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The circuit below depicts a continuous saturation state and uses 2N3904:

enter image description here

From the above simulation the base current is 11mA, collector current is 14mA and the power is 11mW.

I'm trying to compare this circuit currents and voltages to the max datasheet parameters to ensure the parameters are within datasheet safe range. But stuck with two parameters. Regarding power: in my case 11mW and datasheet states Rja = 200°C/W. So 11mW would correspond only a 2°C increase in junction temperature. So if I'm not wrong powerwise there is no issue. The collector current 14mA is also less than the max continuous rating 200mA.

But I couldn't find the max base-collector voltage(VBC) and max base current in the datasheet. Is there a way to infer these?

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  • \$\begingroup\$ What about Vceo and Vcbo? And Ib_max = 0.2..0.5 * Icmax as a general rule. But power dissipation is a key factor here. See here media.digikey.com/pdf/Data%20Sheets/NXP%20PDFs/2N3904.pdf IB_peak = 100mA But no one should work at such a high currents using this small-signal BJT. If more current is needed use bigger BJT \$\endgroup\$
    – G36
    Commented Apr 4, 2020 at 11:22
  • \$\begingroup\$ I see so 20mA can be Ibmax then... Vceo and Vcbo are given in the first page, but Im asking for max Vbc(not Vcb) like how much the base voltage can be higher than the collector voltage. \$\endgroup\$
    – user1245
    Commented Apr 4, 2020 at 11:47
  • \$\begingroup\$ But why you are the only one who cares about Vbc_max? Do you care about Vbe max also? When BJT is in saturation region the base-collector junction is in forward bias (Vbc > 0.4V). So why bother? \$\endgroup\$
    – G36
    Commented Apr 4, 2020 at 11:52

1 Answer 1

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V(CBO) is 60V, so you can have Vc at 60V higher than Vb.

Max Ib is not defined in this datasheet, but the typical tests are done at below 10mA current and the Ib curve goes up to 10mA with 100mA Ic. For a 200mA transistor, there is no point giving the base more than 20mA of base current, there is a rule of thumb that says transistor is saturated already when current gain has dropped to 10, which can be seen in datasheet tests as well.

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  • \$\begingroup\$ Vceo and Vcbo are given in the first page, but Im asking for max Vbc(not Vcb) like how much the base voltage can be higher than the collector voltage. \$\endgroup\$
    – user1245
    Commented Apr 4, 2020 at 11:50
  • \$\begingroup\$ Well that is not something that usually needs to be considered in a properly designed circuit that uses the transistor in a conventional amplifier or switch in forward biased mode, where both Vbe and Vce are positive, and Vce can go to zero if you cut collector supply off. But of you think the transistor diode model, usually the Vbc is slightly higher than Vbe for the PN junction to conduct. \$\endgroup\$
    – Justme
    Commented Apr 4, 2020 at 14:19

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