Power Supply for LM4780 based car amp

[j.wright]

OK guys I'm going to take the plunge soon to build a car amp based on the LM4780 chip(s).

I am very new to building amplifiers and am going to build some home audio chip amps first to get some hands on practice.

I was hoping someone has built a car amp using LMxxxx chips and could give me some guidance on building a powersupply for said amplifier.

Thanks!
J

 

[AndrewT]

The PSU is the car battery and the charging system.

 

[j.wright]

SMPS

 

[Perry Babin]

The permanent thread at the top of the car audio forum has a supply.

What's the total RMS power of the amplifier (all channels combined)?

 

[j.wright]

Roughly 600 watts...

 

[Perry Babin]

You'll need a transformer core.

This one will work:
F-193A-F

From:
http://www.cwsbytemark.com/prices/toroidal.php

You'll also need magnet wire, it you don't have a local source, let us know.

 

[j.wright]

What gauge mag. wire should I look for ?

J

 

[Perry Babin]

I generally use multiple strands of 14g. I'd use 4 strands of 14g for each of the primary windings. If you want to use more strands of smaller wire, use something roughly equal. 4x14g is approximately 16,000 circular mils. 16 strands of 20g would be approximately the same.

 

[j.wright]

This is going to sound rather dumb... but... I assume the SMPS will convert the 12v power supplied by the cars electrical system to be compatible with the amplifier needs ?
Correct or am I off base ?

 

[Perry Babin]

You have to build it to be compatible. The winding ratio (primary to secondary) determines the unregulated voltage of the supply.

If you build an unregulated supply, you have to use a ratio that will not produce more than the maximum voltage that the amp can handle. If you're using chip amps, the absolute maximum supply voltage is listed on the datasheet.

If you build a regulated supply, you will over-wind the secondary. Without regulation, this would cause the transformer to produce too much voltage but the regulator controls the duty cycle of the drive pulses and holds the voltage at the regulated voltage.

The unregulated circuit is somewhat easier to build but you'll lose a bit of power. The regulated supply requires a few more parts but the output voltage will not dip when the input voltage drops or when current demand is high (at high power).