Charger circuit from mp3 3. Power supply from the television module. PSU Surge Protector

It is often required to “power” the amateur radio structure with 12 volts at home. Switching power supplies from old third-generation TVs (see Fig. 3.14) of the Slavutich-Ts202, Raduga-Ts257, Chaika-Ts280D and similar models come to the rescue.

Their circuitry is, as a rule, universal; an output voltage of 12 V will provide such a power supply with a useful current of up to 0.8 A.

The output voltage is removed from the contacts:

2 - 135 V (for horizontal scanning);

Contacts 1, 3, 6 of connector X2 (AZ) - as it is indicated on the board and on the electrical diagram - are combined and connected to the "common wire". On fig. 3.15 shows a schematic diagram of the MP-3-3 power supply module (similar to the MP-3-1 module used in some models of color TVs of the ZUSTST-61-1 type series).

Rice. 3.14. View of the television power module

Fig, 3.15. Electrical diagram of the MP-3-3 module

The power cord to the 220 V network is connected to connector XI.

The main difference between these “related” units is in the indicators: in the more recent MP-3-3, the AL307BM LED indicator is installed, and in the older version, the INS-1 gas discharge lamp is installed through a 135 V supply limiting resistor. If these indicators after power is applied to a known-good MP-3, they do not light up (which often happens without a connected load), which means that the power module needs to be started artificially. To do this, it is often enough to connect between contacts 1 and 2 (at the output 135 V) a load equivalent - a constant resistor of the MLT-1 type with a resistance of 6.8 kOhm ± 30%. After such refinement, the pulse generator "starts", the transformer T1 begins to "sing" softly, and the power supply module is ready to work across the entire range of output voltages. Resistor R27 (designation on the diagram and on the board) within a small range can adjust the voltage at the 12 V output. There is no need to install additional filtering oxide capacitors (at the output), the output voltage shape on the oscilloscope screen has a clear straight line, not burdened by pickups.

The most likely reason for the failure of these power supply modules lies in the malfunction of the blocking generator transistor KT838 (VT4). The electrical diagram (Fig. 3.15) shows the values ​​\u200b\u200bof the control voltages at various points, so it will not be difficult for any radio amateur to repair such a power supply. And the elements for repair can be found in the "bins", without spending material resources on the purchase of new radio components, as would inevitably have to be done when repairing more compact, but often more "capricious" pulse adapters for modern radio equipment. In this, undoubtedly, the "obsolete" power supply modules of the MP-3 type (various modifications) outperform the more modern ones, so it is too early to write off the first ones.

Literature: Kashkarov A.P. Electronic devices for coziness and comfort.

Chapter 3. Schemes of switching power supplies.

In this article, we will consider a scheme in which key management is done according to a different principle. This scheme, with minor changes, is used in many TVs, such as Akai CT-1405E, Elekta CTR-2066DS and others.

A comparison device is assembled on the transistor Q1, its circuit is no different from the others considered earlier. Only here the n-p-n transistor is used, as a result, the polarity of the switch-on has changed. The comparison circuit is powered by a separate winding from a D5 rectifier with a C2 filter. The initial bias on the key Q4 is fed through the resistor R7, which usually consists of several resistors connected in series, which is apparently due to better heat transfer, the elimination of breakdown between the terminals (after all, the voltage drop across it is 300 V) or the manufacturability of the assembly. I myself don’t know why this is done, but in imported equipment you see this all the time.

The feedback loop is connected here in a different way than we have discussed before. One output of the feedback winding is connected as usual to the base of the key, and the other to the diode distributor D3, D4.

What is the result? Transistors Q2 and Q3, which are a composite transistor, are adjustable resistance. This resistance (between the plus of the capacitor C3 and the emitter of Q3) depends on the error signal coming from Q1. Since transistor Q2 has p-n-p conductivity, with an increase in the voltage coming to its base, its current decreases, transistor Q3 closes, that is, the resistance of the composite transistor increases. This schema property is used.

Consider the moment of launch. Capacitor C3 is discharged. The feedback circuit is connected positively to the base, negatively connected through D4 and R9 with a common wire. There is a process of linear increase in the collector current, which ends with the saturation of the key and its closing. In this case, the polarity of the voltage on the feedback winding is reversed and capacitor C3 is charged through the diode D3 with this voltage. When the energy of the transformer is used up, capacitor C3 will be connected to the base-emitter junction of the key through the resistance of the composite transistor with a minus to the base and close the key.

The discharge time C3 and the magnitude of the closing potential depend on the magnitude of the resistance of the composite transistor. At the time of starting the power supply, this resistance is large and the discharge of the capacitor C3 does not delay the next cycle, however, in the steady state, the delay of the next cycle is sufficient to adjust the average power delivered to the load. Thus, we see that the circuit in question is not exactly PWM. If in the previous schemes the time of the open state of the key was regulated, then in this scheme the time of the closed state of the key is regulated.

Fig 2

The figure shows the path of the discharge of the capacitor C3. At the time t0, the switch collector current begins to rise and continues until the time t1. At this time interval, the voltage Ube of the key increases. This does not affect the charge of C3 in any way, since C3 is connected to the feedback winding through diode D3, which is closed at this moment. As soon as the growth of the collector current of the key ends, the polarity of the voltage on the feedback winding is reversed, the diode D3 opens and the charge of C3 begins. At the same time, this voltage is applied through the resistance of the composite transistor Rsost to the base-emitter junction of the key, reliably locking it. The charge C3 continues until the time t2, that is, until the accumulated energy of the transformer is transferred to the load. At this moment, the charged C3 through Rstat and the opened diode D4 will be connected to the base-emitter junction of the key. The figure shows how the voltage of the charged capacitor C3 is divided between the resistance of the composite transistor Rcom (Ucom) and the resistance of the base-emitter section of the key Rcl (Ube), which is determined by the sum of the resistances R9 and the resistance of the open diode D4. The resistance of resistors R6, R9 and R10 is small and can be ignored. With a high resistance Rstat, the C3 discharge occurs more slowly and the key opening threshold will be reached later than with a low Rstat. At time t3, the voltage C3 will decrease to such a value that the blocking voltage at the base of the key will disappear and the cycle will repeat. So the resistance of the composite transistor is involved in the process.

Schemes of domestic switching power supplies.

The vast majority of domestic UPS circuits are built according to the same scheme, according to the same principle, and differ only in the startup circuit, and in the output voltages of the secondary rectifiers. And one more feature - domestic UPSs are not designed to operate in standby mode (that is, in almost idle mode). All UPSs have protection against overload and short circuit in the load, against undervoltage in the network below 160 V, idle. In some models with remote control, the UPS is turned off using an artificially created overload, in which case the overload protection is activated and generation is disrupted.

Since there are still a lot of domestic TVs with such UPSs, I will talk about them in more detail, despite the fact that I will repeat myself in some ways. What I will talk about applies to all UPS models built on discrete elements. We will consider domestic UPSs built using the K1033EU1 chip (analogous to TDA4601) in the next chapter, in which I will describe the operation of the UPS on chips. Newer UPSs, in which the developments of foreign manufacturers are applied, I will not consider here.

Schematic diagram of the power supply module MP-3-3

Consider the schematic diagram of the MP-3-3 power supply module. The module includes a low-voltage rectifier (VD4-VD7 diodes), a trigger pulse shaper (VT3), a pulse generator (VT4), a stabilization device (VT1), a protection device (VT2), a T1 pulse transformer, VD12-VD15 diode rectifiers, a stabilizer voltage 12 V (VT5-VT7).

Fig 3

The pulse generator is assembled according to the oscillator circuit with collector-base connections on the VT4 transistor. When the TV is turned on, a constant voltage from the output of the filter of the mains rectifier (capacitors C16, C19, C20) through the winding 19-1 of the transformer T1 is supplied to the collector of the transistor VT4. At the same time, the mains voltage from the diode VD7 through the resistors R8 and R 11 charges the capacitor C7, and also goes to the emitter of the transistor VT2, where it is used in the device for protecting the power supply module from low mains voltage. When the voltage on the capacitor C7, applied between the emitter and base 1 of the unijunction transistor VT3, reaches a value of 3 V, the transistor VT3 opens. Capacitor C7 begins to discharge through the circuit: emitter-base junction of transistor VT3, emitter junction of transistor VT4, resistors R14 and R16 connected in parallel, capacitor C7.

The discharge current of the capacitor C7 opens the transistor VT4 for a time of 10 ... 15 μs, sufficient for the current in its collector circuit to increase to 3 ... 4 A. The flow of the collector current of the transistor VT4 through the magnetization winding 19-1 is accompanied by the accumulation of energy in a magnetic field core. After the end of the discharge of the capacitor C7, the transistor VT4 closes. The cessation of the collector current causes the appearance of an EMF of self-induction in the coils of the transformer T1, which creates a positive voltage at terminals 6, 8, 10, 5 and 7 of the transformer T1. In this case, current flows through the diodes of half-wave rectifiers in the secondary circuits VD12-VD15.

With a positive voltage at the terminals 5, 7 of the transformer T1, the capacitors C14 and C6 are charged, respectively, in the anode and control electrode circuits of the thyristor VS1 and C2 in the emitter-base circuit of the transistor VT1.

Capacitor C6 is charged through the circuit: terminal 5 of transformer T1, diode VD11, resistor R 19, capacitor C6, diode VD9, terminal 3 of the transformer. Capacitor C14 is charged through the circuit: terminal 5 of transformer T1, diode VD8, capacitor C14, terminal 3 of the transformer. Capacitor C2 is charged through the circuit: terminal 7 of transformer T1, resistor R13, diode VD2, capacitor C2, terminal 13 of the transformer.

Similarly, subsequent switching on and off of the oscillator transistor VT4 is carried out. Moreover, several such forced oscillations are sufficient to charge the capacitors in the secondary circuits. With the end of the charging of these capacitors between the oscillator windings connected to the collector (pins 1, 19) and to the base (pins 3, 5) of the transistor VT4, positive feedback begins to act. In this case, the oscillator goes into self-oscillation mode, in which the VT4 transistor will automatically open and close at a certain frequency.

In the open state of the transistor VT4, its collector current flows from the plus of the capacitor C16 through the winding of the transformer T1 with terminals 19, 1, the collector and emitter junctions of the transistor VT4, resistors R14, R16 connected in parallel to the minus of the capacitor C16. Due to the presence of inductance in the circuit, the increase in the collector current occurs according to a sawtooth law.

To eliminate the possibility of failure of the transistor VT4 from overload, the resistance of resistors R14 and R16 is selected in such a way that when the collector current reaches a value of 3.5 A, a voltage drop is created across them sufficient to open the thyristor VS1. When the thyristor is opened, the capacitor C14 is discharged through the emitter junction of the transistor VT4, resistors R14 and R16 connected in parallel, an open thyristor VS1. The discharge current of the capacitor C14 is subtracted from the base current of the transistor VT4, and the transistor closes prematurely.

Further processes in the operation of the oscillator are determined by the state of the thyristor VS1. Opening it earlier or later allows you to adjust the rise time of the sawtooth current and thereby the amount of energy stored in the transformer core.

The power module can operate in stabilization mode and in short circuit mode.

The stabilization mode is determined by the operation of the UPT on the transistor VT1 and thyristor VS1. At a mains voltage of 220 V, when the output voltages of the secondary power sources reach the nominal values, the voltage on the winding of the transformer T1 (terminals 7, 13) will increase to a value at which the constant voltage at the base of the transistor VT1, where it enters through the divider R1-R3, becomes more negative than at the emitter, where it is completely transmitted. Transistor VT1 opens in the circuit: terminal 7 of the transformer, R13, VD2, VD1, emitter and collector junctions of the transistor VT1, R6, control electrode of the thyristor VS1, R14-R16, terminal 13 of the transformer. The current of the transistor, summing up with the initial current of the control electrode of the thyristor VS1, opens it at the moment when the output voltage of the module reaches the nominal values, stopping the increase in the collector current.

By changing the voltage at the base of the transistor VT1 with a trimmer resistor R2, you can adjust the voltage across the resistor R10 and, therefore, change the opening moment of the thyristor VS1 and the duration of the open state of the transistor VT3, i.e., set the output voltages of the secondary power sources.

With an increase in the mains voltage (or a decrease in the load current), the voltage at the terminals 7, 13 of the transformer T1 increases. This increases the negative base voltage with respect to the emitter of the transistor VT1, causing an increase in the collector current and a voltage drop across the resistor R10. This leads to an earlier opening of the thyristor VS1 and closing of the transistor VT4, the power delivered to the secondary circuits decreases.

With a decrease in the mains voltage (or an increase in the load current), the voltage on the transformer winding Tl and the base potential of the transistor VT1 with respect to the emitter become correspondingly smaller. Now, due to a decrease in the voltage created by the collector current of the transistor VT1 on the resistor R10, the thyristor VS1 opens at a later time and the amount of energy transferred to the secondary circuits increases.

A significant role in the protection of the transistor VT4 is played by the cascade on the transistor VT2. When the mains voltage decreases below 150 V, the voltage on the winding T1 with terminals 7, 13 is insufficient to open the transistor VT1. In this case, the stabilization and protection device does not work and it creates the possibility of overheating of the transistor VT4 due to overload. To prevent the failure of the transistor VT4, it is necessary to stop the oscillator. The transistor VT2 intended for this purpose is turned on in such a way that a constant voltage is supplied to its base from the divider R18, R4, and a pulsating voltage with a frequency of 50 Hz is applied to the emitter, the amplitude of which is stabilized by the zener diode VD3. When the mains voltage decreases, the voltage at the base of the transistor VT2 decreases. Since the voltage at the emitter is stabilized, a decrease in the voltage at the base leads to the opening of the transistor. Through the open transistor VT2, trapezoidal pulses from the VD7 diode enter the control electrode of the thyristor, opening it for a time determined by the duration of the trapezoidal pulse. This stops the oscillator from working.

The short circuit mode occurs when there is a short circuit in the load of secondary power supplies. In this case, the module is started by triggering pulses from the trigger device (VT3 transistor), and the module is turned off using the VS1 thyristor according to the maximum collector current of the VT4 transistor. After the end of the trigger pulse, the device is not excited, since all the energy is consumed by the short-circuited circuit.

After removing the short circuit, the module enters stabilization mode.

Impulse voltage rectifiers connected to the secondary winding of the transformer T1 are assembled according to a half-wave circuit.

The rectifier on the VD12 diode creates a voltage of 130 V to power the horizontal scanning module. The ripple of this voltage is smoothed out by capacitor C27. Resistor R22 eliminates the possibility of a significant increase in voltage at the rectifier output when the load is disconnected.

A 28 V voltage rectifier is assembled on the VD13 diode, designed to power the vertical scan module. The filter at its output is formed by capacitor C28 and inductor L2.

A 15 V voltage rectifier for powering the UZCH is assembled on a VD15 diode and a capacitor C30.

The 12 V voltage used in the control unit, color module, radio channel module and vertical scan module is created by a rectifier on the VD14 diode and capacitor C29. At the output of this rectifier, a compensation voltage stabilizer is included. It consists of a regulating transistor VT5, a current amplifier VT6 and a control transistor VT7. The voltage from the output of the stabilizer through the divider R26, R27 is supplied to the base of the transistor VT7. Variable resistor R27 is designed to set the output voltage. In the emitter circuit of the transistor VT7, the voltage at the output of the stabilizer is compared with the reference voltage at the zener diode VD16. The voltage from the collector VT7 through the amplifier on the transistor VT6 is fed to the base of the transistor VT5, connected in series to the rectified current circuit. This leads to a change in its internal resistance, which, depending on whether the output voltage has increased or decreased, either increases or decreases. Capacitor C31 protects the stabilizer from excitation. Through the resistor R23, voltage is supplied to the base of the transistor VT7, which is necessary to open it when it is turned on and restored after a short circuit. Inductor L3 and capacitor C32 - an additional filter at the output of the stabilizer.

USST series televisions are gradually losing ground, and often, a completely serviceable TV, but with a used kinescope, is thrown out. It makes no sense to convince readers of how many wonderful devices can be made from the details of this "poor fellow."

One of the most interesting components of this type of TV is a switching power supply, which is quite light and compact, being in good condition, giving good output characteristics. This article describes how to make a power source based on MP-3-3.

If you were engaged in the repair of the USCT, then you should know that if the MP-3-3 is simply plugged into the network without load, it does not work. The protection system is activated, which monitors not only overload, but also "underload". Therefore, in order for the MP-3-3 to be used as a laboratory one, that is, with a variety of loads, it must be loaded.

In L.1 it is proposed to load each of the MP-3-3 output sources with starting loads, but, as practice shows; it is not necessary to do so. The fact is that the protection system does not monitor the currents in all the secondary windings of the pulse transformer.

It is important for her that the block is loaded on the secondary circuit. And then, for which secondary circuit, it does not matter. In addition, to bring the source to the stabilization mode, it is required to load it with at least 20W, and with the resistances of the resistors indicated in L.1, in total, no more than 3-4 W is obtained. To bring the source to the operating mode, this is not enough.

The pulse generator of a serviceable MP-3-3 source is turned off when the load power is less than 15-20W. Therefore, we take the most unnecessary output of 135V and load it with a power of about 20-25L /, simply by connecting an incandescent lighting lamp from the refrigerator to its output. Or a wire resistor of the "PEV" type for 600-800 Ohms with a power of 20-30W.

With such a load, the source goes into stabilization mode. Now you can use its outputs with voltage 28V (up to 1 A), MU (up to 2 A), 15V (up to 2 A). How to use them depends on what voltages you plan to receive from the source.

Rice. 1. A fragment of the MP-3-3 power supply circuit.

You can replace all secondary circuits with others, replace the 12V transistor regulator with an adjustable integrated regulator, use adjustable stabilizers on all outputs, etc. It should be noted that a separate transformer winding is used for the 15V output, this will make one of the outputs galvanically isolated from the others.

And yet, perhaps the most unexpected application of MP-3-3 - after finalizing the output circuits, even a small lamp UMZCH can be powered from it, using an output voltage of 135V to power its anode circuits.

Karavkin V. Rk2005, 1.

Literature:

1. Kashkarov A. Power supply from the TV. well. Radiomir 9, 2004.
2. S.A. Elyashkevich. Color TVs ZUSST.