# Using resistor network instead of regular resistors

This might be a simple question but I'm kind of new to resistor networks so for me it's not so straightforward:

I have a digital electronics project. As part of the project I have 8 pins of an IC connected to 8 LEDs. Each LED has its own 100 ohm resistor (it sits between the IC and LED itself).
In order to simplify the PCB design I'd like to use a single 100 ohm resistor network for those LEDs instead of each LED having its own resistor.

Is it possible? How should I connect the replacement exactly?

This is a simplified part of the schema involved (I drew only 2 LEDs and resistors for simplicity). The LEDs are typical 3 mm Kingbright. All 8 LEDs might be on at the same time but for very short period, less than a second.

• Please link the data sheet for the resistor network. Commented Apr 1 at 17:02
• It's possible, but the array might build up more heat, as it's in a tighter spacing, so check the datasheet. Please share a sketch of a circuit you are planning to make. Commented Apr 1 at 17:02
• In the special case of only one LED being on at a time, you can use a single resistor. Depending on your circuit and its application, you may be able to use a device that has built in current limited LED driver pins.
– vir
Commented Apr 1 at 17:52
• I have attached the circuit Commented Apr 1 at 20:46
• Arrays seem neat.. until they go end of life. I now prefer the flexibility of single resistors, both from a layout and sourceability perspective. Commented Apr 1 at 23:49

It depends on the exact topology of your array, but it's generally possible.

Supposing you have an IC configured as follows:

simulate this circuit – Schematic created using CircuitLab

Assuming that the current requirements (and necessary voltage drop) of each resistor is low enough (so that your resistor network part doesn't overheat), you can directly replace your eight resistors with a resistor network of eight isolated resistors on the same package. These networks are just eight independent resistors sharing a package, as shown in this screenshot:

(all datasheet screenshots are from https://www.ctscorp.com/wp-content/uploads/74x.pdf)

You can also do this with a bussed resistor network, having a topology like this:

However, because all of the resistors are tied together on one end, may need to rearrange your initial circuit a bit first if it isn't already designed with resistors tied together:

simulate this circuit

Swapping the order of series components (resistance and diode) like this won't change their behavior significantly.

In this case, the common pin of the network goes to the supply rail, and each individual resistor pin goes to the LED.

• Yes, initial drawing you posted looks very like what I have. Please check my updated question for actual schema involved :) Commented Apr 1 at 20:51
• @guest86 Yes, in that case you can use independent resistors with no changes, or tied/bussed resistors by switching the location of LEDs/resistors in the schematic as shown. JUst connect the shared net to your transistor rather than directly to a supply rail. Commented Apr 1 at 20:53
• Hmmm but I think (I might be wrong) there's a problem. Each of those 2N2222s from my schema controls 64 such LEDs (I'm building a LED cube) so a resistor network behind LED wouldn't work in that case, right? Commented Apr 1 at 21:03
• @guest86 A resistor network of independent resistors would always work topologically (thermal limits are a different thing). It's just some number of independent resistors physically epoxied together. If you have 64 LEDs under a single 2N2222, you can have eight bussed resistor networks of eight resistors each with the commons tied together to the transistor, and the individual ends connected to each LED. Again, the relative position of the LED and resistor can always be swapped from a schematic standpoint, as long as each LED is in series with its corresponding resistor. Commented Apr 2 at 14:06
• @guest86 see the last schematic in my post; the schematic editor is too hard to use on my phone. The three resistors in that schematic can be three resistors with a common connection on one end in a resistor network package Commented Apr 2 at 15:27

Yes it is possible, and commonly done in commercial equipment.

There are different types of resistor arrays, some have one pin of each resistor available, and the other end of the resistors are all connected to one common pin. These are good for things like pullups or pulldowns where you need a bunch of the same value resistors all connected to Vcc or ground. Others have each resistor independent from the others, both sides of each resistor have pins to connect them.

You can generally use either type for LEDs, to use the ones that have a common pin you would just move the resistors in your circuit to the other side of the LEDs so that you can hook the common to your LED power or ground depending on if you're driving them high side or low side. For the ones without a common connection just wire them like regular resistors.

You do need to be mindful of total power dissipation, I've seen a number of products that used resistor arrays for 7 segment displays have segments go out because the resistors had failed from overheating.

You can do this if you use networks that are appropriately rated (watch the power rating and allow adequate safety margin for your environment extremes and reliability requirements). It's a very common approach. If you have a spare resistor or two you can combine them in series or parallel to make other values.

The most flexible networks to my mind are the 4 resistor networks with both sides of each resistor brought out. A 1206 (Imperial) Yageo YC-164 4-resistor network is rated for 1/16 W for each resistor so if you derate to 50% that's only about 30mW each. Smaller networks such as YC-104 have half the rating (and are not marked).

Note that (depending on your via diameters etc. ) it may not make the PCB all that much smaller or easier to lay out since you've now got some strong constraints on where the traces have to go and SMT layouts are naturally almost like single-sided PCB layouts.

It's also a bit less convenient to deal with since switching resistor positions to ease layout and avoid vias and/or leave a more intact ground plane involves back-and-forth between layout and schematic. This will be easier with some EDA software than with others. That's optional, of course, and there's the intermediate step of just flipping (not rotating, you can do that in layout) the network on the schematic when the traces are all coming out twisted.

• Well my idea is to have as little holes to drill and solder as possible because i'm actually building a 8x8x8 LED cube so I'll have (in total) a lot of LEDs and resistors so I'm trying to make some adjustments to simplify the process :) Commented Apr 1 at 20:54
• I suggest you give it a try and see if it helps. Commented Apr 1 at 21:37