PhotoMOS Relays For Industrial Systems Too

August 06, 2012
By Anonymous

If you think PhotoMOS relays are just for test and measurement applications, think again. These solid state relays can also switch and protect small motors, power supplies and control devices with load currents up to 6 amps.

PhotoMOS relays combine high switching speed with low control current and reliable overcurrent protection.

In fact, these industrial uses represent the next wave of applications for PhotoMOS technology, which has been widely accepted as a way to switch high-precision data acquisition and measurement systems. These systems take advantage of PhotoMOS’s  high switching speeds, low on-resistance, low capacitance and minuscule package size. The same technical advantages apply to industrial devices too. But motors, power supplies and controls can reap other benefits by moving from traditional electromechanical relays to PhotoMOS solid state relays: Low Power Consumption. A typical PhotoMOS relay requires 10 to 20 times less power than an equivalent electromechanical relay. For example, a 5 mA PhotoMOS can often do the same job as a electromechanical relay that requires anywhere from 50 to 100 mA, depending on the electromagnetic force needed to close the coil. A few milliamps here or there may not sound like a big deal, but in plant with many small devices the savings add up quickly.

PhotoMos: AQV DIP6 PhotoMos: AQV DIP6

 

Protection. Thanks to a built-in protective circuit in our latching-type models, PhotoMOS can safeguard motors, power supplies and other industrial devices from possible disturbances on the output side. These disturbances–such as voltage peaks or overcurrent conditions–can arise due to short circuits or improper use.  The protective circuit is located on the output side of the component and recognizes high currents.  This arrangement protects both the DMOSFET on the output side and the load circuit against overcurrent conditions. As soon as a dangerous load current arises, the load circuit switches off completely. It can be switched on again only after the input signal has been reset. Elevated Temperature Tolerance. The PhotoMOS protective circuit can play a particularly important role when the relay must perform at elevated operating temperatures. Because the voltage drop across the shunt increases as rising temperatures drive up resistance in the component, the protective circuit responds to lower and lower current levels as temperatures rise. In essence, it exhibits a negative temperature coefficient, which allows it to offset the increased power dissipation associated with elevated temperatures. A more detailed look at how the protective circuit works can be found here. Reliability. Solid state relays such as PhotoMOS shine when it comes to reliability. Without the moving parts of an electromechanical relay, solid state relays typically have an excellent mean time to failure (MTTF). In general, solid state relays tolerate shock and vibration loads that threaten electromechanical relays. Solid state relays also eliminate the buzzing that can affect electromechanical relays driven by PWM and other methods intended to conserve input power.

MTTF = (1/the failure rate λ). λ is expressed in terms of failures per unit of time (FIT), where 1 FIT=1 failure per billion device hours. The PhotoMOS failure rate is 20 FIT which means that MTTF is 1/(20*10*-9) based on the THB test per MIL HDBK‑217F.  Based on the MTTF, expected time to first failure exceeds 50 million hours of operation.

Low operating cost. Solid state relays may have a higher price tag than electromechanical relays. The total cost over the relay’s life-cycle, however, tips the scales back in favor of solid state technology. Most of the operating cost advantage come from reductions in power consumption and a longer life-cycle for fewer relay replacements. Factor in the cost benefit of motor protection and the value proposition becomes even more compelling. Keep in mind, too, that the savings can be greater in applications that require the relay to remain in its closed state for long periods of time. Solid state relays can be operated closed without the elevated temperatures and extra current draw of their electromechanical counterparts. Saves space, speeds development. Integrating the protective mechanism in the relay, rather than relying on a separate component, saves space. And it speeds development time because there's one less component to work into your design.

PhotoMOS: AQZ20 PhotoMOS: AQZ20

 

Many application choices. More than 300 different types of PhotoMOS relays are available to meet a wide variety of electrical and package size requirements. The PhotoMOS products most suited to motor protection and other industrial uses include:

AQZ207 SIL package with 1A load current.

AQY277A DIP4 SMD with 0.65A load current. 

AQV252G with 2.5A load current. 

For help in selecting the right PhotoMOS for your industrial application, contact Aiman Kiwan.

 

 

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