What is Optocoupler CTR?

The gain of the optocoupler is expressed as a current transfer ratio (CTR), which is the collector current (IC) of the output divided by the forward current (IF) of the input and multiplied by 100 %. (1) There are typically a number of CTR groups (binning) to choose from when selecting an optocoupler.

What is CTR in circuit?

CTR stands for current transfer ratio. In bipolar junction transistor this is the so called current gain or simply beta. It is the ratio of the collector to forward current of an Optocoupler. In circuit design involving optocoupler, you may be dealing with the device CTR and circuit CTR.

How do you use an Optocoupler in a circuit?

How It Works. A current is first applied to the Optocoupler, which makes the infrared LED emit a light that’s proportional to the current. When the light hits the photosensitive device, it switches on and starts to conduct a current as any ordinary transistor might.

Does Optocoupler need resistor?

The input current to the optocoupler LED must be limited via a series-connected external resistor which, as shown in Figure 10, can be connected on either the anode or the cathode side of the LED.

What is optocoupler current transfer ratio?

Current transfer ratio or commonly known as CTR is the ratio of the collector current to the forward current of an optocoupler. It is synonymous to a current gain of a bipolar junction transistor. Wherein Ic is the collector current while If is the forward current. The device CTR is specified in the datasheet.

What is CTR engineering?

CTR stands for Cost, Time, Resource.

What is opto output?

An optocoupler (also called optoisolator) is a semiconductor device that allows an electrical signal to be transmitted between two isolated circuits. The photosensor is the output circuit that detects the light and depending on the type of output circuit, the output will be AC or DC.

What are the CTR values of an optocoupler?

Each optocoupler type will have a range of CTR values set out in the manufacturer’s datasheet.

How to calculate optocoupler efficiency in a circuit?

The most convenient way of specifying optocoupling efficiency is to quote the output-to-input current transfer ratio (CTR) of the device, i.e., the ratio of the output collector current (I C) of the phototransistor, to the forward current (I F) of the LED. Thus, CTR = I C /I F.

What is the forward current of an optocoupler?

It consists of collector-emitter voltage (VCE) and collector current (IC) as a function of the base current (IB). With optocouplers, the emitter forward current (IF) is approximately equivalent to the transistor’s base current (IB) and is plotted as forward current (I F) in various steps.

What kind of resistor does an optocoupler use?

The optocoupler infrared LED is driven at about 4mA via a 1kΩ resistor from IC1 output. As the CTR of the PC817 is around 115% the phototransistor can supply about 9mA as the supply to the phototransistor output is now taken from the 12V motor supply. This is more than the 5mA minimum required to drive the 2N3904 into saturation.

What is optocoupler CTR?

The gain of the optocoupler is expressed as a current transfer ratio (CTR), which is the collector current (IC) of the output divided by the forward current (IF) of the input and multiplied by 100 %. (1) There are typically a number of CTR groups (binning) to choose from when selecting an optocoupler.

How reliable are optocouplers?

Optocouplers have several weaknesses, including parametric instability with temperature and device aging, significant internal parasitic couplings, long propagation delay times, narrow operating temperature ranges, and relatively low reliability.

What is a current transfer ratio?

The current transfer ratio is a parameter similar to the DC current amplification ratio of a transistor (hFE) and is expressed as a percentage indicating the ratio of the output current (IC) to the input current (IF).

What should the CTR of an optocoupler be?

The test circuit lets us evaluate the CTR of the TLP521-1 (GR), but we also use it to test many types of optocouplers with a CTR that is within 1 to about 3.8 without making changes to it.

How to calculate the optocoupler current transfer ratio?

It is defined as ratio of the output or collector current of the device (i.e. Ic) with the input current applied to LED coupling device. The above equation or formula is used for Optocoupler CTR calculation. CTR is usually expressed as a percentage.

How does the CTR affect a power supply?

The CTR determines the DC gain of a power supply’s open-loop frequency response, which affects the loop’s phase margin. An optocoupler influences multiple operating parameters, so CTR variations between devices can cause production tests to reject a power supply.

What does saturation mean for an opto isolator?

In the latter case the transistor is in saturation, this means the collector-emitter voltage across it is so low that the transistor is unable to further increase the current by changing its conductivity (due to more light from the LED). Thanks for contributing an answer to Electrical Engineering Stack Exchange!