RU139333U1 - QUASI-RESONANT DC CONVERTER WITH SWITCHING AT ZERO VOLTAGE - Google Patents

Abstract

1. A quasi-resonant DC / DC converter with switching at zero voltage, containing the transformer primary winding, a current sensor and a 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 connected to the first and second input terminals of the converter the input for determining the zero voltage is connected to the first output of the control winding, while the secondary winding of the transformer through a rectifying diode is connected to an output capacitor connected to the output terminals of the converter, characterized in that the second terminal of the transformer control winding is connected to the input of the converter through the first resistor and capacitor connected in parallel and the connection point of the power switch and current sensor through the series-connected diode and second resistor. 2. The quasi-resonant converter according to claim 1, characterized in that the controller has a current control input connected to a connection point of the current sensor, diode and power switch.

Description

- Field of technology

The utility model relates to a conversion technique and can be used in the construction of secondary power sources.

- Prior art

Known flyback converter with current control in the primary and secondary circuits (WO 2004042906 A1, IPC H02M 3/335, published May 21, 2004).

The disadvantage of the converter is the continuous current mode of operation, which leads to increased losses in the rectifier diode and a decrease in the efficiency.

Known quasi-resonant DC voltage Converter with switching current at zero voltage (RU 2478253 C1, IPC H02M 1/12, published 03/27/2013).

The disadvantage of the converter is that the power switch control circuit is assembled on discrete elements, which leads to increased losses and does not allow efficient use of the converter with a large input voltage or in a wide range of input voltages.

Known flyback converter with switching at zero voltage (EP 0757428 A1, IPC H02M 1/08, published 1997-02-05).

The disadvantage of the converter is the uncontrolled increase in the current of the power switch in the starting mode with a large input capacitance and low active resistance of the transformer windings, which is typical for flyback converters with relatively high power.

The known converter on the chip of the PWM controller ucc28810 (Texas Instruments) with switching the power switch at zero voltage (www.ti.com).

A disadvantage of the known converter is the uncontrolled increase in the current of the power switch in the starting mode when trying to use the converter at extremely high powers, which reduces its reliability.

Also known is a quasi-resonant converter with current switching at zero voltage, described in patent US 20120299561 A1 (IPC G05F 1/46, published November 29, 2012).

The disadvantage of the converter is a violation of the quasi-resonant mode at start-up and an uncontrolled increase in current in the power key with a large output capacitance and low active resistance of the transformer windings. The reason for this is a voltage close to the threshold that controls the switching of the power switch in the start-up mode of the converter during the reverse operation, due to the small energy dissipation in the transformer (low active resistance of the windings) and the slow transfer of energy to the output capacitance, which is associated with an almost zero output voltage, the current in the transformer does not decrease, which leads to saturation of the transformer, a rapid increase in the current of the transformer and the power switch and the failure of the power switch. For the same reason, the circuit may fail when operating in short circuit mode. In practice, the efficiency of the circuit is achieved by using a transformer with a large saturation threshold, which leads to an increase in its dimensions. At the same time, a transistor with a large allowable current is used. These solutions ultimately add value.

The decision according to US 20120299561 is the closest analogue and is taken as a prototype.

The technical result of the claimed solution is to minimize the dimensions and increase reliability by reducing overload on the power key in the starting mode and short circuit mode.

- Detailed solution description

A quasi-resonant DC / DC converter with switching at zero voltage, containing the transformer primary winding, a current sensor, and a power switch, the control input of which is connected to the controller output, one input of which is connected to the second input output of the converter, and the definition input zero voltage is connected to the first output of the control winding, while the secondary winding of the transformer through a rectifying diode is connected to one capacitor connected to the output terminals of the converter, characterized in that said second control transformer output winding connected to the second input terminal of the inverter connected in parallel across the first resistor and the capacitor and the diode and a second resistor with a power key point connection and a current sensor connected in series.

As an embodiment of the claimed device, it should be indicated that the controller has a current control input connected to the connection point of the current sensor, diode, and power switch.

- Brief description of the drawings

The solution is illustrated by the following graphic materials:

in FIG. 1 shows the electrical circuit of the device according to the first claim;

in FIG. 2 shows a variant of the device according to the second claim;

in FIG. 3 shows diagrams of voltages and currents in various nodes of the circuit of the device shown in FIG. one;

in FIG. 4 shows diagrams of voltages and currents in various nodes of the circuit of the device shown in FIG. 2.

The quasi-resonant converter (Fig. 1) contains the primary winding 2 _{1 of the} transformer 2 connected to the first 1 ₁ and second 1 ₂ input terminals of the converter, a current sensor 4 and a power switch 3, the control input of which is connected to output 5 _{3 of} controller 5, one input 5 ₁ connected to the second input terminal 1 of _{2 of} the transmitter and the input of the zero voltage on February ₅ is connected to a first terminal of the control winding 2 _2, wherein the secondary winding of the transformer ₂ March through rectifying diode 6 is connected to the output capacitor 7, the connection mu to the output terminal 8 ₁ and 8 _{2 of} the transmitter, characterized in that the second terminal management winding 2 ₂ transformer 2 is connected to a second input terminal 1 of _{2 of} the transmitter through parallel-connected first resistor 9 and a capacitor 10 and a series-connected diode 11 and the second resistor 12

The claimed quasi-resonant converter can be represented by a variant in which the controller 5 has a current control input 5 ₄ connected to the connection point of the current sensor 4 of the diode 11 and the power switch 3.

The principle of operation of the circuit is to prevent the current growth in the transformer in the start-up mode and short circuit mode in the converter load and is achieved by automatically increasing the pause duration between the open states of the power transistor in proportion to the current accumulated in the transformer, by adding the voltage of the current sensor to the voltage of the secondary winding 2 ₂ . The duration of the pause between the open states of the transistor 3 in the starting mode is proportional to the voltage generated by the current sensor 4 and inversely proportional to the discharge rate of the capacitor 10.

The maximum open time of the transistor 3 in the converter of FIG. 1 is determined by the maximum gate pulse width of the controller, usually less than 50% of the minimum gate pulse repetition period, and is independent of the transformer current.

In the embodiment of the converter shown in FIG. 2 the maximum duration of the open state of the transistor is determined by the current limiting level Ilim. The advantages of the converter according to the second paragraph of the formula (FIG. 2) are that the maximum current in the transformer is significantly lower than that of the first embodiment shown in FIG. one.

Explanations for the diagrams shown in FIG. 3 and FIG. four:

I. U _prim - voltage of the primary winding of the transformer (winding 2 ₁ );

II. I _prim - current of the primary circuit of the converter (current of the winding 2 ₁ and transistor 3);

III. I _sec - the current of the secondary circuit of the Converter (current winding 2 ₃ and diode 6);

IV. U _RC is the voltage across the capacitor 10 and the resistor 9;

V. U _sec - voltage of the secondary winding of the transformer (windings 2 ₂ and 2 ₃ );

VI. U _TZ - input voltage 5 ₂ of the control circuit (total voltage of the winding 2 ₂ and the capacitor 10).

Explanation of the symbols on the diagrams:

dTZ is the duration of the delay in determining the zero energy of the transformer (minimum pause between the open states of transistor 3);

TI _min - delay time of the current limiting circuit, (minimum duration of the open state of transistor 3);

I _lim is the current limiting level of the primary circuit of the converter;

I _max - maximum current level of the primary circuit of the converter;

U _TZE - threshold level of input 5 ₂ control circuits for determining the zero voltage.

The device operates as follows.

Initial conditions: conclusions 1 ₁ and 1 _{2 of the} converter are connected respectively to the positive and negative poles of the supply voltage source, currents and voltages in all nodes of the circuit are equal to zero.

When the converter is turned on, the controller 5 opens the power transistor 3, connecting the input voltage to the primary winding 2 _{1 of the} transformer 2. Current increases in winding 2 ₁ (Fig. 3, diagrams I, II, time period from T0 to T1) when the maximum duration of the open state of the transistor is reached, the controller turns off transistor 3. The current in winding 2 ₁ stops, and, as a result of induction of the transformer, starts flowing current through winding 2 ₃ and diode 6, charging capacitor 7.

At this moment, the voltage on the capacitor 7 is zero, respectively, during the flow of current through the diode 6, the voltage on the winding 2 ₃ is zero (Fig. 4, diagram IV, time period from T1 to T2). Due to the fact that the voltage on the winding 2 ₃ is equal to or close to zero, the energy output by the transformer and the current decrease in it, during the closed state of the transistor 3 (reverse), are small and at the moment of turning on the transistor 3 in the primary winding 2 _{1 of the} transformer current. (Fig. 3, plot III, time period from T1 to T2). The voltage generated by the current sensor 4 is proportional to the current flowing through the primary winding 2 _{1 of the} transformer 2, through the diode 11 and the resistor 12 charges the capacitor 10 (Fig. 3, diagram V), is added to the voltage on the winding 2 ₂ . (Fig. 4, diagram IV) and enters the input 5 _{2 of the} controller 5 (Fig. 3, diagram VI). The controller 5 opens the transistor 3 when the voltage at the input 5 ₂ decreases below a certain threshold U _TZE with a certain delay dTZ. During start-up, the voltage on the winding 2 _{2 is} proportional to the voltage on the winding 2 ₃ and, accordingly, is equal to or close to zero, therefore, the pause time between the open states of the transistor 3 is determined by the discharge time of the capacitor 10 through the resistor 9 (voltage reduction of the URC on the diagram V during time periods T1- T2, T3-T4, T5-T6). Thus, since the capacitor 10 is charged to a voltage proportional to the current through the current sensor 4, the pause between the open states of the transistor 3 is proportional to the current of the primary winding 2 ₁ . With an increase (accumulation) of current in the transformer-inductor 2, there is an increase in the pause between the open states of the transistor 3 and, accordingly, the time of transformer energy transfer to the capacitor 7 and the load connected to terminals 8 increase (Fig. 3, diagram III, the maximum current value Iprim grows, pauses T1-T2, T3-T4, T6-T7 increase). Thus, the current of the transformer-inductor 2 is automatically controlled in the starting mode (Fig. 3, diagrams I and II, the time period from T1-T7).

With the accumulation of energy in the capacitor 7 and an increase in the voltage on the capacitor 7, the voltage drop across the winding 2 ₃ increases. and accordingly, on the winding 2 ₂ , when the magnitude of the voltage change across the winding 2 _{2 is} exceeded to the level U _TZE , the converter goes into quasi-resonant mode (Fig. 3, time period T7-T12).

The normal mode of operation of the converter when controlling the duration of the open state of the transistor 3 is determined by the controller 5 according to the voltage level on the winding 2 ₂ the voltage span on the winding 2 ₂ is above the level U _TZE (Fig. 3, time period T12-T15).

The parameters of the elements should be chosen so that the normal voltage span Usec on the winding 2 ₂ exceeds the level U _TZE several times (Fig. 3, plot IV time period T12-T15).

A detailed description of the converter according to the second paragraph of the formula:

Initial conditions: conclusions 1 ₁ and 1 _{2 of the} converter are connected respectively to the positive and negative poles of the supply voltage source, currents and voltages in all nodes of the circuit are equal to zero.

When the converter is turned on, the controller 5 opens the power transistor 3, connecting the input voltage to the primary winding 2 _{1 of the} transformer 2. Current increases in winding 2 ₁ (Fig. 4, diagrams I, II, time period from T0 to T1) when the current reaches Ilim, the controller turns off transistor 3 with a certain delay Timin 3. The current in winding 2 ₁ stops, and, due to induction of the transformer , current begins to flow through winding 2 ₃ and diode 6, charging capacitor 7.

At this moment, the voltage on the capacitor 7 is zero, respectively, during the flow of current through the diode 6, the voltage on the winding 2 ₃ . equal to zero (Fig. 4, plot IV, time period from T1 to T2). Due to the fact that the voltage on the winding 2 ₃ is equal to or close to zero, the energy output by the transformer and the current decrease in it, during the closed state of the transistor 3 (reverse), are small and at the moment of turning on the transistor 3 in the primary winding 2 _{1 of the} transformer current (Fig. 4, plot III, time period from T1 to T2). The voltage generated by the current sensor 4, proportional to the current flowing through the primary winding 2 _{1 of the} transformer 2, the diode 11 and the resistor 12 charges the capacitor 10 (Fig. 4, plot V), is added to the voltage on the winding 2 ₂ (Fig. 4, plot IV) and enters the input 5 _{2 of the} controller 5 (Fig. 4, plot VI). The controller 5 opens the transistor 3 when the voltage at the input 5 ₂ decreases below a certain threshold U _TZE with a certain delay dTZ. During start-up, the voltage on the winding 2 _{2 is} proportional to the voltage on the winding 2 ₃ and, accordingly, equal to or close to zero, therefore, the pause time between the open states of the transistor 3 is determined by the discharge time of the capacitor 10 through the resistor 9 (Decrease in the voltage of the ICS on the diagram V in time periods T1 -T2, T3-T4, T5-T6, T7-T8).

Thus, since the capacitor 10 is charged to a voltage proportional to the current through the current sensor 4, the pause between the open states of the transistor 3 is proportional to the current of the primary winding 2 ₁ . With an increase (accumulation) of current in the transformer-inductor 2, there is an increase in the pause between the open states of the transistor 3 and, accordingly, the time of transformer energy transfer to the capacitor 7 and the load connected to the terminals 8 increase (Fig. 4, diagram III, the maximum current value Iprim grows, pauses T1-T2, T3-T4, T5-T6, T7-T8 increase). Thus, the current of the transformer-inductor 2 is automatically controlled in the starting mode (Fig. 4, diagrams I and II, the time period from T1-T13).

With the accumulation of energy in the capacitor 7 and an increase in the voltage on the capacitor 7, the voltage drop across the winding 2 ₃ increases. and accordingly, on the winding 2 ₂ , when the magnitude of the voltage change across the winding 2 _{2 is} exceeded to the level U _TZE , the converter goes into quasi-resonant mode (Fig. 4, time period T13-T19).

The normal mode of operation of the converter, in which the current does not reach the Ilim level, the regulation of the duration of the open state of the transistor 3 is determined by the controller 5 by the voltage level on the winding 2 ₂ the voltage span on the winding 2 ₂ is higher than the level U _TZE (Fig. 4, time period T19- T23).

The parameters of the elements should be chosen such that when the primary winding reaches the Ilim level (Fig. 4, diagram II, time instants T1, T14, T16, T18), the voltage across the capacitor 10 should be approximately equal to U _TZE (Fig. 4, V period time T0-T18). The normal voltage span Usec on the winding 2 ₂ should exceed the level U _{TZE by} several times (Fig. 4, plot IV time period T16-T23). The advantages of the converter according to the second claim (Fig. 2) are that the maximum current in the transformer is much lower than that of the converter according to the first claim.

The quasi-resonant converter according to paragraph 2 of the formula formed the basis for the drivers of the PSL80 / PSL100 / PSL120 series used in the construction of street LED lamps. The design of the luminaires required the developers of drivers to use a power transformer of the smallest size, which required the development of special measures restricting the growth of current in the starting mode, while the use of this solution significantly reduced the requirements for the maximum current of the transistor used.

- Industrial applicability

The design features of the quasi-resonant converter described in the description are not exhaustive. Equivalent features may be used to achieve the indicated technical result. The quasi-resonant converter can be manufactured by known methods on high-performance automated equipment.

Claims (2)

1. A quasi-resonant DC / DC converter with switching at zero voltage, containing the transformer primary winding, a current sensor and a 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 connected to the first and second input terminals of the converter the input for determining the zero voltage is connected to the first output of the control winding, while the secondary winding of the transformer through a rectifying diode is connected to an output capacitor connected to the output terminals of the converter, characterized in that the second terminal of the transformer control winding is connected to the input of the converter through the first resistor and capacitor connected in parallel and the connection point of the power switch and current sensor through the diode and second resistor connected in series. 2. The quasi-resonant converter according to claim 1, characterized in that the controller has a current control input connected to a connection point of the current sensor, diode and power switch.

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