Naos Raptor 10A Wiring

One of my current projects involves a Naos Raptor 10A DC/DC converter. When you search for a wiring diagram a lot of e-cigarette mod related wiring diagrams pop up, they show which components to use, but do not explain why they are dimensioned as they are or what they do at all.

Some of them are quite obvious, depending on your knowledge about electrical circuits. Most of them can of be derived from the Naos Raptor 10A datasheet. And one clever hack is included.

Pin 5, resistor in series to the Potentiometer. This one may be obvious since the potentiometer is used to adjust the voltage the resistor in series is the lower limit. Why is it 220Ohm? Because from the datasheet you can see that the lowest resistance allowed is 220Ohm, at this resistance the converter will deliver 6V. The max limit is unlimited ohm, basically not connected at all. At this point it will only deliver about 0.6V. With about 2k9 Ohm the converter will deliver 1V, so to have a nice range, we substract the min from the max and have a value that would make sense for the Potentiometer:

2900 – 220 = 2680

A cap between  pin 2 and 3. Those pins are the input voltage, so I suspect some kind of smoothing. Consulting the datasheet I see that it is in deed there to smooth out the inputs ripple voltage. The converter expects a low ac source, and this helps to filter that “noise” that may be produced by inductive sources. Suggested is one or two 22uF ceramic caps in parallel. So since my supply voltage will be quite smooth I am opting for a single 22uF cap.

Resistor between pin 1 and 3. Pin 3 is ground, pin 1 is On/Off and is high active. So this resistor is just a pull down resistor. Consulting the datasheet we can see, that it is not only a pull down resistor, but since the state for undefined is on, this resistor defaults the module to be off.

So now to the really interesting part, the Z diode. What does that do? Well, that is what I call a nice hack: The Z Diode. in this case a 5.6V one will let current through in reverse direction as long as the supplied voltage is above 5.6V. In the above example the circuit is driven by two 18650 batteries. The are rated for 3.7V and should not be discharged below 2.8V, since two of them are in series, the threshold for discharge is 5.6V. Very clever.