Design Documentation

Solid State Relay Module, MBARI 101226

4:36 PM 5/29/01 Dave Wright

General:

The Solid State Relay module provides sixteen channels of current "sinking" switch for the control of relays, solenoids, or other loads.

Circuit description:

Each channel is comprised of an N channel mosfet and associated catch diode. The mosfet is an International Rectifier type IRF7313, capable of peak currents well in excess of 5A. Continuous current is primarily limited by thermal considerations. The 1N4148W diode serves to clamp flyback currents, and is rated for 1A transients of 1 second or less. The module is intended to drive transient loads such as latching valves, stepper motors, and solenoids for short periods. For loads that are energized for periods in excess of one second, or have high repetition rates, due consideration must be given to the thermal limitations of the mosfets. The mosfets are driven by U1, an NJU3716 device. This component serves as an SPI compatible output expander with 25ma output drive. Clock, data, and latch signals from the host controller serve to shift data into the internal register and then present it at the outputs. Connector J1 presents the input voltage and the mosfet output at each pin pair. PTC1, a resettable current limiting device, prevents any long term overloads from occuring which might damage the mosfets or attached load.  



Physical:

The module dimensions are 2.200" x 1.50". Mounting holes for #2 machine screws are provided at each corner. All thruhole connectors, and mounting holes, register with a 0.1" grid. This is to facillitate mounting of the module on standard perfboard for prototyping or "one off" construction. Active components are mounted on the "top" side, and power output connectors on the "bottom" (non silkscreen) side. When mounted to a motherboard or other substrate, the component side faces "inward" to allow access to the connectors. Connector P1 contains the signals that are routed to the host microcontroller and power sources.


Assembly Notes:

The connector for the power output, J1 mounts on the solder side of the board. All other components, including P1, mount on the component (silkscreen) side of the board.



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