RU2301438C1 - Secondary power supply - Google Patents

Abstract

FIELD: electric energy transformation technologies.

SUBSTANCE: secondary power supply belongs to group of reverse drive transformers with pulse-width modulation based control over stabilization of output voltage. Device contains force transformer (3) with primary winding, accumulating energy from primary source (7), secondary windings for transferring energy to load (4) and creating reverse connection voltage, commutation element (2), current indicator in form of current transformer with active load, generator with pulse duration control input, controlling the open state of commutation element (2), comparison device (5), outputting signals for pulse-width modulated output signals of generator (1) and support voltage element (stabilitron) (12).

EFFECT: ensured serviceability of secondary power supply with stabilization of load voltage in broad range of voltage values of primary supply.

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Description

The invention relates to the field of conversion of electrical energy.

The closest in technical essence to the claimed device is a secondary power source (see Patent RU 2095848, class G05F 1/56, 1/571 of 11/10/97, published in BI "Inventions" No. 31 for 97, p. 500 ), containing a rectangular pulse generator, connected to the input of the switching element by the output, the first output of which is connected to the first end of the primary winding of the power transformer, the secondary windings of which are connected to the load and the comparison device, the output of which is connected to the generator input. The device described above is taken as a prototype of the claimed device.

The disadvantage of the prototype is the need to use a special control chip of the switching element, which cannot ensure the operability of the secondary power source for some application conditions, in particular when the output voltage of the primary power source is in the range 4.5 ... 7.5 V.

The task at hand is the creation of a secondary power source. The technical result is to ensure operability in a wide range of voltage values of the primary source.

The technical result is achieved by the fact that the secondary power source contains a square-wave pulse generator, connected to the input of the switching element by the output, the first output of which is connected to the first end of the primary winding of the power transformer, the secondary winding of which is connected to the load, a comparison device. What is new is that a current transformer has been introduced, the first end of the primary winding of which is connected to the second end of the primary winding of the power transformer, and the second end to the first output of the primary power source, the second output of which is connected to the second output of the switching element, the first end of the secondary transformer winding current is connected to the first terminal of the first resistor and the first input of the comparison device, the second input of which is connected to the first terminals of the second resistor, capacitor and the first th power transformer, a second end which, through a series connected diode and a zener diode connected to the second terminals of the capacitor, the second resistor, the first resistor and the second end of the secondary winding of the current transformer, the comparator output is connected to the input of the generator of rectangular pulses of the feedback secondary winding.

The block diagram of the inventive secondary power source is shown in figure 1. Figure 2 shows the electrical schematic diagram of one of the possible options according to the invention.

The device contains a rectangular pulse generator 1, the output of which is connected to the input of the switching element 2, and its first output is connected to the first end of the primary winding of the power transformer 3. The primary end of the current transformer 6 is connected to the second end of the primary winding of the power transformer 3, its second end the primary winding is connected to the first output of the primary power source 7, and its second output is connected to the second output of the switching element 2. One of the secondary windings of the power circuit 3 sformatora its pin through a diode 13 is connected to a load, - a parallel resistor 4 and a capacitor 14; the other secondary winding (feedback winding) through the diode 11 and the zener diode 12 connected in series is loaded on the resistor 9 and the capacitor 10 connected in parallel. The secondary transformer winding is loaded on the resistor 8. The resistor 8 and resistor 9 connected in series with the capacitor 10 connected in parallel to it to the inputs of the comparison device 5, the output of which is connected to the input of the generator 1. The supply voltage to the generator 1 and the comparison device 5 is supplied from the outputs of the primary power source 7.

As the generator 1, any known oscillator circuit having the ability to control the output signal can be used. The generator 1 of the power source, according to the scheme of figure 2, is made on two elements of the "Schmitt trigger" chip 1526TL1 (you can use analogues 564TL1, 561TL1); resistors 16, 17, diode 15 and capacitor 18 are time-consuming elements (set the duration of the "high" and "low" signal level at the output of the generator 1). The switching element 2 of the secondary power source of the embodiment according to FIG. 2 is made on the 1526LA10 microcircuit (564LA10, 561LA10 can be used), in which there are two logic elements 2I-NOT 21, 22, at the output of each of them an open drain CMOS transistor with maximum current up to 100 mA and maximum dissipation power up to 100 mW (resistance in open state ≈1 Ohm); To reduce the resistance of the switching element in the open state, parallel connection of both elements 21, 22 of the microcircuit is used. The comparison device 5 of the variant of figure 2 is made on a bipolar n-p-n transistor 23, the collector of which is connected to the positive power pole - point 27 through the load resistor 24; the output of the comparison device 5 is a common connection point of the collector of the transistor 23 and its load - resistance 24; the input of the comparison device 5 is the base-emitter junction of the transistor 23. The power leads of the microcircuits of the generator 1 and the switching element 2 are connected to points 27, 28 (27 - plus power, 28 - minus power). In the embodiment of figure 2, the diode 25 is used as a decoupling to prevent energy from being returned to the primary power source 7, accumulated by the inductance of the primary winding of the transformer 3 during the open state of the switching element 2, through its internal diode connected between the drain of the transistor (output of the switching element) and the plus power of the chip 1526LA10 (not shown in figure 2); the capacitor 26 acts as a damper, reducing the amplitude of the pulse at the output of the switching element 2, due to the energy accumulated in the dissipation inductance of the primary winding of the power transformer 3.

The secondary power source operates as follows. In the initial position, when the primary power source 7 is turned off, in the serial electric circuit: the primary winding of the current transformer 6, the primary winding of the power transformer 3 and in the switching element 2, the electric current is zero; capacitors 10 and 14 are discharged; generator 1 does not work (there are no electrical signals at its output). When the primary power source 7 is connected, the generator 1 starts to work, giving out to the input of the switching element 2 a sequence of pulses leading to the periodic alternation of its two states: open and closed. Thus, the signal at the output of the generator 1 has two phases that define two states of the switching element. In the open state phase of the switching element 2, the duration of T _p , to the primary winding of the power transformer 3 through the primary winding of the current transformer 6 and the switching element 2 is applied the output voltage U _{1 of the} primary power source 7. This leads to the appearance of current in the serial circuit: the primary winding of the transformer current, primary winding of the power transformer, switching element, primary power source. The current in the primary winding of the power transformer 3 from the moment of switching the switching element 2 to the open state increases almost linearly, reaching the maximum value I _max by the end of the open state phase, defined by the expression:

where U ₁ is the voltage value of the primary power source;

L ₁ - inductance of the primary winding of the power transformer;

T _p - the duration of the phase of the open state of the switching element.

Expression (1) is valid for sufficiently small values of the active resistance of the primary winding of the power transformer and the switching element in comparison with the value determined by the ratio of the inductance L ₁ to the duration T _{p of} the open state phase of the switching element (one of the main requirements for the correct design of such secondary power sources ) The energy stored in the inductance of the primary winding of the power transformer is proportional to the square of the current value and is determined by the well-known expression:

The inductance of the primary winding of the current transformer should be much less than the inductance of the primary winding of the power transformer, while its effect on the process of energy storage in the power transformer can be neglected. After the pulse switching of the switching element to the closed state during T _n, the current path in the primary winding of the power transformer 3 is interrupted, the energy stored in it is transmitted through the secondary winding and diode 13 to the load - resistor 4 and capacitor 14, and partially through the feedback winding to elements: diode 11, zener diode 12, resistor 9 and capacitor 10. In the absence of control signals at the input of generator 1, the energy stored in the primary winding of the power transformer must be greater than the nominal value. The process of accumulation and transfer of energy to the load is described in the literature on switching power supplies, for example [1] B.Yu. Semenov. "Power Electronics". SOLON-R, Moscow, 2001, pp. 216-227. The relationship between the parameters of the load and the secondary power source is determined by the expression:

where U _n - voltage at the load (resistor 4);

R _n - the value of the load resistance;

- коэффициент заполнения;

- fill factor;

U ₁ is the voltage value of the primary power source;

f is the conversion frequency;

k is the transformation coefficient (the ratio of the number of turns of the secondary winding of the power transformer 3 to the number of turns of the primary winding).

The process of transferring the stored energy by the inductance of the primary winding of the power transformer 3 in phase T _p to the load (resistance 4) takes place with the participation of the charge of the capacitor 14 (connected in parallel to load 4) in the phase T _n and its discharge throughout the entire period T = T _p + T _n following the signals at the input of the switching element 2. This process can be described by the following equations:

where I _1max is the current value in the primary winding by the time the phase of the conductive state of the switching element 2 ends;

C is the value of the capacitance of the filter capacitor 14;

U _i-1 , U _i is the voltage value across the capacitor 14 at time instants corresponding to (i-1) T and iT;

Δq _zar , Δq _bit - changes in the charge of the capacitor 14, due to the transfer of energy from the primary winding and the discharge current at the load resistance 4, respectively;

- среднее значение напряжения на нагрузке 4.

- the average value of the voltage at the load 4.

In the transient mode of operation of the secondary power source, the voltage across the capacitor 14 and, accordingly, on the load 4 gradually increases due to portions of energies transmitted with each period of the output signals of the generator 1 from the primary winding of the transformer 3. From the analysis of expressions (4), (5) , (6) follows:

- when the energy W accumulated in the primary winding is constant, the charge increment Δq _zar and, accordingly, the voltage of the capacitor 14 decreases as the average voltage on it increases;

- the discharge of the capacitor 14 Δq _bit due to the current supplied to the load 4 for the period T, increases with increasing average voltage across the capacitor.

In transition mode, Δq _zar > Δq _bit .

The steady state is characterized by the termination of the growth of the average voltage across the capacitor 14 and, accordingly, at the load 4. In this case, the equality of changes in charges:

When replacing in the expression (4) the factor C (U _i -U _i-1 ) by the right side of equality (7) we get:

Equality (8) also follows from the principle of conservation of energy.

In the steady state, the average load voltage U _cp can be determined from formula (8) taking into account formula (1):

From the expression (9) it can be seen that the average voltage at the load is determined by the values: voltage of the primary power source U ₁ , the duration of the phase of the open state of the switching element T _p , load resistance R _n , the inductance of the primary winding of the power transformer L ₁ and the period of the signals T on the control input switching element. If the values of T _p and T are constant (there are no control signals at the input of the generator 1), the voltage at the load will change when the voltage of the primary power source and the load resistance change. The voltage at the load is stabilized by changing the duration T _p - pulse-width modulation (PWM), by applying to the control input of the generator 1 pulse signals from the output of the comparison device 5. At the front of the pulse signals at the input of the generator 1, the phase of the signal determining the open state of the switching element, sets the signal level corresponding to the closed state of the switching element (phase T _n ). The duration of the phase T _n is determined by the timing elements of the generator 1. After the end of the phase T _n , a new cycle of generating the signal of the phase T _p begins, the energy is accumulated in the inductance of the transformer primary winding and transferred to the load. The pulse signal at the output of the comparison device 5 is formed at the moment when the alternating voltage at its input reaches a certain (threshold) value of U _then . The voltage at the input of the comparison device 5 U _in is determined by the sum of the voltages at the resistors 8, 9.

Where

k _dt is the transformation coefficient of the current transformer 6;

R _dt is the value of the resistor 8 connected to the secondary winding of the current transformer 6;

U _OS - the amplitude of the voltage on the feedback winding of the power transformer 3 that occurs when the key element 2 is locked;

U _d - voltage drop across the diode 11 during the flow of direct current;

U _article - stabilization voltage of the zener diode 12;

U ₁ - voltage of the primary power source 7;

i ₁ (t) is the time dependence of the current in the serial circuit — primary source 7, primary windings of current transformers 6 and power transformer 3, switching element 2;

W _OS , W ₂ - the number of turns of the feedback winding and the secondary winding of the power transformer 3;

U ₂ - the value of the amplitude of the voltage at the terminals of the secondary winding of the power transformer 3 in the phase of the closed state T _n switching element 2.

Depending on the selected parameters of the secondary power source, namely

- the range of values of the output voltages of the primary power source 7;

- inductance of the primary winding of the power transformer 3 (L ₁ );

- the repetition period of the signals at the input of the switching element 2 and the phase duration T _n ;

- the transformation coefficient of the current transformer 6 and the resistance value 8 of the load of its secondary winding;

- the ratio of the number of turns of the windings of the power transformer 3 (W _OS , W ₂ );

- the value of the threshold voltage of the comparison device 5,

three characteristic operating modes are possible.

(T_по - длительность фазы открытого состояния коммутирующего элемента 2 при отсутствии сигнала управления на входе генератора 1) на выходе устройства сравнения отсутствуют сигналы управления; установившееся напряжение на нагрузке определяется выражением (3).At

(T _by is the duration of the open state phase of the switching element 2 in the absence of a control signal at the input of the generator 1) there are no control signals at the output of the comparison device; steady-state voltage at the load is determined by the expression (3).

сигнал на выходе устройства сравнения 5 и, соответственно, на входе генератора 1 появляется через время T_п от момента начала перехода коммутирующего элемента 2 в открытое состояние.At

the signal at the output of the comparison device 5 and, accordingly, at the input of the generator 1 appears after a time T _p from the moment the switching element 2 starts to open.

что обеспечивает постоянство передаваемой энергии в нагрузку и ограничивает ток коммутирующего элемента на безопасном уровне (определяется формулой (2)). Однако для этого случая стабильность напряжения на нагрузке будет невысокая, так так при постоянстве передаваемых порций энергии в нагрузку период их следования может изменяться в зависимости от значений T_п. Более высокая степень стабилизации вторичного напряжения (на нагрузке) достигается для режима, при котором:In this mode, for all values of the voltage of the primary power source U _1, the current amplitude in the primary winding of the power transformer is limited to

which ensures the constancy of the transmitted energy to the load and limits the current of the switching element at a safe level (determined by formula (2)). However, for this case, the voltage stability at the load will be low, so if the portions of energy transferred to the load are constant, the period of their repetition can vary depending on the values of T _p . A higher degree of stabilization of the secondary voltage (at load) is achieved for the mode in which:

for the entire operating voltage range of the primary power source. The formation of the output signal of the comparison device 5 occurs at the moment when the equality:

Hence the value of the voltage at the load U ₂ is equal to:

выражение (16) можно в первом приближении представить в виде:For cases when U _Art ≫U _then considering that

expression (16) can be represented as a first approximation in the form:

Providing the required value of the output voltage of the secondary power source is achieved by choosing a zener diode 12 with the value of the stabilization voltage and the ratio of the number of turns of the secondary winding W ₂ and the feedback winding W _{os of the} power transformer, satisfying condition (17).

транзистор заперт, потенциал на его коллекторе и, соответственно, на входе элемента 19 близок к уровню логической "1", элемент 19 выполняет функцию инвертора. Работа генератора определяется процессом заряда (перезаряда) конденсатора 18 по цепи - выход элемента 20, конденсатор 18, резистор 16 в параллель с диодом 15, резистор 17, выход элемента 19. В фазе формирования T_п при достижении суммы напряжений на резисторах 8 и 9, приложенной к базо-эмиттерному переходу транзистора 23, значения, превышающего 0.5...0.6 В, его коллекторный ток резко увеличивается, а потенциал коллектора и входа элемента 19 уменьшается, что приводит к изменению напряжения на выходе элемента 19 и входе элемента 20 с уровня "0" до "1", а на выходе элемента 20 (выход генератора) напряжение изменяется с уровня "1" на "0". Таким образом, заканчивается фаза T_п и начинается фаза T_н, коммутирующий элемент переходит в закрытое состояние, ток в первичной обмотке спадает до 0, и, соответственно, уменьшается напряжение на резисторе 8 (уменьшая сумму напряжений U_бэ), транзистор 23 запирается, потенциал на его коллекторе и на входе элемента 19 увеличивается до уровня "1". Энергия, накопленная в первичной обмотке силового трансформатора к концу фазы T_п передается во вторичную обмотку, подзаряжая конденсатор 14, и частично в обмотку обратной связи через стабилитрон 12 и диод 11, заряжая конденсатор 10 до значения, равного разности напряжений

. В фазе T_н происходит перезаряд конденсатора по цепи выход элемента 19 (с высоким уровнем напряжения), резистор 17, диод 15, параллельно подключенный к резистору 16, конденсатор 18, выход элемента 20 (с низким уровнем напряжения). По достижению потенциала в точке соединений выводов: конденсатора 18, резистора 16, диода 15 и выхода элемента 19 уровня, превышающего порог переключения элемента 19, потенциал на его выходе изменится с высокого на низкий, а на выходе элемента 20 - с низкого уровня на высокий (конец формирования фазы T_н), начинается новый цикл формирования выходного сигнала генератора 1 с фазы T_п. В дальнейшем процесс повторяется.In the device according to figure 2, the generator is made according to the multivibrator scheme on two inverters with RC timing elements. Two-input elements “2I-NOT” 19, 20, microcircuits 1526ТЛ1 or 564ТЛ1 (“Schmitt trigger”) are used as inverters. The resistors 16, 17, the capacitor 18 and the diode 15 set the duration of the phases T _by and T _n . The diode, the shunt resistor 16, increases the recharge rate of the capacitor 18 in the phase T _n (phase "zero" state at the output of the generator), reducing its duration compared with the phase T _on . This allows you to get the initial duty cycle γ, greater than 0.5, to compensate for its decrease (by adjusting the feedback circuit) at maximum voltages of the primary power source 7. Feedback in the generator is carried out through a capacitor 18 connecting the output of the generator (output of element 20) with the input of element 19, its second input is connected to the output of the comparison device made on the bipolar npn transistor 23, the collector of which, through the resistor 24, is connected to the power bus with a positive potential through the diode 25. З Achen threshold voltage of the comparator equal to the voltage of the pn junction forward-biased base-emitter junction of transistor 23 _since U = 0.5 ... 0.6 V. With values base-emitter voltage

the transistor is locked, the potential at its collector and, accordingly, at the input of element 19 is close to the logic level "1", element 19 performs the function of an inverter. The operation of the generator is determined by the charge (recharge) process of the capacitor 18 in the circuit - the output of the element 20, the capacitor 18, the resistor 16 in parallel with the diode 15, the resistor 17, the output of the element 19. In the formation phase T _p when the sum of the voltages across the resistors 8 and 9 is reached, applied to the base-emitter junction of the transistor 23, a value exceeding 0.5 ... 0.6 V, its collector current increases sharply, and the collector and input potential of the element 19 decreases, which leads to a change in voltage at the output of the element 19 and the input of the element 20 from the level " 0 "to" 1 ", and the output e 20 (generator output), the voltage changes from level "1" to "0". Thus finishes the phase T _f and phase T _n starts, the switching element switches to a closed state, the current in the primary winding falls to 0, and thus decreases the voltage across the resistor 8 (by reducing the amount of voltages U _BE), a transistor 23 is locked, the potential on its collector and at the input of element 19 increases to level "1". The energy accumulated in the primary winding of the power transformer at the end of phase T _p is transferred to the secondary winding, recharging the capacitor 14, and partially to the feedback winding through the zener diode 12 and diode 11, charging the capacitor 10 to a value equal to the voltage difference

. In the phase T _n , the capacitor is recharged through the circuit, the output of the element 19 (with a high voltage level), the resistor 17, the diode 15, connected in parallel to the resistor 16, the capacitor 18, the output of the element 20 (with a low voltage level). Upon reaching the potential at the connection point of the terminals: capacitor 18, resistor 16, diode 15 and the output of the level element 19, which exceeds the switching threshold of the element 19, the potential at its output will change from high to low, and at the output of element 20, from low to high ( the end of the formation of the phase T _n ), begins a new cycle of formation of the output signal of the generator 1 with phase T _p . In the future, the process is repeated.

According to the scheme according to figure 2, experimental samples of a secondary power source were manufactured and tested; test results confirmed their performance; voltage instability at load no more than 1%. Two valves of the 1526TL1 microcircuit were used as elements 19, 20, a 1526LA10 microcircuit, transistors 23-2T399A, a zener diode 12-2C156A, diodes 2D522B were used as elements 21, 22, and a current transformer was made on a M2000-NM1 K5 × 3 × 1.5 ferrite core , the power transformer is made on a ferrite core M2000-NM1 K7 × 4 × 2 with an air gap.

Claims (1)

A secondary power source containing a square-wave pulse generator connected to an input of a switching element with a first output connected to the first end of the primary winding of the power transformer, the secondary winding of which is connected to the load, a comparison device, characterized in that an additional current transformer is introduced, the first end of the primary the winding of which is connected to the second end of the primary winding of the power transformer, and the second end to the first output of the primary power source, the second the stroke of which is connected to the second output of the switching element, the first end of the secondary winding of the current transformer is connected to the first terminal of the first resistor and the first input of the comparison device, the second input of which is connected to the first terminals of the second resistor, capacitor and the first end of the feedback winding of the power transformer, the second end of which through a series-connected diode and a zener diode connected to the second terminals of the capacitor, the second resistor, the first resistor and the second end of the secondary trans current formatter, the output of the comparison device is connected to the input of the rectangular pulse generator.

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