DC Solid State Power Relay with Current Feedback

Optically Coupled Power MOSFET Relay with Galvanically Isolated Current Monitor Output

This project employs CPC1718J 100V Single-Pole, Normally Open DC-Only Power Relay and ACS71240 Galvanically Isolated Current Sensor IC with Common-Mode Field Rejection and Overcurrent Detection. The board can be used for applications such as industrial controls, motor control, robotics, and electronics switching. The relay is normally open and requires a 3.3V to 5V input signal to operate with a maximum operating load power supply of 100V DC, and load up to 6.75A without a heatsink and 17.5A with a heatsink.

Connections and Other Details

• CN1: Pin 1 = VCC Input Up to 90V DC, Pin 2 = GND
• CN2: Pin 1 = +Load, Pin 2 = GND-Load
• D1: Power LED Logic Supply for Current Sense Circuit
• CN3: Pin 1 = 3.3V Input for Current Sense IC, Pin 2 = Current Monitor Output, Pin 3 = Fault (Active Low), Pin 4 = GND(Logic), Pin 5 = LED Anode, Pin 6 = LED Cathode

Features

• Load Power Supply 90V DC (Range up to 100V)
• Load Current 6.75A Without Heatsink, 17.5A with heatsink and Fan
• Power Relay Low 0.075W On-Resistance
• 2500Vrms Input/Output Isolation
• Relay Turn-on Time 7.5mS to 20mS
• Relay Turn Off Time 0.19mS to 5mS
• Relay Input Signal 3.3V to 5V @ 10mA
• PCB Dimensions 52.71MM X 50.17MM
• 4 X 4MM Mounting Holes
• 100uF /100V DC Bus Capacitor
• Screw Terminals for Load and Load Power Supply

Current Sense

• Operating Power Supply 3.3V DC @ 15mA
• Power LED
• Output 132mV/A
• Zero-Current Output Voltage 1.65V
• Current Sense Range up to 10Amps (Read Note2 for Higher Current)
• Overcurrent FAULT available between 50% and 200% IP with 1.5 µs (typ) response time
• Fault Output Active Low
• Current Sensor Accuracy Error 5%

Current Monitor Output

The project also consists of a current sensor for load current feedback. The current sense circuit is built using ACS71240. The current sense output is also galvanically isolated and can be used to monitor the load current, fault condition, open load, and short circuit. The current sense circuit requires 3.3V Supply, and the sensor output is 132mV/A, Zero-Current Output Voltage 1.65V. The normal output of the current sensor is 1.65V when the load is disabled or not connected.

The ACS71240 current sensor IC is an economical and precise solution for AC or DC current sensing in industrial, automotive, commercial, and communications applications. The device consists of a precise, low-offset linear Hall sensor circuit with a copper conduction path located near the surface of the die. Applied current flowing through this copper path generates a magnetic field which is sensed by the integrated Hall IC and converted into a proportional voltage. The resistance of the integrated conductor is far less than typical sense resistors, which reduces power loss and improves efficiency.  Rejection of external common-mode magnetic fields is achieved through differential sensing, enabling high accuracy in magnetically noisy environments. A precise voltage proportional to the measured current is generated by the low-offset, chopper stabilized Hall front end

What is DC MOSFET Relay?

A MOSFET relay offers superior performance to an electromechanical relay in many applications. It is a solid-state device that replaces a coil-activated mechanical switch with an optically isolated input stage driving a MOSFET. Internally, a MOSFET relay includes an input-side LED and an output side with a photodiode a control circuit, and an output FET block.

Schematic

Parts List

Connections

Block Diagram

Switching Timing

Gerber View

Photos

Video

ACS71240 Datasheet

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