• Author Author: ralphjy
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Tenma Handheld DC Power Supply - USB Output Functionality

ralphjy

One of the more obvious shortcomings of this power supply is that the documentation is poorly written and inaccurate.  The operational modes of the power supply are reasonably easy to verify, so this probably is not that big of an issue.

 

The next function that I'm verifying is the USB outputs.  There are two USB A jacks each labeled 5V 2A.  Since the power supply will only provide 3.75A  total, you can't get 2A simultaneously from both outputs.  The outputs are provided for charging USB devices but I'm hoping to use them to characterize some USB powerbank circuitry.  The functional description in the user manual is somewhat confusing so I'll need to determine how they actually operate.

 

The USB outputs are referenced in 3 sections of the user manual.

 

Quick Start Section 1.3

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Output Check Section 1.4

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Operation Section 3.8

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So, here's what I actually see on the power supply.

  1. The default settings for USB are 5.1V and 2.5A, You cannot adjust the voltage in USB mode which means that I can't use these outputs the way I wanted.  I'll just need to build an adapter to interface a USB socket to the regular output jacks.  Both Sections 1.3 and 1.4 state that you adjust the voltage, but in USB mode you can only adjust the current.  All Sections have the default voltage incorrectly as 5.2V.  Section 3.8 implies that the USB outputs are doing port detection so maybe need to stick to using these only as charging ports.  It would have been nice to be able to adjust the voltage in this mode.
  2. One thing that you need to be aware of is that when you are in USB mode and you turn on the output - the voltage is also present at the regular output jacks. 
  3. When you turn on USB mode:
    1. If the output was enabled it will shut off
    2. The voltage and current settings will change to 5.1V and 2.5A
    3. You can then change the current setting but I'm not sure how this makes sense if there is port detection.  I'll need to look into this more.
    4. Section 3.8 incorrectly states that the voltage will display before the output is turned on.  You will see 0V.
    5. You then enable the output which enables both the USB and regular output jacks and current and voltage can be displayed.
  4. When you turn off USB mode:
    1. The USB outputs will turn off but the regular output jacks will remain on at the USB settings unless you also turn off the output.
    2. The voltage and current settings prior to entering USB mode are not recalled (there is a separate function to save and recall settings).

    

The USB ports could be handy but if they're only used for charging, I would have preferred if they were implemented as fully independent from the power supply output..