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AN604

Diode forward characteristics

Doc ID 3607 Rev 3

3/12

Diode forward characteristics

1.1

Junction temperature dependence

For two different junction temperatures, the current versus forward voltage curves cross at a

current level point Ic, depending on the diode technology. When the current is lower than Ic,

the temperature coefficient

αVF of the forward voltage is negative. When the current is

higher, the temperature coefficient becomes positive. This behavior is shown in Figure 2.

For Schottky and bipolar diodes, Ic is high and the working area corresponds to αVF < 0. For

SiC and GaN technologies, Ic is low and the αVF can be positive or negative. When of αVF <

0, the forward voltage and the conduction losses decrease when the junction temperature

increases.

Figure 2.

Forward (IF,VF) characteristics of a diode

1.2

Diode forward characteristics modeling: VT0(Tj), RD(Tj)

Forward characteristics (IF and VF) can be modeled by a straight line defined by a threshold

voltage VT0, and a dynamic resistance RD. VT0 and RD are calculated for 2 forward current

levels (IF1, IF2) for a given junction temperature as shown in Figure 3. Thus we can write:

Equation 1

Equation 2

Using Equations 1 and 2, we obtain VT0(Tj) and RD(Tj) expressions:

Equation 3

Equation 4

VF > 0

VF < 0

j2 >Tj1

VF = 0

)

⋅

)

⋅

)

−

)

−

⋅

−

⋅

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