The Spark Gap · 17 Sept 2014 · 38m
Hosts Carl and Corey explain the design and operation of an adjustable constant current electronic load (E-load), detailing how to build one using a MOSFET, a sense resistor, and an op-amp. They discuss critical component selection, emphasizing the importance of low temperature coefficient resistors and the Safe Operating Area (SOA) graphs for MOSFETs to prevent thermal failure. The conversation covers practical challenges such as driving high-capacitance gates, managing heat dissipation across different voltage rails, and using parallel resistors to improve precision and power handling.
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Dave Jones of EEVblog and Chris Gammell of Contextual Electronics discuss the technical nuances of 1N400x diodes, specifically why manufacturers produce multiple voltage ratings for the same package, and Gammell’s transition from Fusion 360 to FreeCAD. They also cover the internal operation of the LM317 linear regulator, the ongoing global semiconductor shortage affecting parts like the RP2040, and the importance of lab organization and measurement traceability.
Dave Jones and Chris Camel discuss the quirks of online circuit simulators like Falstad and LTSpice, specifically the confusing use of 'beta' for MOSFETs. They analyze Derek Muller's (Veritasium) follow-up video on energy flow in transmission lines, debating Poynting's theorem versus the lumped element model. The conversation shifts to embedded systems debugging with SEGGER tools, the ongoing microcontroller supply chain crisis, and the challenges of adopting open-source solar microinverters.
Chris Gammell and Dave Jones discuss the challenges of finding replacement components, specifically a Sino Power MOSFET with built-in ESD protection, and the broader issue of obscure semiconductor sourcing. They analyze the technical and economic trade-offs of using SO8 packages versus power packages, and the scarcity of ideal diode controllers. The conversation shifts to the practical failures of floating solar farms and the complexities of grid management, before concluding with an analysis of the current hardware engineering labor market, focusing on the disparity in compensation between software and hardware engineers and the impact of remote work mandates on retention.
Hosts Dave Jones and Chris Gammell take calls from Trevor Sutherland, Todd, Sam, Arsenio, Chris Kessler, and William regarding power grid generators, surface wave transmission, multimeter troubleshooting, and product development advice. They diagnose SCR latch-up in a power sequencing circuit for Chris Kessler and discuss the challenges of measuring microamp currents for William's USB tester. The episode concludes with updates on Dave's EEVblog multimeter crowdfunding and upcoming travel plans.
Matt Liberty, creator of Joulescope, explains the engineering challenges of measuring high dynamic range currents in low-power IoT devices, specifically addressing the difficulty of switching between milliamp active states and microamp sleep states. He details how Joulescope uses a shunt ammeter design with seamless auto-ranging to minimize burden voltage, preventing device brownouts, and leverages Lattice iCE40 FPGAs for precise, sub-microsecond switching. The conversation covers practical applications for optimizing firmware power profiles, debugging leakage currents from components like bypass capacitors, and managing the supply chain and manufacturing processes for a small-batch hardware startup.
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