The network power supply with high specific parameters

A.MIRONOV, Lyubertsy

B brought to attention of readers to article is described by the Moscow Region the pulse converter for a food of electronic devices by tension 5 In from a network of an alternating current. The converter does not contain scarce and expensive elements, is simple in manufacturing and adjustment.

the Power supply is supplied with protection against throws of target tension and against an overload on a current with automatic return to an operating mode after its elimination.

the Key technical parameters

Entrance tension, In..... 150... 240

Frequency of entrance tension, Hz................... 50... 60

Frequency of transformation, kHz......................... 100

Target tension, In......... 5

Amplitude of pulsations of target tension, мВ, no more..................... 50

loading Current, And................ 0... 6

Ambient temperature, °C..............-10. . +50

Static instability of target tension at change of entrance tension, a loading and ambient temperature current in a full interval, %, from nominal rate, no more......... 3

Dimensions, mm............. 60x95x30

On fig. 1 is shown to p the device circuit. The knot of management realizes a pulse-width principle of stabilization of target tension. On the elements DD1.1, DD1.2 the setting generator working at frequency about 100 kHz at porosity, close to two is executed. Impulses duration about 5 microsec via the C11 condenser arrive on an element DD1.3 entrance, and then amplify on a current the elements DD1.4 included in parallel — DD1.6. To stabilize target tension of the power supply, duration of an impulse during regulation decreases." Shortens" impulses the VT1 transistor. Opening every period operation of the generator, he compulsorily establishes low level on an element DD1.3 entrance. This condition is kept till the end of the next period by the discharged C11 condenser.

On transistors VT2, VT3 is executed by p the powerful amplifier of the current providing forced switching of the switching VT4 transistor. Tension charts on basic elements of the power supply during its start are shown on fig. 2. When the VT4 transistor is open, the current proceeding through it and a winding of the I T1 transformer, linearly accrues (fig. 2,6). Pulse tension from the sensor of a current of R11 via the R7 resistor moves on base of the VT1 transistor. To exclude false opening of the transistor, emissions of a current are smoothed by the C12 condenser. The first after start some periods instant tension on the basis of the VT1 transistor remains less tension of opening of U6э откр * 0,7 In (fig. 2, in). As soon as instant tension during the next period will reach a threshold 0,7 In, the VT1 transistor will open that, in turn, will lead to closing of the switching VT4 transistor. Thus, the current in a winding of I, so, and in loading cannot exceed some value which has been in advance defined by resistance of the R11 resistor. It provides protection of the power supply against an overload on a current. Phasing of windings of the T1 transformer is established to p by

such that during an open condition of the VT4 transistor VD7 and VD9 diodes are closed by return tension. When the switching transistor will be closed, tension on all windings changes a sign and increases until these diodes will not open. Then the energy which has been saved up during an impulse in a magnetic field of the T1 transformer, goes on a charging of condensers of the target C15 filter — С17 and the C9 condenser. Let's notice that as phasing of windings by II and III coincides, tension on the C9 condenser in a mode of stabilization of target tension is also stabilized irrespective of value of entrance tension of the power supply.

the Regulating element of the power supply — DA2 Kr142en19a chip. When tension on an operating conclusion of 1 chip will reach 2,5 In, through it and via radiating diode оптрона the current increasing with growth of target tension starts to proceed. The phototransistor оптрона opens, and the current proceeding through R5, R7 and R11 resistors, creates on them the power failure which is also increasing with growth of target tension. Instant tension on the basis of the VT1 transistor, equal to the power failure sum on the R7 resistor and the sensor of a current of R11, cannot exceed 0,7 Century. Therefore at increase in a current of the phototransistor оптрона constant tension on the R7 resistor increases and the amplitude of a pulse component on the R11 resistor decreases that, in turn, occurs only because of reduction of duration of an open condition of the switching VT4 transistor. If duration of an impulse decreases, the "portion" of energy which is pumped over every period by the T1 transformer in loading is reduced also.

Thus if target tension of the power supply less nominal rate, for example, during its start, duration of an impulse and the energy transferred to an exit, are maximum. When target tension will reach nominal level, there will be a feedback signal owing to what duration of an impulse will decrease to value at which target tension is stabilized. If for any reasons target tension increases, for example, at sharp reduction of a current of loading, the feedback signal also increases, and duration of an impulse decreases up to zero and target tension of the power supply comes back to nominal rate.

On a chip of DA1 is executed by p knot of start of the converter. Its appointment — to block work of knot of management, if supply voltage less than 7,3 Century. This circumstance is connected with that the switchboard — the field IRFBE20 transistor — not completely opens at tension on a lock less than 7 Century

Knot of start works as follows. At turning on of the power supply the C9 condenser starts to be charged via the R8 resistor. While tension on the condenser makes units of volts, on an exit (a conclusion 3) chips of DA1 keeps low level and work of knot of management is blocked. At this moment DA1 chip on a conclusion 1 consumes a current 0,2 мА and power failure on the R1 resistor makes about 3 V.Primerno through 0,15... 0,25 about tension on the condenser will reach 10 In, at which tension on a conclusion of 1 chip of DA1 to equally threshold value (7,3 In). On its exit there is the high level allowing operation of the setting generator and knot of management. Converter start begins. At this time the knot of management eats the energy reserved in the C9 condenser. Tension on an exit of the converter will start to increase, so, it will increase and on a winding of II during a pause. When it becomes more tension on the C9 condenser, the VD7 diode will open and the condenser will be recharged further every period from an auxiliary winding of II.

Here, however, should pay attention to important feature of the power supply. The current of a charging of the condenser via the R8 resistor, depending on entrance tension of the power supply, makes 1... 1.5 мА, and consumption of knot of management in operating time — 10... 12 мА. It means that during start the C9 condenser is discharged. If its tension decreases to threshold level of a chip of DA1, the knot of management will be switched off, and as in the switched-off condition it consumes no more than 0,3 мА, tension on the C9 condenser will increase before repeated inclusion. Such occurs either at an overload, or at big capacitor loading when tension on an exit is not in time for starting time 20... 30 ms to increase to nominal rate. In this case it is necessary to increase C9 condenser capacity. By the way, the specified feature of work of knot of management allows the power supply to be in an overload mode beyond all bounds long as it in this case works in a pulsing mode, and operating time (start) in 8. . 10 times are less than time of a non-working condition. Switching elements thus do not heat up at all!

One more feature of the power supply — protection of loading against an overvoltage which occurs, for example, at refusal of any element in a feedback chain. In an operating mode tension on the C9 condenser — about 10 In and the stabilitron of VO1 is closed. In case of break in a feedback chain target tension increases over nominal rate. But together with it tension on the C9 condenser increases and at value about 13 VD1 In a stabilitron open. Process lasts 50... 500 ms during which the current through a stabilitron smoothly accrues, repeatedly exceeding its maximum value. Thus the crystal of an element heats up and melts — the stabilitron practically turns into a crossing point with resistance from units to several tens ohm. Tension on the C9 condenser decreases to the values insufficient for inclusion of knot of management. Target tension, having received depending on a loading current an increment in 1,3... 1,8 times, decrease to zero.

On the elements L2C19 is executed by p the additional filter reducing amplitude of pulsations of target tension.

to reduce penetration of high-frequency hindrances into a network, on an entrance is established the C1 filter — C3L1C4 — С7 which besides smoothes a pulse current consumed in operating time with frequency of 100 Hz.

Termorezistor RK1 (TR-10) has rather high resistance in a cold condition that limits a starting current of the converter at inclusion and protects rectifier diodes. In operating time the thermoresistor heats up, its resistance decreases several times and power supply efficiency practically does not influence.

When closing VT4 transistor on a winding of the I T1 transformer arises a tension impulse (on fig. 2, g it is shown by a dotted line on the first three periods of tension of UcVT4). which amplitude is defined by inductance of dispersion. That it to reduce, in the converter VD8R9C14 chain is established. It eliminates danger of breakdown of the switching transistor and reduces requirements for the maximum tension on its drain that increases reliability of the converter as a whole.

the Power supply is executed by p generally on standard domestic and import elements, except for uterine products. Throttles of L1 and L2 are reeled up on rings К10x6x4,5 from пермаллоя by MT 140. Magnitoprovoda at first isolate one layer лакоткани. Each winding reel up PETV 0,35 wire a round to a round in two layers on the half of a ring, and between windings of a throttle of L1 there should be a gap not less than 1 mm. Windings of a throttle of L1 contain on 26 rounds, and L2 throttle — on seven rounds, but in eight conductors everyone. The reeled-up throttles impregnate with BF-2 glue and dry at temperature near 60°С.

the Transformer — the main and most responsible detail of the power supply. Reliability and stability of operation of the converter, its dynamic characteristics and work depends on quality of its manufacturing in an idling and overload mode. The transformer is executed on ring К17x10x6,5 from пермаллоя МП140. Before winding магнитопровод isolate two layers лакоткани. A wire stack densely, but without a tightness. Each layer of a winding coat with BF-2 glue, and then wind to a lakotkanye.

of the First reel up a winding of I. It contains 228 rounds of a wire of PETV 0,2... 0,25, reeled up a round to a round in two layers between which one layer лакоткани is laid. A winding isolate two layers лакоткани. Following reel up a winding of III. It contains seven rounds of a wire of PETV 0,5 in six conductors, distributed evenly on ring perimeter. Over it stack one layer лакоткани. And at last, the last reel up a winding of II, containing 13 rounds of a wire of PETV 0,15... 0,2 in two conductors which evenly stack on ring perimeter with some tightness for a dense prileganiye to a winding of III. After that the ready transformer wind with two layers лакоткани, coat outside with BF-2 glue and dry at temperature 60°С.

On a place of the VT4 transistor can apply another with admissible tension on a drain not less than 800 In and the maximum current 3... 5 And, for example, BUZ80A, КП786А, and on a VD8 diode place — any high-speed diode with admissible return tension not less than 800 In and a current 1... 3 And, for example, FR106.

the Power supply is executed by p on a payment in the sizes of 95x50 mm and thickness of 1,5 mm. In corners of a payment and in the middle of the long parties six openings through which a payment screw on a heat-conducting path are located. On the one hand payments are soldered the VT4 transistor and the VD9 diode by flanges outside, and with another — other details are established. For reduction of the sizes of a payment all elements, except condensers C8, С9, chips of DD1, the R9 resistor, the transformer and оптрона, are established vertically that their maximum height over a payment did not exceed 20 mm.

the Heat-conducting path connect p to the general point of condensers C1 and С2. In this case the power supply is better for connecting to the three-contact socket with grounding. The specified measures allow to reduce hindrances radiated by the converter considerably.

a converter Heat-conducting path — a P-shaped bracket in length 95, width 60 and height of 30 mm, bent from sheet aluminum in thickness not less than 2 mm. The converter establish on "bottom" of this "trough" metal flanges of the elements VT4 and VD9 down and draw MZ screws through openings in a payment. Flanges isolate previously heat-conducting laying, for example, firms of "Nome game", "Bergkvist", or as a last resort mica the in thickness of 0,05 mm. Thus, structurally the converter appears as though in the metal casing protecting it from mechanical influence. For reliability increase a payment of the converter it is desirable for p to cover

with 2 — 3 varnish coats for an exception of probability of breakdown at the increased humidity of environment.

If all elements of the power supply are serviceable, correctly made and connected by p according to the circuit, in adjustment it is not difficult. Parallel to the R10 resistor connect an oscillograph. To the C9 condenser in the corresponding polarity connect the laboratory power supply, for example, B5-45, with the established maximum current no more than 15. . 17 мА also start to increase slowly tension, since zero. At tension 9,5... 10,5 In on an exit of a chip of DA1 tension of the logic unit is established, the setting generator turns on and on the screen of an oscillograph there should be rectangular impulses with frequency about 100 kHz and porosity about 2 (fig. 2, and). Farther to increase tension does not follow, as at value about 13 In VD1 stabilitron can open. The current consumed by knot of management, should not exceed the established maximum. If now to reduce supply voltage, at 7,2... 7,6 In generation will disappear. It means that the knot of management of the converter works correctly.

connect Further loading to an exit of the converter resistance 4... 5 Ohm and capacity 10... 15 W, and on an entrance submit tension from the second laboratory B5-49 power supply and at the working knot of management start to increase entrance tension. At first establish it at level 7. . 10 In and an oscillograph check correctness of connection of windings of the T1 transformer. Besides, supervise a tension form on a VT4 transistor drain (fig. 2, g), and the voltmeter check tension on a converter exit. At entrance tension 150... 170 In tension on an exit reaches 5 In and it is stabilized. After that the power supply of knot of management disconnect and continue to work at one entrance. Further increase of entrance tension should lead to reduction of width of the managing director of an impulse (fig. 2, and) which also should be supervised on the R10 resistor. Further at entrance tension 200 In increase a loading current (but no more than 7 And) and fix its value at which target tension of the converter starts to decrease. Esland at a current to 7 And it it is not possible to make, increase resistance of the R11 resistor. As a result of adjustment its face value should be established such, that at a current of loading 6,5... 7 And and minimum admissible entrance tension target tension of the converter starts to decrease. On it adjustment of the power supply comes to an end.

At bad quality of winding of the T1 transformer increase tension "emissions" on the transistor \l "4 that can become the reason of unstable operation of the power supply and even breakdown of the switching transistor.

If is necessary for p a source with other target tension, it is necessary to make the following: to change resistance of resistors R13, R14, considering that threshold tension of a chip of DA2 is equal 2,5 In; to change in direct ratio number of rounds and in inverse proportion section of conductors of a winding of III; to pick up the VD9 diode and C15 condensers — С17, С19 on the corresponding tension; to establish the R16 resistor with resistance (in ohms), R16=100 (UBblx-4) calculated on a formula.

during adjustment and work with the converter remember that its elements are under a high voltage, life-threatening. Be attentive and careful!

!>