RU2692466C1 - Quasi-resonance constant voltage converter with low pulsations of output voltage during operation in conditions of high negative temperatures - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to conversion equipment and can be used as a source of supply of LED lamps from AC rectifier, in operation under conditions of high negative ambient temperatures.

EFFECT: technical result consists in reduction of output ripple of output voltage/current transducer pulsation at negative temperature due to adjustment of voltage on transistor of current stabilizer, compensating pulsation, in compliance with ambient temperature, and use of increased power allocated on transistor of current stabilizer, for heating of output electrolytic capacitor.

1 cl, 6 dwg

Description

Technical field

A quasi-resonant DC / DC converter with low ripple output voltage refers to converter technology and can be used as a power source for LED luminaires from an AC rectifier, when operating in conditions of high negative ambient temperatures.

Prior art

The main source of electrical energy for lighting devices is the AC network. The power supply of LED lamps in most cases is carried out by a converter containing a diode rectifier. The main characteristic of current consumption by such a converter is the shape factor of the current consumed. The current regulatory documents impose strict requirements on LED lighting control devices in terms of the shape of the current consumed (power factor).

To meet the requirements of regulatory documents, a converter control method is used that provides a satisfactory form factor for the current consumed. Such a converter is called a power factor correction converter, or often simply a power factor corrector. A negative consequence of the application of this method will be increased output voltage ripple with the ripple frequency of the mains rectifier, causing current ripple of the LED load and light ripple.

The level of pulsation of the light flux is regulated by regulatory documents, with a tendency to toughen in the future, to ensure low pulsations of light, less than 5%, it is necessary to apply special measures.

Pulsations at the output of the converter with power factor correction are mainly determined by the size of the output capacitor, since the cut-off frequency of the feedback loop does not exceed (10-15) Hz, the equalizer does not work out higher frequencies, and the highest ripple frequency at the output is 100 Hz (double frequency of rectified mains voltage). Since the frequency of 100 Hz is quite low, a sufficiently large amount of output capacitance is required.

Output voltage ripple causes current ripple in the load. If the load is LEDs, then the ripple of current will be the ripple of the light flux of the LED lamp with the ripple frequency of the mains rectifier. Pulsations of the luminous flux and low-frequency illumination (below 400 Hz) increase fatigue and are harmful to human vision.

There is a solution when the first stage is a power factor corrector, and the second is either a flyback or LLC type output current regulator. The second stage has a cut-off frequency of the feedback loop of up to several kilohertz and performs pulsations with a frequency of 100 Hz at the output of the equalizer.

The disadvantage of this solution is increased complexity, high cost (we have two conversion stages instead of one) and large weight and size parameters.

A similar solution was used in the PMP8911 “High Eff 2Stage Univ Input Power Supply Transition Mode PFC LLC Resonant Conv Reference Design” test board developed by Texas Instruments) (USA) (http://www.ti.com/lit/df /slura79/slura79.pdf, 06/25/2018)

A pulsed opto-isolated stabilized DC source for an LED lamp with small ripple output current is known. (Patent RU 137169 U1, IPC H05B 37/00, published Jan. 27, 2014), in which small ripples of the output current are provided by a source of stable current at the field-effect transistor.

The disadvantage of this solution is that at high negative temperatures the internal resistance increases and the capacity of electrolytic capacitors used in the stabilized power supply decreases, which leads to an increase in the ripple of the output voltage of the stabilized power source beyond the limits compensated by the source of stable current and, as a result, to an increase in the ripple current LED load.

Known outdoor frost-resistant lamp (patent RU 2465687 C1, IPC H01L 33/00, published 10/27/12), in which the normal mode of operation of electrolytic capacitors at low temperatures is provided by a heater, controlled by a temperature-sensitive element.

The disadvantage of this solution is that at low temperatures there is a significant delay in turning on the LEDs until the power supply of the LEDs is heated.

A quasi-resonant DC / DC converter with zero voltage switching is also known (patent RU 139333 U1, Н02М 3/338, published April 10, 2014).

The disadvantage of this solution is that when using the converter as a power factor corrector and large negative temperatures, the ripple of the output voltage of the converter increases.

The decision on RU 139333 has the largest number of matching features and is taken as a prototype.

The technical result of the claimed solution is to quickly turn on the converter in the operating mode, with large negative ambient temperatures, reducing the output voltage / current ripple, increasing the operating parameters, and minimizing dimensions.

The result is achieved by automatically adjusting the voltage ripple compensation at the transistor current regulator, automatically heating and maintaining the temperature of the output electrolytic capacitor in the optimal operating limits in accordance with the ambient temperature, due to the use of increased power generated by the transistor.

Detailed solution description

The claimed solution is characterized by the following set of features:

Quasiresonant dc voltage converter with zero voltage switching, containing transformer primary winding connected to the first and second input terminals of the converter, first current sensor and power switch, the control input of which is connected to the controller output, one input of which is connected to the second input terminal of the converter, and input determining the zero voltage is connected to the first output of the control winding, while the secondary winding of the transformer is connected via a rectifying diode on the output capacitor connected to the output terminals of the converter, and the second terminal of the transformer control winding is connected to the converter input through a parallel-connected first resistor and capacitor and the connection point of the power switch and the first current sensor through a series-connected diode and second resistor, characterized in

that a transistor, a second current sensor, a temperature-sensitive element, a current stabilizer control circuit are additionally introduced, and the first terminal of the second current sensor’s resistor is connected to the common point of the output capacitor and the secondary winding of the transformer, the second terminal of which is connected to the negative output the converter connected to the third input of the current regulator control circuit, the gate of the transistor is connected to the first output of the current stabilizer control circuit , the first two inputs of which are connected to a temperature-sensitive element, the fourth input is connected to the common point of the resistor of the second current sensor and the source of the transistor, and the second output is connected to the auxiliary input of the controller, while the capacitor, transistor and temperature-sensitive element are in thermal contact with each other or installed with the possibility of heat exchange.

Brief Description of the Drawings

The solution is illustrated with the following graphics:

in fig. 1 shows the electrical circuit of the device;

in fig. 2 shows the voltage plots on the output capacitor (upper curve) and on the drain of the current regulator transistor (lower curve);

in fig. 3 shows the voltage plots on the output capacitor (upper curve) and on the drain of the current stabilizer transistor (lower curve) at a low negative temperature in the absence of a thermo-dependent element;

in fig. 4 shows the voltage plots on the output capacitor (upper curve) and on the drain of the current regulator transistor (lower curve) at low negative temperature with thermo-dependent feedback;

in fig. 5 - graphs of the ripple current coefficient, measured immediately after switching on at different ambient temperatures;

in fig. 6 - graphs of the ripple coefficient of the current, measured after heating the devices, at different ambient temperatures.

The explanations for the diagrams shown in FIG. 2, 3 and 4:

Upulse - the amplitude of the pulsations on the output capacitor;

Uc is the voltage on the output capacitor;

Uc media - the average voltage at the output capacitor;

Ump is the voltage on the current regulator drain;

Ump media - the average voltage on the transistor current regulator;

Ump max - the maximum voltage on the transistor current regulator;

Pulse Tr - Pulsation Span at the Current Stabilizer Transistor;

Upulz abd tempo - pulsation on the output condenser at low negative temperature;

Pulse rp temp - the amplitude of the pulsations on the transistor current regulator at a low negative temperature;

To ensure the required parameters of the LED lamp at negative temperatures, the original current regulator was added to the converter, which includes a control transistor 13, a current sensor 14, a temperature sensor 15 and a control circuit for a current stabilizer 16. At the same time, an electrolytic capacitor 7, a control transistor 13 and the heat-sensitive element 15 is arranged so as to ensure good thermal contact and good heat transfer among themselves.

The principle of the scheme. To reduce current ripple in series with the output of the quasi-resonant converter, a current stabilizer is included. The current stabilizer provides a constant load current with almost no ripple, while the voltage regulating element U - _{pulse mp} arises on the regulating element of the current stabilizer - transistor 13, coinciding in frequency and phase with the voltage ripple on the output capacitor 7 of the _pulse U converter (Fig. 2) and compensating for them .

Full ripple suppression is possible if the maximum voltage U _{mp max} on the regulating element of the current stabilizer transistor 13 is greater than or equal to the amplitude of the ripple voltage U _pulse on the output capacitor 7. In case of equality, the losses at the transistor will be minimal.

The maximum voltage U _{mp max} on the current regulator transistor is stabilized by the converter according to the feedback signal 16 ₆ -5 ₄ from the control circuit of the current stabilizer 16 to the controller 5.

Electrolytic capacitors, which have a significantly better ratio of capacitance to volume and mass, as well as lower cost, than other types of capacitors, are used as output capacitors in most converters. However, the characteristics of electrolytic capacitors are temperature dependent. At negative temperatures, the capacitance decreases and the internal resistance increases, if the temperature drops below the critical (about -25 ° C), then the internal resistance can increase 8-10 times, respectively, the voltage pulsations on the output capacitor 7 of the converter U _{pulse pulse temp} (Fig. 3 ) will increase by 8-10 times compared to the normal level of U _{pulse rate} .

When pulsation U is exceeded, the _{pulse is decelerating} , the _{Ump max} level stabilizes the current stabilizer and compensates only part of the output capacitor voltage ripple (shaded part U _{pulse in} Fig. 3) as a result of the voltage ripple at the converter output and the current ripple of the load current sharply increase.

The ripple of the load current at negative temperatures can be normalized in two ways: by heating the capacitor until its parameters normalize, or by increasing the maximum voltage U _{mp max} on the regulator element of the current stabilizer, the transistor.

To implement both methods of eliminating pulsations at the same time, a current stabilizer is added to the quasi-resonant converter (Fig. 1), which includes: a transistor 13, a current sensor 14, a temperature-sensitive element 15, a current stabilizer control circuit 16.

The control circuit of the current stabilizer 16 outputs a control signal 16 ₅ to the gate of the transistor 13, providing a given level of stabilized current and a given level of load current ripple, due to the full or partial compensation of the voltage ripple on the output capacitor U _pulse (Fig. 3). The transistor 13 is used to stabilize the load current. The voltage from the resistor of the current sensor 14 is proportional to the current flowing through the transistor 13, is fed to the input 16 ₄ of the control circuit of the current stabilizer 16. The temperature-sensitive element is connected to the inputs 16 ₁ 16 ₂ of the control circuit of the current stabilizer, according to the voltage level of the temperature-sensitive element corresponding to the temperature control 16, giving a signal from its output 16 ₆ to the input 5 _{4 of the} controller 5, adjusts the operation of the power factor corrector to maintain the drain-source voltage level of the transistor 13 to compensate for pulsations. The voltage of the drain-source of the transistor 13 is fed to the input 16 ₃ of the control circuit of the current regulator.

Voltage ripple compensation is possible if the output voltage ripple (U _pulse on the capacitor 7 does not exceed the drain-source voltage drop of the transistor 13 (U _{mp max} Fig. 3).

At normal temperature, the task of the control circuit is to stabilize the current and maintain the maximum efficiency of the converter, due to the minimum power loss.

Power loss at the field-effect transistor

P _mp = U _{mp cf.} * I _cm , where

U _{mp cp} is the effective drain-source voltage at the field-effect transistor

I _cm - stabilizer current.

At normal operating temperature, the control circuit of the 16 current stabilizer maintains the minimum required drain-source voltage level of the transistor 13 (U _{mp cp of} Fig. 2), which ensures the minimum losses on the transistor 13 and the maximum efficiency of the converter.

With a decrease in the temperature of the electrolytic capacitor 7, the _{amplitude of} the pulsation on it increases the U _{pulse omp temp} (Fig. 4). On the other hand, the voltage from the temperature-sensitive element with a decrease in temperature affects the control signal 16 ₆ in such a way as to increase the voltage on the transistor current stabilizer U _{mp max} (Fig. 4). The increased voltage on the current stabilizer transistor compensates for the increased ripple on the output capacitor.

By increasing U _{mp max} , the losses in the field effect transistor increase, and the efficiency of the converter decreases. The heat generated by the transistor 13 is used to heat the output capacitor 7 to the temperature of normalization of its parameters, for which the capacitor 7 transistor 13 is placed with the possibility of good heat exchange with each other and with a temperature-sensitive element. After some time required to warm up the output capacitor, its parameters return to normal and the voltage ripples on it decrease. The thermosensitive element 15 signals the temperature rise, and the control circuit 16, controlling the controller 5, controlling the current and the drain-source voltage drop of the transistor 13, reduces this voltage to the level corresponding to the temperature. With a further increase in temperature, the voltage drop in the drain-source of the transistor decreases to a minimum level, which ensures minimum losses at the field-effect transistor and maximum efficiency of the converter.

Thus, automatic regulation and minimization of the pulsations at the output of the power factor corrector are carried out over the entire operating temperature range.

On the basis of the proposed solution, the PSL95C-0.7-140 / 80-1 LED lamp power supply unit was manufactured and tested. For comparison, the power supply variant PSL95C-0.7-140 / 80-1 without a temperature-sensitive element with a fixed minimum voltage at the current regulator transistor was tested, the characteristics of this variant of the unit roughly correspond to the characteristics of the device described in patent RU 137169. During testing, the current ripple LED was compared loads at different ambient temperatures. Graphs of the ripple coefficient of the output current of the blocks as a function of the ambient temperature are shown in FIG. 5 and FIG. 6

Line 1 - Pulsation coefficient of the output current of the converter with a current stabilizer without a temperature-sensitive element, with a minimum voltage drop at the transistor of the current stabilizer, similar to the device described in Patent RU 137169, immediately after switching on, at different ambient temperatures.

Line 2 - Pulsations of the output current of the converter in accordance with the proposed solution, immediately after switching on at various ambient temperatures.

The tests showed a 2.5-fold smaller ripple of the output current, measured immediately after switching on, at a temperature below minus 50 ° С, at the PSL95C-0.7-140 / 80-1 power supply, manufactured in accordance with the claimed solution, compared to a device similar to that described in the Patent RU 137169.

The graphs of the ripple coefficient of the output current of the blocks after heating and in the steady-state temperature at various ambient temperatures are shown in FIG. 6

Line 3 - Pulsation coefficient of the output current of the converter with a current stabilizer without a temperature-sensitive element, with a minimum voltage drop at the transistor current regulator, similar to the device described in the patent RU 137169, 20 minutes after switching on in a steady-state temperature mode, at different ambient temperatures.

Line 4 - Pulsation coefficient of the output current of the converter in accordance with the proposed solution, 5 minutes after switching on, at different ambient temperatures.

Line 5 - Pulsation coefficient of the output current of the converter in accordance with the proposed solution, 20 minutes after switching on, after switching on, in a steady-state temperature mode, at different ambient temperatures.

The tests showed more than 2 times smaller ripple of the output current, at steady state temperature, at a temperature below minus 25 ° С, at the power supply PSL95C-0,7-140 / 80-1, manufactured in accordance with the claimed solution, compared to a device similar to that described in patent RU 137169. At the same time, the ripple of the output current of the PSL95C-0.7-140 / 80-1 power source, measured 5 minutes after energizing, is close to the ripple in the steady-state temperature mode after the product is fully heated. Thus, the minimum level of pulsations is achieved 4 times faster than in the analogue described in patent RU 137169.

Compared with the analogue patent RU 2465687, the advantage is even more significant since The patent RU 2465687 turns on with a delay after the power supply required for warming up, which is several minutes, and PSL95C-0.7-140 / 80-1, made in accordance with the claimed solution, is turned on immediately after the power supply with acceptable parameters.

Industrial Applicability

The design features of the quasi-resonant transducer given in the description are not exhaustive. Equivalent features can be used to ensure the achievement of the specified technical result. The converter can be manufactured by known methods on high-performance automated equipment.

Claims (1)

Quasiresonant dc voltage converter with zero voltage switching, containing transformer primary winding connected to the first and second input terminals of the converter, first current sensor and power switch, the control input of which is connected to the controller output, one input of which is connected to the second input terminal of the converter, and input determining the zero voltage is connected to the first output of the control winding, while the secondary winding of the transformer is connected via a rectifying diode on the output capacitor connected to the output terminals of the converter, and the second terminal of the transformer control winding is connected to the converter input through a parallel-connected first resistor and capacitor and the connection point of the power switch and the first current sensor through a series-connected diode and second resistor, characterized in that A transistor, a second current sensor, a temperature-sensitive element, a current stabilizer control circuit are introduced, with the common point of the output capacitor and the second The transformer winding is connected to the first output of the second current sensor resistor, the second output of which is connected to the source of the transistor, the drain of which is the negative output of the converter connected to the third input of the current regulator control circuit, the gate of the transistor is connected to the first output of the current regulator control circuit, the first two inputs of which connected to a temperature-sensitive element, the fourth input is connected to the common point of the resistor of the second current sensor and the source of the transistor, and the second output union of the controller with the additional input, the capacitor, the transistor and the sensing element are in thermal contact with each other or are arranged to the heat exchange.

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