Ic: The maximum theoretical current that can flow through a transistor
Io: The maximum current that can be used for a digital transistor

DTA/C Series Explained
• 100mA can flow through a digital transistor. In this case Ic=100mA.
• これをIc=100mAを定義しております。
• Integrating resistances R1 and R2 into the transistor will make it digital.
• When a current Ic of 100mA flows through this digital transistor, an appropriate base current is required, necessitating a high input voltage Vin.
• However, on the other hand, the input voltage Vin(max) is limited by the absolute maximum permissible loss (package power) of the input resistor R1.
• However, when Ic=100mA Vin(max) will be exceeded. Therefore, Io is listed in order to ensure that the input voltage is less than the rated specification.
• As you may know, regarding the absolute maximum ratings since no more than 1 item can be supplied at the same time only Ic was listed, which should not cause any problems. However, in order to facilitate usage Io has been added as well.
• From the above, taking into account circuit design, Io is considered to be the absolute maximum value.

h_FE : DC current gain in general transistors G_I : DC current gain in digital transistors

Explanation:
• Both h_FEE and G_I denote emitter-common DC current gain
• Digital transistors feature 2 internal resistance connections
• Since the DC current gain is defined by the ratio between the input and output currents it is not affected by the input resistor R1.
• Therefore, in digital transistors only integrating R1, the gain should be equivalent to h_FE.
• However, if R2 is connected between the base and emitter the input current some of the current flowing through the transistor is shunted through R2. Because of this, the gain will decrease. This gain is referred to as GI.

It is easy to mistakeV_I(on) with V_I(off) and vice versa. V_I(on): The minimum voltage required to turn the transistor ON.

Common misunderstanding :

	: The input voltage increases constantly from 0V
	: After a short time the voltage will reach 1.8V, turning the digital transistor ON
	: Since this voltage is below the 3V listed in the specifications, it is considered no good.

Actual operation :

	: First, increase the input voltage Vin to a level sufficient to turn ON the transistor (i.e. 10V)
	: Gradually lower the voltage to the level noted in the specifications (i.e. 3V). If the transistor remains ON it is considered good.
	: Continue to decrease the voltage supplied to the base until the transistor turns OFF. Since this point is below 3V, the transistor works.

V_BE, h_FE, R1, and R1 will vary depending on the ambient temperature
• h_FE will change by: 0.5%/ºC (approx.)
• V_BE will vary by around -2mV/C (within the range of -1.8 to -2.4mV/C)
• R1 will change based on the graph below

• The digital transistor output voltage-output current characteristics are measured using the method below.
Therefore, with Io (in the low current region), no current will flow through the base, resulting in an increase in the output voltage Vo [VCE(sat)].
• Measurement method With a DTC114EKA transistor,
Io/Ii=20/1
From Ii=I_B+IR2 (IR2=V_BE/10k=0.65V/10k=65uA
I_B=Ii-IR2=Ii-65uA
In other words, when Ii decreases below 65uA I_B current will not flow, increasing Vo [V_CE(sat)].
This makes it impossible to measure Vo in the low current region.

1.Transistor operation

For NPN transistor operation, voltage is supplied as in Diagram 1.
In this circuit, forward voltage is supplied between the base (B) and emitter (E), resulting in current flow through the base. In other words, the base is infused with holes.
When this happens the free electrons in the emitter (E) are drawn towards the base. However, since the base region is extremely narrow, free electrons flow through the base region to the collector due to voltage bias from the collector. Because of this current flows from the collector to the emitter.

2.Switching operation

Transistor operation consists of both amplification and switching.
During amplification, Ic, equivalent to the amount of h_FE times the base current, flows. The output current in the active region can be obtained by continuously controlling the collector current based on the input signal.

Switching operation entails saturation conditions while ON (decreased collector-emitter saturation voltage). In this saturation region there is an excessive number of holes, which then exit through the base terminal from the base region. Collector current flows until all of the + holes exit from the base region. The time is takes for this to occur is referred to as tstg (OFF time).
The quicker the holes exit the base region the shorter the OFF time.
In digital transistors R1 and R2 act in series as a path for the holes to exit the base region while the transistor is OFF. R2 should be made as small as possible (with a given fixed R1) in order to minimize OFF time.