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About information presented in this cross reference

The information presented in this cross reference is based on TOSHIBA's selection criteria and should be treated as a suggestion only. Please carefully review the latest versions of all relevant information on the TOSHIBA products, including without limitation data sheets and validate all operating parameters of the TOSHIBA products to ensure that the suggested TOSHIBA products are truly compatible with your design and application.
Please note that this cross reference is based on TOSHIBA's estimate of compatibility with other manufacturers' products, based on other manufacturers' published data, at the time the data was collected.
TOSHIBA is not responsible for any incorrect or incomplete information. Information is subject to change at any time without notice.

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Is it OK to use a transistor as diodes?

Since a bipolar transistor is essentially two diodes, it can function as such. However, since bipolar transistors are not designed to be used as diodes, using them as diodes might cause a problem in terms of current and other ratings. For example, transistors are generally used with a base current that is less than one-tenth the required collector current. Therefore, the elements in the vicinity of the base terminal (e.g., on-chip wires and a bonding wire) are designed for this intended use, and the current ratings are specified accordingly (see Table 1). In addition, although the base-emitter and base-collector diodes look identical, the dopant concentrations in the emitter and collector regions of a bipolar transistor are quite different (nc << ne in the case of an npn transistor), causing the characteristics of the two diodes to be substantially different.

Here is an example of using the same transistor as a diode in the temperature compensation circuit for the transistor etc. Even in such a case, be sure to use transistors within the ratings specified in the datasheet. Use dedicated diodes for typical diode applications instead of bipolar transistors.

Figure 1 npn transistor
Figure 1 npn transistor
Table 1 Absolute maximum ratings of a bipolar transistor (2SC2712)
Table 1 Absolute maximum ratings of a bipolar transistor (2SC2712)
Figure 2 Example of a temperature compensation circuit for a common-emitter amplifier circuit
Figure 2 Example of a temperature compensation circuit for a common-emitter amplifier circuit