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What will be the voltage across an ideal diode (that never burns) if it is connected directly to a 5 volt ideal voltage source directly without any current limiting device?

Will the voltage across the diode be 5 volts or 0.7 volts, or it will be 4.3 volts with a short circuit?

JRE
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Alex
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2 Answers2

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You could get an ideal diode and ideal power supply and try the experiment yourself. Oh, no you can't...nobody seems to be supplying ideal components these days.

This is similar to the old question of what happens when an irresistible force meets an immovable object. The voltage across the diode would be undefined. The ideal diode would conduct an infinite amount of current, so we're in the realm of calculus here, but still with conflicting voltage results. This is the reason ideal components don't exist in reality, where limitations on the physical operation of devices result in some solution that balances all the parameters. Ideal parts are approximations of reality, not something that can be implemented.

Cristobol Polychronopolis
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As @PeterBennett alluded to, it depends on your definition of "ideal". You end up with some "undefined" since you're doing some divide-by-zero and multiply-by-infinity.

  • If "ideal" means zero voltage drop in the forward direction, then the voltage across the diode will be undefined and the current will be infinite.
  • If "ideal" means a constant (e.g. 0.7V) forward voltage drop, then the voltage across the diode will also be undefined and the current will be infinite.
  • If "ideal" means that the diode perfectly obeys the Shockley diode equation and has no parasitic resistance etc, then the voltage across the diode will be 5V and the current will be some finite but enormous quantity (like 10^40). This would require your voltage source to provide the combined power of several thousand Kardashev type III civilizations.
vir
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