Purple LT3042 ebay / aliexpress

[hkknudsen]

These new purple LT3042 boards are spreading on aliexpress and ebay like a virus, and they are very cheap.

But do they look to be any good? Would all that is needed to change the output voltage be to replace one of the resistors?

Thanks

 

[Mooly]

The output voltage is set via a single resistor on these. The data sheet gives details, and also describes the PGFB (power good feedback) which may or may not be used.

http://www.analog.com/media/en/technical-documentation/data-sheets/3042fb.pdf?domain=www.linear.com

 

[hkknudsen]

Thanks Mooly... my next doubt was if I am able to replace a smd resistor with a regular, but that seems possible (with my limited experience). And next is what others think of one that is that cheap (it's around half price of the usual offers).

Would I be right in assuming that I can get -10V, 0V, +10V from this one, by combining the 2 outputs at the 0V (can I be sure they're independent)?

 

[Mooly]

Replacing an SMD resistor with a regular one is fine as long as its done neatly.

I don't think combining two PSU's as you describe would be very successful, not least because each would need a truly independent voltage source feeding them.

 

[hkknudsen]

Not sure if we're talking past each other, but the last one is dual from the beginning, so I'm just wondering if I can combine those 2 outputs to +, 0 and -, which seems to me to normally be possible. Its just for a preamp drawing only 2 x 20mA or so, so I would'nt think the outputs would effect each other much

 

[Mooly]

My mistake, I was thinking of you combining to regular PSU's although I'm afraid the answer is still the same.

The one in the link definitely will not work as -10 0 10 because both regulators share the same bridge rectifier and reservoir cap which means that they will also share the same ground. This means there can not be any isolation between them.

 

[hkknudsen]

Aha, thanks, very useful! But if I buy 2 single's instead it'll be fine?

 

[Mooly]

Only if you run each from a separate isolated transformer winding. They can not share the same source voltage.

The two supplies have to be 100% independent to allow series connection.

 

[Luke]

Is it possible that they use fake reg chips?
If I buy 2K X LT1963 from mouser, they cost around 3 dollars, so how do these guys sell this for a profit?
LT1963 Power Converter 12V to 5V DC DC Step Down Buck Power Supply Module-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group

 

[hkknudsen]

Only if you run each from a separate isolated transformer winding. They can not share the same source voltage.

The two supplies have to be 100% independent to allow series connection.

Excellent, I finally get it. I thought the regulator itself was somehow a decoupling layer.

Thanks for your help and patience Fortunately I use 2 independant secondaries.

I am also a bit worried about the authenticity from aliexpress/ebay. I know that opamps can't be trusted at all, but have no knowledge about regs.

 

[Mooly]

I've no idea either whether the stuff is 100% genuine although its hard to see what the regs could be faked by. Opamps can be remarked but the reg is a special one off device.

 

[marcelooms]

I bought one of these cheap purple LT3042 boards. It looks ok, but the resistors dont match up with the data sheet.
I resistor R4 is open..
Does anyone know how to hook these up?

The output voltage is set via a single resistor on these. The data sheet gives details, and also describes the PGFB (power good feedback) which may or may not be used.

http://www.analog.com/media/en/technical-documentation/data-sheets/3042fb.pdf?domain=www.linear.com

 

[Mooly]

No idea tbh. The PCB vendor should provide basic details like that. You could perhaps figure it out by looking where each PCB connection point goes to and try and piece it together from the standard application circuit (data sheet examples).