* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Photorelay White Paper Draft 3.qxd
Switched-mode power supply wikipedia , lookup
Ground (electricity) wikipedia , lookup
Portable appliance testing wikipedia , lookup
Brushed DC electric motor wikipedia , lookup
Alternating current wikipedia , lookup
Mechanical-electrical analogies wikipedia , lookup
Electrical substation wikipedia , lookup
Control theory wikipedia , lookup
Stray voltage wikipedia , lookup
Buck converter wikipedia , lookup
Distributed control system wikipedia , lookup
Distribution management system wikipedia , lookup
Surge protector wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Resilient control systems wikipedia , lookup
Mains electricity wikipedia , lookup
Voltage optimisation wikipedia , lookup
Telecommunications engineering wikipedia , lookup
Power electronics wikipedia , lookup
Mechanical filter wikipedia , lookup
Electronic musical instrument wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Electrical engineering wikipedia , lookup
Electromagnetic compatibility wikipedia , lookup
Power MOSFET wikipedia , lookup
Control system wikipedia , lookup
Electronic engineering wikipedia , lookup
Variable-frequency drive wikipedia , lookup
White Paper Advanced Photorelays Prove ‘Less Is More’ in Component Design By Roger Shih, Business Development Engineer, Optoelectronics Discrete Business Unit Toshiba America Electronic Components, Inc. Highlights • Paper discusses how use of photorelays instead of mechanical relays can help design engineers develop systems with lower power consumption, less heat and longer life. • Provides a comparison of mechanical relays versus photorelays, with illustrated examples of each, and discusses the basic functions of photorelays. • Various photorelay applications are noted and a list of questions to ask when specifying photorelays. Introduction Design engineers, in their ongoing quest to develop systems with lower power consumption, less heat and longer life are increasingly turning to photorelays over mechanical and other types of relays. With the proliferation of photorelays in an increasing number of devices, especially test and measurement equipment, even small improvements can have a ignificant impact on the performance of the end product. Many electrical applications require the use of relays to control the application of a high voltage (or load) by using an electrical signal. This high voltage must be isolated from the control electronics section where the electrical circuits might be more vulnerable to the voltage. Isolation between circuits also protects each one from being disturbed by the mutually generated noise. Today relays are found in the vast majority of applications including motor control, heating control, signal coupling and interfacing, just to name a few. The invention of relays came from the quest for: • the ability to turn a device on or off • translation from a lower voltage signal level to a higher voltage level, (or vice versa) • isolation of the control circuit section from the much different drive section where electrical potentials must not be the same as the grounding used in the control circuit The general idea is to utilize a weaker electrical signal to control a much larger electrical current in the device being controlled. As electronic components go, the mechanical relay is one of the oldest. Solid-state relays, or photorelays, are a relatively recent development, although they have been in widespread use for many years. The major characteristics and benefits of each are summarized below, and a comparison of their basic operation is shown in Fig. 1. Figure 1. The two most widely used types of relays used to separate circuits with different voltage levels in electronic devices are mechanical and photorelays. A mechanical relay is a switch controlled by an electro-magnet, while a photorelay uses an optical signal from an LED to transmit a signal to a photo-detector/MOSFET. White Paper Mechanical Relays An electro-mechanical relay consists of an electromagnet where the weaker control current flows through its copper winding, and a set of contacts which are mechanically manipulated by the energizing and de-energizing of the electro-magnet to move them to the on or off configurations. photodiode array which generates a gate voltage signal causing the output MOSFET to turn on (or off). See Fig. 2, Photorelay Function, which shows a diagram for a normally-closed type of photorelay. In this case, when the LED triggers the MOSFET, the switch opens (turning “off ” the photorelay). Figure 2. Photorelay Basic Function This type of technology has its advantages and disadvantages: • High ruggedness and durability within its expected lifetime • When open, the set of contacts offers very high “off” resistance and very low capacitance • When closed, the set of contact offers reasonably low on-state resistance • Performance consistency is low due to the mechanical wear and aging of the contacts, as well as the contamination level of the surrounding environment • Slow response Photorelays With the advent of light-emitting diodes, phototransistors and MOSFETs, a more advanced type of relay evolved: photorelays or solid-state relays. In a photorelay the control signal drives a light-emitting diode. The emitted light stimulates a photo-transistor or MOSFET, which in turn switches itself on or off. With this configuration, most of the performance parameters of the relay are now determined by the performance of the light-emitting diode and the MOSFET device. Photorelays hold several significant benefits over conventional mechanical relays: • High speed switching (typically one-fifth the speed of mechanical relays, or 80 percent faster) • Lower drive power consumption (typically two orders of magnitudes smaller than mechanical relay) • Longer life, which comes from not having any mechanical components that might be worn out with use. Reliability of photorelays surpasses that of mechanical relays by design. • No chattering noise since switching is controlled optically • Smaller devices require less board space A typical photorelays consist of four chips. As an example, in a Toshiba photo relay the input side consists of a gallium arsenide (GaAs) infrared light emitting diode (LED). The output side includes a light receiving photodiode array and two output MOS field effect transistors (MOSFETs). When the LED emits light, the photons energize the optically-coupled In the normally closed type of photorelay, the signal from the LED turns off the photorelay. Photorelays are available in normally-open or normally-closed configurations. Photorelay Applications Because of their advanced performance characteristics, photorelays are ideal for a wide range of products. These include, but are not limited to: Analog modems Measuring instruments Digital line cards Programmable controllers Gate drives for thyristor Public phone line cards Industrial robots Relay output I/O boards Logic testers STBs Memory testers Various actuator drivers Below are several examples of how design engineers build photorelays into their product designs: • In an induction-heating cooker, photorelays control the electrical signals between the control circuit and several subsystems within the product, such as the fan motor, heater and coil. • In an inverter air conditioner, photorelays control electrical flow between the indoor and outdoor unit controllers, the fan motors, control air-flow motor and compressor motor. • In a refrigerator, photorelays manage electrical flow between the control circuit and multiple devices, including the fan motor, defroster/heater, damper motor, interior lamp and compressor motor. • In a washing machine, photorelays control electrical flow to and from the drain valve motor, water supply valve, softener supply valve, and multiple other devices within the unit. • In a more complex system, such as an automatic meter reading system, photorelays control electrical flow between the telephone lines and the modem and controller that process information from the water, gas and electricity meters. Photorelays play an especially important role in automated test and measurement equipment, where isolation requirements, along with low on-resistance, are design parameters. Furthermore, because of their size advantage (i.e., SSOP packages at 4.2mm by 1.9mm), they are ideal for such board-space intensive applications. Recent developments in photorelays have focused on miniaturization, both of the photodetector and by integration of the MOSFET and photodetector into a single chip. Another trend is low CxR values for test equipment, with values for new devices approaching 1pFW. Questions to Ask When Choosing Photorelays Photorelays are not all alike! It is important to ask specific questions when selecting photorelays for specific applications. Several key questions can be found below: • What technology did the manufacturer use to produce the photorelay? For example, white mold technology typically results in a higher level of optical coupling efficiency than other technologies. • How extensive is the manufacturer’s line of photorelays? A broad line means the engineer can likely spec all the photorelays he/she needs for different applications from one manufacturer. • What is the manufacturer’s experience in designing and manufacturing photorelays? An experienced manufacturer can often design photorelays to be more cost efficient and reliable than competitive products. • Have the photorelays received approval from relevant national and international safety standards? Standards bodies most involved with providing approvals are UL, TUV, BSI and SEMKO. Toshiba Photorelay Lineup for General Applications White Paper TAEC Regional Sales Offices NORTHWEST San Jose, CA TEL: (408) 526-2400 FAX: (408) 526-2410 Photorelays are an excellent example of where the “less is more” adage rings true. These innovative devices are an omnipresent Portland, OR TEL: (503) 784-8879 FAX: (503) 466-9729 Toshiba Photorelay Lineup for ATE (Tester) Applications component of many everyday products. Maximizing the performance of these devices results in a superior end product. SOUTHWEST Irvine, CA TEL: (949) 623-2900 FAX: (949) 474-1330 Richardson, TX TEL: (972) 480-0470 FAX: (972) 235-4114 CENTRAL Buffalo Grove, IL TEL: (847) 484-2400 FAX: (847) 541-7287 NORTHEAST Marlboro, MA TEL: (508) 481-0034 FAX: (508) 481-8828 Parsippany, NJ TEL: (973) 541-4715 FAX: (973) 541-4716 SOUTHEAST Duluth, GA TEL: (770) 931-3363 FAX: (770) 931-7602 The information contained herein is subject to change without notice. • The Toshiba products listed in this document are intended for usage in general electronics applications (computer, personal equipment, office equipment, measuring equipment, industrial robotics, domestic appliances, etc.). These Toshiba products are neither intended nor warranted for usage in equipment that requires extraordinarily high quality and/or reliability or a malfunction or failure of which may cause loss of human life or bodily injury (“Unintended Usage”). Unintended Usages include atomic energy control instruments, airplane or spaceship instruments, transportation instruments, traffic signal instruments, combustion control instruments, medical instruments, all types of safety devices, etc. Unintended usage of Toshiba products listed in this document shall be made at the customer’s own risk. • The products described in this document may include products subject to foreign exchange and foreign trade laws. • The products contained herein may also be controlled under the U.S. Export Administration Regulations and/or subject to the approval of the U.S. Department of Commerce or U.S. Department of State prior to export. Any export or re-export, directly or indirectly in contravention of any of the applicable export laws and regulations, is hereby prohibited. www.Toshiba.com/taec © Copyright 4/2007 TAEC