Electronic transformer composed of MR9830

    Abstract: MR9830 is an integrated power module launched by Mitsubishi. It is usually used in electronic ballasts for fluorescent lamps and energy-saving lamps. It requires very few peripheral components. This article introduces the performance and general applications of MR9830, and focuses on its application circuit on electronic transformers.

    Keywords: electronic transformer MR9830 electronic ballast dead zone

1 Overview

MR9830 is a thick film circuit module that integrates oscillation, drive and power output. It requires very few peripheral components, is very convenient to make electronic ballasts, is reliable in operation and low in price. The MR9830 is internally composed of an oscillation circuit, a duty cycle and dead zone control circuit, a push circuit and a half-bridge power output circuit. Its internal structural block diagram is shown in Figure 1.

MR9830 has an internal self-oscillator similar to the 555 time base circuit. By selecting an external capacitor, an oscillation frequency of 1kHz to 100kHz can be obtained. The relationship between frequency and external capacitance is:

f=71×10 -6/Cf

One of the important circuits inside the MR9830 is the dead zone control circuit. The push-pull output tube in a general electronic ballast circuit is not completely in the ideal state of one on and one off. Instead, one tube is not completely cut off and the other tube begins to conduct. Although it cannot be reversed due to the strong positive and negative force. Due to the existence of overlapping conduction time zones, this power switch tube is easily damaged. The MR9830 sets a time zone (also called a "dead zone") in which both output power switch tubes are in a cut-off state (also called a "dead zone") at the switching moment when the two output power switch tubes are turned off and on, thereby eliminating the possibility that the two power switch tubes will be turned on at the same time. possible.

The power output of MR9830 is a half-bridge power output stage composed of two MOSFET power switch tubes, with a current capacity of 2.5A. Since its withstand voltage can reach 600V, 220 AC mains power can be directly rectified and filtered as the working power supply.

2 Functional parameters of MR9830

The power supply of MR9830 can choose a DC voltage of 200~350V, its oscillation frequency is 1kHz~100kHz, the output power is 40W, and it has a dead time of 1~ μs .

MR9830 only has 4 pins. The function description of each pin is as follows:

Pin 1 is the "+" terminal of the power supply (Vcc);

Pin 2 is the power output terminal (OUT);

Pin 3 is the public terminal (GND);

Pin 4 is the connection terminal of the capacitor Cf for the oscillator frequency. The oscillation frequency can be set as follows:

f=71×10 -6/Cf

3 Application circuit

3.1 Typical applications

MR9830 can be used as an electronic ballast for fluorescent lamps and energy-saving lamps. The specific circuit is shown in Figure 2.

Electronic ballasts assembled with MR9830 can reliably drive various fluorescent lamps and energy-saving lamps with power below 40W. It has small size, high efficiency, extremely low failure rate, and very simple assembly process. The parameters of C1, C2, Cf and inductor L in Figure 2 can vary according to the power required to drive fluorescent tubes and energy-saving lamps. See Table 1 for specific parameter settings.

Table 1 Parameter settings of electronic ballast composed of MR9830

3.2 Assemble electronic transformer with MR9830

The application of traditional iron-core transformers is limited in many aspects due to factors such as large size, heavy weight, and low power factor. The electronic transformer assembled with MR9830 has the advantages of small size, light weight, high power factor, and no interference with electrical appliances. It can easily replace the power transformer of black and white TVs, the power transformer of some DVD players, and some power amplifiers. Selling iron core transformers below 40W, etc. The specific electronic transformer circuit is shown in Figure 3 and Figure 4.

Figure 3 and Figure 4 are two electronic transformer circuits with different connection methods. The principle is that the high-frequency voltage output by pin 2 of the MR9830 is stepped down and isolated by the ferrite transformer T and then output. Among them, Figure 3 shows the 2-pin output of MR9830 isolated by C3 to obtain the negative terminal of the power supply to form a loop. Figure 4 uses C3 and C4 to create an artificial "neutral point", and the high-frequency voltage output by pin 2 of the MR9830 passes through the primary winding of T to this "neutral point" to form a loop. After actual testing, it was found that the voltage waveform output in Figure 3 is poor, while the waveform output in Figure 4 is almost a standard square wave, indicating that in the circuit of Figure 4, the internal power switch tube of MR9830 is in an ideal switching state, and the circuit of Figure 4 The heat loss is very small and it can work stably for a long time when the measured output power is 40W. The secondary of the small transformer T can be wound with an appropriate number of turns of φ1.25mm enameled wire as needed. The reference data is 1.5V/turn, and E50×70 core can be used.

Since the electronic transformer outputs a high-frequency voltage, the secondary output of T in the circuit only needs to be half-wave rectified and filtered by a high-frequency diode, and then stabilized by a three-terminal voltage regulator to obtain the required voltage. of DC voltage.