.GIF (54.3 KB, 126 views)
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Old 14th February 2016, 08:43 AM   #9
wwenze is offline wwenze  Singapore
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Quote:
Originally Posted by lcd950 View Post
Which resister should I use for red circled place on the attached image

As I have 35VAC transformer , is this transformer suitable for this amp
The resistor is inside the darlington package already, you don't have to put in anymore stuff outside.
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Old 14th February 2016, 10:54 AM   #10
AndrewT is offline AndrewT  Scotland
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I hope you have a 230:35-0, 35-0Vac transformer.

You need a dual polarity supply for that amplifier and that requires 70Vac to get 50Vdc

The pic in top right shows a 60V centre tapped transformer (30-0-30Vac). ignore the + they made a mistake. AC voltage is not +
And you can't get 300W per channel into 8ohms with a maximum supply voltage of 40Vdc
Expect 50W into 8ohms from the maximum recommended 35Vdc shown under POWER :

There are so many mistakes in that page that I would find a different supplier that knows their product.
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Last edited by AndrewT; 14th February 2016 at 11:02 AM.
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