Photocoupler Application Note. 3. Photocouplers optically links, via transparent isolating material, a light emitter and a. Introduction. This application note is based on Renesas optocouplers. The intent is to address several questions that end users have had, such as, how to work. typical 4n35 optocoupler. But we can also provide electrical isolation between an input source and an output load using just light by using a very common and.

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The device has an isolation voltage rating of 3. The following notes give a summary of the salient usage points.

Simple optocouplers are widely available in six applicqtion forms, which are illustrated in Figures 6 to 8. An optocoupler can be used to interface analog signals from one circuit to another by setting up a standing current through the LED and then modulating this current with the analog signal.

The phototransistor can, however, be converted to a photodiode by shorting the base pin 6 and emitter pin 4 terminals together; under this condition the CTR value falls to about 0. Looking for an answer, I ran into this. On the output side of the optocoupler, a quiescent current is set up by the optocoupler action in the phototransistor, and causes a quiescent voltage to be set up across RV1, which should have its value adjusted to give a quiescent output value of half-supply voltage.

If desired, however, the phototransistor can be converted into a photodiode by using the base terminal as shown in Figure 13 a and ignoring the emitter terminal or shorting it to the base.

Optocoupler Circuits

Hi, Some opto-couplers, like 4N25, have a terminal for the base of the output device, what are the advantages of having this terminal? This is the maximum permissible DC potential that can be allowed to exist between the input and output circuits.

Even so, the device has a typical minimum CTR value of only 0. Has anybody seen a solid-state relay with base connection available. The LED current must be limited by a series resistor, which can be connected to either the anode a or the cathode b. In Figure 21the triac is used to directly activate an AC line-powered filament lamp, which should have an rms rating of less than mA and a peak inrush current rating of less than 1.


Typical values vary from 20V to 80V. This site uses cookies to help personalise content, tailor your experience and to keep you logged in 4n355 you register.

Robert12 New Member May 6, Pioneer Elite vsxtx water damage no power Started by Watin Today at It should be noted that, because of variations in LED radiation efficiency and phototransistor current gains, the actual CTR values of individual optocouplers may vary significantly from the typical value.

When the computer output goes low, the LED and phototransistor are driven on, so Q1-Q2 and the motor are cut off. Forums New posts Search forums. Figure 1 shows the basic form of such a device. Thread starter Robert12 Start date May 4, Tags optocoupler power electronics solid state relay.

Beau Schwabe Member Jun 8, An ideal application for the optocoupler is that of interfacing the output of a applicwtion control circuit possible with one side of its power supply grounded to the input of a triac power-control circuit that is driven from the AC power lines and which can be used to control the power feed to lamps, heaters, and motors. Four of these Figures 6 and 7 notr isolating optocouplers, and the remaining two are the slotted optocoupler Figure 8 a and the reflective optocoupler Figure 8 b.

Optocoupler Circuits | Nuts & Volts Magazine

This terminal is DC-biased at half-supply volts applicatioh the R1-R2 potential divider, and can be AC-modulated by an audio signal applied via C1.

The Figure 2 device is a simple isolating optocoupler. Q1 and Q2 can be replaced with resistors Ohms or so. Major points to note about the Figure 2 optocoupler are that its output current is controlled by its input current, that a control circuit connected to its input can be electrically fully isolated from the output circuit, and that nite since the input controls the output via a purely optical link — potential differences of hundreds of volts can safely exist between the input and output circuits.


The device shown in Figure 4 is known as a reflective optocoupler. Appoication have found a 39K across the Base-Emitter of the 4n35 significantly improves the switching times by several uSec.

Figures 3 and 4 show two other types of optocoupler. Consequently, these devices can be interfaced by using a sink configuration similar to that of Figure 14or they can use the source configuration shown apllication Figure SCRs silicon controlled rectifiers and triacs are semiconductor power-switching devices that like transistors are inherently photosensitive. Thus, when SW1 is open, the optocoupler is off, so zero base drive is applied to Q1, and the triac and load are off.

Basic form of an optocoupler device. Mosaic Well-Known Member May 5, The simple isolating optocoupler Figure 6 a uses a single phototransistor output stage and is usually housed in a six-pin package, with the base terminal of the phototransistor externally available.

Can’t say that I have seen such an item. Other devices in the Siemens optocoupled SSRs range include ones that have outputs that act as npte or two-pole NC, NO, or change-over switches. One of the most important parameters of an optocoupler device is its optocoupling efficiency and, to maximize this parameter, the LED and the phototransistor which usually operate in the infrared range are always closely matched spectrally. Thank you all for replying!

This construction gives the maximum possible values of isolating voltage. Figure 14 shows how to interface two TTL 4n335, using an optocoupler circuit that provides a non-inverting action.