Troubleshooting my ULN2003A Chip Setup

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SUMMARY

The ULN2003A chip is a darlington transistor array that does not step up voltage; it operates at the supply voltage provided. In this discussion, the user connected pin 1 (IN1) to 5V, expecting an output of approximately 50V, which is a misunderstanding of the chip's functionality. The output voltage will be slightly less than the supply voltage, confirming that the setup is correct but the expectations regarding voltage increase are incorrect. The datasheet clarifies that the output is limited to the supply voltage, and the chip includes a flyback protection circuit for inductive loads.

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  • Understanding of ULN2003A chip functionality
  • Basic knowledge of darlington transistor arrays
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  • Research flyback protection circuits and their importance in inductive load scenarios
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Electronics enthusiasts, hobbyists working with stepper motors, and engineers looking to understand the ULN2003A chip's operation and applications.

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I recently purchased a few ULN2003A chips with the goal of eventually powering a stepper motor. So far I'm just testing out the chips, but I've run into a bit of a roadblock. I'm not quite sure how to use the chips.

My setup is as follows:
I have connected pin 8 (gnd) to gnd. I have supplied pin 1 (in 1) with 5 VCC.
Using a resistor (because I don't have any LEDs) I have supplied one lead with 5VCC and the other lead to pin 16 (out 1). I then proceed to measure the voltage drop across the resistor and I get about 5 volts.

Since I'm supplying a constant voltage to pin 1, shouldn't it be stepped up to ~50V (the maximum)? Is my understanding of the chip's operation incorrect? Or do I just have the setup wrong?

The datasheet is available here [link]http://www.ortodoxism.ro/datasheets/SGSThomsonMicroelectronics/mXtyyvx.pdf[/link]
 
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The output voltage is limited to the supply voltage.
You should get slightly less then 5v with a 5v supply.
 
The 2003 is simply a darlington transistor array with all of the emitters connected together to one pin of the IC which is usually grounded. This IC does NOT step up voltage if that is what you are after. I believe the collector of each transistor is tied to the high voltage lead through a diode which forms a flyback protection circuit to protect the transistors against inductive loads.
 
Most likely this can only be answered by an "old timer". I am making measurements on an uA709 op amp (metal can). I would like to calculate the frequency rolloff curves (I can measure them). I assume the compensation is via the miller effect. To do the calculations I would need to know the gain of the transistors and the effective resistance seen at the compensation terminals, not including the values I put there. Anyone know those values?

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