EP0041027B1 - Supply circuit for discharge lamps comprising voltage multipliers - Google Patents

Description

The present invention relates to a direct current supply device for discharge tubes according to the preamble of claim 1.

It can be used to supply discharge tubes of the Argon or Neon type (called cold cathode) or fluorescent tube, laser, small model or for any other use.

We already know the technique of supplying discharge tubes which require a supply of at least 2 different input resistors: one with high voltage and very low current to generate the discharge current, and then this high voltage is no longer necessary to maintain the discharge current.

The methods known to date use various forms of transformers with high magnetic leakage, inductors in series, starters, or electronic systems which consisted in having a voltage doubler with low impedance for maintaining the discharge, and in parallel two other voltage doublers with a set of diode matrix, to prevent the low voltage voltage doubler from charging the second which is high resistance, and a higher voltage.

The aforementioned devices have the disadvantage of being expensive, heavy in weight, less reliable, if components of equal quality are used given the quantities of the components used. A known device; described in the document CH-A-481 550 is composed of the combination of a multistage voltage multiplier which delivers the discharge current combined with a voltage doubler for the priming of the tube, connected in parallel to the multipliers. This additional circuit also increases the number of components of the device.

The invention aims to remedy the aforementioned drawbacks by creating a supply device having at least two output impedances, one entirely independent of the other with a large impedance gap.

This object is achieved by the features of the first claim.

Fig. 1 shows a three-stage example comprising six multiplicative voltage cells symmetrical with respect to the sector in order to reduce the maximum output voltage with respect to the sector, which can improve job security.

Of course, the multiplier can be executed by a lesser or greater number of voltage multiplier cells.

This device comprises the diodes 1-2-3-4-5-6 and the capacitors 7-8 connected as indicated in claim 1, which are of great value for ensuring, determining and maintaining the discharge current in the tube .

Capacities 9-10 can be of high value close to the previous ones, if one wishes to make them support an important function in the discharge current, on the other hand they can be of very low value if one wishes to make them execute the function unique boot; capacities 11-12 which are of very low value are only used for priming the tube.

Resistor 13 is of low value, and serves to limit the intensity during commissioning, the peak current; it can be replaced or seconded by a selfic impedance or resistance to coefficiant of negative temperature or any other means limiting the peak intensity.

The resistor 14 has the function of limiting the peak current in the discharge tube, it is presented by way of example, an ohmic resistor and can be replaced or seconded by an active component, such as a transistor (see fig. 2) .

The active current limiter is shown in fig.2. It includes an output resistor 15, a Zener diode 16, and a resistor 17 at the input and the transistor 18, which serves to limit the discharge current. The retraction circuit 19-20 and the basic resistor 21 are common components in regulators or current limiters.

With three multiplier stages, the output voltage in the absence of load is six times the peak input voltage. It is directly related to the number of cells used.

The discharge tubes tend to decrease their internal resistances, when the discharge current increases, this reality can cause unpleasant effects which consist in flashing the lighting at an indefinite frequency, if the choice of the resistance 14 is too low . In general it is of the order of a few hundred Ohmes to a few Kilo-Ohmes. This is improved by the active circuit according to fig. 2.

Claims (4)

1. Discharge tubes direct current feed divice made up of at least two voltage multiplier stages, of which the first is composed of two legs for the respective half-waves. Each leg is made up of a first diode (1, 2) and a first condenser (7, 8) and connected in central circuit between input terminals (B1, B2) of the device that has the common point of first diodes (1, 2) and first condensers (7, 8) on the output terminal from which voltage comes out duplicated. The second multiplier stage is composed of two other legs, each one made up of a second diode (3, 4) and a second condenser (10, 9) connected in series between the input terminal (B1) on first diode's (1, 2) side and the output terminal (B5, B6) of the first multiplier, and fitted out of output terminals (B'3, B'4) at the common point of the second diodes (3, 4) and the second condensers (10, 9), from which voltage comes out multiplied. Characterized by an appreciably higher capacitance of the stage's condensers (7, 8) which maintain the tube's discharge current while the low capacitance condensers of output stage (9, 10 or 11, 12) produce only the tube's firing current.

2. Feed device as described in claim 1, composed of three multiplier stages and characterized by the high capacitance of the second stage's condensers (9, 10) which is closed to the capacitance of the first condensers' (11, 12) capacitance is low.

3. Feed device as described in claim No 1, composed of three multiplier stages and characterized by low capacitance of second stage's condensers (9, 10) which is close to the capacitance of the third condensers (11, 12).

4. Feed device as described in claims 1 to 3, fitted out which a current limiter resistance between an output terminal (B4) of the last multiplier stage and the discharge tube, characterized by that resistance which is made up of a current limiter active circuit including essentially a transistor (18) connected in series with a zener diode (16) parallel to its input.

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