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To get the power in watts, square the current and multiply by the resistor''s value. Thus: A 1/8 watt resistor will handle the job just fine. You can go bigger but never smaller. That answers my
Notable is the use of constant current sources (current limiters) for LED inputs on the associated opto-couplers. Here I''ll look at current limiter circuits using the popular LM334 and the LM317. The idea is
In choosing appropriate values for R1, the value for the current limiting resistor is set to produce the correct forward current (I F) through the infrared LED in the optocoupler.
The output side of the opto is going in to a micro controller, so the current needs are next to nothing. How can I determine the proper sized resistor to put on the input side of the opto?
I understand that I need a current limiting resistor on the input side of the optocoupler, so here is how I calculated it: From the datasheet, we see that the forward voltage is (typically, @20mA)
Regarding the optocoupler: don''t short the base connection to the emitter, but leave it open, or use a high ohmic resistor to control the sensitivity of the optocoupler.
Optocoupler Circuit Design Example: This calculator helps determine the appropriate resistor value (R1) for an optocoupler circuit. It''s crucial to limit the current through the LED to
CTR is one of the main parameters of the device and will be described in a later section. Also shown are the safety agency certification options, package types (e.g. DIP and SMD), and lead bending options
The simplest method of achieving the current drive is to provide a series current-limiting resistor, as shown in Figure 4, such that the difference between VAPP and VF is dropped across the
To determine the value of the current limiting resistor, first look up the maximum LED current in the manufacturer''s data sheet. Then choose a resistor so that the LED current is less than
Since the diode turns on at 2mA, a simple 1kOhm resistor should limit the current enough to be used with logic levels from 3V - 25V. I have also seen a JFET used to regulate the current to
Regarding the optocoupler: don''t short the base connection to the emitter, but