High frequency heating apparatus

• US 6,362,463 B1
• Filed: 04/26/2001
• Issued: 03/26/2002
• Est. Priority Date: 08/06/1998
• Status: Expired due to Fees

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Nagata, Hidetomo, Moriya, Hiokaki, Ishio, Yoshiaki, Mihara, Makoto, Bessyo, Daisuke, Sakai, Shinichi, Suenaga, Haruo, Yasui, Kenji, Omori, Hideki, Sakamoto, Kazuho
• Primary Examiner(s): Leung, Philip H.
• Application Number:
  US09/762,334
• Time in Patent Office: 334 Days
• Field of Search: 219/702, 219/715, 219/716, 219/723, 219/721, 363/17, 363/21, 363/97, 363/98, 363/16
• US Class Current: 219/715
• CPC Class Codes: H05B 2206/043 Methods or circuits intended to extend the life of the magnetron
• CPC Class Codes: H05B 6/666 Safety circuits emergency protective circuits in general H02H
• CPC Class Codes: H05K 1/0254 High voltage adaptations; Electrical insulation details; Overvoltage or electrostatic discharge protection electrostatic discharge protection for electric apparatus in general H05K9/0067, H05K9/0079; Arrangements for regulating voltages or for using plural voltages
• CPC Class Codes: H05K 1/18 Printed circuits structurally associated with non-printed electric components H05K1/0201, H05K1/023, H05K1/0243, and H05K1/16 take precedence

Abstract

A high frequency heating apparatus including a circuit for driving a magnetron. A circuit comprises a leakage transformer, a second capacitor connected in series to primary coil of said leakage transformer, a second switching device connected in parallel with a series circuit of said primary coil and second capacitor, a first capacitor connected in parallel with said second switching device, and a first switching device connected in series to said second switching device. Under a structure of the present invention, the switching device and the leakage transformer, both being the key components of the circuit, may respectively be used in common either on a circuit of 200V-240V commercial power supply or on a circuit of 100V-120V commercial power supply. This enables volume production of the key components, which leads to a benefit of reduced cost of the components as well as the cost of heating apparatus.

Claims

1. A high frequency heating apparatus comprising:

a DC source (31),

a leakage transformer (32) connected to the positive terminal (+) of said DC source (31),

a second capacitor (35) connected in series to primary coil (33) of said leakage transformer (32),

a second switching device (37) connected to the positive terminal (+) of said DC source (31),

a first capacitor (34) connected in parallel with said second switching device (37),

a first switching device (36) connected in series to said second switching device (37), also connected to the negative terminal (−

) of said DC source (31),

driving means (38) for driving said first switching device (36) and said second switching device (37),

rectifying means (40) connected with secondary coil (39) of said leakage transformer (32), and

a magnetron (41) connected with said rectifying means (40).

2. The high frequency heating apparatus of claim 1, wherein the second capacitor (35) is provided with a great capacitance for enabling the output control through pulse width.

3. The high frequency heating apparatus of claim 1, wherein

the mutual relationship among capacitance C₂ of second capacitor (35), primary coil (33) inductance L₁ of leakage transformer (32), resonance frequency f_R given in $f_R=\frac{1}{2·\; <li></li>\mathrm{\pi <br><br>}·<br><br>\sqrt{L_1·<br><br>C_1}},$

 

and operating frequency f₀ of driving means (40) satisfy $2.45<<br><br>\sqrt{L_1·<br><br>C_1}<<br><br>3.55$$1.38<<br><br>\frac{f_0}{f_R}<<br><br>4.$

4. The high frequency heating apparatus of claim 1, wherein a series circuit formed of said first capacitor (34), said second capacitor (35) and said leakage transformer (32) assumes either one of the following structures:

(1) said first capacitor (34) is connected in parallel with said second switching device (37), and a series circuit of said second capacitor (35) and primary coil (33) of said leakage transformer (32) is connected in parallel with said second switching device (37),

(2) said first capacitor (34) is connected in parallel with said first switching device (36), and a series circuit of said second capacitor (35) and said primary coil (33) is connected in parallel with said second switching device (37),

(3) said first capacitor (34) is connected in parallel with said first switching device (36), and a series circuit of said second capacitor (35) and said primary coil (33) is connected in parallel with said first switching device (36), or

(4) said first capacitor (34) is connected in parallel with said second switching device (37), and a series circuit of said second capacitor (35) and said primary coil (33) is connected in parallel with said first switching device (36).

5. The high frequency heating apparatus recited in one of claims 1 through 4, deriving the DC source (31) from a rectified commercial power supply of 200V to 240V, wherein the higher the voltage of said commercial power supply the greater is the capacitance value of second capacitor (35), while constant of the leakage transformer (32) remains the same.

6. The high frequency heating apparatus recited in one of claims 1 through 4, comprising a DC source (31) derived from a rectified commercial power supply, a voltage detection section (52) for detecting voltage of said DC source (31), and a pulse width modulation section which uses output of said voltage detection section as the base signal, wherein

signal from said pulse width modulation section is delivered to driving means (38), and said driving means (38) drives switching device (36, 37) in accordance with said signal.

7. The high frequency heating apparatus of claim 6, wherein the pulse width modulation section is provided with a limiting function for setting an upper limit on the duty.

8. The high frequency heating apparatus of claim 6, wherein magnetron (41) output is controlled through both the pulse width modulation and the frequency modulation, with a priority placed on the output control through pulse width modulation to the output control through frequency modulation.

9. The high frequency heating apparatus recited in one of claims 1 through 4, comprising a DC source (31) derived from a rectified commercial power supply, a voltage detection section (52) for detecting voltage of said DC source (31), and a frequency modulation section which uses output from said voltage detection section as the base signal, wherein

signal from said frequency modulation section is delivered to driving means (38), and said driving means (38) drives switching device (36, 37) in accordance with said signal.

10. The high frequency heating apparatus of claim 9, wherein the frequency modulation section is provided with a limiting function for setting a bottom limit to the frequency.

11. The high frequency heating apparatus of claim 9, further comprising a start-up frequency setting section for releasing the frequency modulation at the start-up period to perform the control at a fixed frequency.

12. The high frequency heating apparatus of claim 11, wherein the frequency modulation is applied as soon as the magnetron (41) starts operation.

13. The high frequency heating apparatus of claim 9, wherein magnetron (41) output is controlled through both the pulse width modulation and the frequency modulation, with a priority placed on the output control through pulse width modulation to the output control through frequency modulation.

14. The high frequency heating apparatus recited in one of claims 1 through 4, wherein a series-connected first resistor (44) and second resistor (45) is connected in parallel with said DC source (31), and the connecting point of said first resistor (44) and said second resistor (45) is connected to the connecting point of said first switching device (36) and said second switching device (37).

15. The high frequency heating apparatus recited in one of claims 1 through 4, wherein said DC source (31) further comprises an anti-toppling device (57) provided at the foot of circuit components mounted on a printed circuit board (56), aiming for preventing said circuit components from toppling and making contact with other circuit components that have different potential.

16. The high frequency heating apparatus of claim 15, wherein one of the constituent circuit components is used also for the anti-toppling device (57).

17. The high frequency heating apparatus of claim 1, comprising a DC source (31) formed of rectifying means (46), and a filter composed of an inductor (47) and a third capacitor (43) for smoothing the output of said rectifying means (46), further comprising a surge absorber (50) at the output end of said filter (43, 47).

18. The high frequency heating apparatus of claim 1, comprising a DC source (31) formed of rectifying means (46), and a filter composed of a inductor (47) and a third capacitor (43) for smoothing the output of said rectifying means (46), further comprising a surge absorber (50) connected parallel to said semiconductor device.

19. The high frequency heating apparatus of claim 1, including voltage detecting means (52) and stop control means (53), wherein

said voltage detecting means (52) detects voltage at the point of connection of primary coil (33) of said leakage transformer (32) and said second capacitor (35) connected in series, and delivers signal to said stop control means (53), said stop control means (53) stops said driving means (38) in accordance with the signal.

20. The high frequency heating apparatus of claim 19, wherein said voltage detecting means (52) detects output voltage of said capacitor (43) of said DC source (31).

21. The high frequency heating apparatus of claim 19, wherein said voltage detecting means (52) detects voltage to be applied on said first switching device (36).

22. The high frequency heating apparatus of claim 1, further including a series circuit of third resistor (54) and fourth resistor (55) provided between the connection point of said leakage transformer (32) and second capacitor (35) and the negative terminal (−

) of said DC source (31).

23. The high frequency heating apparatus of claim 22, further comprising a comparator (30) connected to said fourth resistor (55), wherein said comparator compares the voltage of said fourth resistor (55) with a reference value and controls said driving means (38).