Electricity: measuring and testing – Electric lamp or discharge device
Patent
1994-01-10
1996-10-15
Regan, Maura K.
Electricity: measuring and testing
Electric lamp or discharge device
324771, 324102, 363 98, 219716, G01R 3100, H05B 668
Patent
active
055657818
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns the control of a unidirectional current load placed in a DC or rectified voltage supply circuit such as, for example, a magnetron, and more particularly a device for detecting the malfunctioning of the load.
2. Description of the Related Art
A unidirectional current load such as, for example, a magnetron operating at start-up with a high power setting, connected to the secondary winding terminals of a high-voltage transformer of a power supply, is sometimes subject, during operation, to voltage fluctuations due to variations of power and temperature. The fluctuations cause undesirable variations of the output power which generally bring about overheating of the magnetron. Consequently, repetition of the voltage fluctuations would bring about deterioration of the magnetron.
The aim of the invention is to remedy this drawback by mounting, on the power supply of the unidirectional load, a device enabling the operation of the unidirectional load to be monitored to avoid voltage fluctuations from recurring too often.
SUMMARY OF THE INVENTION
According to the invention, the device for detecting the malfunctioning of a unidirectional load comprises: terminals of the high-voltage transformer; the event of a difference in value, an excess signal, and; which the malfunctioning of the load appears.
By using the device according to the invention, the voltage fluctuations are measured, stored and analyzed in order to monitor the operation of the unidirectional load such as a magnetron. In this way, regular overheating of the unidirectional load is limited, or indeed even eliminated, which prolongs the life of the magnetron and protects the electrical and electronic components against overvoltages. Moreover, it is not necessary to put costly safeguards into the supply circuit, enabling a saving to be achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
The characteristics and advantages of the invention will appear in the description which follows by way of a non-limitative example, with reference to the accompanying drawings in which:
FIG. 1 shows an example of connecting up a device for malfunction detection, according to the invention, positioned in a magnetron supply circuit;
FIG. 2 shows a circuit of a device for detecting the malfunctioning of a unidirectional load, suitable for mounting in the circuit of FIG. 1;
FIGS. 3a-3h show voltage and clock signal waveforms used to explain the operation of the device according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the example embodiment described in FIG. 1, the circuit is intended more especially for powering a magnetron 1 of a microwave oven from an alternating mains supply arriving at the terminals 3 and 4 of the circuit. These terminals 3 and 4 are connected to a rectifier 5 which is formed by a full-wave diode bridge whose output is connected to two supply lines 6 and 7 of a high-voltage transformer 8. The rectifier 5 has at the output an anti-parasitic filter composed of a coil 9 and a capacitor 10. The lines 6 and 7 are connected respectively to the ends 11 and 12 of the primary winding 13 of the transformer 8. The line 7 also includes a switching element 14 having a gate 15 connected to a control circuit 16. The switching element 14 consists of a unidirectional current switch. The circuit also includes a capacitor 18 connected in parallel to the winding 13, and a self inductor 17 mounted in series with the assembly constituted by the capacitor 18 and the primary winding 13. The self inductor 17 is coupled to a secondary winding 17' whose ends are connected to the heating element 20 of the magnetron 1.
The secondary winding 19 of the transformer 8 has respectively two terminals 21 and 22 connected respectively to two supply lines 23 and 24, one 23 connected to the cathode 20 of the magnetron 1 and the other 24, to the anode 25 of the magnetron, which is also connected to earth 26.
The device 27 for detecting malfunctioning of the magnetron is connected, for example, i
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