Heating principle of high frequency induction IGBT

The transfer characteristic of IGBT refers to the relationship curve between the output drain current Id and the gate-source voltage Ugs. It has the same transmission characteristics as MOSFET. When the gate-source voltage is less than the turn-on voltage Ugs(th), the IGBT is in the off state. In most of the drain current range after IGBT is turned on, the relationship between Id and Ugs is linear. The maximum gate-source voltage is limited by the maximum leakage current, and its optimal value is generally around 15V.

The switching characteristics of IGBT refer to the relationship between leakage current and drain-source voltage. When IGBT is on, its PNP transistor is a wide base transistor, so the value of B is extremely low. Although the equivalent circuit is Darlington structure, the current flowing through MOSFET becomes the main part of the total current of IGBT. At this time, the on-state voltage Uds(on) can be expressed by the following formula: Uds(on) = Uj 1+Udr+IdRoh, where Uj 1 is the DC voltage of Ji junction, and its value is 0.7 ~ IV. Udr- the voltage drop across the spreading resistor Rdr. Roh channel resistance.

On-state current Ids can be expressed by the following formula:

Ids=( 1+Bpnp)Imos

Where imos is the current flowing through the MOSFET.

Due to the conductance modulation effect in N+ region, the on-state voltage drop of IGBT is small, and the on-state voltage drop of IGBT with withstand voltage of 1000V is 2 ~ 3 V. When IGBT is turned off, only a small leakage current exists.

IGBT with dynamic characteristics runs as a MOSFET most of the time during the turn-on, but in the later period when the drain-source voltage Uds drops, the PNP transistor changes from the amplification region to saturation, which adds another delay time. Td(on) is the turn-on delay time and tri is the current rise time. In practical application, the leakage current conduction time ton is the sum of td(on)tri. The falling time of drain-source voltage is composed of tfe 1 and tfe2.

During the turn-off of IGBT, the waveform of drain current becomes two segments. Because the charge stored in PNP transistor is difficult to be quickly eliminated after MOSFET is turned off, which leads to a long tail time of leakage current, td(off) is the turn-off delay time, and trv is the rise time of voltage Uds(f). In practical application, the falling time Tf of the drain current usually consists of two sections (t(f 1) and t(f2) in Figure 2-59, and the off time T (off) of the drain current = TD(off)+TRV Ten T (f) (2-16), where TD (.

All high-frequency induction heating equipment adopts IGBT principle to heat, which not only ensures the quality of equipment, but also improves the stability in production, and improves the productivity of customers more efficiently, stably, safely and environmentally.

IGBT picture:

Case study of using IGBT heating equipment;