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PDF AN9012 Data sheet ( Hoja de datos )
| Número de pieza | AN9012 | |
| Descripción | Induction Heating System Topology Review | |
| Fabricantes | Fairchild | |
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t4U.com July, 2000
taSheeAN9012
.DaInduction Heating System Topology Review
w Discrete Application
w Power Device Division
w Fairchild Semiconductor
m1. Introduction
oAll IH (induction heating) applied systems are developed using electromagnetic induction which
was first discovered by Michael Faraday in 1831. Electromagnetic induction refers to the phenom-
.cenon by which electric current is generated in a closed circuit by the fluctuation of current in
another circuit placed next to it. The basic principle of induction heating, which is an applied form
of Faraday’s discovery, is the fact that AC current flowing through a circuit affects the magnetic
Umovement of a secondary circuit located near it. The fluctuation of current inside the primary circuit
t4provided the answer as to how the mysterious current is generated in the neighboring secondary
circuit. Faraday’s discovery led to the development of electric motors, generators, transformers,
and wireless communications devices. Its application, however, has not been flawless. Heat loss,
ewhich occurs during the induction heating process, was a major headache undermining the overall
efunctionality of a system. Researchers sought to minimize heat loss by laminating the magnetic
frames placed inside the motor or transformer. Faraday’s Law was followed by a series of more
hadvanced discoveries such as Lentz’s Law. This law explains the fact that inductive current flows
inverse to the direction of changes in induction magnetic movement.
SHeat loss, occurring in the process of electromagnetic induction, could be turned into productive
taheat energy in an electric heating system by applying this law. Many industries have benefited
from this new breakthrough by implementing induction heating for furnacing, quenching, and weld-
aing. In these applications, induction heating has made it easier to set the heating parameters with-
out the need of an additional external power source. This substantially reduces heat loss while
.Dmaintaining a more convenient working environment. Absence of any physical contact to heating
devices precludes unpleasant electrical accidents. High energy density is achieved by generating
sufficient heat energy within a relatively short period of time.
wThe demand for better quality, safe and less energy consuming products is rising. Products using
wIH include electronic rice cookers and pans. Safe, efficient and quick heating appliances attract
more customers. This document describes induction heating, power systems, and IH applications.
w taSheet4U.comRev D, July 2000
www.Da1
1 page  
Formula 3-5 states that the skin thickness is determined by the resistivity, permeability, and fre-
quency of the object. Figure 3-2 below is the distribution chart of current density in relation to skin
thickness.
io
current
density
0 do
x
Figure 3-2: Distribution Chart of Current Density and Skin Thickness
4. Topology Of Power System
Generally, semiconductor switching devices operate in Hard Switch Mode in various types of PWM DC-
DC converters and DC-AC inverter topology employed in a power system. In this mode, a specific
current is turned on or off at a specific level of voltage whenever switching occurs, as shown in Fig-
ure 4-1. This process results in switching loss. The higher the frequency the more the switching
loss, which obstructs efforts to raise the frequency. Switching loss can be calculated in a simple
way as shown in Formula 4-1 below. Switching also causes an EMI problem, because a large
amount of di/dt and dv/dt is generated in the process.
PSW
=
1--
2
VS
WIS
WfS
(
ton
+
toff)
(Formula 4-1)
where, Psw
Vsw
Isw
fs
ton
toff
: switching loss [W]
: switching voltage [V]
: switching current [A]
: switching frequency [kHz]
: switch turn-on time [s]
: switch turn-off time [s]
Rev D, July 2000
5
5 Page 
reliability. Quasi-resonant converters are now generally used because of the smaller heat sink and
PCB size and a simpler operating process. The following describes the operation of a half-bridge
series resonant converter and a quasi-resonant converter.
5-2-1. Half-bridge Series Resonant Converter
A variety of design methods are available for a power system using a half-bridge series resonant
converter. Figure 5-2 is a block diagram of a power system in a very simplified form in which reli-
ability and economy are factored in. This system is comprised of an AC power supply, main power
circuit, control circuit, input current detection circuit, resonant current detection circuit, and gate
operation circuit. All the necessary procedures for designing and testing the system are shown in
the block diagram. The drawing below does not contain the heater and cooling fan. The operation
of a power system as a whole is illustrated in the following figure.
Main Power Circuit
input current
detection
control
circuit
SGH40N60UFD
SGH40N60UFD
Llooaadd
resonant
current
detection
MCICOOMM
gaGteatderiDverivceircCuiirtcuit
Figure 5-2: Power System Using Half-bridge Series Resonant Converter
The AC (220V/60Hz) power passes through the rectifier to be transmitted to the capacitor. Capaci-
tors in existing power systems are too small in capacity to do the leveling work leading to the cre-
ation of rectified current in 120Hz, which is not the proper level for DC operation. The system for an
IH rice cooker, however, does not require a big capacitor to make DC more leveled, as the primary
purpose of the system is to generate heat energy. Rather, the rugged form of DC helps improve the
power factor of the system. In this system, the leveling capacitor serves as a filter preventing the
high frequency current from flowing toward the inverter and from entering the input part. Input cur-
rent becomes the average of the inverter current, and the ripples flow to the leveling capacitor.
The voltage passing the leveling capacitor is turned into a square wave in the process of high fre-
quency switching in the inverter. The high frequency harmonics contained in the square wave are
eliminated by the Lr, Cr filter. The square wave enables resonance in the resonant circuit, which in
turn, creates a magnetic field around the resonant inductor affecting the load (rice container). Eddy
currents are formed around the surface of the object, generating heat energy.
Rev D, July 2000
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet AN9012.PDF ] | |
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