ULN2003A driving IRF540N mosfet

Question

Hey guys,

I am trying to expand the number of outputs on a board that I built 6 months ago that controls high current LED strips but am unsure if the following would work. Could someone please let me know if what I am trying to do in the following schematic will even work??

Thanks is advance.

PS: I am aware of the 'negative logic' on the march 2014 version.

Robert Peter Oakes · Answer

The ULN2003 is not providing a voltage to the mosfet, it is an open collector device (Meaning it can ONLY sink current, not source it) and will only be able to sink the voltage provided to the mosfet through the resistor (R2 in your diagrams above), when the ULN2003 output is turned on fully it will try to take its output to ground but because of the characteristics of a transistor, the Collector to Emitter voltage will never go below 700mV even with a low current which is the case here. see this excerpt from the data sheet Look at the Vce(sat) for what were talking about If you want a device compatable with the ULN2003 but with better Vce then go for the FET version from TI, the "TPIC2701 7-CHANNEL COMMON-SOURCE POWER DMOS ARRAY" its on voltage is significantly lower and it is basically the same device to you Data sheet here http://www.ti.com/lit/ds/slis019a/slis019a.pdf in the diagram below the equivalent parameter is the Vds(on) So its not that the device is preventing the gate voltage to the MOSFET going high enough, it is just there's a risk it cant pull it low enough to turn off the MOSFET completely as the MOSFET Vgs(threshold) is typically 2 - 4V. It should be ok, but there is not much room for error with the ULN2003, the 2701 on the other hand is way better Here is the snipet from the mosfet datasheet, look at the Vgs(th) Hope this helps