Electronic load and ripple measurements

[salomonander]

Hey there,
Im often testing linear power supplies in audio equipment. I would love to have an electronic load for convenience. But would a dc load mess up my ripple measurements by introducing its own ripple to the measurement somehow? Ai told me its fine. But i never trust ai in case it is a problem, does it only apply to budget units? I see that some high end manufacturers list ripple current in their datasheets. Is that a critical value? The psus im testing are low noise - often lm317 circuits

Thanks!

Dont know how to post without this poll… oh well

[David Hess]

No, the electronic load should not be introducing even measurable amounts of ripple.

[twospoons]

*Should not*, but do. At least the Tenma one we have seems to have stability issues sometimes. Bad enough that I built a load bank out of manually switched power resistors for our load testing.

[lhk5195]

Code: [Select]

In fact, electronic loads already include ripple testing functionality. For example, the UNT8512+ I purchased recently has a manual that clearly specifies the measurement accuracy, and you need to determine whether it is suitable for your particular application.

[epitaxial]

There is a nice simple design published using the LM10 and a large pass transistor as a variable load. It's self powered and only uses a handful of passives besides those two parts. I've built it numerous times. The original schematic seems to have vanished from the internet but I have a copy saved. Let me try and locate the thing.

[zike]

There's a commercial product based on this open source design. The schematic and BOM are shown, as is a link to the original EDN Magazine article. I am currently testing one (Saelig carries them in stock). Very simple to DIY your own, too. Can't vouch for noise yet but there's not much to go wrong.

I use an East Tester 400W load and it's great, but it absolutely DOES put switch-mode ripple back on the DUT inputs. My HP6060B is significantly quieter if you are testing for microvolt-level ripple and noise. But I suspect these self-powered designs are best of all, short of a simple power resistor.

There is a nice simple design published using the LM10 and a large pass transistor as a variable load. It's self powered and only uses a handful of passives besides those two parts. I've built it numerous times. The original schematic seems to have vanished from the internet but I have a copy saved. Let me try and locate the thing.

[epitaxial]

Are the new cheap loads using a mosfet and doing PWM or something to achieve an average?

[zike]

Are the new cheap loads using a mosfet and doing PWM or something to achieve an average?

There are some reverse-engineering posts here and on YouTube; the East Tester output stage is a bank of IRF250's driven by LM324's in linear mode (this much I have confirmed by inspection). I don't know how the reference voltage is generated, if it's PWM or a static DAC. Either way, my guess would be the hash comes from an internal (low-power) switching supply that provides its operating voltages. IMO for all it needs to do a small linear supply would be a better choice, but I do not see any mains transformer inside.