Transcript
RELAYS
Replacing Mechanical Relays with IR’s PVT412L Microelectronic Relay in Fax/Modem Designs
THE POWER MANAGEMENT LEADER By Andy Serkuczewski, International Rectifier
Here is information on how our PVT412L microelectronic relay (MER) will save time and money while improving performance and reliability in FAX/Modem designs.
because there are no physical parts making and breaking the contact.
DESIGN TIP
• R2 and R3 fusible resistors are no longer required thanks to the internal active, current- limiting feature of the Figure 1 is the schematic of a basic modem showing K1 PVT412L. Even more important than the savings in spac mechanical relay. It is the equivalent of a hook-switch in the 95-1a andDT cost, should one or both of the fusible resistors fuse traditional telephone set and in this case, K1 is either an elecInternational Rectifier • 233 Kansas Street, El Segundo, CA re90245 USA open in a lightening surge, the modem would fail and tromechanical relay (EMR) or a reed relay. Because such require costly repair or replacement. This situation is lays inherently cause contact bounce upon contact closure, REPLACING RELAYS IR’S PVT412L MICROELECTRONIC avoided by using the PVT412L in place of an electromach R1, MECHANICAL C1 debouncing circuitry is WITH required. While the 560Ω resisanical or reed relay. tor is small and inexpensive, the 1KV capacitor is both bulky RELAY IN FAX/MODEM DESIGNS and expensive. Additionally, there are two 10Ω fusible resisBy Andy Serkuczewski The initial cost differential of approximately 15% between tors (R2 and R3) in series with the Tip and Ring lines that are the PVT412L required for this circuitry to pass the FCC’s PartWhile 68 lightning is required. the 560Ω resistor is smalland a typical EMR (at high volume OEM pric ere is information on how our PVT412L miing) will more than offset by: surge test of up to 1000-volt, 200-Amp short-duration pulse. and inexpensive, the 1KV capacitor is be both oelectronic relay (MER) will save time and bulky and expensive. Additionally, there are two oney while improving andthe reliWithout performance these resistors K1 relay would almost certainly 10Ω fusible resistors (R2 and R3) in series bility in FAX/Modem designs.due to contact welding • reduction in component count (3 resistors, 1 capacitor) be destroyed during such surge. with the Tip and Ring lines that are required for When theofK1a electromechanical or reed relaytoispass replaced this circuitry the FCC’s Part 68 lightgure 1 is the schematic basic modem ning surge test of upand to 1000-volt, 200-Amp with our PVT412L MER, as in Figure 2, the following cost • savings of printed circuit board real estate howing K1 mechanical relay. It is the equivashort-duration pulse. Without these resistors nt of a hook-switch in savings the traditional telephone space are realized. the K1 relay would almost certainly be deet and in this case, K1C1 is either an electrome• R1, debouncing circuitry is no longer • elimination of costly failures due to lightening surges. stroyed due to contact welding during such hanical relay (EMR) or a reed relay. Because needed. Solid-state surge. uch relays inherently cause contact switching bounce is bounce-free
pon contact closure, R1, C1 debouncing circuitry
560 Ohm
0.005µF/1kV
1:1
X
K1 Relay
6.8V
10 Ohm fusible
+5V
Varistor
OH
To Telephone Company Network
10 Ohm
0.47µF/250V 10K RI 10K +5V
Figure 1. Basic Modem Using Mechanical EMR
For more information in North America call +1 310 252 7105, in Europe call +49 6102 884 311, or visit us at www.irf.com
DT95-1a
