H11B3S(TB)

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Optoisolators utilize principles of light-induced electric current to allow the isolation of two electrical circuits. An optoisolator, or optocoupler, is a device designed to provide such insulation between two circuits, generally of different systems. While a myriad of optoisolator types exist, one type is especially relevant to the H11B3S(TB) application field; the transistor-photovoltaic output optoisolator. This type provides isolation between input and output signals which is especially important for the protection of the connected systems as well as to ensure proper device operation.

At the most basic level, the H11B3S(TB) optoisolator consists of an LED on one end of the device and a phototransistor on the other. This type of optoisolator serves as a sensor, allowing low voltage/current inputs to be amplified, passed through the isolation gap, and then utilized in higher voltage/current systems in order to produce a desired output. The optoisolator acts as an interface between the two systems, allowing the input system to become completely electrically isolated from the output system.

It is important, however, that the LED and input system be matched in terms of the voltage and current. The LED requires forward bias in order for it to turn on and produce photons that will then hit the phototransistor housed next to it, generating an output. If the current is not sufficient to allow the LED to turn on, the correct output will not be produced. A voltage of up to 5V can be allowed though it is highly recommended that the LED bias voltage be kept as low as possible in order to ensure the LED is being operated within its limits.

Once the LED is biased, a current will be allowed to flow from the input source through the LED. From this an output current, or photocurrent, is generated by the phototransistor due to the photons released by the LED. This photocurrent is then used to switch on the phototransistor, creating an output voltage from the collector-emitter terminals. From here the isolated output current can then be used within the output system.

In addition to providing immunity to the isolated output, the H11B3S(TB) optoisolator also has additional functions to ensure it is being operated within the user’s specifications. A series base resistor, which is installed between the LED’s cathode terminal and ground, provides additional safety to the system, allowing for current limiting and protection. Lastly, the optoisolator\'s collector-emitter terminal can serve as a transistor pull-up resistor to ensure the output is held low when not in use or when the LED bias is not present.

Such is the basic working principle of the H11B3S(TB) optoisolator. This type of device provides immunity between two systems while also ensuring proper operation of the system. Its LED and phototransistor combination allows a low voltage input to be amplified before the output can be used in higher voltage environments. It is also important to note, that additional components, such as series base resistors, can be used for safety and to ensure the optoisolator is operated correctly.

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