Analysis, operation, and modification of a switchmode power supply (SMPS) for variable output voltage


Lindsay Wilson did a teardown/modification of a Chinese SMPS to allow an adjustable output voltage:

I’m currently working on a product which uses a size 2430 “hobby” brushless motor and 25A electronic speed controller (ESC). In its “intended” use, the controller runs from two lithium-ion batteries with a total voltage of around 7.4V, but I want to run it from a mains-derived power supply instead. However, there are no off-the-shelf supplies available with that output voltage.
Fortunately, there is no shortage of inexpensive Chinese switchmode supplies with standard outputs of 5,12,24V etc. Most (all?) of these have the ability to adjust the output voltage slightly, by around ±10%. I reckoned that it should be possible to modify such a supply to provide a fully-adjustable output voltage which could be set to the desired 7.4V. This is by no means a novel idea – many people have modified supplies (a common mod is to increase the output to 13.8V, for ham radio use) – but I haven’t seen a good operational analysis of these supplies, so it’s a good excuse to do some detective work and figure out what makes them tick.

Full details at Imajeenyus homepage.

Check out the video after the break.

Teardown, repair and experiments with the Anritsu 37347A 20GHz Vector Network Analyzer

Here’s another great video teardown from TheSignalPath:

In this episode Shahriar repairs an Anritsu 37347A 20GHz Two-Port Network Analyzer. The unit does not boot up and as a result its internal state is unknown. The boot fault is traced to a bad RTC module which has a built-in integrated battery. A replacement unit is located which allows the unit to fully boot.
The instrument initially displays an unlock condition on the internal PLL. This problem is resolved by loading the PLL calibration files from the HDD. The complete block diagram of the unit is examined in detail and an unusual PLL intermittent locking problems is demonstrated. Various measurements on several of the internal PLLs confirm their functionality. As a final experiments, the instrument is calibrated and the S-parameters of a tune-able band-pass filter is measured.

More details at The Signal Path homepage.

Inside card sorters: 1920s data processing with punched cards and relays


Ken Shirriff did an in-depth write-up of the punched card sorter:

Punched card sorters were a key part of data processing from 1890 until the 1970s, used for accounting, inventory, payroll and many other tasks. This article looks inside sorters, showing the fascinating electromechanical and vacuum tube circuits used for data processing in the pre-computer era and beyond.

More details at Ken Shirriff’s blog.

Check out the video after the break.

Elektor 500ppm LCR meter case tips

LCR meter

NopHead wrote a blog post review of Elektor 500ppm LCR meter:

I recently bought a 500ppm LCR meter from Elektor because I didn’t have anything for measuring inductors or the ESR (equivalent series resistance) of capacitors, both of which are important for modern electronics, particularly switch mode regulators that have become ubiquitous.
It is also more accurate than any of my multimeters and has wider measurement ranges. For example it can measure resistance from 0.1mΩ to 1GΩ and capacitance between 0.1pF and 0.1F. This means I can now measure parasitics like contact resistance, stray capacitance and lead inductance. The principal reasons it can do this while my multimeters can’t is because it uses a four wire Kelvin connection to the device under test, and as well as measuring voltage and current, it also measures the phase between them.

More details at HydraRaptor blog.