# How to Use a Photocoupler “Output Current”

Step 2. Calculate output current of the phototransistor from IF and CTR.

What is the value of the photocoupler’s output current (IC)?

Calculate the variation of the output current (IC) at the input current (IF) = 10 mA from the current transfer ratio (CTR=IC / IF). From the IC - IF curve, you can see that IC=10 mA(@IF=5mA, VCE=5V, Ta=25℃). So the CTR of this sample is 200%, which is the same value of minimum BL rank (200% to 600%). Also you can see that IC = 20 mA (@IF=10 mA、VCE=5V、Ta=25℃).
Next, we derive RL using the value of IC obtained here. In this calculation, design the value of RL so that VCE becomes saturation voltage even at the minimum value of IC.

## Chapter V : Optical Semiconductors (Isolators/Solid State Relays)

Types of Optical Semiconductors
Light-Emitting Principal of LEDs
The wavelength range of LEDs
What Is a Photocoupler?
Why Are Photocouplers Necessary?
Types of Photocouplers
Types of Photocouplers (Packages)
Types of Photocouplers (Internal Structure)
Safety Standards of Photocouplers
Characteristics of Photocouplers (Current Transfer Ratio: CTR)
Principal Characteristics of Photocouplers (Trigger LED Current)
Aging Variation Data of Photocouplers
How to Use a Photocoupler
How to Use a Photocoupler “Input Current”
How to Use a Photocoupler “Output-Side Resistor”
How to Use a Photocoupler Check

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