Beware of Analog Switch Leakage Current
Leakage currents in analog switches can quietly wreck precision reference circuits at elevated temperature. Jason M. Sachs walks through three switch-topology implementations for a switchable 1.25 V reference and shows which topology gives the smallest worst-case output error using real part specs. He explains why op amp input bias is usually negligible and gives practical fixes: lower resistances, better switches, or limiting temperature range.
How to Analyze a Three-Op-Amp Instrumentation Amplifier
The three-op-amp instrumentation amplifier gives you high input impedance, improved net bandwidth, and much lower sensitivity to resistor mismatch than a single-op-amp differential stage. Jason M. Sachs walks through the algebra, numeric examples, and historical notes to show how the preamp isolates common-mode, why splitting gain boosts bandwidth, how overall gain can be set with one resistor, and what practical limits to watch.
Lost Secrets of the H-Bridge, Part V: Gate Drives for Dummies
Learn the most important issues in power MOSFET and IGBT gate drives: - Transistor behavior during switching - Calculating turn-on and turn-off times - Passive components used between gate drive IC and transistor - Reverse recovery - Capacitively-coupled spurious turn-on - Factors that influence a good choice of turn-on and turn-off times - Gate drive supply voltage management - Bootstrap gate drives - Design issues impacting reliability
Turn It On Again: Modeling Power MOSFET Turn-On Dependence on Source Inductance
This is a short article explaining how to analyze part of the behavior of a power MOSFET during turn-on, and how it is influenced by the parasitic inductance at the source terminal. The brief qualitative reason that source inductance is undesirable is that it uses up voltage when current starts increasing during turn-on (remember, V = L dI/dt), voltage that would otherwise be available to turn the transistor on faster. But I want to show a quantitative approximation to understand the impact of additional source inductance, and I want to compare it to the effects of extra inductance at the gate or drain.
Modeling Gate Drive Diodes
This is a short article about how to analyze the diode in some gate drive circuits when figuring out turn-off characteristics --- specifically, determining the relationship between gate drive current and gate voltage during turn-off of a power transistor.
Make Your Own MCU Boards (2023 Teardown Conference)
Ditch the development boards! Products like the Nucleo development boards serve a wonderful purpose, but they’re ill-suited for projects that need to be small and cheap, such as hobby projects or products just beginning a production run. In this talk (a recording from the 2023 Teardown Conference), you’ll learn how to put a microcontroller or other custom circuit on a PCB a little larger than a stick of gum for less than $3 a board.
Tolerance Analysis
Jason Sachs walks through practical tolerance analysis by designing a 24V overvoltage detector from the ground up, combining resistor tolerances, temperature coefficients, reference and comparator errors, hysteresis, and dynamic RC behavior. He demonstrates worst-case stacking with real datasheet numbers, shows how solder and mechanical stress affect resistor choice, and sizes filtering so the comparator meets a microsecond-range trip requirement. The article is a hands-on guide full of worked examples and trade-offs for embedded hardware engineers.
Getting smacked by the long tail of poor design habits
In the 80’s I did a fair amount of consulting and enjoyed it greatly.
I would come in, hear what it was the person hiring me wanted; meet with the people that I needed to work with and proceed to toss together a design, parts list, and program. Sometimes I would work with them to get a board into production. I knew my chips and code and could make all kinds of amazing toys.
One of my biggest repeat customers eventually offered a good salary at the same time that my wife was feeling...
Wye Delta Tee Pi: Observations on Three-Terminal Networks
Three-terminal passive networks, wye, delta, tee, and pi, are more interchangeable than many engineers expect. Jason Sachs walks through Kennelly's wye-delta formulas, Z and Y matrix representations for tee and pi two-port networks, and worked examples ranging from balanced to highly skewed impedances. The post highlights practical payoffs, including using topology transforms to substitute hard-to-source capacitors with simpler, precision-friendly parts.
The Least Interesting Circuit in the World
Jason Sachs pulls apart the humble power-on reset and shows why the common RC-and-Schmitt trick is the least interesting but most dangerous circuit in your design. He walks through voltage thresholds, brown-out reset behavior, and how slow or noisy Vdd ramps can let parts start in indeterminate states. Read this for practical rules on choosing supervisors, comparators, and reset pulse timing to ensure reliable embedded startup.
Lost Secrets of the H-Bridge, Part V: Gate Drives for Dummies
Learn the most important issues in power MOSFET and IGBT gate drives: - Transistor behavior during switching - Calculating turn-on and turn-off times - Passive components used between gate drive IC and transistor - Reverse recovery - Capacitively-coupled spurious turn-on - Factors that influence a good choice of turn-on and turn-off times - Gate drive supply voltage management - Bootstrap gate drives - Design issues impacting reliability
How to Analyze a Three-Op-Amp Instrumentation Amplifier
The three-op-amp instrumentation amplifier gives you high input impedance, improved net bandwidth, and much lower sensitivity to resistor mismatch than a single-op-amp differential stage. Jason M. Sachs walks through the algebra, numeric examples, and historical notes to show how the preamp isolates common-mode, why splitting gain boosts bandwidth, how overall gain can be set with one resistor, and what practical limits to watch.
How to Read a Power MOSFET Datasheet
Jason Sachs takes a soapbox to stop a recurring mistake: misreading power MOSFET datasheets. This practical guide separates marketing blurbs and typical graphs from the specifications you can actually rely on, and explains how to use RDS(on), VGS, gate charge, SOA and thermal data in real designs. Read this before you pick a MOSFET or size a gate driver.
Thermistor signal conditioning: Dos and Don'ts, Tips and Tricks
Jason Sachs shows how to keep thermistor conditioning simple and accurate for embedded systems. He warns against analog linearization and excessive analog stages, and explains why ratiometric dividers, proper ADC buffering, and using the same reference voltage give better results. The post also covers thermal pitfalls like self-heating and lead conduction, plus practical tips for ADC autocalibration and polynomial temperature conversion.
Tolerance Analysis
Jason Sachs walks through practical tolerance analysis by designing a 24V overvoltage detector from the ground up, combining resistor tolerances, temperature coefficients, reference and comparator errors, hysteresis, and dynamic RC behavior. He demonstrates worst-case stacking with real datasheet numbers, shows how solder and mechanical stress affect resistor choice, and sizes filtering so the comparator meets a microsecond-range trip requirement. The article is a hands-on guide full of worked examples and trade-offs for embedded hardware engineers.
Beware of Analog Switch Leakage Current
Leakage currents in analog switches can quietly wreck precision reference circuits at elevated temperature. Jason M. Sachs walks through three switch-topology implementations for a switchable 1.25 V reference and shows which topology gives the smallest worst-case output error using real part specs. He explains why op amp input bias is usually negligible and gives practical fixes: lower resistances, better switches, or limiting temperature range.
Analog-to-Digital Confusion: Pitfalls of Driving an ADC
Wayne's thermistor board showed one ADC channel changing when another was heated, a classic case of ADC input cross-coupling. The post walks through how multiplexed ADCs, the small sample-and-hold capacitor, source impedance, sampling time, repeated sampling rates, and added charge reservoirs interact to create errors. Learn practical fixes including increasing sample time, sizing external caps, adding op-amp buffers, and using an RC dampener with PCB layout tips.
Lost Secrets of the H-Bridge, Part IV: DC Link Decoupling and Why Electrolytic Capacitors Are Not Enough
Switching H-bridges can kick nasty voltage spikes onto the DC link, and a single electrolytic capacitor rarely fixes the problem. Jason Sachs uses simulations and practical PCB layout advice to show how a three-tier decoupling strategy — bulk electrolytic, mid-value ceramics or film, and many small HF bypass capacitors plus PCB plane capacitance — tames spikes, reduces EMI, and avoids harmful resonances when parts and vias are placed correctly.
The Other Kind of Bypass Capacitor
Most engineers treat bypass capacitors as supply decoupling, but Jason Sachs digs into the other kind: a capacitor placed in the feedback path to tame unpredictable high-frequency plant behavior. He walks through real examples, Bode plots, and a simple RC model to show how the cap forces unity-gain feedback at high frequency, stabilizing switching regulators and wideband amplifiers while revealing the speed versus stability tradeoff.
R1C1R2C2: The Two-Pole Passive RC Filter
Jason Sachs walks through the math and simulation for the common two-pole passive RC filter, turning repetitive algebra into a compact reference you can reuse. He derives the closed-form transfer function, extracts the natural frequency and damping ratio, and explains why the topology cannot be underdamped without inductors or active stages. The post finishes with a state-space simulation recipe and practical component guidance.
How to Read a Power MOSFET Datasheet
Jason Sachs takes a soapbox to stop a recurring mistake: misreading power MOSFET datasheets. This practical guide separates marketing blurbs and typical graphs from the specifications you can actually rely on, and explains how to use RDS(on), VGS, gate charge, SOA and thermal data in real designs. Read this before you pick a MOSFET or size a gate driver.
Thermistor signal conditioning: Dos and Don'ts, Tips and Tricks
Jason Sachs shows how to keep thermistor conditioning simple and accurate for embedded systems. He warns against analog linearization and excessive analog stages, and explains why ratiometric dividers, proper ADC buffering, and using the same reference voltage give better results. The post also covers thermal pitfalls like self-heating and lead conduction, plus practical tips for ADC autocalibration and polynomial temperature conversion.
Analog-to-Digital Confusion: Pitfalls of Driving an ADC
Wayne's thermistor board showed one ADC channel changing when another was heated, a classic case of ADC input cross-coupling. The post walks through how multiplexed ADCs, the small sample-and-hold capacitor, source impedance, sampling time, repeated sampling rates, and added charge reservoirs interact to create errors. Learn practical fixes including increasing sample time, sizing external caps, adding op-amp buffers, and using an RC dampener with PCB layout tips.
Byte and Switch (Part 1)
Driving a 24V electromagnet from a 3.3V microcontroller looks trivial, but Jason Sachs shows how that simple switch can fail spectacularly. He walks through the cause of MOSFET destruction when an inductive load is turned off, and explains the practical fixes you actually need: a flyback diode, a gate series resistor, and a gate pulldown to keep the transistor well behaved.
10 Circuit Components You Should Know
Jason Sachs pulls together ten underrated but highly practical circuit components that every embedded engineer should know. From multifunction logic gates that act like a Swiss Army knife for glue logic to TL431 shunt regulators and tiny charge-pump inverters, each item is presented with real-world use cases and caveats. Read this to expand your parts toolbox and simplify future designs.
Lost Secrets of the H-Bridge, Part IV: DC Link Decoupling and Why Electrolytic Capacitors Are Not Enough
Switching H-bridges can kick nasty voltage spikes onto the DC link, and a single electrolytic capacitor rarely fixes the problem. Jason Sachs uses simulations and practical PCB layout advice to show how a three-tier decoupling strategy — bulk electrolytic, mid-value ceramics or film, and many small HF bypass capacitors plus PCB plane capacitance — tames spikes, reduces EMI, and avoids harmful resonances when parts and vias are placed correctly.
Lost Secrets of the H-Bridge, Part V: Gate Drives for Dummies
Learn the most important issues in power MOSFET and IGBT gate drives: - Transistor behavior during switching - Calculating turn-on and turn-off times - Passive components used between gate drive IC and transistor - Reverse recovery - Capacitively-coupled spurious turn-on - Factors that influence a good choice of turn-on and turn-off times - Gate drive supply voltage management - Bootstrap gate drives - Design issues impacting reliability
R1C1R2C2: The Two-Pole Passive RC Filter
Jason Sachs walks through the math and simulation for the common two-pole passive RC filter, turning repetitive algebra into a compact reference you can reuse. He derives the closed-form transfer function, extracts the natural frequency and damping ratio, and explains why the topology cannot be underdamped without inductors or active stages. The post finishes with a state-space simulation recipe and practical component guidance.
Which MOSFET topology?
Jason Sachs breaks down the four basic MOSFET topologies for switching a two-wire load, showing why low-side N-channel is usually the simplest and cheapest option. He explains why grounding or chassis return can force a high-side switch, how P-channel devices trade performance for simpler gate drive, and why high-side N-channel options need extra driver circuitry. He also stresses adding freewheeling diodes for inductive loads.
Byte and Switch (Part 2)
Running a thermistor front end from a single AA cell exposes problems you might not expect. Jason Sachs walks through a switchable-gain divider using a P-channel MOSFET and shows how MOSFET off-state leakage and low supply voltages can corrupt high-impedance temperature readings. The post compares bipolar transistors and analog switch ICs as fixes and gives practical component guidance for one-cell designs.
