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THE MAGAZINE FOR COMPUTER APPLICATIONS Circuit Cellar Online offers articles illustrating creative solutions and unique applications through complete projects, practical tutorials, and useful design techniques. |
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Solid-State Relays by Bob Paddock This month, an AskUs question lead me to attempt to find the perfect switch, exactly the type of component that would go well with the Perfect Battery (Fuel Cells and Radiological Heater Units) that I've covered in the past.
The perfect switch should have the following attributes:
One practical avenue you can take to find the perfect switch is solid-state relays (SSRs). The biggest imperfection
of most any solid state switch is false turn on. That is, the
switch turns itself on without a signal commanding it to turn on
at that time. This typically is a problem when driving inductive
loads. The typical solution to prevent false turn on is to
use a "Snubber" circuit. But, I'll cover Snubbers in a separate
Resource
Page. Maxim
has a paper (How
to Select the Right CMOS Analog Switch) that should point
you in the right direction if you are looking to control low-level
signals. However, in this
An in-a-nut-shell introduction to "Industry Standard" Solid-State Relays and Mounting Racks can be found at Industrologic, Inc. You can build your own SSR by using parts from International Rectifier and Supertex. IRF's AN-1015, The PVI: A Versatile Circuit Element shows a unique application of their Photovoltaic Isolator. By using the IRF PVI along with Supertex's DN25 series depletion mode FETs (this type of FET is normally "on," versus the more common kind type that is normally "off") you get closer to that mythical perfect switch. See Application Note AN-D18, "High Voltage Regulators and Linear Circuits using DN25".
If you don't want to build your own, you can pick up a ready-made one from Agilent in their HSSR-8400, 400 V/10-ohm, General-Purpose, 1 Form A, Solid State Relay or one of International Rectifier's own Microelectronic Relay (MER) replaces for Mercury-wetted reed relays. The PVX6012 is a single-pole, single-throw, normally-open (1 Form "A") relay using a pair of inverse-series-connected IGBTs to form the output switch. Parallel to each of the two IGBTs is a FRED (Fast Recovery Epitaxial Diode) allowing low-voltage-drop conduction in the reverse polarity. The PVT442 is a specialized telecom microelectronic relay with single-pole, single-throw, and normally-closed (otherwise referred to as 1 Form B) contacts. Its intended use is in peripheral telephone equipment where a connection to the telephone line is required during power outages. It might be worth a look for your application.Just as a brief "aside," I find it interesting that IRF is pointing out how bad Mercury has become for the environment, yet thousands of dentist put pounds of Mercury in our mouths everyday in the form of fillings, or say even the vaccines with mercury-containing preservative thimerosal we give our children. For some reason, Mercury is not considered toxic waste as long as it is in your body. Do you see a problem with this picture? As someone suffering from Mercury poisoning I agree with IRF myself. Because SSR inputs are almost universally LEDs, it would be a good idea to review some of the application notes related to LED drivers. Agilent Technologies optocouplers can be used in an array of isolation applications, ranging from power supply and motor control circuits to data communication and digital logic interface circuits. Agilent's Designer's Guide to Isolation Circuits is a 82-page book that contains 50 application circuits. The handbook begins with a section discussing critical optocoupler design parameters such as insulation and withstand voltage, regulatory agency safety standards, common-mode transient rejection, product life, and light emitting diode (LED) aging. Marktech Optoelectronics' book LED Driver Application Notes covers the history of the LED to pulsed applications. Sharp
Microelectronics of the Americas has numerous applications
notes related to LED's and LED drivers. The type of solid-state
relay used in an application depends upon the load to control. Click
on the links below to compare each type and to learn more about
situations where they are used.
The
above is part of Cutler-Hammer
University.
Iif your new to the field, it
offers the 101
Basics Series that will greatly improve your understanding
of the products
involved in distributing, controlling, and using electricity.
The Cutler-Hammer 101 Basics Series is a self-directed, distance
learning program comprised of a number of different modules. Each
module focuses on a specific product group. The 101 Basics
Series is designed to establish a solid foundation understanding
of the products manufactured by Cutler-Hammer and will prepare
you for subsequent classroom and distance learning courses. Often,
the 101 Basic Series or specific modules within the series are
required as prerequisites for intermediate and advanced Cutler-Hammer
courses. You can take a look at the concepts for Analog Devices Micromachined Relays. How would you like a 16-poll relay in a BGA package (7.5 x 7.5 x 1.0 mm)? They are are looking for people to give them ideas and applications. Products based on the µmRelay technology will not be available until mid-to-late 2001. Although definition of the initial µmRelay product has not been finalized, it will likely be similar to the product described below. Follow-on products will provide increased integration with various switch/relay counts, as well as the inclusion of other semiconductor functions.
Initial Product Concept:
16-channel high-density switch Power consumption*: 0.3 mW max. On resistance: 0.5 ohms max. Input-output capacitance: 50 fF max. Maximum input voltage: 150 V min. Maximum carrying current: 1 A (average) min., 5 A (peak) min. Switching time: 6 µs max. –3-dB bandwidth: 2 GHz. min. Mechanical and electrical lifetime**: 10^9 cycle min. Budgetary pricing: <$16 (<$1 per switch)
Aromat is part of Matsushita Electric Works, Ltd. (MEW) in Osaka, Japan. They make old-fashion, heavy, metal relays, as well as their PhotoMos Relays.
One gripe I
have about their home page
is that it is over 650K, a real pain when all you have is a dial-up
connection. I almost didn't include them here because I was tired
of waiting for it to load. 
Axiomatic Technologies' line of solid-state relays includes the following products:
Solid
state relay with turn-on delay is designed to accept standard
input voltages of 24 VDC or 129 VDC. The relay provides for a 3-ms
time delay to prevent accidental short pulses from activating the
relay. It was originally designed for electrical substation
applications. California Eastern Laboratories is NEC's authorized North American source for photocouplers, solid-state relays, and optoelectronic devices.
Several design
tips can be found in Optocoupler
Applications.pdf. OptoMOS® products were the first optically coupled MOSFET devices for any telecom application. However, there are many other applications where Clare's OptoMOS® devices may provide a solution for design requirements.  
Continental Industries has several helpful hints on applying SSRs. They even give you nice clear schematics of what the modules do, I wish more of the web pages I saw when making this Resource Page did that. Sometimes there where tables full of descriptions that still left you wondering what was different between Device-A and Device-B.
Their product
line ranges from 4 to 100 A/660 VAC, with special inputs (such
as 4–20 mA or 0–10 V) available on some models.
A Prime Technology Company High
Reliability DC Control Relays
Eurotherm is a global organization with market leading products in industrial and process automation.
If you'd like to design your own PID controller, take a look at Zilog's application note on the subject (http://www.zilog.com/pdfs/z8otp/pid_motor_control.pdf). There are typically three kinds of continuous modes of closed-loop control—proportional, integral, and derivative (or PID for short). The control output is set depending on P, I, and D functions of the "error." Error is simply the difference between the current position (where you are) and the desired position (where you want to be). Thus: Output = (P × E) + (I × E) + (D × E) If you want to learn more about PID control, check out some of the back issues of Circuit Cellar. Circuit Cellar Ink, December 90/January 91, "Magnetic Levitation: An Example in Closed-Loop Control" by Jeff Bachiochi (Pronounced BAH-key-AH-key). Circuit Cellar Ink, Issue #42, January 1994, "PID-Pong Challenge" by Tom Cantrell. Circuit Cellar Ink, Issue #50, September 1994, "PID-Pong: Point, Set, Match: Using a Hitachi H8 for Real-time Control" by Tom Cantrell. Circuit Cellar Ink, Issue #69, April 1996, "Fuzzy PID-Pong" by Tom Cantrell. Circuit Cellar Ink, Issue #76, November 1996, "Self-Tuning PD Algorithm for the 68HC11" by Kenneth Baker. 
Grayhill
I/O
racks are passive backplanes into which I/O modules can be installed
and removed. I/O racks connect one of the logic side terminals from
each module to an associated pin on the logic side connector for
interface to the controller. I/O bases have an integral processor
and dual port memory chip. The I/O handles scanning and storage
of the I/O information which can be accessed over the bases address/data
bus. Up to eight buses can be stacked along a DIN rail.
The Quad Relay is processed
in a MIL-PRF-38534 qualified facility to specific MIL-STD-883 test
methods. Micropac offers a wide range of custom
and standard product design in solid-state relays, solid state power
controllers (270 V, 115 V, and 28 V), and remote power controllers.
Omron has introduced an innovative new solid state relay (SSR) designed to prevent short circuit failure caused by external surges in the output and to ensure designers a "fail safe" condition. The new fail safe technology developed by Omron involves precise notching of the wirebond connected to the internal die form triac (SSR output). When a damaging over current is present at the triac, the heat generated by the over current is focused on the stress notch causing it to fail at the wirebond, rather than internally within the triac. This technology results in the triac failing open or "safe," thus eliminating the need for an external fuse or protection circuitry. In these days of allocation of every type of part, it's nice to find someone second sourceing parts. Omron's MOSFET Relay Cross Reference provides part number crosses for Aromat, CP Clare, Infineon (Siemens, AT&T), and NEC (CEL).
Opto 22 manufactures and sells electronic equipment suitable for any process control, monitoring, or data acquisition application. With hardware like the SNAP I/O® system, Opto 22 is the world's leading supplier of reliable, flexible monitoring and control hardware. Q: What is Opto 22's SNAP Ethernet I/O system? A: Opto 22's SNAP Ethernet I/O system is the combination of a SNAP Ethernet brain, a mounting rack, assorted I/O or serial modules, and a power supply. With a SNAP Ethernet I/O system and an Ethernet connection, you can monitor and control both analog and digital inputs and outputs, or interface to serial devices anywhere in your facility, or anywhere else in the world. The SNAP-B3000-ENET or SNAP-ENET-D64 brains are at the heart of Opto 22's Ethernet I/O system. The SNAP Ethernet brain's built-in web server allows you to monitor your equipment in the field using only a web browser; no special software is required. Visit Internet I/O and check out the live, hands-on demo of SNAP Ethernet I/O. For a hands-on demonstration of monitoring and controlling real-world devices over the Internet, you can connect to one of three demo stations set up at Opto 22's headquarters in Temecula, California. Each station has an Opto 22 SNAP Ethernet I/O system connected to real-world devices that you can monitor and control in real time, viewing your changes over a live web camera. For more information
on extending the reach of your IT network to include real-world
devices, visit http://www.ManagetheRealWorld.com.
4 to 32 VDC input 10, 15, 25 and 40 A at 250 VAC Also, 25 and 40 A at 480 VAC Solid epoxy body 4,000-V isolation Zero crossing Switching Built-in Snubber Network High-surge resistance 
Sharp Microelectronics has SSRs that range from 0.4 A/100 V to 8 A/600 V, 12 A/600 V, and just about every thing in between that you might need. Some of the units come with internal Snubbers, as well as zero crossing detection in some models. There are two application notes worth note in relation to their SSRs: "Photocoupler,
Photothyristor Coupler, and Phototriac Coupler Application Circuit"
(56 KB) 
The SR75 is a DC solid state relay with built-in short circuit and overload current protection. The operating voltage range is from zero to 60 VDC (SR75-1), zero to 300 VDC, or 120-Vrms AC (SR75-2) when connected with a diode bridge. This series provides protection of AC or DC loads against damage from overload currents. The SR75 offers protection against short circuit and overload currents by continuously monitoring the instantaneous load current and the output switch junction temperature. If either condition exceeds predetermined limits the relay will turn-off and remain off until it is reset by removing the overload condition and cycling the input control voltage. This action mimics a resetable circuit breaker but with a turn-off time of micro-seconds in the presence of short circuit currents. The SR75 can respond to large excess currents fast enough to prevent serious damage to the relay, system wiring, or other system components. The related application note describes the operational considerations when using this relay and the technical benefits of the features offered. They offer a gamut of relays from 100 mA to 200 A. I know I missed a couple
of the big names in solid-state relays here, but either their web
pages where totally devoid of any data at all about their products
or the site lead me around in circles. I know you have better
things to do with your time just as I do, than waste it on a poorly
designed site.
Stop by the
The fact that an item is listed here does not mean we promote its use for your application. No endorsement of the vendor or product is made or implied. If you would like to add any information on this topic or request a specific topic to be covered, contact Bob Paddock. Circuit Cellar provides up
to date information for engineers, www.circuitcellar.com
for more information and additional articles.
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