SU752665A1 - Controllable voltage converter - Google Patents

Description

one

The invention relates to electrical engineering, in particular to stabilized voltage transducers, and can be used in automation and computer technology in radioelectric power supply units.

Devices are known that contain a key element, a master oscillator, a power transformer, a control circuit, and a galvanic isolation transformer in a feedback circuit (I, 2.

The disadvantages of these devices include the possibility of the appearance of overvoltages at the output when the load is switched, as well as when the power is turned on. This is due to the presence in the feedback circuit of an isolation transformer device, the output voltage of which disappears both when the squall pulses at the output of the control circuit are equal to zero and equal to one. This disrupts the lifespan of the control circuit and reduces the reliability of these devices.

The closest in technical essence to the present invention is an adjustable transistor converter controlled by a clock generator 3. This adjustable constant-voltage transistor converter is 30

It has a clock generator, it has galvanically developed input and output. A power transformer is located at the input and output circuits, and an output circuit is galvanically connected to the output circuit to control the fill ratio of the pulses in the starting semi-circular circuit. The latter acts on one of the several transistors located in the input circuit depending on the result of the comparison of the triangular and constant voltages in the differential amplifier. The voltage emulsions generated through a comparison through a transformer affect the clock generator by changing the duty cycle of its output signals. The power of this device is the presence of long-lasting overvoltages at the output of the converter when the load is switched, as well as when the power supply P1 is turned on, which violates its stable operation and reduces the reliability.

This disadvantage is due to the following. In the established mode of operation, the input of the transformer of galvanic uncoupling receives a signal from the output of the threshold device, the duty cycle of which is determined by mol: tentam equal to the reference voltage and the sum of the output and sawtooth voltage generated by the sawtooth generator. The voltage removed from the output winding of the galvanic isolation transformer acts through the actuator transistor on the clock generator, thereby determining the open and closed state of the key element.

With a sudden switching of the load current, for example, with a discharge, the energy accumulated in the storage choke is transferred to the load, causing an output voltage surge. If the amplitude of this surge exceeds the amplitude of the sawtooth voltage, a voltage drop of long duration, equal to the duration of the transient process, occurs at the output of the threshold device. If the time constant of the galvanic isolation transformer is less than the transitional process time at the output of the converter, which is usually done in practice in order to reduce the size and weight of the galvanic isolation transformer, its core is thick, the pulses on its output winding disappear, which leads to operation of the key element with the maximum fill ratio determined by the clock generator. As a result, the voltage at the output of the converter rises to a value determined by the transformation ratio of the power transformer and the value of the supply voltage, and remains so indefinitely for a long time.

When the power is turned on, if the rate of increase of the output voltage exceeds the rate of increase of the voltage of the onor source of the threshold device, the impulses at the output of the transformer of its transformer may also disappear, which leads to unstable and unreliable operation of the device.

The aim of the invention is to increase the stability of the converter and to reduce the size and weight of the isolation transformer.

The goal is achieved by the fact that in a regulated voltage converter with galvanic isolation of input and output, the content of a key element, the input of which is connected to the output of a clock generator, a power transformer, the primary winding of which is connected in series with the key element a secondary rectifier with a filter is connected to the secondary winding, a power supply node, the input of which is connected to the output of the converter and the sawtooth voltage former, and the output is connected to a nervous its transformer, the secondary winding of which is connected to the control of the clock generator, the power transformer is equipped with an additional winding, one output of which is connected to the output of the converter, and the second output through an additional diode connected to the first output of the primary winding of the transformer, the second the output of which is connected through the output of the threshold node with the first output of the additional winding of the transformer. This allows the occurrence of overvoltage at the output of the converter to decouple the switching of the transformer with the frequency of the clock generator, even with a constant signal at the output of the threshold device.

As a result, the fill factor of the pulses of the key element decreases to almost zero, which means that the instantaneous perturbation and reduction of the output voltage to the nominal value is instantaneous. This significantly increases the stability of the converter, improves its reliability and speed.

In addition, the duration of the pulses transmitted by the isolating transformer in the proposed device is about 10 times less than in the known device, which makes it possible to significantly reduce the size and mass of the isolating signal.

transformer.

The drawing shows a functional diagram of the device.

Adjustable voltage converter contains key element 1, input

which is connected to the output of clock geiepaTOpa 2, power transformer 3, the primary winding 4 of which is connected in series with the key element 1 in the circuit of the primary source of the pitapi, and

The secondary winding 5 is connected to a rectifier 6 with a filter 7, and a threshold node 8, the input of which is connected to the output of the converter and the former 9 of the sawtooth voltage, and the output is connected to

the primary winding 10 of the isolation transformer 11, the secondary winding 12 of which is connected to the control input of the clock generator 2. The power transformer 3 is provided with an additional winding

13, one output of which is connected to the output of the converter, and the second output through an additional diode 14 is connected to the first output of the primary winding 10 of the isolating transformer 11, the second output of which is connected to the output of the threshold node 8.

The proposed device works as follows.

In a steady state of operation, the voltage at the output of the clock generator 2 opens the key element 1 and a voltage is formed on the primary winding 4 of the power transformer 3. This voltage is transformed into the secondary winding 5 and through the rectifier 6 and the filter 7

is transmitted to the output of the converter. At the input of the threshold node 8, the output voltage of the converter and the sawtooth voltage generated by the sawtooth voltage generator 9 is summed up. The sum of these voltages is compared with the reference voltage of the threshold node 8.

During the time when

out +,

where f / out is the output voltage of the converter;

JV is the voltage amplitude at the output of the imager 9; Uon is the voltage of the reference source of the threshold node 8,

There is no voltage at the input of the output transistor of the threshold device 8, and it is closed. When a sawtooth voltage reaches, at which

Bb.x +,

A gate voltage is applied to the input of the output transistor of the threshold node 8, which opens the specified transistor. Since the output stage of the threshold node 8 is powered from the auxiliary winding 13 of the power transformer 3 through a supplementary diode 14, the voltage on which is in phase with the voltage on the primary winding 4 of the power transformer 3, a voltage is applied to the primary winding 10 of the isolation transformer 11, which is transformed into its secondary winding 12 and is applied to the control input of the clock generator 2. As a result, the voltage at the input of the key element 1 disappears and the latter closes after a time determined by the resorption time of minority carriers. In this case, an impulse is formed on the primary winding 19 of the isolation transformer 11, the duration of which is determined only by the turn-off time of the key element. During an abrupt commutation of the load, for example during a reset, the energy accumulated in the storage element of the filter 7 is transferred to the load, causing a sharp increase in the output voltage. If the amplitude of this transient process exceeds the range of the saw-tooth voltage, i.e.

,,

A long voltage drop occurs at the input of the output transistor of the threshold node 8, which opens the specified transistor. At the moment of formation at the output of the clock generator 2 of the next unlocking pulse, the key element 1 opens and a voltage is formed on the additional winding 13 of the power transformer 3, which is applied to the primary winding 10 of the isolation transformer 11, is transformed into its secondary winding 12 and is applied to the control input clock generator 2, turning off the last. As a result, a trigger pulse is formed at the input of the key element 1, the length of which is determined only by the speed of the control circuit. In this case, the key element 1 is open for a time determined by the total delay of the control circuit and the key element, which leads to a sharp decrease in the pulse factor of the key element 1 and the output voltage to decrease to the nominal value.

When the converter is turned on, if the rate of increase of the output voltage exceeds the rate of increase of the voltage of the reference source, the processes occurring in the converter are similar to those described above.

Thus, the proposed device allows switching of the isolation transformer at a constant signal at the output of the threshold device. At the same time, the fill factor of the pulses of the key element decreases almost to zero, resulting in an instant perturbation of the disturbance. This makes it possible to almost completely eliminate overvoltages at the output of the converter and thereby increase its stability.

work, allotment and speed.

In addition, the proposed device makes it possible to reduce dimensions II by about 10 times the mass of the isolation transformer. This circumstance is due to

The fact that the duration of pulses transmitted by the isolating transformer is equal to the delay time for switching off the key element, determined by the resorption time of minority carriers, the value of which is 0.1–1 µs. for modern powerful transistors. In the known device, the maximum duration of the pulses transmitted by the transmitting transformer is half the oscillation period of the clock generator, which, at a frequency of 50 kHz, is 10 microseconds. A reduction in the pulse duration by a factor of 10, as compared with the known device, makes it possible to decrease the cross section of the core of the transformer, and, consequently, its mass and dimensions.

These circumstances favorably distinguish the proposed device from the known one.

Claims (3)

1. US patent No. 3818306, cl. 321-2, 1974. 2. USSR Author's Certificate No. 433607, H 02M 3/335, 1974. 3. Forward Germany No. 2226689, cl. H 02 P 13/22, 1974.