LED Constant Current Driver Circuit Design An LED converts current into light, and the voltage across it is a consequence rather than a control. A constant current driver is therefore the normal way to power one, and the design questions are about where the current is measured, how much voltage…

Battery Charger Constant Current Constant Voltage Design A rechargeable lithium cell charges in two phases, and the circuit that does it has to switch between them without overshooting. The transition, the accuracy of the two set points and the way the charge is terminated are what separate a charger that…

Wave Solder Flux Application and Control In wave soldering the flux has to do its work in seconds, on a surface that is partly oxidised by the preheat. How much flux is applied and how it is applied decides whether the joint fills and what residue is left behind. What…

DC-DC Converter Input Filter Design A switching regulator draws a pulsed current from its input, and everything upstream of it sees that pulse train as noise. The input filter is what keeps the noise out of the supply, the cable and the rest of the system, and its design is…

Solder Paste Metal Load and Powder Selection Solder paste is a mixture of metal powder and flux, and the ratio between them is the metal load. It affects the print, the reflow and the residue, and it is one of the few paste properties that can be compared directly between…

Conformal Coating Adhesion and Surface Preparation A conformal coating that lifts from a surface has failed at the interface, and the interface is decided before the coating is applied. Adhesion is a surface property rather than a property of the coating. What Adhesion Requires The coating must wet the surface,…

Component Tolerance Stack Up In Assembly Every dimension on an assembly drawing is a nominal value with a tolerance, and the clearance that decides whether the product fits together is the difference between two or more of those dimensions. Whether the parts still fit when each dimension sits at its…

PCB Etch Process Control in Outer Layer Fabrication Etching is the step that turns a plated image into copper conductors, and it is the last chance the process has to hold the line width that the design assumed. Controlling the etch process means controlling chemistry, equipment and the steps that…

AI Vision Processor Board Design for 8K Camera Systems A camera that records 8K video and runs neural network inference in the same device puts two heavy loads on one board. Designing around an ai vision processor means planning the high speed interfaces, the power delivery and the thermal path…

Solder Paste Aperture Area Ratio and Release The area ratio is the aperture area divided by the aperture wall area. It is the single number that predicts whether a stencil will release paste well, and it is easier to calculate than to measure. Why the Ratio Matters When the stencil…