Power supply for LM4702

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rtarbell

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Joined 2005
#1
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?
 
#4
rtarbell said:
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?
Click to expand...


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!
 
#5
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.
 
#6
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.
:att'n:
 
#7
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.
arrsix





Always cut towards your friend
Old RN saying
 
#8
lm4702 amplifier circuit

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

As I have 35VAC transformer , is this transformer suitable for this amp
 

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#10
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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#12
Do NOT wind extra layers to connect with the primary , safety isolation WILL be compromised.

Do wind extra layers and connect in antiphase with the secondary , reducing the output (and VA rating equally)

Or build a stabilised power supply for your LM4702,but unstabilised for the power transistors. You will also loose some headroom and output this way.
 
#13
AndrewT said:
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.
Click to expand...


after rectified the 35 0 35vac transformer's output, i am getting +50 0 -50 vdc. this is a 7 ampere transformer, isn't that enough for this amp?
 
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