HCPL-4731

Output Type:	Darlington
Supplier Device Package:	8-DIP
Package / Case:	8-DIP (0.300", 7.62mm)
Mounting Type:	Through Hole
Operating Temperature:	0°C ~ 70°C
Vce Saturation (Max):	--
Current - DC Forward (If) (Max):	10mA
Voltage - Forward (Vf) (Typ):	1.25V
Current - Output / Channel:	60mA
Voltage - Output (Max):	18V
Series:	--
Input Type:	DC
Rise / Fall Time (Typ):	--
Turn On / Turn Off Time (Typ):	3µs, 34µs
Current Transfer Ratio (Max):	8000% @ 500µA
Current Transfer Ratio (Min):	600% @ 500µA
Voltage - Isolation:	3750Vrms
Number of Channels:	2
Part Status:	Active
Packaging:	Tube

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Optoisolators - Transistor, Photovoltaic Output: HCPL-4731 Application Field and Working PrincipleOptoisolators or optical couplers are components used in electronics to isolate two circuits electrically while providing a connection path with an optical link. This is typically done to prevent high voltages from damaging other components. The HCPL-4731 optoisolator is a photovoltaic version of the popular family of opto-isolators. This article will discuss the capabilities of the HCPL-4731, its application fields, and its working principle.

Features of the HCPL-4731

The HCPL-4731 is a single channel, photovoltaic detector which utilizes a transistor output. It offers an effective isolation of 5000VRMS for one minute of exposure, and 2500VRMS for one second. The optoisolator has a capacitance of 0.7pF, an operating temperature of -40°C to 85°C, and a storage temperature of -50°C to 150°C. It is a 4-pin device, with pins 2 & 3 for the input and pin 4 as the output. The device does have polarity, with the Cathode pin 2 being the negative polarity.

Application Fields

The HCPL-4731 is designed mainly for communication systems where isolation between channels and devices is needed. Examples include linking audio/video equipment, input/output devices, and interfaces for different protocols. It is used extensively in industrial, commercial and automotive applications such as bar code scanners, switches, home automation, and medical equipment. It is popular among circuits where high voltages or EMI might be present.

Working Principle

The HCPL-4731 makes use of a coupler having both an input and output stage. The input stage consists of a p-n junction diode and a resistor connected in series. This diode converts the incoming light signal from the transmitter into an electrical current, which flows through the resistor. This current is then amplified using a Transistor-Switch pair to provide an isolated high voltage drive to activate the load. The HCPL-4731 uses an emitter-follower topology. When voltage is applied to the diode, the current output is increased. The increase in current causes a corresponding increase in voltage across the resistor, thus activating the phototransistor. When activated, the phototransistor provides an amplified drive to the output transistor. This amplified drive is then used to switch on or off the load.

Conclusion

The HCPL-4731 optoisolator is a type of one-channel, photovoltaic optoisolator which uses a transistor output. It is a 4-pin device, with pins 2 & 3 for the input and pin 4 as the output. The device has a good level of isolation, with effective ratings up to 5000VRMS for one minute and 2500VRMS for one second. It is used in a wide variety of applications, mainly due to its ability to provide a high level of electrical isolation. The working principles of the device can be adequately explained using an emitter-follower topology.

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