Teensy + Transistor Array (how to get common ground?)

A

airpanther

Active member
I have been able to use the ULQ2003 (NPN transistor array) to control high voltage outouts with the Teensy 4.1. Works quite well, but the problem is, it makes the outputs common positive voltage instead of commmon ground. This means significant rewiring of my common ground circuits.

Any idea how to get common ground using a transistor array (or something else)? Am i using the wrong array or component altogether? I need to be able to control 30V devices woth the Teensy, which the ULQ does very well. Equivalent PNP arrays seem a lot harder to find, especially in a surface mount package.

I thought about level shifters, but I need the supply voltage to be able to be different for each pin.

Any thoughts are appreciated.
 
airpanther said:
it makes the outputs common positive voltage instead of commmon ground
Click to expand...
I'm not sure that I understand you fully.
The ULQ2003 is a low-side switch: it switches an individual output to the common GND at pin 8.
ULN2003inner.png

The COM pin #9 is for the common-cathode suppression (flywheel/flyback/catch) diodes when you are switching inductive loads like a relay.
When you are switching resistive loads, you can leave pin 9 unconnected.
ULN2003.png
Capture.PNG

Paul
 
Good point. Issue is, since it is switching against ground, the power supply has to be attached on the side of the device opposite the ULQ2003 output pin. So for instance, in the image below, the LED negatives are connected to the individual ULQ output pins, and the positive ends of the LEDs are all tied together, which effectively makes this a common positive from a wiring perspective. Maybe I'm connecting it wrong? Any way to make it where all the grounds can be tied together instead, and the positive side of the LED connected to the output pins instead?

ULQ2003.jpg

Thanks!
Robert
 
Except for the current limiting resistors for the LEDs, the schematic is OK.
What you are looking for is a high-side switch, useful info here.
High-side switches are also known as "load switches".
With a high-side switch array, the anodes of the LEDs would be connected to the output pins and the cathodes grounded together.
I'm not familiar with a commonly used high-side switch array though.

Paul
 
in the image below, the LED negatives are connected to the individual ULQ output pins, and the positive ends of the LEDs are all tied together, which effectively makes this a common positive from a wiring perspective
Click to expand...
No, it makes it a common-anode LED array, driven from a low-side driver array (which is common ground).
 
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