TW201318482A - Magnetron power supply - Google Patents

Abstract

A power supply for a magnetron has a high voltage converter 101, a microprocessor 103 and a resistor 109. The high voltage converter comprises an integrated circuit oscillator IC1, switching transistors T1, T2, an inductance L1, a transformer 106 and a rectifier 107. A voltage source 4 supplies an augmented DC voltage to the converter 101. An operational amplifier 122, arranged as an error signal magnifier with an integrating capacitor C7 and a resistor R9, compares a control signal from microprocessor 103 and resistor 109 and supplies an output signal to the oscillator IC1. Oscillator IC1 controls switching transistors T1, T2, the output of which connect to inductance L1 and the primary winding of the transformer 106. The secondary winding of the transformer 106 is connected to half bride diodes D3, D4, D5, D6 and capacitors C5, C6 which provide DC current from the transformer to the magnetron 102.

Description

Magnetron power supply

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a power supply for a magnetron, specifically, but not exclusively, and to a power supply for use with a magnetron for powering a lamp.

Known systems, magnetrons can change modes unintentionally, that is, they may unintentionally stop oscillations at one frequency and begin to oscillate at another frequency. In these cases, they exhibit a negative impedance. This can cause damaging high currents. For this reason, it can be known that a constant/controlled voltage power supply is not suitable for a magnetron; a constant/controlled current power supply is often used to supply power to the magnetron.

The anode voltage in the magnetron is high and both the anode voltage and the anode current are difficult to measure.

In the prior power supply invented by the inventor of the present invention, the measured values of both the voltage applied to the converter in a magnetron power supply and the current flowing through the converter are used to match a microcomputer pair. The power supplied to a magnetron provides immediate control. The microcomputer will be programmed to calculate the following results:

1. The power consumed,

2. The difference between the power and the power, and

3. The difference between the power difference and the measured current.

This second difference signal is used to control the converter. It should be noted that these three steps are performed in software. Unexpectedly, this power supply still has some degree of instability, resulting in appreciable flicker of the light produced by its magnetron-powered lamp.

Experience has shown that the output is extremely susceptible to light flicker in magnetron-powered plasma lamps. It has now been recognized that the limited speed and resolution in the microprocessor's output capability can degrade the perceived flicker. In addition, both of the inputs to the microprocessor (ie, the voltage applied to the converter and the current drawn through the converter) may also have noise, and the system of the letter, The product of these two noise signals will cause this instability.

Direct filtering of noise from the microprocessor can shorten the reaction time of the control circuit and cause this instability in an unacceptable manner, and should be kept in mind that it is possible to react quickly to changing magnetron conditions. Necessary. Accordingly, there is a need in the art for a novel approach.

It is an object of the present invention to provide an improved power supply for a magnetron.

According to the present invention, there is provided a power supply for a magnetron, comprising:

‧ a DC voltage source;

‧ a converter for boosting the output voltage of the DC voltage source, the converter having:

‧ a capacitive-inductive resonant circuit,

a switching circuit that is adapted to drive the resonant circuit at a varying frequency above the resonant frequency of the resonant circuit, the varying frequency being controlled by a control signal input to provide an alternating voltage,

a transformer that is connected to the resonant circuit to boost the AC voltage,

a rectifier for rectifying the elevated AC voltage into an elevated DC voltage for application to the magnetron;

‧ a measuring member for measuring a current from the DC voltage source through the converter;

a microprocessor that is programmed to generate a control signal indicative of the desired output power of the magnetron;

‧ an integrated circuit that is arranged in a feedback loop and adapted to apply a control signal to the signal based on the signal from the current measuring component and the signal from the microprocessor A converter switching circuit for controlling the power of the magnetron at the desired power.

Providing the integrated circuit to be a discrete component separate from the microprocessor provides a fast control loop that is not limited by the speed of the microprocessor (the microprocessor is likely to be due to its specifications) Economic constraints are very slow). Therefore, the power supply of the present invention is inherently stable and provides illumination that is less susceptible to flicker.

The present invention is designed such that the integrated circuit may be a digital device; however, in an economic benefit, it is preferably an analog device. In the preferred embodiment, the integrated circuit is an operational amplifier.

In the preferred embodiment, the operational amplifier is arranged as an integrator having a feedback capacitor whereby its output voltage is adapted to control a voltage to frequency circuit to control the converter.

Preferably, the microprocessor is programmed to filter the noise from the current converter current signal. Alternatively, a filter circuit may be placed between the microprocessor and the operational amplifier.

In the preferred embodiment, the switching circuit is adapted to control the frequency of the converter based on a varying voltage signal output from the operational amplifier. In this technique, the increase in frequency corresponds to a drop in the magnetron drive voltage and microwave output.

Alternatively, the switching circuit may be adapted to control the duty cycle of the converter based on the operational amplifier output, whereby a decrease in duty cycle corresponds to a decrease in magnetron drive voltage and microwave output.

In the preferred embodiment, the converter is a zero voltage switching device; however, it may also be a zero current switching device.

In general, the switching circuit has its own oscillator; however, the invention may also be designed such that it can be timed by a clock in the microprocessor.

In an embodiment, the integrated circuit is adapted and arranged to directly compare the measured current signal with the desired power signal, and the integrated circuit is connected to receive only The signal is controlled such that the converter current is controlled according to the desired power, and the desired power is not dependent on the transient change of the voltage of the DC voltage source. This embodiment controls the average power to be constant over multiple voltage source chopping cycles.

In another embodiment, the integrated circuit is adapted and arranged to compare not only the measured current signal with the measured power signal but also the transient of the voltage of the DC voltage source. a change, a signal indicating the voltage of the voltage source is also input to the integrated circuit, so that the converter current is controlled, so that the power passing through the converter is received according to the power of the converter. control. This embodiment controls the instantaneous power to be constant over multiple voltage source chopping cycles.

In general, the switching circuit has its own oscillator; however, the invention may also be designed such that it can be timed by a clock in the microprocessor.

First, referring to Fig. 1, there is shown a prior art power supply having an oscillator 1 which is connected for powering a magnetron 2 and controlled by a microprocessor 3. An increased mains voltage DC voltage source 4 typically supplies 400 volts to line 1 to the oscillator 1. This feeds the alternating current to a transformer 6 and a rectifier 7, from which the 4000 volt DC is supplied to the magnetron on line 8. This oscillator, transformer, and rectifier are referred to as "high voltage converters." The power to be supplied to the magnetron is measured as the voltage across a resistor 9 located in the ground loop of the converter. This voltage represents the current in the resistor 9 and is proportional to the power to be supplied to the magnetron, provided that a constant voltage is coming from the voltage source 4. The resistor voltage is an input to the microprocessor on line 10. Another input on line 11 applies a voltage on line 5 to the microprocessor. A desired power control value of 12 will be set external to the microprocessor or will be set as a manual input to the microprocessor.

The microprocessor is programmed to perform the following steps:

1. Multiplying the voltage on line 5 by the current in resistor 9 to calculate the power to be supplied to the magnetron, assuming that there is high efficiency;

2. Comparing the calculation result of the power to be consumed with the power of the desired, and thereby calculating the current (expected current) that should be consumed;

3. comparing the expected current with the measured current, and applying a higher and higher voltage to the power supply when the current is high to drive the converter at a higher frequency; or, at the current Applying lower and lower voltages at very low levels. It should be noted that if the converter operates at a higher frequency, the final voltage across the magnetron will drop.

As mentioned above, this circuit is not stable in use and cannot achieve the purpose of the flicker-free operation of the magnetron as a light source.

Referring now to Figure 2, a power supply of the present invention includes the following similar components that are connected in the same manner:

‧ oscillator / high voltage converter 101;

‧ magnetron 102;

‧ transformer 106;

‧ rectifier 107;

‧ Resistor 109.

A microprocessor 103 will also be incorporated, but it operates in very different ways. It simply divides the desired power control value 112 by the increased mains DC voltage on line 105 and provides a necessary current signal on line 121 to indicate the current flowing through the converter 101 so that The magnetron is operated at the power level. The signal on line 121 is fed to an input of an operational amplifier 122/EA1. The other input to the operational amplifier 122 is from line 110 of resistor 109, which represents the actual current through the converter. The op amp is connected as an integral error signal amplifier.

Referring next to Figure 3, there is shown a more complete circuit diagram of the power supply of Figure 2. The quasi-resonant oscillator 101, which is a high voltage converter, has a MOSFET field effect switching transistor T1, T2. These transistors are switched by an integrated circuit oscillator IC1 in the manner to be described below. An inductor L1 and a primary side coil of the transformer 106 are connected in series to a common point of the transistors T1, T2. Capacitors C3, C4 complete the series resonant circuit. The inductors and the capacitors determine the resonant frequency, and the converter operates above the resonant frequency, typically around 70 kHz, so that it is primarily considered to be an inductive circuit by the downstream magnetron circuit. This includes four half-bridge diodes D3, D4, D5, D6 and smoothing capacitors C5, C6 that are connected to the secondary side coil of the transformer and provide DC current to the magnetron 102. The transformer has a turns ratio of 10:1, so a voltage of 4000 volts is applied to the magnetron, and the increased mains DC voltage on line 105 will typically be 400 volts.

The converter circuit is characterized in that when the transistors T1, T2 are first switched on and then switched off, the energy stored in the inductor L1 will reverse across the voltage. This will drive the voltage at the common point C down before the TR2 switch is turned on and drive the common point voltage up before the TR1 switch is turned on. Thus, switching can occur at zero volts or near zero volts across the transistor that is about to be switched on, that is, ZVS mode (zero voltage switching mode). This will increase reliability and extend life.

At high switching frequencies (i.e., above the resonant frequency), the voltage between the common points between the capacitors C3, C4 will remain substantially constant at half the voltage on line 105, thus, in the transistor When switching, a ramp-up current that is substantially a triangular waveform flows through the inductor L1. This will be transmitted to the transformer and will eventually be transferred from there to the magnetron.

Decreasing the operating frequency closer to the resonant frequency increases the voltage swing at D farther than half the voltage on line 105 and increases the voltage at the magnetron, increasing its current and its microwave output.

The current flowing through the converter is measured at resistor 109/R1, which is typically 100mΩ, and a voltage representing the current is delivered to the operational amplifier through feedback resistor R5 (which is typically 470Ω). An input 123 of 122. The microprocessor 103 receives the voltage from line 105 via a voltage divider R3, R4. A necessary power setting is set via a manual input 112. The microprocessor is programmed to divide the necessary power by the line voltage and apply a voltage representing the converter current required by the necessary magnetron to another of the operational amplifiers through a 6kΩ resistor R10. Enter 125. The operational amplifier has an integrating capacitor C7, which is typically 470 nF, which is connected in series with a 1 MΩ resistor R9. Resistors R9, R10 determine the gain of the op amp. This will also be set to suppress the mains voltage flash as much as possible. The amplifier transmits an integrated voltage representative of the desired power to the frequency control circuit 126 of the oscillator IC1, which is a voltage to frequency circuit, typically a Texas Instruments IRS2153 or ST Thomson L6569. The circuit includes a 18kΩ resistor R2, capacitors C1, C2 (both 470pF), and diodes D1, D2 that operate to control the frequency of the converter. When the output of the operational amplifier is zero, the capacitor C1 will be connected in parallel with C2 and will reach the lowest frequency. This will correspond to the maximum magnetron power. On the other hand, when the output is at its maximum value, the diodes are not turned on and the frequency is controlled by C2 alone. The maximum frequency and minimum power (one tenth of the maximum value) will be supplied. At the intermediate voltage, C1 has an intermediate effect and the frequency and power are thus controlled.

Therefore, the magnetron may be controlled to operate at the power input to the microprocessor. The microprocessor is susceptible to voltage variations induced on the line 105 by flicker. However, the signal sent to R10 can be filtered internally by software or externally by an RC filter not shown in the figure. If the magnetron power consumption shifts (when its magnet heats up and its resistance changes), the op amp reacts quickly to the change in current measured at the resistor R1 and adjusts the frequency of the converter to The power consumption of the magnetron is corrected in a manner that is independent of the signal on line 125 of the microprocessor.

That is, if there is flicker on the voltage source line, the power of the magnetron will only be constant after averaging the blinking period. Due to the cost of large smoothing capacitors, there is a tendency for the dual supply frequency to flicker on the voltage source line.

It should be noted that the power supply described above is particularly suitable for controlling the LER magnetron power supply lamp as described in WO 2009/063205. It is free to control the light output of the lamp and, if necessary, to fully illuminate from a low level of background light to full power.

A simplified representation of the lamp driven by the magnetron is shown in FIG. It has a light transmissive crucible 201 having a Faraday cage 202. A void 203 in the crucible has a filler 204 comprised of an excitable material. The magnetron 205 is arranged to project its microwaves into a waveguide/transfer region 206 from which it exits in a coaxial connection 207 to an antenna 208, thereby releasing them to the crucible. Among them. Powering the magnetron by the power supply 209 of the present invention causes the excitable material to illuminate. The advantage of this light produced by the power supply of the present invention is that flicker can be avoided.

Referring next to Figure 5, there is also shown an improved high voltage converter in accordance with the present invention. It not only takes into account changes in the converter current, but also the magnetron current; it also maintains frequency chopping at the output of the voltage source, or, more specifically, twice the main frequency ripple. This chopping does not cause appreciable flicker in the light emitted from the LER, but it causes bandwidth expansion in the output of the magnetron.

The correction of FIG. 5 incorporates a resistor R6 (in the form of two series 1 MΩ resistors) from the voltage source line to the op amp input 123, and a feedback resistor R5 is coupled to the op amp input. 123. The voltage divider will cause the voltage across the resistor R5 to be substantially the same as the voltage across the current measuring resistor, assuming that the op amp input is 200 mV, then both are typically 100 mV in size. The actual voltage will vary with the actual current in the converter and the actual voltage on the voltage source line. It should be understood that the increase in the 200 mV op amp input due to the increase in the voltage source line would be equivalent to the increase in the 200 mV op amp input due to this increase in current. Both increase the integrated output voltage of the op amp, which results in a reduced current.

The actual increase in the op amp input caused by a 5% increase in the voltage source voltage would be 5% because the voltage across the current measuring resistor is less than the voltage source voltage. Similarly, the current increases by 5% and the voltage across the current measuring resistor also increases by 5%. This will be added to the voltage at the input of the op amp. Therefore, a 5% increase in voltage or current or an increase in other small percentages will reduce the same percentage.

This then causes a 5% or other reduction in the percentage of power to be applied to the magnetron. Therefore, this configuration will maintain a constant instantaneous power. In this regard, for example, the instantaneous system is used to indicate that power will remain constant throughout the cycle of such voltage chopping.

This operation can be explained in the following mathematical sense: the power of the magnetron is the product of the voltage source voltage U and the converter current I, that is:

P=UxI

Expressed in units of voltage and current u and i:

P=(C ₁ xu)x(C ₂ xi)

P=Kx(uxi)

If u and i have unit values, this formula can be rewritten as:

P=Kx(u+i)/2

This relationship remains nearly correct in small voltage changes and small current changes (ie, at u ± δu, i ± δi).

The above formula can be rewritten as:

P=K ₃ +K ₄ xδV+K ₅ xδv

Thus, the power of the magnetron can be expressed as a constant plus another constant multiplied by any deviation of the actual voltage source from its nominal value plus another constant multiplied by any deviation of the current from its nominal value. The current deviation value itself can be represented across the voltage of the current measuring resistor.

It can be seen with appropriate constants and only considering changes in the input of the operational amplifier that the voltage divider does input the sum of the voltage source voltage change and the converter current change to the operational amplifier. The only condition is that the following approximation is satisfied only when the voltage across R5 is approximately equal to the voltage across R1:

P=UxI Kx(u+i)/2

This will satisfy the following values:

U=400 volts

R1=0.1Ω

R5=470Ω

R6=2MΩ

Figure 6 shows the values of these series connected resistors and associated voltages.

It should be noted that the size of resistor R6 is seven orders larger than R1, and the size of R5 is four orders larger, any change in U (which will be noticeable in the voltage at the input of the op amp) It is impossible to make a significant change in the voltage across R1 because the voltage of R1 is only controlled by the current flowing through it. Accordingly, the voltage across R1 is added to the voltage across R5, and the sum is input to the operational amplifier.

It should be understood that this type of operation is not completely linear; however, it provides a significant improvement. Referring to Figure 7, there is shown a saddle relationship diagram of the frequency of the frequency of the output of the magnetron. The frequency of its output will depend on the current flowing through it. A feature of the magnetron is that it has similar characteristics to the Zener diode in controlling the voltage across it. Therefore, if more power is available, its current will increase and its operating frequency will decrease. Among them, there will be a chopping wave related to the mains voltage at the voltage of the voltage source, the frequency of the magnetron will change, and the bandwidth will have a slightly saddle shape. Conversely, with the power control of the embodiment of Figure 5, the bandwidth will be narrower and have a Gaussian distribution. Therefore, this facilitates less interference with Bluetooth communication networks and the like.

Next, referring to Figure 8, a multiplier circuit 301 is shown at the input of the operational amplifier. Although this circuit is an analog device; however, a digital device can also be used, and the midpoint of the common point of the R6-R7 potential divider is applied to one input, and the voltage signal from the current measuring resistor R1 is Will be applied to another input. The multiplier multiplies the two voltage representative signals by the current representative signal to generate a signal indicative of the magnetron power and apply it to the input of the operational amplifier. The accuracy of this embodiment is superior to the embodiment of Figure 5, but is relatively expensive because the multiplier circuit is rarely used and is relatively expensive. Therefore, the embodiment of Fig. 5 can be considered to be preferred because, in addition to being accurate enough, it is relatively inexpensive at the same time.

1. . . Oscillator

2. . . Magnetron

3. . . microprocessor

4. . . DC voltage source

5. . . line

6. . . transformer

7. . . Rectifier

8. . . line

9. . . Resistor

10. . . line

11. . . line

12. . . Power control value

101. . . Oscillator / High Voltage Converter

102. . . Magnetron

103. . . microprocessor

105. . . line

106. . . transformer

107. . . Rectifier

109. . . Resistor

110. . . line

112. . . Power control value / input

121. . . line

122. . . Operational Amplifier

123. . . Input

125. . . Input

126. . . Frequency control circuit

201. . . crucible

202. . . Faraday cage

203. . . Void

204. . . Filler

205. . . Magnetron

206. . . Waveguide/transfer zone

207. . . Coaxial cable

208. . . antenna

209. . . Power Supplier

301. . . Multiplier circuit

To assist in understanding the invention, a particular embodiment of the invention has been described above by way of example and with reference to the accompanying drawings in which:

Figure 1 is a block diagram of a prior art power supply for a magnetron;

Figure 2 is a block diagram of a power supply according to the present invention;

Figure 3 is a more detailed circuit diagram of the power supply of Figure 2;

Figure 4 is a schematic view of a lamp powered by a magnetron having a power supply of the present invention;

Figure 5 is a circuit diagram of a second embodiment of the present invention;

Figure 6 is a detail of the voltage divider of the embodiment of Figure 5;

Figure 7 is a comparative spectrogram of the magnetron output of the embodiment of Figures 3 and 5;

Fig. 8 is a circuit diagram showing a third embodiment of the present invention.

102. . . Magnetron

106. . . transformer

107. . . Rectifier

110. . . line

112. . . Power control value / input

125. . . Input

126. . . Frequency control circuit

Claims (17)

A power supply for a magnetron, comprising: a DC voltage source; a converter for boosting an output voltage of the DC voltage source, the converter having: a capacitive-inductive resonant circuit a switching circuit that is adapted to drive the resonant circuit at a varying frequency above the resonant frequency of the resonant circuit, the varying frequency being controlled by a control signal input to provide an alternating voltage, a transformer, which is connected to the resonant circuit for boosting the alternating voltage, a rectifier for rectifying the boosted alternating voltage into a boosted DC voltage for application to the magnetron; </ RTI> used to measure the current from the DC voltage source through the converter; a microprocessor that is programmed to generate a control signal indicative of the output power of the magnetron; and a circuit that is arranged in a feedback loop and adapted to apply a control based on a comparison of signals from the current measuring component and signals from the microprocessor The resolution converter to the switching circuit for controlling the power to the magnetron power at the Greek. The power supply of claim 1, wherein the integrated circuit is an analog device. The power supply device of claim 2, wherein the integrated circuit is an operational amplifier connected to an error signal amplifier, wherein the error signal is a signal indicating the measured value of the converter current and the magnetic control The difference between the output power of the tube. For example, in the power supply of claim 1, item 2, or item 3, wherein the integrated circuit is arranged as an integrator having a feedback capacitor, so that its output voltage is adjusted to Used to control a voltage to frequency circuit to control the converter. For example, in the power supply of claim 1, item 2, or item 3, wherein the integrated circuit is adapted and arranged to directly compare the measured current signal with the desired power. a signal, the integrated circuit is connected to receive only the signals, whereby the converter current is controlled according to the desired power, and the desired power and the transient change of the voltage of the DC voltage source Not dependent. The power supply of claim 5, wherein the current measuring member is a resistor connected in series with the converter, one end of the resistor is grounded, and the other end is connected to one of the integrated circuits. The input is preferably passed through a feedback resistor. For example, in the power supply of claim 1, item 2, or item 3, wherein the integrated circuit is adapted and arranged to compare not only the measured current signal with the current The power signal also considers the transient change of the voltage of the DC voltage source, and a signal for indicating the voltage of the voltage source is also input to the integrated circuit, so that the converter current is controlled, This allows the power through the converter to be controlled based on the desired power. A power supply according to claim 4, wherein: ‧ the current measuring member is a resistor connected in series with the converter, one end of the resistor is grounded, and a potential locator is provided Input to the integrated circuit, the quantile comprising two output resistors between an output rail of the DC voltage source and a non-ground terminal of the current measuring member, the two two-position resistors The common connection point is connected to an input of the integrated circuit. A power supply according to claim 8 wherein: ‧ the current measuring member is a resistor connected in series with the converter, one end of the resistor is grounded, and ‧ is provided: ‧ a potential locator, It includes two level resistors between an output rail of the DC voltage source and a zero volt rail, and a ‧ a multiplier circuit that applies a voltage at the current measuring resistor to a multiplier input The voltage at the common connection point of the classifier resistors is applied to another multiplier input, and the multiplier output is applied to the integrated circuit for output to the microprocessor. Comparison. For example, in the power supply of claim 1, item 2, or item 3, wherein the microprocessor is programmed to filter the noise from the current converter current signal. A power supply as claimed in claim 1, item 2, or item 3, comprising a filter circuit disposed between the microprocessor and the operational amplifier. For example, in the power supply of claim 1, item 2, or item 3, wherein the switching circuit is adapted to control the converter according to a variable voltage signal output from the operational amplifier. The frequency, by which the increase in frequency, corresponds to a drop in magnetron drive power and microwave output. For example, in the power supply of claim 1, item 2, or item 3, wherein the switching circuit is adapted to control the duty cycle of the converter according to the output of the integrated circuit, thereby working The drop in cycle will correspond to a drop in the magnetron drive voltage and microwave output. A power supply as claimed in claim 1, item 2, or item 3, wherein the switching circuit is adapted to be scheduled by a clock in the microprocessor. For example, the power supply of claim 1, item 2, or item 3, wherein the switching circuit has its own oscillator. For example, the power supply of claim 1, item 2, or item 3, wherein the converter is a zero voltage switching device. For example, the power supply of claim 1, item 2, or item 3, wherein the converter is a zero current switching device.