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I just bought a pack of 2222A NPN transistors from a local electronics shop.

I found some datasheets online (e.g. https://www.onsemi.com/pdf/datasheet/p2n2222a-d.pdf ) that say the emitter-base voltage is 6v.

Does that mean that I cannot use this transistor with a 3v or 5v power supply?

(In the past I never looked at the specs and just wired the transistor with a resistor at the base, and it all worked. I am trying to reconcile my cowboy experience with a new practice of reading datasheets, and I am getting confused.)

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The emitter-base voltage of 6V is the Maximum rating. Go beyond that and it will destroy the device. It is NOT the normal operating voltage. That entire section is the ratings to avoid destruction.

Also, although the data-sheet is vague on the point, the emitter-base voltage of 6V is the maximum reverse voltage (ie with the base negative with respect to the emitter).

The "Maximum" or "Absolute Maximum" section is often close to the beginning of a datasheet.

The characteristics or normal operating conditions part of the datasheet is the place you will find the data on how to use the device normally.

Biasing the base with a resistor is a perfectly reasonable way to use the transistor and 3-5V for the collector supply is also perfectly reasonable.

A transistor can operate over a wide range of voltages and currents so even if your design doesn't match the conditions shown in the datasheet it may still be legitimate (providing you don't exceed the limits indicated in the absolute maximum section).

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    \$\begingroup\$ The specification in question was Veb which is the reverse emitter to base voltage. \$\endgroup\$
    – PStechPaul
    Commented Nov 1, 2022 at 0:11
  • \$\begingroup\$ OKay, thank you very much, that is helpful. \$\endgroup\$ Commented Nov 1, 2022 at 0:12
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    \$\begingroup\$ The datasheet is not vague on the point--it specifically says 6 V is the maximum emitter-base voltage, not the maximum base-emitter voltage (which would be in the vicinity of 0.6-0.7 volts, as it's a diode). The first node mentioned is to be considered positive with respect to the second node (or, if the voltage named is negative, negative). \$\endgroup\$
    – Hearth
    Commented Nov 1, 2022 at 3:20
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    \$\begingroup\$ @Hearth - I consider that vague. This rule is violated in this data sheet for a PNP transistor for example: onsemi.com/pdf/datasheet/2n3906-d.pdf \$\endgroup\$ Commented Nov 1, 2022 at 14:23
  • \$\begingroup\$ Regarding the last paragraph, there are surprisingly many parts that can be used "off-datasheet". A classic example is using a backwards transistor, and a capacitor, to make an oscillator. Another one is using a CMOS NOT gate with negative feedback to make an amplifier. \$\endgroup\$ Commented Nov 1, 2022 at 14:52

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