AN3951| Application Note
Maxim/Dallas > App Notes > AUTOMATIC TEST EQUIPMENT (ATE)
SWITCHES AND MULTIPLEXERS
TELECOM
Keywords: Relay, Telecom Relay, ATE Relay, Low Power Relay, Relay Driver
Nov 09, 2006
APPLICATION NOTE 3951
Power-Save Mode Reduces Power Consumption When Driving Relays
This application note discusses a relay driver, the MAX4822/MAX4824, with an internal power-save circuit that reduce overall power consumption. In a typical application, overall power savings ranges from 5.5% to 68.5%, depending on the type of relay used. Power-save mode also helps to reduce the size and cost of the power supply used to supply the relay coils. The overall result will be smaller and less-expensive systems.
Introduction
Certain types of equipment such as telecommunications or automated test equipment (ATE) often use multiple banks of relays to achieve nearly lossless switching of almost any kind of signal. In these products, many relay coils can be supplied from a single power supply, which must be large enough to drive all the coils simultaneously. In addition, the relays can be densely packed into a very small area, making power dissipation from the coils a design concern. Relays require a significantly higher voltage across the coil to become energized than to remain energized. Knowing this, it is possible to design a circuit that will reduce the drive current through the coil to save power. This application note discusses a relay driver device that features an internal power-save circuit to help reduce overall power consumption.
The Power-Save Design Approach
The MAX4822/MAX4824 relay drivers include a power-save feature that reduces the voltage across the driver a short time after the FET is first turned on. Initially, the output driver is a fully saturated FET that is turned completely on. After an adjustable timeout period, the voltage across the FET is regulated to a register programmable value. The timeout period is adjustable with an external capacitor (Figure 1).
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