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Phototransistor minimum Vcc

G1234

Nov 29, 2017
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Nov 29, 2017
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Hi, I am a software maker dipping my hands in HW.
I want to use a phototransistor in a standard resistor/phototransistor circuit on a 1.8v Arduino board.
What is the minimal Vcc I can use with components like below?
[URL='https://www.mouser.co.il/ProductDetail/Everlight/EAPST1608A0/?qs=sGAEpiMZZMs50KUSuyRkpv2Oi4GVgrPoltPHSYTzwteJtk7%252boj5Yng%3d%3d']EAPST1608A0[/URL]
[URL='https://www.mouser.co.il/ProductDetail/Everlight/EAPST1608A0/?qs=sGAEpiMZZMs50KUSuyRkpv2Oi4GVgrPoltPHSYTzwteJtk7%252boj5Yng%3d%3d'][URL='https://www.mouser.co.il/ProductDetail/Everlight/EL-PT15-21C/?qs=sGAEpiMZZMs50KUSuyRkpolwhqNgcmNlb0pxugrAH9U%3d']EL-PT15-21C[/URL][/URL]
PT11-21C/L41/TR8
APT2012P3BT
Will it work with 1.8v ?
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Harald Kapp

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Nov 17, 2011
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The parameter too look for is Collector-Emitter saturation voltage. It is ~0.4 for all these couplers. Therefore your output will go up to 1.8 V -0.4 V = 1.4 V for a logic high.
An 1.8 V arduino's logic threshold should be at ~ 0.9 V (1/2 * 1.8 V), therefore 1.4 V should be detected as logic high without problems.

Note that the above calculation is valid for saturation of the phototransistor which means the transistor is illuminated to dribe a higher current than is provided by the resistor Re. Re limits the current to Ie = 1.4 V / Re. A sensible value for Re is e.g. 10 kΩ for a current of 0.14 mA.
 
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