Driving Precision: Onsemi's MOSFET-Powered Upgrade for Electric Power Steering

If you’ve ever wrestled with a failing hydraulic steering pump, you'll appreciate the shift to Electric Power Steering (EPS). With EPS, energy is only used when you turn the wheel—goodbye to parasitic losses and fluid leaks. But while EPS solves one problem, it introduces another: how to manage power, heat, and control in a compact, high-reliability system that needs to react in milliseconds.

That’s where onsemi steps in, offering a silicon-rich solution stack designed to power, protect, and optimize modern EPS architectures.

MOSFETs Made for Motion

At the core of onsemi’s EPS portfolio is their T10 MOSFET series, built for both 12V and 48V systems. These aren’t your average FETs—they’re optimized for high-efficiency BLDC motor control, with low R_DS(ON), gate charge under 10 nC, and robust protection against reverse polarity and overcurrent. The devices are tailored for pulse-width-modulated (PWM) operation under rapidly changing load conditions—essential for precision steering.

To handle automotive stress, the T10 series incorporates shielded-gate trench tech and wafer thinning to improve thermal and electrical efficiency. A built-in soft-recovery diode cuts down on EMI and voltage overshoot, reducing the risk of damaging noise in sensitive environments.

Cooling Trick: Flip the Heat Path

Power-dense EPS systems generate heat, and traditional PCB cooling just doesn't cut it. Enter TCPAK57, onsemi’s Top Cool packaging. With a 5x7 mm footprint and a 16.5 mm² thermal pad on the top side, this package lets you sink heat directly from the top, bypassing the board. That’s more watts in less space—without frying your FR4.

Gate Drivers with Brains and Brakes

Controlling the motor is only half the job—protecting it is the other. onsemi’s gate drivers like the FAD3151MXA and FAD3171MXA bring serious protection features: desaturation detection, soft shutdown, and support for up to 110V. If something goes wrong—say, a sudden disconnect under load—they shut things down without blowing up the MOSFETs.

Need a classic half-bridge driver? The NCV51511/13 series handles both high- and low-side operation with internal dead-time, interlock protection, and enough drive current to flip even beefy power FETs.

Know Your Current, Control Your Torque

On the sensing side, precision matters. Torque and speed regulation depend on accurate current feedback, and onsemi’s NCV21x, NCV2167x, and NCV703x amplifiers deliver. Featuring ultra-low offset, zero-drift design, and tolerance for up to 80V common-mode voltage, these amps hold their accuracy across the automotive temperature range. They're rail-to-rail, compact, and miserly with power—great for cramped ECU designs.

One Vendor, All the Brains and Brawn

Rather than cobble together a power stage from half a dozen vendors, onsemi offers a vertically integrated EPS solution—MOSFETs, drivers, sense amps, and thermal management—all engineered to work together. For automotive designers chasing reliability, efficiency, and ADAS-level response time, that’s a compelling package.

Got your own EPS control board project or retrofitting an old column? This level of integration might just spark your next build—or save your next board spin.

Read more: Onsemi’s MOSFET-Based Solution for Electric Power Steering (EPS) System Optimization

Demystifying Load Resistors: Why That “Dumb” Component Might Just Save Your Project

We tend to overlook resistors. They're everywhere, and most of the time, they just sit there—quietly dropping voltage, limiting current, or pulling lines low. But sometimes, a very specific kind of resistor—the load resistor—can make or break your entire circuit.

So what exactly makes a load resistor different? And why do you suddenly need one when switching to LEDs in your car or bench-testing a power supply? Let's break it down.

So, What’s a Load Resistor?

In simple terms: a load resistor mimics a real-world load.

Say you're testing a power supply, but don’t want to hook it up to your $200 motor just yet. Enter the load resistor. It sucks power, generates heat, and simulates the current draw of a real device. If your circuit can handle the load resistor, it’ll probably handle the actual load.

But Wait—Isn’t That Just a Normal Resistor?

Not quite.

While regular resistors are mostly there to shape signal paths, bias transistors, or limit current in low-power applications, load resistors are built to take abuse. They often need to dissipate watts—or tens of watts—without going up in smoke.

Think: big ceramic resistors bolted to a heatsink, not those puny quarter-watt jobs on your breadboard.

When Do You Actually Need a Load Resistor?

Here are some scenarios where you’ll definitely want one:

🔧 LED Turn Signal Conversion (aka Hyperflash Fix)

You swap out incandescent bulbs for LEDs in your car. Great! Now your car thinks the bulb is burnt out and flashes like a maniac.
Solution: Add a load resistor to simulate the current draw of the original bulb (~21W). Problem solved.

🔌 Testing Power Supplies Without Risk

Want to validate your PSU or boost converter under load? A load resistor lets you stress test it safely, without risking an actual device.

🎛️ Audio Amp Testing

Driving a 4Ω speaker at full volume while debugging? Not ideal.
Dummy load resistors (with the right impedance and power rating) let you test your amp silently—no blown drivers, no angry neighbors.

📏 Signal Conversion (4–20mA loops)

Need to convert a 4–20mA current loop into a readable voltage? Slap in a precision load resistor. Boom—now your microcontroller can read 1–5V instead.

How to Choose the Right Load Resistor

🔣 Use Ohm’s Law (Always)

To simulate a load:

• R = V / I

Example: Running a 12V system and want to simulate 1A load?

• R = 12V / 1A = 12Ω

• Power = V × I = 12V × 1A = 12W

So, you’ll want a resistor rated at least 15–20W to stay on the safe side.

♨️ Mind the Heat

Load resistors are glorified space heaters. If you're not using a heatsink or airflow, they’ll cook themselves—and maybe your table too. Mount them properly.

Got a Hack?

Are you using load resistors in a clever way? Maybe replacing a car’s halogen with a PWM-controlled LED array and spoofing the CAN system? Share your builds or tag us—we love seeing resistance put to good use.

Differences between EL817 vs PC817

When selecting an optocoupler for electronic circuit isolation, the EL817 and PC817 are two popular choices, each offering distinct advantages for specific applications. Both optocouplers provide essential signal isolation between different voltage domains, preventing electrical interference and ensuring safety in various circuits. While they share some similarities, such as their 4-pin DIP packaging and infrared LED coupled to a phototransistor, each model has unique features that make it better suited for particular tasks. 

In this comparison, we will explore the differences between the EL817 and PC817 in terms of their pinout, features, applications, and other factors, helping you determine the best option for your project needs.

What is EL817

The EL817 is an optocoupler consisting of an infrared emitting diode (LED) optically coupled to a phototransistor. Designed for electrical isolation, the EL817 is packaged in a standard 4-pin DIP, available in various configurations, including surface-mount options. Its main purpose is to provide a secure means of transferring electrical signals between two isolated circuits, making it ideal for interfacing microcontrollers with high-voltage AC or DC systems.

How to use EL817

To use the EL817, connect its input side (pins 1 and 2) to the control circuit with a current-limiting resistor for the LED. The output side (pins 3 and 4) is connected to the high-voltage side, typically with the collector tied to a pull-up resistor. This configuration allows the EL817 to switch the output based on the input signal, ensuring electrical isolation while transmitting the control signal effectively.

What is PC817

The PC817 is another optocoupler widely used for signal isolation, featuring an infrared LED coupled to a phototransistor in a 4-pin DIP package. Like the EL817, it ensures safe and noise-free transmission of electrical signals between circuits operating at different voltage levels. The PC817 is renowned for its reliability and compatibility with various industrial and consumer electronics applications.

How to use PC817

To use the PC817, connect its input terminals (anode and cathode) to the control circuit with a resistor to limit the LED current. On the output side, connect the collector to the power supply through a pull-up resistor and the emitter to the ground of the output circuit. This setup allows the PC817 to isolate and transfer control signals between circuits efficiently.

EL817 vs PC817: Pinout

EL817 vs. PC817: Pinout

Both EL817 and PC817 share a similar 4-pin DIP pinout:

• Pin 1 (Anode): Connects to the LED’s positive terminal.
• Pin 2 (Cathode): Connects to the LED’s negative terminal.
• Pin 3 (Emitter): Phototransistor output.
• Pin 4 (Collector): Connects to the high-voltage side via a pull-up resistor

EL817 vs PC817: Features

EL817 Features

Maximum Supply Current: 95µA

Maximum Offset Voltage:

200µV (EL8170)

1000µV (EL8173)

Maximum Input Bias Current: 3nA

Bandwidth (-3dB):

396kHz (Gain = 10)

192kHz (Gain = 100)

Single-Supply Operation:

Input Voltage Range: Rail-to-rail

Output Swing: Rail-to-rail

Compliance: Pb-Free (RoHS Compliant)

PC817 Features

Input Diode Forward Voltage: 1.25V

Maximum Collector-Emitter Voltage: 80V

Maximum Collector Current: 50mA

Cut-off Frequency: 80kHz

Rise Time: 18µs

Fall Time: 18µs

Packaging Options: Available in 4-pin DIP through-hole or SMT package

EL817 vs PC817: Application

EL817 Applications

• Measuring Instruments
• Home Appliances
• Telecommunication Devices
• Programmable Controllers

PC817 Applications

• Electrical Isolation Circuits
• Microcontroller I/O Switching
• Signal Isolation
• Noise Coupling Circuits
• Isolation Between Digital and Analog Circuits
• AC/DC Power Control

EL817 vs PC817: Equivalent

EL817 Equivalent

TLP181

LTV817

K817P

PC817 Equivalent

TLP321

MCT2E

LTV817

EL817 vs PC817: Advantages

EL817 Advantages

• Low Input Current Requirement:...