Features of the power supply module MP-403. Scheme, description

Free technical library

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

Features of the power supply module MP-403. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Телевидение

Comments on the article

In order to successfully repair electronic equipment, in particular televisions, you need to have a good understanding of the operation of the units and components of the device and know the purpose of their elements. For example, switching power supplies usually cause great difficulties during repair. In the article published here, the author talks about the operation of the MP-403 power module, which was used in many TV models.

The MP-403 television power module has already been discussed in [1 and 2] with varying degrees of detail. However, in [1] the process of launching the module is not entirely accurately described and its main self-oscillating mode is not described (a link is given to the MP-1 module). In the book [2], of the entire startup process, only the supply of opening voltage to the base of the VT9 key transistor is actually explained, and then it is stated that the startup processes proceed in the same way as in the MPZ-3 module. The main self-oscillating mode of operation is also not mentioned. Meanwhile, when troubleshooting a switching power supply module, it is very important to know the operation in these two main modes. Unfortunately, the outline of the circuit diagram in both editions is such that it is inconvenient to use.

In this article, an attempt is made to eliminate these gaps, i.e., to describe the operation of the module at startup, in a steady-state self-oscillating mode, and in the event of a short circuit, to explain the purpose of individual elements and assemblies, as well as to provide a “readable” circuit diagram. She is shown in the picture.

(click to enlarge)

The module launcher is assembled using transistors VT4, VT6 and VT7. The last two directly provide start-up, and the first serves to turn them off when the module switches to self-oscillating mode.

After turning on the TV, capacitor C9 begins to charge (through elements R19, VD4, R14, R16) with a pulsating voltage generated on the rectifying diode VD7. While the voltage on capacitor C9 is low, transistor VT4 is closed. Transistor VT7 is opened by the base current flowing through resistors R28, R25, R14, R16. The opening voltage is supplied to the emitter junction of transistor VT9 through resistors R28, R14, R16, transistor VT7, emitter junction of transistor VT6 and winding 5-3 of transformer T1. Transistor VT9 begins to open.

A linearly increasing current flows through winding 19-1 of the transformer, which induces 5-3 mutual induction emf in the positive feedback winding (POF). The base current of transistor VT9, created by the PIC winding, passes through elements R27, VD11 and VT6. The collector current of transistor VT9, flowing through resistors R14 and R16, provides an increasing voltage across them.

Having reached a certain value, the voltage on resistors R14, R16 through the circuit C5R11 (charging the capacitor) opens the thyristor VS1. The latter, through inductor L1, uncharged capacitor C7 and resistors R14, R16, bypasses the emitter junction of transistor VT9, closing part of the current in winding 5-3 of the transformer to itself. As a result, the base and collector currents of transistor VT9 decrease, the voltage on winding 5-3 changes polarity, the transistor and thyristor close.

Voltage pulses appear on the secondary windings of the transformer, which begin to charge the filter capacitors of the secondary rectifiers. Since the charging currents are large (almost short circuit mode), the voltages on the secondary windings and the PIC winding (5-3) are small and quickly disappear. In other words, the energy of the windings is quickly transferred to uncharged capacitors.

Again, the trigger current through the emitter junction of transistor VT6 opens transistor VT9, then being saturated with the current of the PIC winding, the SCR opens and closes transistor VT9 and itself. Consequently, a certain number of cycles of turning on and off the transistor VT9 occurs, during which the capacitors C28, C31, C32, C34, C35 of the secondary rectifiers are charged to voltages close to the nominal ones. Their recharging currents take the form of pulses that exponentially decrease to zero, which allows the module to exit the short circuit mode.

By this time, capacitor C9 has time to charge to the opening voltage of transistor VT4. Its collector current increases the voltage drop across resistor R28 and closes transistors VT7 and VT6 of the trigger device. The module switches to a self-oscillating mode of operation, in which capacitors C5, C7 (through the diode VD6 from the PIC winding) and C8 are already charged.

In steady state, when transistor VT9 opens, a linearly increasing current flows through it in the same way as during startup. A voltage of the same shape is created on resistors R14, R16, which is added algebraically with the voltage on capacitor C5 and through the divider R11R13 acts on the control electrode of the thyristor VS1. Until the sum of the voltages becomes positive and does not exceed a certain value (about 0,6 V), the latter is closed. The PIC voltage of winding 5 - 3 creates the base current of transistor VT9 through resistor R20 and transistor VT5, maintaining transistor VT9 in the open state.

Transistor VT5 serves as a unit for proportional control of the base current of transistor VT9. In addition, capacitors C5, C8 are charged through it and transistor VT9 is opened. In steady state, transistor VT5 is opened by the voltage of capacitor C5 applied through resistors R17 and R20 to its emitter junction.

The increasing voltage from resistors R14, R16 through elements C8 and R20 affects the emitter junction of transistor VT5, proportionally reducing its resistance to the base current of transistor VT9 passing through it, which ensures an approximately constant degree of saturation of transistor VT9 with an increase in its collector current. When the collector current of transistor VT9 increases to approximately 3,5 A, the sum of the voltages across resistors R14, R16 and capacitor C5 becomes sufficient to open SCR VS1. Through it, inductor L1 and resistors R14, R16, the voltage on capacitor C7 is applied in closing polarity to the emitter junction of transistor VT9. The discharge current of the capacitor is directed opposite to the base current of the transistor and exceeds the latter. Transistor VT9 closes very quickly, the discharge circuit of capacitor C7 through the thyristor is interrupted, the latter’s current decreases, causing it to close.

Voltage pulses appear on the collector of the VT9 transistor and the windings, and currents flow through the windings, which recharge the filter capacitors. As they decrease, they induce PIC voltage on winding 5-3 (plus at pin 5). It opens the collector junction of transistor VT5 through resistor R17, diode VD5 and inductor L1. As a result, transistor VT5 opens in the opposite direction. In this case, the charging current of capacitor C5 flows through the transistor and elements R20, VD5, L1. At the same time, capacitors C7 (via diode VD6 and inductor L1) and C8 (via the collector junction of transistor VT5 and resistors R14, R16, R26) are recharged.

By the voltage of POS winding 5-3, transistor VT9 is maintained in the closed state through transistor VT5, open in the opposite direction, and resistor R20.

When the charging currents of the secondary rectifier filter capacitors decrease to zero, the voltage on winding 5-3 also becomes zero. At this moment, the voltage of capacitor C5 opens the emitter junction of transistor VT5 through resistors R20 and R17, opening the transistor itself in the forward direction. At the same time, the voltage of capacitor C8 passes through its collector junction and winding 5-3 to the emitter junction of transistor VT9. In this case, the initial base current of the latter arises and the increase in its collector current begins again under the influence of the PIC.

In the short circuit mode in the secondary circuit, when transistor VT9 is closed, all the magnetic energy accumulated by transformer T1 is absorbed by the circuit that closes the secondary winding. The load current drops much more slowly than in normal mode, which is why the EMF practically ceases to be induced in the POS 5-3 winding of the transformer (plus at pin 5). This causes not only the cessation of charging of capacitor C8, but even its recharging in the opposite direction by the voltage of capacitor C5 through resistors R14, R16 and R17.

Since transistors VT6, VT7 of the triggering device are closed by a constantly saturated transistor VT4, transistor VT9 does not have any voltage source for initial opening, and even, on the contrary, is closed by the voltage of capacitor C5 through resistor R17, the collector junction of transistor VT5 and winding 5-3 of transformer T1.

Therefore, unlike the MPZ-3 module, which operates in short pulse mode during a short circuit, the MP-403 module is completely turned off. Therefore, if the power module was turned off by an artificial short circuit on elements VD16, R31, VT11, then to turn it back on, capacitor C9 must be discharged. To do this, unplug the TV and then turn it on again after 5...10 s.

Purpose of nodes and elements of the module:

VD7-VD10, C10-C13, C17, C18 - mains voltage rectifier;
VT1, VD3, C2, VD1, R5, R1-R3, C1, R7, C4 - output voltage stabilization unit;
VT2, VT3, R9, R6, R4 - surge protection device in case of malfunctions in the stabilization unit;
VT11, R31, VD16 - unit for creating an artificial short circuit to turn off the module in the event of a horizontal scan malfunction (MP-403 module) or by a signal from the control unit;
VT13-VT15, VD18, R33, R34, R37-R39 - voltage regulator +12 V;
VT9 - power pulse transistor switch;
VS1 - trinistor control the moment of closing the transistor VT9;
C7 - capacitor for closing transistor VT9 through an open thyristor (a feature of its operation should be indicated that during startup, current flows through it in the direction opposite to its nameplate polarity, which must be taken into account when assessing its reliability);
VD6 - switching diode for charging capacitor C7;
C5 - capacitor to create a negative bias voltage on the control electrode of the thyristor;
VD5 - switching diode for charging capacitor C5;
VD4 is a diode that serves to ensure that, during startup, the charging current of capacitor C9 does not pass through the control electrode of thyristor VS1 and does not charge capacitor C5 in the opposite direction;
C8 is a capacitor for the initial opening of transistor VT9 in self-oscillating mode; it is included, together with elements VT5 and R20, in the proportional current control unit of transistor VT9;
VT5 - switching transistor of the proportional current control unit of the base of transistor VT9, ensures charging of capacitors C5 and C8;
R14, R16 - resistors of the current sensor of the transistor VT9.

The operation of the module protection device is described in detail in [1], [2], and the operation of the stabilization unit in self-oscillating mode at rated load and at idle does not differ in any way from the similar device used in the MPZ-3 power module.

Literature

Potapov A., Kubrak S, Garmash A. Power module MP-403. - Radio, 1991, No. 6, p. 44-46.
Sokolov V. S., Pichugin Yu. I. Repair of color stationary televisions 4USTST. Reference manual. - M.: Radio and communication, 1995, p. 30-33.

Author: I.Molchanov, Moscow

See other articles Section Телевидение.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Alcohol content of warm beer 07.05.2024

Beer, as one of the most common alcoholic drinks, has its own unique taste, which can change depending on the temperature of consumption. A new study by an international team of scientists has found that beer temperature has a significant impact on the perception of alcoholic taste. The study, led by materials scientist Lei Jiang, found that at different temperatures, ethanol and water molecules form different types of clusters, which affects the perception of alcoholic taste. At low temperatures, more pyramid-like clusters form, which reduces the pungency of the "ethanol" taste and makes the drink taste less alcoholic. On the contrary, as the temperature increases, the clusters become more chain-like, resulting in a more pronounced alcoholic taste. This explains why the taste of some alcoholic drinks, such as baijiu, can change depending on temperature. The data obtained opens up new prospects for beverage manufacturers, ... >>

Major risk factor for gambling addiction 07.05.2024

Computer games are becoming an increasingly popular form of entertainment among teenagers, but the associated risk of gaming addiction remains a significant problem. American scientists conducted a study to determine the main factors contributing to this addiction and offer recommendations for its prevention. Over the course of six years, 385 teenagers were followed to find out what factors may predispose them to gambling addiction. The results showed that 90% of study participants were not at risk of addiction, while 10% became gambling addicts. It turned out that the key factor in the onset of gambling addiction is a low level of prosocial behavior. Teenagers with a low level of prosocial behavior do not show interest in the help and support of others, which can lead to a loss of contact with the real world and a deepening dependence on virtual reality offered by computer games. Based on these results, scientists ... >>

Traffic noise delays the growth of chicks 06.05.2024

The sounds that surround us in modern cities are becoming increasingly piercing. However, few people think about how this noise affects the animal world, especially such delicate creatures as chicks that have not yet hatched from their eggs. Recent research is shedding light on this issue, indicating serious consequences for their development and survival. Scientists have found that exposure of zebra diamondback chicks to traffic noise can cause serious disruption to their development. Experiments have shown that noise pollution can significantly delay their hatching, and those chicks that do emerge face a number of health-promoting problems. The researchers also found that the negative effects of noise pollution extend into the adult birds. Reduced chances of reproduction and decreased fertility indicate the long-term effects that traffic noise has on wildlife. The study results highlight the need ... >>

Random news from the Archive

64MP ISOCELL Bright GW1 sensor for smartphones 09.05.2019

Samsung has announced the release of a new image sensor for mobile devices, called ISOCELL Bright GW1. It has a higher resolution than other comparable devices on the market.

The new Samsung ISOCELL Bright GW1 sensor has a resolution of 64 megapixels with the same pixel size as the previous 48 megapixel model - 0,8 microns. This means that the new product has a larger physical size and is able to capture more light, which should have a good effect on the quality of shooting. Like its predecessor, the default Bright GW1 sensor produces lower resolution images by combining four neighboring pixels into one larger pixel that can capture more light. Thus, by default, photos are 16 megapixels.

Samsung's new sensor is able to descramble the color filter for full 64-megapixel resolution shots in good light. The same feature is available on the 48MP Sony IMX586 sensor, but it was not supported on the previous Samsung device. Now, the Korean manufacturer has released an updated version of the 48-megapixel sensor with support for this feature.

Samsung plans to begin mass production of the 64-megapixel ISOCELL Bright GW1 sensor in the second half of this year. It will appear in ready-made consumer devices towards the end of 2019.

Other interesting news:

▪ Teslaphoresis at the nanoscale

▪ More sushi

▪ Greenhouse vodka

▪ Lunar telescope from improvised materials

▪ Gypsy genealogy

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Electronic directories. Article selection

▪ article Help with bites. Occupational Safety and Health

▪ article Why do Mexicans call Americans gringos? Detailed answer

▪ article Double reef knot. Travel Tips

▪ article Scheme of the electrical equipment of the car VAZ-2106, 21061 and 21063 (1976-1987). Encyclopedia of radio electronics and electrical engineering