Improved current limiting with LTC3780 (part 1)


The existing max current control on the board works as follow :

Current is sensed through a 7 mOhm shunt and multiplied by a variable factor driven by the pot.
The output is then connected to vSense via a diode.

As soon as the output rises over 0.8v, the voltage goes back.

It works, but you have to to it blindly, not easy to measure a gain (resistance) for display purpose.

Let's have a look at the schematic (more detail at beyondlogic ) :



Note that the - output of the DC/DC converter is not directly connected to the - of the input !

The idea here  is to modify as little as possible the existing board.
Additionnaly, messing too much with VOSENSE will destroy the  circuit.

Good news, we have a very good candidate : The diode

On one side, we have a voltage proportional to the current, on the other side the control.

So let's tune the current pot to have a max output of ~ 400 mV, remove the diode and pull two wires to a secondary board.

The chip to remove is that one (double check with a multimeter it's a diode !) :

Not difficult to remove, there is a bit of room around.

So now we have a voltage proportional to the current and a control pin to back down the DC/DC converter.

Part2 : Add a secondary control board.


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