Three working states of transistor

Bipolar Junction Transistors (BJTs) are fundamental semiconductor components, functioning through three distinct operating states that enable their versatility in electronics. As a leading manufacturer, YFW Microelectronics (https://www.yfwdiode.com) produces BJTs optimized for each state, catering to automotive, industrial, and consumer electronics needs.
Cut off state: When the voltage applied to the emitter junction of the transistor is less than the conduction voltage of the PN junction, the base current is zero, and the collector current and emitter current are both zero. At this point, the transistor loses its current amplification function, and the gap between the collector and emitter is equivalent to the open state of the switch. We call the transistor in the cut off state.

Amplification state: When the voltage applied to the emitter junction of the transistor is greater than the conduction voltage of the PN junction and is at an appropriate value, the emitter junction of the transistor is forward biased and the collector junction is reverse biased. At this time, the base current controls the collector current, making the transistor have a current amplification effect. The current amplification factor β=Δ Ic/Δ Ib, and the transistor is in an amplification state.

Saturated conduction state: When the voltage applied to the emitter junction of a transistor is greater than the conduction voltage of the PN junction, and when the base current increases to a certain extent, the collector current no longer increases with the increase of the base current, but remains relatively stable near a certain value. At this point, the transistor loses its current amplification function, and the voltage between the collector and emitter is very small. The collector and emitter are equivalent to the conduction state of a switch. The state of a transistor is called saturation conduction state.

Based on the high or low potential of each electrode during the operation of a transistor, the working state of the transistor can be determined. Therefore, electronic maintenance personnel often use a multimeter to measure the voltage of each pin of the transistor during maintenance, in order to determine the working condition and status of the transistor.

Each state leverages the BJT’s structure—three doped layers and two junctions—to enable switching and amplification. YFW’s BJTs are engineered to perform reliably across all states, with strict quality control ensuring consistency in mass production. For technical specifications of YFW’s BJT series，visit https://www.yfwdiode.com.