3 ms·

I have one of the more basic UNI-T multimeters and can highly recommend it. It's always there when I need it (the single 9V battery keeps it going for years) an

I have one of the more basic UNI-T multimeters and can highly recommend it. It's always there when I need it (the single 9V battery keeps it going for years) and has great precision. One thing that I don't have - and really want to have - is a variable power supply with constant voltage/current. They can be used when you have an unusual battery you need to charge safely, for instance. Unfortunately, they always seem inordinately expensive considering that all they are inside is a few coils and some ICs. I've looked into building one myself, and found the very informative EEVBlog series on it[1]. However, there's one thing I don't understand: how do you compensate for the voltage drop over your current measuring resistor? Is it a simple linear equation and you just boost the voltage accordingly? I'd love an explanation! [1]: https://www.youtube.com/watch?v=CIGjActDeoM https://www.youtube.com/watch?v=CIGjActDeoM

dekhn 3y ago
Just buy this: https://www.amazon.com/gp/product/B00FPU6G4E https://www.amazon.com/gp/product/B00FPU6G4E worth every penny the answer to your question is in Art of Electronics.
- qbasic_forever 3y ago
  Yep I've had that Korad for years and it's great. I'm sure there are far better power supplies out there but this one is great for hacking on digital stuff and maker projects that aren't demanding or sensitive to the PSU quality (which is like 90% of projects).
sersnth 3y ago
In a power supply you can sense your output voltage with a differential amplifier between the positive and negative outputs that way the voltage drop across your current sense resistor is not included in the measured differential voltage. Alternatively you can use high-side current sensing where your current sense resistor is before your positive output. You can also use a differential amplifier for that, but there are purpose made current sense amplifiers which are probably best.
crote 3y ago
The reason lab PSUs are so expensive is that they are incredibly stable. A regular cheap power supply will provide a sort-of stable voltage, but there will be a loooot of noise on it. Meanwhile, even a basic lab PSU will guarantee the output voltage to within a few mV, no matter what you throw at it. This allows you to completely rule out the PSU as a potential source of faults.

dekhn 3y ago

Just buy this: https://www.amazon.com/gp/product/B00FPU6G4E https://www.amazon.com/gp/product/B00FPU6G4E worth every penny the answer to your question is in Art of Electronics.

qbasic_forever 3y ago
Yep I've had that Korad for years and it's great. I'm sure there are far better power supplies out there but this one is great for hacking on digital stuff and maker projects that aren't demanding or sensitive to the PSU quality (which is like 90% of projects).

sersnth 3y ago

In a power supply you can sense your output voltage with a differential amplifier between the positive and negative outputs that way the voltage drop across your current sense resistor is not included in the measured differential voltage. Alternatively you can use high-side current sensing where your current sense resistor is before your positive output. You can also use a differential amplifier for that, but there are purpose made current sense amplifiers which are probably best.

crote 3y ago

The reason lab PSUs are so expensive is that they are incredibly stable. A regular cheap power supply will provide a sort-of stable voltage, but there will be a loooot of noise on it. Meanwhile, even a basic lab PSU will guarantee the output voltage to within a few mV, no matter what you throw at it. This allows you to completely rule out the PSU as a potential source of faults.