# resistor on top of each other....?

#### supermankid

Joined May 26, 2013
54
Why is the resistor placed one on top of other...instead of using a separate voltage divider from the battery to compare the voltage....this resistor one on top of other just makes it look more complex and complex for calculation too....

Is there a special reason....a hidden trick in this circuit....I don't see the meaning of just complicating(besides saving...3 resistors)....

FYI: MAX8214

#### alfacliff

Joined Dec 13, 2013
2,458
it is a voltage devider. just has a lot of taps probably a adc (analog to digital converter) why would you want individual voltage devders? it sis a voltage devider ladder.

#### Dodgydave

Joined Jun 22, 2012
10,139
Its a voltage ladder,each junction has a different voltage going lower from top to bottom,so that each comparator switches on as the battery voltage decreases,it uses less resistors than your conversion.

#### crutschow

Joined Mar 14, 2008
28,580
By my count it save one resistor, but that's the reason it's preferred. Never use more components then you have too, especially just to simply a calculation.

To simplify the calculation of the string and avoid having to solve any simultaneous equations, you can start out by deciding what current you want through the network (it looks like about 7 microamps for the network shown). Then calculate the resistor values to give each of the desired trip-point voltages for 7 microamps through each resistor starting from the bottom and going to the top. That way you only have to solve one or two simple equations for each resistor value.

#### MrChips

Joined Oct 2, 2009
25,063
Because if you use n voltage dividers you will have severe non-linearity and possible non-monotonicity.

Using a ladder network reduces the non-linearity.

#### NorthGuy

Joined Jun 28, 2014
611
For n-tap ladder you need n+1 resistors. For n individual dividers you need 2n resistors. So you save 2n - (n+1) = n-1 resistors.

#### wayneh

Joined Sep 9, 2010
17,160
Personally, I find the ladder simpler to understand, draw and build as well. To my eye, it's not more complicated, just the opposite. One glance and you see all the reference voltages at once. And it's not just numerical, the ladder arrangement actually gives a graphical cue about how the reference voltages are related.