JPS5831717B2 - induction heating cooker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an induction heating cooker using eddy current.

This type of induction heating cooker is powered by a power source E as shown in Figure 1.
Connect transistors Tr1 and Tr2 in series with
A capacitor C1 coil L and a current transformer CT are connected between the common connection point of both transistors Tr1 and Tr2 and the ground, and the capacitor C is charged and discharged by alternate conduction of the transistors Tr1 and Tr2, and an alternating current flows at that time. The current generates an alternating magnetic flux in the coil L, and this magnetic flux causes the cooking pot 1 to generate heat based on the eddy current product.The control of the transistors Tr1 and Tr2 is based on the alternating current detected by the current transformer CT. Control is performed by the drive circuit 2 alternately in correspondence with the zero-crossing points of the current.

As shown in Figure 2, this 1 drive circuit outputs an H level pulse to the output a when the output of the current transformer CT changes from positive to zero, and outputs an H level pulse when the output changes from negative to zero. It has a zero volt circuit 3 which outputs a zero volt circuit 3, and the pulse of its output a is given to the monomulti 6 through a Nant gate 4 and an impark 5, so that the drive circuit 7 makes the transistor Tr2 conductive for a predetermined period of time, and the output Monomulti 10 via Nantes gate 8 and Nantes gate 9
, and the drive circuit 11 makes the transistor Tr1 conductive for a predetermined period of time.

The drive circuit 1 is started by inputting an L-level start signal d to the Nantes gate 9, and stopped by inputting an L-level stop signal e to the Nantes gates 4 and 8.

However, in this drive circuit, when an L-level stop signal e is input, both transistors Tr1 and Tr2 are subsequently cut off regardless of the state of charge on the capacitor C. Therefore, for example, the transistor Tr1 becomes conductive and the transistor If an L-level stop signal e is input to the Nandt gate 4.8 before Tr2 becomes conductive next, the circuit operation ends with capacitor C remaining charged.
Therefore, even if the next L-level activation signal d is input to the Nantes gate 9 and the transistor Tr becomes conductive, the capacitor C
No charging current flows to the current transformer CT, so the zero-crossing point of the current transformer CT cannot be detected, and there is a possibility that subsequent continuous operation will not be performed.

Therefore, in order to ensure that the charge on the capacitor C is zero after one operation ends and before the next operation starts, a resistor R is connected in parallel to the capacitor C to solve the problem described above. Measures were taken to address the issue.

However, since the charge accumulated in the capacitor C is extremely large, the resistor R is required to have a high withstand voltage and a large power capacity.

Also, when this resistor R generates heat, thermal noise is generated.
In some cases, it had a negative effect on performance.

The present invention has been made in view of the above-mentioned points, and is an object of the present invention to solve the above-mentioned problems by always making one switching element conductive last when the motor is stopped.

Hereinafter, one embodiment of the present invention will be described with reference to FIG. 3 and subsequent figures.

Components that are the same as those in FIG. 2 are given the same reference numerals and their explanations are omitted. 12 is a delay circuit, and therefore the L level stop signal e is input as is to one Nantes gate 8, but to the other gate 8. The Nant gate 4 has a delay time Td caused by the delay circuit 12.
Just come in late.

This delay time Td is set longer than H of the charging/discharging cycle T of the capacitor C.

The above operation will be explained with reference to FIG. 4. Before the operation, both the start signal d and the stop signal e are at the H level, and the output ab of the zero volt circuit 3 is at the L level.

In this state, when the activation signal d is set to L and becomes a bell, the Nantes gate 9 changes to the H level, and therefore the monomulti 10
operates, and the drive circuit 11 causes the transistors Tr,
conducts for a predetermined period of time, and the charging current to capacitor C begins to flow through coil L and current transformer CT.

When this charging current becomes zero, the current change is detected by the zero volt circuit 3, and an H level pulse is generated at the output a, which causes the output of the Nant gate 4 to go to the L level.
If the output of inverter 5 is H level, mono multi 6
is activated, and the drive circuit 7 makes the transistor Tr2 conductive for a predetermined period of time to discharge the charge stored in the capacitor C.

When this discharge current becomes zero, the current change is detected by the zero volt circuit 3, and an H level pulse is generated at the output, so that the Nant gate 8 becomes an L level and the Nant gate 9 becomes an H level donor. , the monomulti 10 is activated and the drive circuit 11 makes the transistor Trt conductive again.

As described above, when the starting signal d is at the L level for a predetermined period of time, from this point on, the transistors Tr and Tr2 are alternately made conductive by charging and discharging the capacitor C, generating an alternating magnetic flux in the coil L, and the cooking pot 1 It begins to generate eddy currents.

If the stop signal e is set to the L level at a certain time, the Nandts gate 8 becomes the H level regardless of the output of the zero-volt circuit 3, so the Nandts gate 9 does not change from the L level state and the transistor Tr1 will no longer conduct.

However, since the L-level stop signal e' is input to the Nant gate 4 after a delay of the delay time caused by the delay circuit 12, the monomulti 6 is affected by the output a of the zero-volt circuit 3 and the transistor Tr2 is turned on until then. can be done.

Therefore, due to the conduction of the transistor Trl, the capacitor C
Even if the operation is stopped by setting the stop signal e to L level at the time when charging starts, the Nant gate 4 closes after T/ of the oscillation period T has elapsed, so charging ends during that time and the operation becomes zero. An H level pulse is output from the output a of the voltage circuit 3, and the monomulti 6 makes the transistor Tr2 conductive, so that the capacitor C is discharged and the charge becomes empty, and the entire operation ends.

Note that the stop signal e becomes H level when the entire operation is to be stopped or when the cooking pot is lifted.

From the above, according to the present invention, when the operation of the cooking appliance is stopped, one of the switching elements always becomes conductive last to discharge the charge of the capacitor C, so that when the cooking appliance is started again, the capacitor C This allows charging current to flow through the battery, allowing normal startup.

Further, since no resistance is required for discharging as in the conventional case, no trouble occurs.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the principle of an induction heating cooker, Fig. 2 is a conventional one-drive circuit diagram, Fig. 3 is a drive circuit diagram of an embodiment of the present invention, and Fig. 4 is a timing diagram of the drive circuit. It is a chart diagram. d...Start signal, e...Stop signal.

Claims (1)

[Claims] 1. A capacitor between the common connection of two switching elements connected in series to a DC power source and one pole of the power source,
A coil and a current detection means are connected in series, and the current detection means detects two types of zero-crossing points of the charging/discharging current and alternately conducts the two switching elements to generate an alternating magnetic flux in the coil. In an induction heating cooker that heats by heat generated by an eddy current product, a part of the stop signal that prevents conduction between the two switching elements is delayed, and the switching element that charges the capacitor is stopped and then discharged. An induction heating cooker characterized in that the operation of a switching element is stopped.