24-VAC multi-channel solid state relay reference design using digital isolator


Design files


This reference design demonstrates a multi-channel solid state relay (SSR) using a single isolation. The design uses a multi-channel digital isolator with a single isolated power supply and common ground gate-drive circuit to control multiple SSRs independently. The design is rated for 24-VAC powered relays with current rating up to 2 A, but scalable up to 240 VAC and higher current rating. Each SSR channel consumes less than 75-mm2 space with a maximum height of the component around 3-mm, enabling considerable size saving compared to electromechanical relays. The use of single isolated power supply reduces board space and BOM cost.

  • Multiple solid-state relays using a single isolation with multichannel digital isolator, easily scalable to any number of SSR channels with minimum extra cost
  • SSR drive voltage 24 VAC ±20%, drive current 2-A RMS (voltage and current rating, scalable by using appropriately rated components)
  • SSR turn on and turn off time: 15–300 μs (adjustable), average current consumption per SSR drive (referred to primary) < 4 mA (adjustable down to 20 μA per channel)
  • SSR size < 75 mm2 per channel. Height is around 3 mm.
  • Functionally isolated open-loop flyback based power supply without the need of an MCU
  • Surge and switching overvoltage protection
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A fully assembled board has been developed for testing and performance validation only, and is not available for sale.

Design files & products

Design files

Download ready-to-use system files to speed your design process.

TIDUEZ1.PDF (2667 K)

Reference design overview and verified performance test data

TIDM822.PDF (580 K)

Detailed schematic diagram for design layout and components

TIDM823.PDF (359 K)

Complete listing of design components, reference designators, and manufacturers/part numbers

TIDM824.PDF (224 K)

Detailed overview of design layout for component placement

TIDM826.ZIP (1896 K)

Files used for 3D models or 2D drawings of IC components


Design file that contains information on physical board layer of design PCB

TIDM825.PDF (383 K)

PCB layer plot file used for generating PCB design layout


Includes TI products in the design and potential alternatives.

Digital isolators

ISO7740Robust EMC, quad-channel, 4/0, reinforced digital isolator

Data sheet: PDF | HTML
Digital isolators

ISO7760Robust EMC, six-channel, 6/0, reinforced digital isolator

Data sheet: PDF | HTML
Fixed-direction voltage translators

SN74LV1T34Single Power Supply BUFFER Logic Level Shifter (no enable)

Data sheet: PDF | HTML
Linear & low-dropout (LDO) regulators

TLV760100-mA, 30-V, low-dropout voltage regulator

Data sheet: PDF | HTML
Low-side switches

TPL7407LA30-V, 7-ch NMOS array low-side driver

Data sheet: PDF | HTML
N-channel MOSFETs

CSD17382F430-V, N channel NexFET™ power MOSFET, single LGA 1 mm x 0.6mm, 67 mOhm, gate ESD protection

Data sheet: PDF | HTML
N-channel MOSFETs

CSD19538Q2100-V, N channel NexFET™ power MOSFET, single SON 2 mm x 2 mm, 59 mOhm

Data sheet: PDF | HTML
Real-time clocks (RTCs) & timers

TLC5552.1-MHz, 250-µA, Low-Power Timer

Data sheet: PDF | HTML

Technical documentation

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* Design guide 24-VAC Multi-Channel Solid-State Relay Reference Design Using Digital Isolator PDF | HTML Mar. 22, 2021

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