Re-building Crest Audio LT1000

[darw82]

Dear All,
I'm building LT1000 amplifier. When I take a look the schematic closer. I think I found an error. But I'm not sure.

Please see attached picture or you can download the schematic at
http://www.crestaudio.com/media/pdf/LT_Schematic.pdf

The sense resistor output votage (below low side FET) is negative, while the over current offset voltage is positive. How come this work?

Please tell me, is this an error?

Thank you

[darw82]

Here is the board layout.

[boonthae]

do you have pcb file!

[luka]

Hi

On this resistor you get image of negative and posivit current, so both + and - lines are protected. I think there is no error.

I have is the same just without amp. But I do have sense resistor on both rails

[darw82]

Luka,

Are u sure this will work? I have simulate it using electronic workbench. It doesn't work.

But if this work. I'll build exactly same with the schematic.

Anyway, I also have a question regarding the power supply.
This amp will be use in car.

I seen many car amplifier, using open loop push pull power supply and without output inductor.

The question is,
1. which is better. open loop or closed loop?
2. Should I use output inductor in the power supply?

Thanks.

[luka]

Hi

Op amp is there to amplifie thevoltage drop on resistor, after that it is the sam I have. when overcurrent is detected, 555 is trigered and shuts down amp. I didn't realy check if this happens for both sides, but it sure does for lower side. If you are not sure you can make the same circuit for upper resistor and drive the same 555

electronic workbench is not good for testing, I have used multisim with is adv. electronic workbench.

1.) Don't know what would be better but I will go for closed loop, so that I can make solid rails without saging for power that I need.
2.)I had, but many don't. I don't know why not. Probably because they have open loop.

[darw82]

If you are not sure you can make the same circuit for upper resistor and drive the same 555

It will be more complicated if sense resistor placed in high side configuration. I'll need differential amplifier, such as INA168. But I try to build this overcurrent module only. So if this doesn't work. All I need to do is change it. not the whole amp.

By the way, I have attached super large picture of this board + the protel 2004 file on your email.

Thanks.

[luka]

Hi

Thank you very much. Please do let me know how it will work. Use "modules". One would be this overcurrent. So if something doesn't work you just make new one.