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Boost Converter Outputs 28Volts?

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wuchy143

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All,

I'm looking to use a boost converter https://www.onsemi.com/pub_link/Collateral/CAT4238-D.PDF to drive my LCD display.(Manufacturer = Densitron 84-0102-000). I've never used a boost converter before and was a little confused on the voltage output. What determines it? The forward voltage drop of the LCD/LED is 28V from it's datasheet. The datasheet(for the boost conv) goes into great detail on the current which makes sense but it only gives a range for the voltage output which is up to 36 volts. It appears that this device is a constant current source so depending on what impedance you hook up to this will change the voltage output but the current will always be what you set it up to?

If anyone can help me make sense of this part it would be appreciated.

Thanks.
 
Yes, it is designed to supply constant current to leds. It will try to make the voltage across the feedback resistor a constant .3 volts. Same voltage across the resistor - same current thru the leds.
 
You do not want a constant current supply for an LCD, you want a constant voltage. LEDs need constant current.
 
In the case of the series stack of LED's, the output voltage is whatever the LED's need. The circuit is controlling the current through the LED's by the sense resistor at the bottom of the LED stack. The feedback sense reference is 0.3 vdc so the resistor is sized based on the needed LED current. Rfeedback = 0.3v/Iled

You can optimize the switcher duty cycle by value of inductor based on LED total stack voltage and LED current.
 
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