#Optical isolator ic 10kv how to#

A binary 1 (typically +24 V) input turns on a high-frequency carrier that’s transmitted through the capacitor barrier. OOK is a variant of amplitude-shift keying (ASK). Capacitive isolators implement a transmitter that uses on-off keying (OOK) modulation to pass the input data through the capacitive-isolation barrier. Since capacitive coupling blocks dc, how do logic signals get from input to output? The answer is modulation. Shown is a functional block diagram of a capacitive isolator such as the TI ISO1211. A comparator with hysteresis shapes the input data signal for transmission to the output across a silicon-dioxide isolation barrier.Ģ. The input is applied to two resistors: a sense resistor (R SENSE) that establishes the amount of current drawn from the input sensor or device, and a threshold resistor (R THR) that sets the input logic thresholds. When compared to optocouplers and other techniques, this new design approach results in advantages that include lower power dissipation, smaller boards and modules, simplified system design, and higher-speed operation.įigure 2 shows a simplified diagram of a capacitive isolator.

Modern capacitive-isolated digital input receivers can also help simplify system design. A capacitive isolator readily blocks dc, but easily passes high-speed data signals and provides the ESD and transient protection indicated earlier. The signal path is via a capacitor with its insulating dielectric. Isolation is excellent because of the insulated separation of the LED and photodetector. The signals to be passed are sent to an internal IR LED that switches off and on with the logic signal input to activate a phototransistor that turns off and on at the output. Optocoupler ICs have long been a popular isolation device (Fig. Common electrical isolation methods include inductive (a), optocoupler (b), and capacitive (c). Though they do a good job of blocking dc, their frequency response can limit data rate unless special high-speed transformers (e.g., Ethernet) are used.ġ. They’re typically larger, heavier, and more expensive than other options. The isolation is excellent, but transformers have some downsides. Signals are passed by magnetic induction from primary winding to secondary winding. 1a is the most obvious-it uses two electrically isolated windings on a common magnetic core. Capacitive-isolation ICs meet all of these requirements while supporting high-speed data rates and lower power consumption over other methods.įigure 1 shows the three common isolation methods. Such protection gives isolated equipment good electromagnetic compatibility (EMC) as required to meet selected certification standards. In addition, isolators protect sensitive equipment from electrostatic discharge (ESD), electrical fast transients (EFTs), and other variations from electrical surges that are common in an industrial setting. Keeping high voltages as great as 10 kV from industrial equipment away from computers, sensitive equipment, and human operators is another function of isolators. Using a single common ground almost always introduces ground loops and the attendant unwanted offset voltages. For instance, a typical isolator prevents dc or ac supply voltages from being passed on, yet at the same time permits data signals to pass.Ī major function of isolators is to separate the common grounds of input-signal devices and the equipment receiving the signals. Known as galvanic isolation, this process prevents direct electrical contact between input and output, but allows for the transfer of signals. Isolation is the process of blocking some signals and electrical connections while allowing others to occur.

#Optical isolator ic 10kv how to#

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That’s where capacitive-isolation ICs, which have been developed and refined for implementation into these critical designs, step in.

Such isolation is a common requirement in most industrial and medical applications. Of the methods available, capacitive isolation provides outstanding advantages over magnetic isolation by transformer or optoisolation with an LED and photodetector. If you’re designing circuits and equipment that require electrical/electronic isolation, it may be time to consider electronic isolation via capacitance. This article is part of the TechXchange : Exploring Digital Isolator Technology