FI97437C - Interference filter for electronic switchgear - Google Patents

Description

97437

Electronic ballast interference filter. - External filter for electronic copying.

The invention relates to a circuit arrangement for use in an electronic connection device of a discharge lamp, which limits the harmonics of the current drawn by the device from the mains and other electromagnetic disturbances generated by the device.

At present, the design of electronic ballasts for low-pressure discharge lamps is regulated by the international standards IEC 928 and IEC 929. The latter requires, among other things, the limitation of harmonics in supply lines to a certain level defined in the international standard IEC 1000-3-2.

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Several solutions are known for limiting the harmonics of the mains current, from filter solutions formed of passive components to actively controlled high-frequency filters. One of the 20 usable filter circuit groups is formed by the so-called charging: pump or condenser pump circuits. These are disclosed in the following patent publications: FI 78807, EP 389847 and DE 3611611. In addition, there are boost-type switch filter circuits.

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The basic connection of a boost-type active network filter is shown in Fig. 1, in which it is delimited by broken lines. ^ The area describes the switch filter circuit whose loaded • · · actual electronic ballast is marked with the symbol • · · · .30 purple A2. The operation of the circuit elements is as follows: V1 is a diode • ·· 'bridge that rectifies the: ***: mains voltage applied to the mains terminals X1-X2. V2 is an electronic switching component, for example a MOSFET transistor controlled by circuit block A1.

When V2 conducts, energy is charged to coil L1. When the switch V2 35 opens, the energy of the coil L1 is transferred through the diode V3 to the charge capacitor C1. The control of the switch V2 can be arranged so that the current flowing through the terminals X1 to X2 is mainly sinusoidal. Circuit solutions based on this principle are described, inter alia, in Application Guide AN-995 ("Electronic Ballasts Using the Cost-Saving IR2155 Driver", International Rectifier, 233 5 Kansas Street, El Segundo, CA 90245) published by International Rectifier, and in U.S. Patent No. 5,514,500. disclosed in patent application FI 945473. Integrated circuits are commercially available for performing the functions of block A1 in Fig. 1.

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The following modes of operation can be distinguished in the operation of boost-type switch filters:

Group 1: discontinuous coil current modes: fixed-15 and variable frequency filters

Group 2: continuous coil current modes: fixed frequency and hysteresis controlled filters.

20 However, the above-mentioned filter constructions have some disadvantages and limitations. The current distortion values of the group 1 fixed frequency • '· filters are not very good and :: a useful result is obtained by adding various corrective waveforms to the control. This, of course, adds:. 25 implementation complexity. Group 1 AC variable frequency • · · · implementations, on the other hand, have a small current distortion, but then • · · detection of a coil current failure is required.

• · • · · · ”/ In Group 2 fixed frequency choppers, current control can be implemented in many different ways and the result in terms of current distortion depends on the implementation. In hysteresis control, where • · ·: ***: the switch switches the maximum and minimum current setpoints *. by sinusoidal conversion, the control requires the measurement of a coil current and the use of a multiplier circuit to achieve a small distortion, i.e. again a small current distortion requires a complex circuit implementation. In the presented solutions, the waveform of the mains current is also not controlled near the zero points of the mains voltage. In addition, not all circuit solutions are suitable for use in adjustable ballasts for discharge lamps where it is desired to dim the lamp.

The object of the present invention is to eliminate the above-mentioned drawbacks and to provide a very small current distortion and a high power factor of the device with a simple circuit structure. The invention is based on a controlled switching of the switch mode between a continuous and a discontinuous mode depending on the operating point of the switch 10. The connection according to the invention is characterized by what is set forth in the characterizing part of claims 1 to 9.

The advantage of the circuit according to the invention is to achieve a very small current distortion and a good power factor with a simple circuit structure. The mains current waveform is also controllable near mains voltage zeros. In addition, this circuit is useful in an adjustable ballast in which it is desired to change the light output produced by the lamp to a level determined by 20 external control signals.

The invention will now be described in more detail by means of an application example with reference to Figures 2 and 3, which show a circuit implementation according to the invention and its operation. In the drawings, the actual ballast is • · · • · · · described in a simplified manner by replacing these parts with block • · · A2, because from the point of view of the filter the ballast is essentially. . constant power load. The control block AI of the power switches may be • · · •• j / separate control circuit or more preferably to the ballast part A2 • · · * · | 30 otherwise belonging oscillator. Diode bridge V1 operates throughout; way rectifier. The operation of the connection is in two phases.

• · ·. ***; In the first stage, switch V2 conducts, causing the supply voltage to • · · *. the current caused by the voltage increases in the coil L1 in relation to the magnitude of the supply voltage. The flow of current in the first stage of operation is shown in Fig. 2, in which a shaded solid line depicts the current path. When transistor V2 is opened in step 2, the energy 97437 4 bound to the coil L1 forces the current to continue in the coil. It now has no other way than to flow through the diode V3 to the charging capacitor C1, charging it, and this situation is shown in Fig. 3 by the shaded line. The amount of energy bound to the coil during one cycle depends on the magnitude of the input voltage and the on time of V2.

In the circuit according to the invention, the connection described above is controlled so that the mode of operation of the switch is changed at a certain operating point. The fixed frequency here is the same as the frequency of the lamp circuit included in block A2 of Figs. 1 to 3. About half of the total time of the network period, the switch according to the invention operates at a fixed 50% pulse ratio.

Near the peak value of the mains voltage, the pulse ratio is in turn set lower in the control block A1. The control parameters are the maximum current of the switch V2 and the output voltage of the switch. The operation of the control circuit is very simple: the value of the current limit is controlled by feedback from the output voltage. The switch coil is dimensioned so that during the 20 fixed pulse ratios, the energy T charged to the coil L1 is completely discharged into the charge capacitor C1, i.e. it is a mode of operation of a discontinuous coil current. Near the peak value of the voltage:: the energy of the coil L1 does not have time to be completely discharged into the charge capacitor C1, i.e. it is a mode of operation of the continuous coil current. By selecting the operating mode switching point ·· · · appropriately, the current drawn from the mains is very precisely • · · sinusoidal (total harmonic distortion less than 7% and circuit.. Power factor 0.98). The selection of the operating mode switching point • · · • · · ...... · «** ·. * Is affected by the magnitude of the load, the ratio of the output voltage to the input voltage • · · * ·] 30, the operating frequency and the inductance of the coil. Said mode of operation is shown in Fig. 4-11, where • · · • · · t:

Fig. 4 shows the voltage waveform of the upper end of the switch V2 (connection point of the circuit members L1 and V3 · ’) Fig. 5 shows the current waveform of the switch V2 in the discontinuous operation state of the switch 5 97437

Fig. 6 shows the current waveform of switch V2 in the continuous operation mode of the switch

Fig. 7 shows the current waveform of the coil L1 at the time of switching the operating mode 5 Fig. 8 shows the current waveform of the current of the coil L1 in the discontinuous operating mode

Fig. 9 shows the current waveform of the coil L1 in the continuous operation state

Fig. 10 shows the current waveform of diode V3 in continuous operation mode

Fig. 11 shows the waveform of the filter mains current at terminals X1 to X2.

The simplicity of the solution according to the invention is due to the fact that no additional windings are required in the coil to indicate a power failure, no multiplier is required in the control circuit and no sinusoidal or other waveform correction is required in the current limit adjustment. Thus, the structure is also very inexpensive to implement.

20: The circuit according to the invention is also useful in adjustable ballasting devices for discharge lamps, in which the lamp:; the power is adjusted lower by increasing the feed frequency.

In this case, the rated power of the chipper also decreases and the distortion values j · * · 25 remain good.

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The circuit arrangement according to the invention can be supplemented with switching. . by placing an inductive circuit element between the mains supply terminal X1 and • · · * * * ‘.W rectifier V1, a capacitive circuit element between terminals • · ·’ · ['30 X1 and X2, or a capacitive circuit element between the rectifier: V1 positive and negative terminals. The purpose of these circuit elements is to attenuate radio frequency electromagnetic interference.

The circuit arrangement according to the invention is particularly suitable for use in electronic ballasts for low-pressure discharge lamps, the basic solutions of which are known from, for example, patent FI 65 524. However, it will be clear to a person skilled in the art in switchgear-operated ballasts.

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Claims (9)

1. An interference filter for the discharge lamp electronic ballast connected between the ballast and the mains supply, * 5 comprising a supply voltage rectifier (V1) and a charging capacitor (C1), at least one energy storage coil (L1) and an electronic switching element (V2) connected so that V2) conducts a current path from the positive terminal of the rectifier (V1) through said switch 10 and coil to its negative terminal and when the switch (V2) is non-conductive there is a current path from the positive terminal of the rectifier diode (V3) and charge capacitor (C1) to its negative terminal, characterized in that the switching element (V2) is controlled by a constant frequency control with a fixed pulse ratio up to a certain operating point with respect to a certain value of the mains voltage, after which the pulse ratio changes. Interference filter according to Claim 1, characterized in that during the fixed pulse ratio the energy charged to the coil · '(LI) is completely discharged to the charge capacitor and during the variable pulse ratio the energy of the coil (LI) does not have time to be completely discharged to the charge capacitor (C1). . I f · · * <4; . ·. 25 Interference filter according to claim 2, characterized in that said mode of operation is achieved by a suitable dimensioning of the inductance of the S · · coil (Li). • · • · i ··· · Interference filter according to Claim 1, 2 or 3, M * f t »» ..... «..«, * · * * 30 characterized in that the pulse ratio is obtained by »•: *; by adjusting the current limit value M1 of the switching element (V2), ** ·. with a feedback signal derived from the output voltage of the filter. '' 35 Interference filter according to Claim 1, 2, 3 or 4, characterized in that the operating point for changing the control mode of the switching element (V2) with respect to the instantaneous value of the mains voltage 97437 8 is selected so that the total harmonic distortion of the mains current is as small as possible. Interference filter according to Claim 1, 2, 3, 4 or 5, characterized in that the operating point for changing the control mode of the switching element (V2) with respect to the instantaneous value of the mains voltage is selected such that the power of the filter circuit and the load circuit (A2) the coefficient is as high as possible. Interference filter according to one of Claims 1, 2, 3, 4, 5 or 6, characterized in that at least one capacitive or inductive circuit element is connected between the mains supply and the rectifier. 7 97437 Interference filter according to one of Claims 1, 2, 3, 4, 5, 6 or 7, characterized in that a capacitive circuit element 20 is connected between the positive and negative terminals of the rectifier. A claim according to claim 1, 2, 3, 4, 5, 6, 7 or 8; ; interference filter according to. : the electronic switching element (V2) is a channel transistor or *, ·. 25 bipolar transistor with isolated gate or • · · bipolar transistor. • * · r 9 9 • · • · ·. · · · «· ·» · »» »« • · · - · ♦