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Is it possible for the base current to exceed the collector current for a BJT in saturation mode? (If the base current was increased without the collector current increasing at all)

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  • \$\begingroup\$ Certainly possible. At some point, the Vce(sat) will stop decreasing and will begin to increase as the base current increases (for a given collector current), so it's not something that is necessarily useful. \$\endgroup\$ Feb 19, 2015 at 18:45
  • \$\begingroup\$ @SpehroPefhany How does it happen? \$\endgroup\$ Feb 19, 2015 at 19:24
  • \$\begingroup\$ The base-collector junction is forward biased in saturation- so current does not just flow to the emitter, but also to the collector. \$\endgroup\$ Feb 19, 2015 at 19:40

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It is possible. Consider the figure below.

enter image description here

The collector current at saturation will be $$I_{Csat} = \frac{V_{CC}-V_{CEsat}}{R_C} \approx \frac{V_{CC}}{R_C}$$

The base current is given by, $$I_B = \frac{V_{CC} - V_{BE}}{R_B} \approx \frac{V_{CC}}{R_B}$$

So it is clear that the currents at saturation are entirely decided by the resistors and hence base current can be greater than the collector current at saturation.

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Yes, it is obvious that the base current can exceed the collector current if you consider the limiting case where the collector is open-circuit. The collector current will be 0, but you can still drive from 0 to the maximum allowed base current thru the base. With the collector open, base to emitter just looks like a diode.

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    \$\begingroup\$ Didn`t the questioner ask for saturation mode conditions? \$\endgroup\$
    – LvW
    Feb 20, 2015 at 9:37

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