PSU Characterisation with Rigol Equipment using SCPI

Introduction 
This brief blog provides a hobbyist solution for characterising the performance of devices such as DC supply modules using measurements from SCPI-capable test equipment.

Set up for Power Supply Test Fixture

Datasheets and Measurements
In most cases, the datasheet for a piece of hardware, be it a component or a printed circuit assembly (PCA), will provide sufficient information. For other cases, the performance or characterisation of the hardware requires a specific test or behaviour to be verified or quantified.

DC Supply Module Test (Example)
In this blog, the power-up voltage of an off-the-shelf power supply module was logged for different temperatures. The Device Under Test (DUT) was the STS1024S05 from XP Power.

A small test fixture was created to test multiple XP Power modules. In this example blog, the schematic shows connections to the supply.

Schematic for Test Fixture

The test fixture used pogo pins to connect to the castellated power module pads and banana sockets to interface with the test equipment.

Assembled Test Fixture with Device Under Test (DUT)

Test Software
The project's test software was originally started with Lab Windows. However, with many PyVISA Python examples available, Python in VS Code was selected instead. A Python script from Core Electronics was almost identical to the script required test setup, so the script was modified for this example. All credits to the team at Core Electronics for the original Python script.

Changes were made to the original script to suit the test setup. In the updated script, the test equipment type, the voltage step size of 100 mV, and the reported and logged voltages were updated as published here.

Measurements
The temperature was verified with a PC210 thermal camera for the duration of the measurement. The temperature variation was around 5 °C, which was attributed to the heating and cooling equipment. 

A full listing of the measurements is available in a combined Excel file here. 

Plotted below are measurements for the voltage range between DC 5.0 V and 6.0 V, where the DUT output was activated. The plot indicates differences in the DUT turn-on voltage for the temperature range sampled.

Measurement Results with STS1024S05

Drill Press Controller Update Part 3

Introduction 
This blog details retesting the drill press controllers' DC-DC power supply, fitting components related to the outputs and testing the output drivers.

Retesting the Power Supply
The original inductor fitted to the PCB (Printed Circuit Board) was removed and replaced with a 10 μH inductor. Testing the supply with the same load as the last post, the regulation at 165 mA and 330 mA was better than 0.1 %. The unloaded voltage was measured at 3.36 V, which is within component tolerances.

A short regulation test was made on the output of the AC-DC bricks after fitting the necessary parts to the PCB. The bricks output was as expected in tolerance.

PCB Setup for Power Supply Testing

Fitting Output Connected Microcontroller
The microcontroller and associated output hardware were fitted to the PCB, after which tests were performed. For the relay outputs, the output driver VND5160J was fitted to the PCB and then load tested. Separate FDN337N devices control the emergency stop and status LEDs, which were also checked.

Solid State Relay (SSR) Outputs
Following the fitting of the microcontroller and the output driver for the SSR, an external AC supply, SSR, and mains lamp were connected.

Instead of the previously mentioned SSR from TE, part SSRD-240D25A, a Multicomp MPKSI240D10-L(070) was selected. The control voltage for the Multicomp part is between DC 4 – 32 V, meaning an installation can be configured with one or two SSR devices. The clip below shows a lamp connected through the SSR powered by a transformer. The PSoC was programmed to toggle the SSR control input.

For reference, the output of the SSR was captured on an oscilloscope.

SSR Output

Status and Emergency Stop LEDs
The EAO illuminated pushbutton featured in the original drill press design was listed as superseded and replaced with the EAO part 84-5241.2B20. The original code was updated to flash the status LED, indicating the code was operating. No changes were needed for the Emergency Stop LED. In the clip below, both LEDs are shown operating.

In the next post, the input circuitry will be fitted and tested.