Standard Circuits 1 - The Transistor Interfacing Circuit
Many output devices will require a transistor switching circuit. In most cases a
darlington pair formed from two transistors is ideal.
However this circuit requires that two separate transistors are used. It is possible to
buy a device that contains the two transistors in a single package. This transistor is
called the BCX38B, and can switch currents up to 800mA. This is the transistor used in
all the circuits through this book.
Note that it is usual to connect a back emf suppression diode across the output device.
This is essential with devices such as relays, solenoids and motors which create a back
emf when power is switched off. The diode type 1N4001 is the device recommended.
Many output devices will require a transistor switching circuit. In most cases a
darlington pair formed from two transistors is ideal.
However this circuit requires that two separate transistors are used. It is possible to
buy a device that contains the two transistors in a single package. This transistor is
called the BCX38B, and can switch currents up to 800mA. This is the transistor used in
all the circuits through this book.
Note that it is usual to connect a back emf suppression diode across the output device.
This is essential with devices such as relays, solenoids and motors which create a back
emf when power is switched off. The diode type 1N4001 is the device recommended.
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