Modifying Another LTC3780 Board


I bought a new board on eBay, for ~ 10 Euros.

Compared to the old ones,  a few differences :

  • No current limiting. Not a problem, we'll add a different one anyway.
  • No tunable minimum voltage. It is hardcoded to ~ 5v
  • Much better connectivity
  • Bad thermal pad under the heatsink, you definitively need to set that right

Now let's have a look at the feedback loop :

So we have FB=Vout*3.3k/(3.3k+100k*Alpha)

Which can be expressed as 

Vout=FB(1+30*Alpha)

On the LTC, FB is 0.8v

Vout=0.8*(1+30*Alpha)

Vout is then between 0.8v and ~ 24v, that matches the spec.

The components are not high accuracy ones, the 3.3k is measured as 3k....

That it that one :





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