JPS60174071A - Electromagnetic induction heater - Google Patents

Abstract

PURPOSE:To prevent an abnormal sound from generating by gradually increasing the input power as a whole at the starting time. CONSTITUTION:The duty ratio of a conduction control signal to intermittently conducting a switching element is gradually increased by controlling with the output of a comparator when an inverter 5 is started, the pulse signal is applied through a drive circuit to a transistor 5e to gradually increase the input voltage, thereby preventing the abnormal sound from generating. After starting, the voltage representing the input power is compared by a comparator. Accordingly, the input power is increased to lower the duty ratio of the pulse signal of the NAND gate output for controlling the conduction of the transistor 5e, thereby stabilizing the input power.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an electromagnetic induction heating device used as a cooker, etc., and more specifically, to prevent abnormal noises during startup and to protect against unsuitable loads. ! ! This paper proposes an electromagnetic induction heating device that enables this.

[Prior Art] - Electromagnetic cookers that use electromagnetic induction to heat an iron pot for cooking are now widely known. In such cookers, the input power increases rapidly when starting up, causing abnormal noises.
This may come as a surprise to users.

In order to prevent this, the inventor of this pongee gradually increased the input power during startup to prevent the generation of abnormal noise.
It proposed a magnetic induction heating device [Patent application 1518/1986]
No. 41]. On the other hand, when used as a cooker, a protection function against unsuitable loads for pots made of aluminum, copper, etc. is required, and for this purpose, the input power is monitored and if this is small, it is judged as an unsuitable load. A new one is being developed.

However, with cast steel, which is originally an appropriate load, if the input power is gradually increased as described above, there is a problem that the input power at startup is low and the load is determined to be an inappropriate load.

〔the purpose〕

The present invention has been made to eliminate such inconveniences, and the input power is gradually increased as a whole at the time of sensitization, but the input power is suddenly increased prior to the first sampling for monitoring. The object of the present invention is to provide an electromagnetic induction heating device that can prevent abnormal noise and protect against unsuitable loads, and can control input power more precisely than noise. [Structure] The electromagnetic induction heating device according to the invention is provided with an I)<-ta circuit, and activates a duty ratio of an equal conduction control signal to make the switching element of the I(-I) circuit intermittently conductive!/C. While the input power is gradually increased by increasing the input power gradually, the input power is monitored and if the input power at startup is less than a predetermined value, the inverter circuit ff1llJ is stopped. Furthermore, the invention is characterized in that the duty ratio is rapidly increased prior to monitoring at the time of startup. This shows the inverter circuit part of an electromagnetic induction heating device related to a commercial frequency AC 1m source l!/
The direct current obtained by the c-connected full-wave rectifier 2Vc should not be applied to the single ended bush-pull type inverter circuit 5 via the choke coil 8 and the smoothing capacitor f4. The inverter circuit 5 includes a series resonant circuit of an induction heating coil 5a and a resonant capacitor 5b, and this series resonant circuit is connected to a switching transistor 5C.
and the flywheel diode 5d.
It is likely to be connected in antiparallel. switching transistor 5
c is a collector with a choke coil 4 and an induction heating coil 5a.
The emitter is connected to the collector of another switching transistor 5e.

The emitter of the transistor 5e is connected to the negative electrode side of the full-wave rectifier 2, and a diode 5f is connected in antiparallel to the transistor 5e. And current iI flowing through induction boosting coil 5a + diode l)d, 5f dogs
If a, Id, If, then La+Id-If and If-1
Current transformer 8.9 to detect each current of d? It is a l-setting.

The base terminal a and emitter terminal bK of the transistor 5c are connected to the terminals a and b of the secondary winding 50b of the pulse transformer 500 shown in FIG. The base terminal C of the transistor 5e is electrically conductive,
The emitter terminal dK is connected to the terminal cod of the drive circuit 19 shown in FIG. 4, and the transistor 5C is intermittently made conductive by a pulse having a duty of 1/2 or less.

Transistor! The duty ratio of the pulse given to le' is determined by input power control, which will be described later.

According to the circuit lc shown in FIG. 1 above, when the transistor 5e becomes conductive, a current flows in the direction of the arrow in the coil 5e and the capacitor 5b is charged by this.8 Next, after turning off the transistor 5C, a pulse signal is sent to the transistor 5C. is applied to make it conductive, the charge in the capacitor 5b is discharged, and a current fliJvl- flows in the opposite direction to the arrow mark through the coil 5a and the transistor 5c. In this way, by making the transistors 6e+5ct conductive alternately at high frequency, a high frequency current flows through the coil SaK, and it becomes possible to heat the pot P placed on the filler 5a and further the food in the pot P. Note that the input power is the transistor beK
Although it is controlled by the duty ratio of the applied pulse, the input power can be adjusted by turning on and off the inverter circuit 5, which has a longer cycle than that.

FIG. 2 shows a drive circuit for a transistor 5C, and a direct current obtained by a full-wave rectifier 2 or the like is applied to a series circuit of a primary winding 60a of a pulse transformer 50 and a transistor 51. It is driven by the output of an oscillator 52 that oscillates a pulse signal with a fundamental frequency f0 and a duty ratio of 1/2, and provides a pulse for driving the transistor 5c to the secondary winding, and both terminals VH, VL of the 8th winding 50c. And a pulse having an opposite phase to the above pulse is obtained at the middle frequency terminal VN.

This pulse is applied to terminals VH and VL of the constant voltage circuit 54 in FIG.
.

Given to VN. In addition, b8 is a reset diode.

Fig. 8 shows the middle five parts of the control system of the device of the present invention? It shows.

When an input power command such as 10% is inputted from the keyboard 61, the microcomputer 6° displays this input value on the display unit 62rc, and also outputs the basic station waveform FOS, that is, IIA of the inverter circuit, between the output terminals C and D. #Outputs a pulse signal of duty Jt 1/IO with a period seven times longer than the J frequency. As a result, the non-explosion J device is heated with a power equal to the maximum input power.

' In addition to controlling the input power as described above, the microcomputer 60 issues a low-active monitoring pulse signal as shown in FIG. 5(a) from the output terminal α.

When this pulse signal becomes low level, the transistor 68 connected to it turns on, so the inverter circuit 5 operates normally, and if a voltage appears between the input terminals A and B of the 7-opto coupler 64, the photo coupler 64 emits light. The microcomputer 6 emits light and the light receiving section receives the light.
The input terminal β of 0 becomes high level as shown in FIG. 5(b). ,vice versa,.

When no voltage appears between the terminals A and B, the terminal β' of Fi becomes 'low label'. That is, the microcomputer Taro o emits a pulse signal from the terminal α, and in response, when the terminal β is at a high level, it determines that the inverter circuit 5 is normal, and even when the terminal α is at a low level, it determines that the inverter circuit 5 is normal. If the terminal β does not go to high level regardless, it is assumed that there is an abnormality and the buzzer 65t is activated.

In addition, in FIG. 5, the period from the time when the cooking start switch (not shown) is turned on and a start command is applied to the inverter W15 until the monitoring pulse signal first becomes low level is ''.
(Let's call it i-TD.

FIG. 4 shows the main part of the control circuit of the inventive device. The pulse signals with a duty ratio of 1/2 applied to the terminals VH, VN, and VL are applied to the constant voltage circuit 54, and are applied to +Vc and -V.
Create a potential of s. Also, the terminal VL emitter f-Vs
given the pace of the transistor Q. As is clear from the polarity of the windings 50b and 50c in Fig. 2, the terminal VL and the terminal a change from -high to low at the same time, so the transistor 5C, which is turned on and off by the output of the terminal a, When off (terminal a*VL is low) 1ctj) transistor Qs is off. The collector of this transistor Q3 is connected to a comparator 14.16a which will be described later.
The output and wired OR are taken. In designing such a circuit, 19, the transistor 58 is not turned on when the transistor 5C is on (therefore, the transistor Q is also on) to prevent a dead short circuit in the inverter circuit 5. It is prevented.

The terminal VHH is applied to the base of the transistor Q1 with emitter f+Vc. This Transis Q.

K is connected in parallel with a capacitor 16b. Therefore V
The capacitor 16b is rapidly charged while VH is at a low level (when transistor 5c is on and transistor 5e is off), but when VH is at a high level (when transistor 5c is off). Therefore, the transistor 5e can be turned on. (KH) The transistor Q1 is turned on and its charge is discharged. Due to this K, the collector side potential V of the transistor Q1 changes as shown in FIG. 6(b).

When a pulse signal at the time of startup is emitted from terminals C and D of the computer 60 shown in FIG. Photocabra 18 a that changes
Output V+u) is applied to transistor 18b, turning it off. Then, the capacitor 18c connected in parallel to this capacitor 18c starts to be charged by +VC, and its terminal voltage V gradually rises as shown in FIG.

is applied to a comparator lid, where it is compared with the desired voltage. Therefore, during the rising period of V, the comparator 18
d output V is inverted, and the output V changes to a low level as shown in FIG. This output v8 is N, AND
Gate 18f [-! y- can be obtained. This NAND gate 18fK is supplied with the collector potential of the transistor 18d as another input. Since this collector potential is at a high level after the transistor 18d is turned off, the NAND output (18f output vs. is shown in Figure 7) is the point at which the terminal C output becomes high level and the transistor 18d is turned off. from comparator 18d output V,
remains at the same low level until it changes to high level. NA
(ND) 18f output v, ti is given to transistor Q2, and while ■ is at low level, transistor 92
Connect it to turn it off. A capacitor 15a of a current control circuit 15 is connected to the collector of the transistor Q through an eleven forward diode.

NAND gate 18f output V output meter is given to transistor Q4 to obtain complementary signal V6 of v3, which is sent to NAND gate 1.
It is given to 1. The voltage Vs is given to the differentiating circuit 18e,
Its differential output v*t4, this'(rR-37 lip 70
It is applied to the set terminal of knob 18. Differential output −hv,
It is a signal that instantly drops to low level at the falling edge of
This sets the shift flip prop 18. The flip-flop 180 set output Q is applied to a NAND gate l1, etc.

Current control circuit 15#-j switching transistor 6C
The collector of s6e is rectified by the output tgM of the current transformer 8 representing the average value t of the current, and the current transformer t5b is rectified, and this output voltage vc'r
- There is no ir capacitor to provide 15aK. The capacitor 15af)) Ifil voltage V, shown in FIG. (2) changes to a high level, then gradually discharges and falls, and eventually reaches a level determined by the current transformer 8 output. This terminal voltage V7T/'i is applied to the single-power terminal of the terminal 14. Figure 6 shows an enlarged view of the period indicated by the arrow in Figure 7 at the beginning of this descent.
? It shows. □ In the comparator 14, as shown in FIG. 6(c), the input signal V7. Vll will be compared. Initially, there is a period when V7 becomes higher than the sawtooth signal V, so
At this time, the output of the comparator 14 becomes the cover low level. As mentioned above, the transistor Q is turned on at the terminal (pulse) with an output duty ratio of 1/2.

Although it is turned off, its collector is wide-ORed with the comparator 14, so its output signal V.

However, when the broken line □ shown in FIG. 6e shows, the pulse signal does not have a duty ratio of 1/2, but becomes a smaller pulse signal. Then, as V and J decrease, it gradually increases, and eventually becomes a pulse signal with a tetuity ratio of 1. Which output signal v,
(d Provided to NAND gate 11'.

゛The input power control circuit 16 is designed to obtain the difference between the outputs of the current transformers 8 and 9 using the differential amplifier 16bK,
Since the output, that is, the input power vp of the induction heating coil is applied to the single-power terminal of the comparator 16a, and Vsk is applied to the single-power terminal of the comparator 16a, it operates in the same manner as the comparator 14. NAND goo) 11 output is drive times 1
619.

With the above configuration, when the inverter circuit 5 is activated, a pulse signal whose duty ratio gradually increases as shown in FIG. This causes the input power to gradually increase and prevent abnormal noise from occurring.Furthermore, after startup, Vp, which represents the input power, is equal to v8 and the comparator 16a'<
Therefore, when the input power becomes large and Vp becomes large, the duty ratio of the pulse signal output from the NAND gate 11 that controls the conduction of the transistor 5e becomes low, and the input power is controlled and stabilized. .

Next, 11 paths for protection against inappropriate loads will be explained. Fastener 15b of current control circuit 15 VCT-
A predetermined reference voltage VR3 is applied to the 1i cosciparator 17 and the 1i cosciparator 17's 1i force VC. When an unsuitable load is placed on the induction heating coil 5a, the VCT-1 and VR3 area become high and R-
A low level input is given to the reset terminal of the 87 flip 70 tube 18, the flip 70 tube 180 set output Q becomes low level, the NAND gate 11 output remains high level, the transistor 5e remains off, and this tL is protected. be done.

On the other hand, the magnitude of human power Vp is given to one input terminal of two comparators 21 and 22, and the reference voltage VRI and
R2 (where LVR2>VRI) is given. The comparator 21 output V21 is given as a trigger signal to a mono staple multi φ pipe rake (hereinafter referred to as mono multi) 28, and this mono multi 23 output V2B
Transistor Q.

is turned on, and its collector is connected to the capacitor 15a through a resistor so that when it is turned on, the terminal voltage V of the capacitor 15a is lowered to the -VS side. Comparator 22 output V22U) is connected to the emitter of transistor Q6, and the base It of transistor Q6;
It is connected to the set output terminal of the R-87 lip 70 tube 18. The collector is connected to the light emitting side terminal AK of the photocoupler 64 shown in FIG. The operation of such a circuit will be explained based on FIG.

When the inverter circuit 5 is activated as the Rfa child Ct of the microcomputer 60, the input power increases gradually as described above, and Vp increases as shown in FIG. The voltage gradually increases as shown in FIG. 8, and when Vp eventually becomes larger than VRl, the output V21H of the comparator 21 changes to the low level [FIG. 8(B)]. As a result, the monomulti 28 signal is triggered and the output V28 fl of ^ becomes low level for a predetermined period of time [FIG. 8(c)]. Then, transistor Q is turned on, and V is forcibly pulled down as shown in FIG. Then, it is clear from Fig. 6 (b) that <V
As the time for s > Qy becomes longer, the duty ratio of V increases, and the input power increases rapidly [Figure 8 (a)]
. Eventually, VP>VR, so as shown in FIG. 8(e), the output V22fl of the comparator 22 changes to low level and the transistor Q6 turns on. As a result, the photo coupler 64 enters the light emitting state, and the
As shown in FIG. 3A, when the terminal α of the microcomputer 60 becomes low level, the terminal β becomes high level. In this way, the time it takes for Vp to reach VR21 at startup is shortened by the action of the comparator 21 and the monomulti 28, which are set as the reference voltage "i VR, which is lower than VRtt".

〔effect〕

In the case of the above-mentioned unexploded men's clothing, it is possible to gradually increase the input power at startup and stabilize the input power at the time of startup, and it is possible to prevent abnormal noises at startup, and to prevent the inverter circuit from unsuitable loads. 5 transistor 5c
, 5al can be protected. In addition, when the input power became excessive and the output of current transformer 8 became large,
Drive of the inverter circuit 5 is stopped by the action of the rib 70 and the rib 18.

Furthermore, even if the input power rises slowly at the time of startup, such as a foundry pot, the input power that gradually increases due to the action of the comparator 21 and the mono-multivibrator 28 is suddenly increased for a predetermined period of time. This prevents it from being mistakenly determined to be a transient load.

This increases the speed at which vp increases, so T
When D is used, it becomes possible to shorten and shorten the darkness. By shortening this TD, the terminal C of the microcomputer 60 is used for input power control.
It becomes possible to shorten one cycle of the pulse signal outputted from. In other words, even if the duty ratio lO% is set for input power control, if one cycle is 10 seconds, the inverter circuit will be controlled to drive for 1 second and stop for 9 seconds, but 1 cycle is 1 second. If so, then the inverter circuit is ready! It becomes possible to perform more fine-grained heating control, such as 0.1 seconds for 111J and 0.9 seconds for total stop. Since the load or input power is checked by the comparator 22 set to VR2k every cycle, if TD cannot be shortened, it is necessary to make the above-mentioned one cycle time long enough to correspond to TD. However, in the case of the present invention, As a result of this TD being shortened, the time for one cycle can also be shortened.

As described above, according to the present invention, it is possible to realize an electromagnetic cooker that is excellent in preventing abnormal noise generation and protecting circuit elements.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of the inverter circuit portion of the device of the present invention, Fig. 2 is a drive circuit diagram of transistor 5C, Fig. 8 is a block diagram of the central part of the control system, Fig. 4 is a main part control circuit diagram, 5
8 through 8 are time charts for explaining the operation. 5... Inverter circuit 5a... Induction heating coil
5c+5e...Transistor 8,9...Current transformer
21.22... Comparator 23... Monomulti 60... Microcomputer Patent Applicant Sanyo Electric Co., Ltd. Agent Patent Attorney Noboru Kono 1 Figure 2 21 ¥l No. 5 Whistle 6 Figure 8

Claims (1)

[Claims] 1. In an electromagnetic induction heating device equipped with an inverter circuit, the input power is gradually increased by gradually increasing the duty ratio of the conduction control signal Ku at the time of startup to cause all switching elements of the inverter circuit to be intermittently conductive. On the other hand, the input power is monitored and if the input power at startup is less than a predetermined value, the drive of the inverter circuit is stopped, and furthermore, the duty ratio is rapidly increased prior to monitoring the startup period. An electromagnetic induction heating device characterized by: