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I bought one of these inexpensive MB102-style breadboard power supplies (Elegoo brand) and the output voltage I measure is incorrect. It is supposed to be 5 V but it is only 4.24 V.

I thought it might be defective so I bought a second one made by a different manufacturer and it also does not produce 5 V. Instead, it produces 4.46 V.

In both cases the 3.3 V output voltage is correct.

So is this problem with the 5 V output voltage then typical of these MB102-style units? Is it an issue with the design perhaps, or just bad build quality? Or maybe it's because ~4.3 volts is often considered "good enough"?

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    \$\begingroup\$ What are you powering it from? Linear regulators need voltage headroom to do their job. Without this headroom they just try and pass the voltage through as best they can with a drop. \$\endgroup\$
    – DKNguyen
    Oct 23, 2019 at 14:00
  • \$\begingroup\$ And yes, I know if I want better control over my voltages I need to be using a proper bench power supply. Yes, I know these MB102 items are cheap and potentially unreliable. I am just wondering if anyone else has any experience with them and/or has any information about the output voltage. \$\endgroup\$ Oct 23, 2019 at 14:02
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    \$\begingroup\$ Impossible to say if you don't give me the voltage rating of your wall wart. \$\endgroup\$
    – DKNguyen
    Oct 23, 2019 at 14:05
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    \$\begingroup\$ @DKNguyen I am using a "Switching Universal Power Supply" rated for output at various voltages (in my case I measure 6 V) and a current of 1700mA. And when I read the specs on the MB102 the minimum input is 6.5 V. Put this in an answer and I'll mark it answered! \$\endgroup\$ Oct 23, 2019 at 14:09
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    \$\begingroup\$ MB102 items are cheap and potentially unreliable. They're absolutely fine for hobby use as long as you understand their restrictions which are the same as for any other linear regulator.So that means: supply enough input voltage (my guess, at least 7V and that needs to be a smoothed voltage (little ripple) ) and to not draw too much current. Drawing more current than the regulators can handle will make them hot and go into thermal protection mode. \$\endgroup\$ Oct 23, 2019 at 14:11

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Linear regulators need voltage headroom to do their job. Without this headroom they just try and pass the voltage through as best they can with a drop. You aren't supplying the regulator with enough voltage.

Too much headroom and it will overheat since it works by burning extra voltage off as heat.

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  • \$\begingroup\$ Yes, it appears my input voltage was incorrect. As mentioned above, I am using a "Switching Universal Power Supply" rated for output at various voltages (in my case I measure 6 V) and a current of 1700mA. And when I read the specs on the MB102 the minimum input is 6.5 V. \$\endgroup\$ Oct 23, 2019 at 14:15
  • \$\begingroup\$ I'd suggest looking for a compatible DC adapter with output between 7-8v at 1-2A or so. \$\endgroup\$
    – rdtsc
    Oct 23, 2019 at 15:15
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These supplies use LDO voltage regulators (1117) - maximum dropout is only about 0.8V according to the datasheet, so they can operate as low as 6ish volts. In general, yes, linear regulators require more voltage but LDO's have a much smaller difference in voltage differential between the input and output. Also, these regulators are limited to a maximum of 16 Volts in. I have also seen where the output voltages are mislabeled - the 3.3V puts out 5V. I would always check these with a meter before plugging into a breadboard.

Also, not too hard to repair - I was able to replace the regulators by clipping the leads and just heating up the top tab.

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  • \$\begingroup\$ One answer only please per question, edit your answer \$\endgroup\$
    – Voltage Spike
    Sep 13, 2020 at 6:57

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