RU2380862C1 - Induction heating device - Google Patents

Abstract

FIELD: electric engineering.

SUBSTANCE: device comprises the main half-bridge made on two field transistors and connected via capacitor to primary winding of insulating transformer. Circuit of field resistors control comprises control microcircuit chip, between outputs RT and CT of which there is time-setting chain arranged, between VCC and VB - diode, which is serially connected to capacitor, and HO and LO outputs are connected via resistors to gates of field transistors. Insulating transformer is arranged with two secondary windings connected via current-limiting resistors to field transistors that create additional half-bridge. One of secondary windings of insulating transformer is connected between gate of one of field transistor and point of its connection to the second field transistor, and the other one - between gate of the second field transistor and common wire. Two serially capacitors are connected in parallel to field transistors, between common point of which and point of field transistors outputs connection there is heating coil connected.

EFFECT: increased reliability of device operation by arrangement of galvanic isolation between power and control circuits.

1 dwg

Description

The invention relates to the field of electrical engineering and may find application for induction heating of metal parts.

A device for induction heating is known, the main element of which is a self-oscillating half-bridge driver, to the terminals of which control elements are connected - a diode, resistors and capacitors and a half-bridge of field-effect transistors (http://www.gaw.ru/pdfAR/ic/ir2153.pdf). The load of the half-bridge is an inductive ballast (heating coil) connected through a capacitor.

The disadvantage of this device is the lack of galvanic isolation of the control circuit from the power, as a result of which the supply voltage of the heating coil is limited to the maximum voltage value for the driver, which limits the heating power. In addition, the probability of failure of circuit elements due to the use of high voltage in the control circuit is increased.

The technical result consists in increasing the reliability of the device due to the implementation of galvanic isolation between the power and control circuits.

The technical result is achieved in that the device comprises a main half-bridge made on two field-effect transistors, connected through a capacitor to the primary winding of an isolation transformer. The control circuit of the field-effect transistors contains a control chip, between which the RT and CT terminals are connected with a directly connected circuit, between the VCC and VB there is a diode connected in series with the capacitor, and the NO and LO terminals are connected through the resistors to the gates of the field-effect transistors. The isolation transformer is made with two secondary windings connected through current-limiting resistors to field-effect transistors, forming an additional half-bridge. One of the secondary windings of the isolation transformer is connected between the gate of one of the field effect transistors and the point of its connection with the second field effect transistor, and the other between the gate of the second field effect transistor and the common wire. In parallel with field-effect transistors, two series-connected capacitors are connected, between the common point of which and the connection point of the terminals of the field-effect transistors a heating coil is connected.

The device (see drawing) contains an isolation transformer 1 with three windings: 2, 3, 4. The primary half-bridge connected to the primary winding 2 through capacitors 5 and 6 is made on two: field-effect transistors 7 and 8. To the secondary windings 3 and 4 of the transformer 1 are connected through current-limiting resistors 9 and 10 to the gates of field-effect transistors 11, 12, which form an additional half-bridge of increased power. In parallel with the field-effect transistors 11, 12, two capacitors 13, 14 are connected in series, between the common point of which and the connection point of the terminals of the field-effect transistors 11, 12 a heating coil 15 is connected. The control circuit of the field-effect transistors 7, 8 contains a microcircuit 16, between the terminals RT and CT of which A blinking circuit is included, including a resistor 17, a variable resistor 18, and a capacitor 19. Between the terminals of the VCC and VB of the microcircuit 16, a diode 20 is connected in series with the capacitor 21. The NO and LO terminals are connected respectively through the resistors 22 and 23 to the gates of the field effect transistors 7 and 8.

The operation of the device is as follows. Let the transistor 7 is open at the initial moment of time (respectively, the transistor 8 is closed). The current flows through the chain positive terminal 24 - diode 20 - transistor 7 - primary winding 2 - capacitor 6. In this case, the capacitor 6 is charged with polarity (+). In the process of charging the capacitor in the secondary winding 3 of the transformer 1, a voltage pulse appears, opening the transistor 11, and the current begins to flow through the chain positive terminal 25 - transistor 11 - heating coil 15 - capacitor 14. In this case, the capacitor 14 is charged to the voltage of the power source 25, and the transistor 12 remains closed, since between its gate and the source a voltage pulse is applied from the secondary winding 4 of the reverse polarity. At the next time, the transistor 11 closes and the transistor 12 opens. The current from the low voltage power supply 24 starts flowing through the chain positive terminal 24 - diode 20 - capacitor 5 - transistor 8. In this case, the capacitor 5 is charged to the voltage of the power source 24 and the capacitor is recharged 6. In the secondary winding 4 of the transformer 1, a voltage pulse appears, opening the transistor 12. The current of the high voltage power supply 25 starts flowing through the chain, positive clamp 25 - condenser 13 - heating coil and 15 - transistor 12. This results in charging of the capacitor 13 and the overcharging of the capacitor 14. Transistor 11 remains closed, since between its gate and source pulse applied reverse voltage. When you open the transistor 7 and close the transistor 8, the process is repeated again.

By changing the resistance value of the resistor 18 with the capacitance of the capacitor 19 at 1000 pF and the resistance of the resistor 17 at 8 kOhm, the generation frequency can be set in the range of 8-1000 kHz (a frequency of about 100-300 kHz was used in the prototype for heating).

The device was made in the form of a layout and showed its performance.

Compared with the known solution, the proposed one allows to increase the reliability of the device due to the implementation of galvanic isolation between the power and control circuits.

Claims (1)

A device for induction heating, containing the main half-bridge made on two field-effect transistors, connected through the capacitor to the primary winding of the isolation transformer, the field-effect transistor control circuit contains a control circuit between which RT and CT are connected, a timing circuit is connected between VCC and VB - a diode, in series connected to a capacitor, and the findings of NO and LO are connected through resistors to the gates of the field effect transistors, characterized in that the isolation transformer is made with two with the secondary windings connected through current-limiting resistors to field-effect transistors forming an additional half-bridge, one of the secondary windings of the isolation transformer is connected between the gate of one of the field-effect transistors and its connection point with the second field-effect transistor, and the other between the gate of the second field-effect transistor and the common wire, with In this case, two series-connected capacitors are connected in parallel with the field-effect transistors, between the common point of which and the connection point of the terminals of the field trans Zistor included heating coil.