JPH0272587A - High frequency heater - Google Patents

Abstract

PURPOSE:To secure safety by detecting currents flowing in a resistor when insulating deterioration occurred in a high voltage transformer so as to interrupt the supply of AC power to the high voltage transformer. CONSTITUTION:When the insulation of a high transformer 2 deteriorates, currents flow through resistors 13 and 14, and voltage drop occurs at both ends of the resister 14. Accordingly, the voltage by this voltage drop is applied to between the gate and the source of a thyristor 18 which is connected to the connection middle point D of current diodes 16 and 17, and the thyristor 18 operates, and currents flow to a relay coil 19 and excitate it, and a relay contact 20 becomes open, and the AC power supply to the high voltage transformer 2 is interrupted. Hereby, the danger of electrical shock to the human body which occurs by the deterioration of the high voltage transformer's 2 deterioration vanishes, and safety can be secured.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a high-frequency heating device, and in particular to its safety circuit.

2. Description of the Related Art A conventional high frequency heating device will be explained based on the circuit diagram shown in FIG.

In FIG. 2, a commercial power supply 1 is connected to a primary winding 3 of a high voltage transformer 2, and a secondary winding 4 of the high voltage transformer 2 is connected to a magnetron 7 via a voltage doubler rectifier circuit consisting of a capacitor 5 and a diode 6. A tertiary winding (heater winding) 8 of the high voltage transformer 2 is connected to a cathode (heater electrode) K of the magnetron 7. Also, magnetron 7
The anode A of the high voltage transformer 2 and one side of the secondary winding 4 of the high voltage transformer 2 are connected to a case 9, and the case 9 is connected to the earth lO via a ground wire 21.

By connecting the main body case 9 and the earth earth lO with the ground wire 21, insulation deterioration occurs between the primary winding 3 and the secondary winding 4 of the high voltage transformer 2, and the potential of the main body case 9 is lowered to the ground. when it becomes high.

This avoids danger to the human body due to electric shock caused when a person touches the case 9.

Problems to be Solved by the Invention However, in the conventional configuration as described above, it is necessary to connect the ground wire 21 to the earth ground 10, so it is not possible to carry it freely, which hinders the degree of freedom in installing the high-frequency heating device. .

The present invention solves the above-mentioned problems, and aims to provide a high-frequency heating device with improved installation flexibility without compromising safety.

Means for Solving the Problems In order to solve the above problems, the present invention provides a high-voltage transformer whose primary winding is connected to a commercial power supply, and two transformers connected in series in reverse and connected in parallel to the primary winding of the high-voltage transformer. a magnetron connected to the secondary winding of the high-voltage transformer; a main body case connected to the anode of the magnetron and one side of the secondary winding of the high-voltage transformer; The transformer includes a resistor connected between connecting midpoints of diodes, and a control means that detects the current flowing through the resistor and controls the supply of AC power to the high voltage transformer.

Effect With the above configuration, when insulation deterioration occurs between the primary and secondary windings of the high voltage transformer, current flows from the secondary winding of the high voltage transformer to the connection midpoint of the detection diode, causing a voltage drop across the resistor. occurs. The control means detects that insulation has deteriorated in the high-voltage transformer due to a voltage drop occurring across the resistor when current flows through the resistor, and controls the supply of AC power to the high-voltage transformer, for example. Cut off. Therefore, there is no risk of electric shock to the human body caused by poor insulation of the high-voltage transformer, and safety is ensured.In addition, there is no need for a ground wire to connect the main body case to the earth, and the high-frequency heating equipment The degree of freedom in installation is improved.

Example An embodiment of the present invention will be described below based on the drawings.

FIG. 1 is a circuit diagram of a high frequency heating device showing an embodiment of the present invention. Note that the same components as those in FIG. 2 of the conventional example are designated by the same reference numerals, and description thereof will be omitted.

In FIG. 1, two detection diodes 11.12 connected in reverse series are connected in parallel to the primary winding 3 of the high-voltage transformer 2, and two detection diodes 11.12 are connected in parallel to the primary winding 3 of the high-voltage transformer 2. resistors 13 and 14 are connected in series,
A smoothing capacitor 15 is connected in parallel with the resistor 14 . In addition, a power supply diode 16°17 connected in series in the opposite direction to the detection diode 11.12 is connected to the high voltage transformer 2.
are connected in parallel to the primary winding 3 of the sensing diode 11.
A thyristor 18 and a relay coil 19 are connected in series between the connection midpoint C of 12 and the connection midpoint of this power diode 16.17, and further between the connection midpoint E of the resistor 13.14 and the gate terminal of the thyristor 18. is connected. Also,
Relay contact 20 that opens when relay coil 19 is excited
(normally closed contact) is interposed in series on one side of the primary winding 3 of the high voltage transformer 2, and the series circuit consisting of the primary winding 3 and the relay contact 20 is connected to the commercial power supply 1 by a detection diode 11°12. and are connected in parallel with the power supply diodes 16 and 17. Note that the ground wire 21 shown in the conventional example has been removed.

The operation when the insulation of the primary winding 3 and the secondary winding 4 of the high voltage transformer 2 with the above configuration deteriorates will be described.

Since the commercial power source 1 is a pole-mounted transformer and one side is grounded to the ground, the connection midpoint C of the detection diodes 11 and 12 becomes approximately at the ground potential during a half cycle period of one cycle of the AC voltage. When the a side of the commercial power supply 1 is grounded, the detection diode 11 becomes almost at the ground potential, and when the b side of the commercial power supply 1 is grounded, the detection diode 12 becomes almost at the ground potential. therefore.

When the insulation of high voltage transformer 2 is good, resistor 13°14
No current flows through resistor 1, but if insulation deteriorates, resistor 1
3.14, and a voltage drop occurs across the resistor 14. Therefore, a voltage due to this voltage drop is applied between the gate and source of the thyristor 18 connected to the middle point of the connection of the power supply diodes 16 and 17, the thyristor 18 operates, and a current flows through the relay coil 19 to excite it. The relay contact 20 is opened, and the supply of AC power to the high voltage transformer 2 is cut off.

In this way, when insulation deterioration occurs in the high voltage transformer 2, the supply of AC power to the high voltage transformer 2 is cut off, so even if the main body case 9 of the transformer 1 is touched, no electric shock occurs, and safety is ensured. Since a ground wire is not required, the degree of freedom of the high-frequency heating device can be improved. Also, compared to using an earth leakage breaker instead of providing a ground wire, it is safe because it operates when insulation deterioration occurs in the high voltage transformer 2, even if the earth leakage current does not necessarily flow through the human body. It has the advantage of a high level of protection.

Note that this embodiment shows a configuration in which the thyristor 18 and relay coil 19 are excited by the current flowing through the resistor 13.14 to ensure safety, but in the case of an inverter power supply, the resistor 13.14 If the switching operation of the switching element is stopped by the current flowing through the transformer 2, the supply of AC power to the high voltage transformer 2 can be stopped, and safety can be ensured.

Effects of the Invention As described above, according to the present invention, when insulation deterioration occurs in the high voltage transformer, the control means detects the current flowing through the resistor and cuts off the supply of AC power to the high voltage transformer. It is possible to avoid the risk of electric shock to the human body due to poor insulation of the transformer, ensuring safety. Further, a ground wire connecting the main body case and the earth is not required, and the degree of freedom in installing the high-frequency heating device can be improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a high frequency heating device showing an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional high frequency heating device. 1... Commercial power supply, 2... High voltage transformer, 3... Primary winding of high voltage transformer, 4... Secondary winding of high voltage transformer. 7... Magnetron, 9... Main body case, 11.1
2...Detection diode, 13.14...Resistor,
16.17...Power diode, 18...Thyristor, 19...Relay coil, 20...Relay contact. Agent Yoshihiro Morimoto Figure 1 Figure 2

Claims (1)

[Claims] 1. A high-voltage transformer whose primary winding is connected to a commercial power source,
two detection diodes connected in series in reverse and connected in parallel to the primary winding of the high voltage transformer;
A magnetron connected to the secondary winding, a main body case connected to one side of the anode of the magnetron and the secondary winding of the high voltage transformer, and a resistor connected between the connection midpoint of the main body case and the detection diode. A high-frequency heating device comprising a body and a control means for detecting a current flowing through the resistor and controlling supply of AC power to the high-voltage transformer.