RU77126U1 - ELECTRONIC TRANSFORMER FOR DISCHARGE LAMPS - Google Patents

Abstract

The utility model relates to electrical engineering and lighting engineering and can be used to power low-pressure discharge lamps, used, for example, for "neon" advertising. Achievable technical result - start and stabilization of the operating current of gas discharge lamps that do not have starting electrodes and filaments. The electronic transformer for discharge lamps contains a half-bridge inverter with MOS transistors controlled by a half-bridge driver with an internal generator and an external RC timing circuit. The lamp is connected to the secondary winding of the step-up transformer, the primary winding of which is included in the diagonal of the alternating voltage of the inverter, while the voltage on the secondary winding of the transformer exceeds the ignition voltage of the lamp, and when it is ignited, the current strength is limited by limiting the coupling coefficient between the transformer windings or the reactive ballast turned on in series with the primary winding of the transformer.

Description

The utility model relates to lighting engineering and can be used for low-pressure discharge lamps.

There are several ways to turn on discharge lamps using low-frequency inductive and high-frequency electronic ballasts. High-frequency electronic ballasts (electronic ballasts) have several advantages associated with increased lamp life, energy savings, reduction of metal consumption of devices.

Until recently, electronic ballasts based on bipolar transistors predominated, they are quite simple in circuit design [1, 2], but have a number of disadvantages associated with the presence of a large number of inductive elements, the dependence of the parameters on the mains voltage.

Modern devices are made according to the schemes of a bridge or half-bridge inverter based on field (MOS) or (IGBT) transistors controlled by a microelectronic driver [3, 4].

As a prototype of an electronic transformer, a half-bridge transistor inverter [3] was selected for MOS transistors controlled by a half-bridge driver with an integrated master oscillator made by MOSFET technology with an external RC timing circuit. The main disadvantage when using this type of generator to power discharge lamps is the insufficient voltage at the midpoint of the half-bridge to which the lamp is connected. Many discharge lamps do not have filaments and trigger electrodes inside the lamp, therefore they require increased voltage to start. So, for example, a neon tube-lamp 1 meter long has an ignition voltage of 1200 V, and when a gas discharge occurs, the operating voltage drops to only 800 V.

The objective of the proposed utility model is to ensure the ignition voltage of the lamp without prior glow and the subsequent stabilization of the operating current of the lamp.

The task is achieved in that the electronic transformer for discharge lamps, containing a half-bridge inverter on MOS transistors controlled by a half-bridge driver, with an internal generator and an external RC timing circuit, is loaded on a step-up transformer, the primary winding of which is included in the alternating current diagonal of the half-bridge formed by two with transistor switches and two capacitors, and a gas discharge lamp or a garland of several series-connected lamps is connected to the secondary winding of the trans a transformer on which a high voltage is generated in excess of the ignition voltage of the lamps.

Figure 1 shows a schematic diagram of an electronic transformer.

The circuit consists of a half-bridge inverter with a control driver 1 included according to a typical circuit. The output step-up transformer 2 is included in the diagonal of the half-bridge 3-4. The discharge lamp 5 is connected to the secondary winding of the transformer 2.

The device operates as follows. When a supply voltage is applied, the potential of point 4, due to the capacitive divider, becomes equal to E _pit / 2. At the same time, the time-consuming capacitor 5 is charging. The time constant of the charge of this capacitor determines the frequency of the generator built into driver 1.

In the initial state, when there is no voltage on the capacitor 5, both keys are closed, when the supply voltage Vcc is supplied to the driver, the capacitor 5 is charged through the resistor 6, and the voltage of the inverter midpoint 3 changes in phase with the voltage on the resistor 6. That is, the upper key first opens, the lower key is closed. The current from the source flows through point 3, the primary winding of the transformer 2 to point 4. As the capacitor 5 charges, the voltage across the resistor 6 decreases, the upper switch closes, and the lower switch opens after a specified delay interval. The current flows from point 4 through the primary winding of the transformer to point 3, the potential of which decreases to zero (if the minus of the power source is connected to a common bus), at the same time, the voltage on the capacitance 5 is reset and the lower key is closed. After the same delay interval, called “dead time”, the upper key opens and the process repeats. Thus, an alternating voltage is generated on the primary winding of transformer 2 with a frequency equal to the driver switching frequency and a voltage amplitude equal to E _pit / 2. A high voltage appears on the secondary winding of the transformer, sufficient to ignite several lamps without pre-heating. When the lamps are ignited, their resistance decreases, which leads to an increase in current strength and power consumption. In order to avoid overload of the inverter, the current must be limited at a predetermined level. This limitation is possible in several ways:

1. The design of the transformer 2 due to the limitation of the coupling coefficient of the primary and secondary windings of the transformer.

2. By limiting the current using a capacitor connected in series with the primary winding of the transformer.

3. By limiting the current using a choke connected in series with the primary winding of the transformer.

The proposed utility model is implemented in the form of a working model of an electronic transformer with an output voltage of 10 kV. When a garland of 10 neon tubes with a length of 8 meters is connected to the transformer, they are ignited, and in the stationary mode, the lamp current is 25 mA. Thus, a useful model of an electronic transformer has been created, which allows you to turn on from 1 to 10 neon lamps and stabilize the mode of their glow.

Literature

1. RU No. 92012808. Device for ignition and power of low pressure discharge lamps. IPC Н05В 41/29.

2. Patent RU No. 2094964. Control gear for powering the discharge lamp. IPC Н05В 41/29.

3. Information material PD 60131 of the International Rectifier company no to the technical characteristics of the half-bridge driver IR 21531, http // www.irf.com (prototype).

4. Patent RU No. 2260899 Transistor generator for resonant loads. IPC Н03В 5/12, Н02М7.

Claims (2)

1. An electronic transformer for discharge lamps, comprising a half-bridge inverter with MOS transistors controlled by a standard half-bridge driver with an internal generator and an external RC timing circuit, characterized in that the discharge lamps are connected to a secondary winding of a step-up transformer included in the variable diagonal voltage of the half-bridge inverter, and the coupling coefficient of the primary and secondary windings of the transformer is limited by the presence of a gap in the core. 2. The transformer according to claim 1, characterized in that the primary winding of the step-up transformer is connected in series with reactive ballast.