KR200213285Y1 - Switching mode power supply with high efficiency - Google Patents

Abstract

The present invention relates to a switching mode power supply, and more particularly to a switching mode power supply capable of operating at a high switching frequency by preventing oscillation that may occur in a circuit, a switching unit for turning on or off according to a predetermined switching signal ; A power conversion unit connected to an input DC power source and the switching unit to supply power to the secondary winding by intermitting power supplied to the primary winding by turning on and off the switching unit; A detector for detecting a current flowing in the primary winding of the power converter according to an on / off operation of the switching unit and feeding it back to the controller; A controller configured to receive an output DC power supply and generate the switching signal according to an error signal comparing the same with a reference signal and a detection signal output from the detection unit; And a rectifying part connected to the secondary winding of the power converter to convert AC power into DC power and outputting the same, and amplifying and converting the power supplied to the switching frequency oscillation part of the PWM control circuit and the switching signal. Even if a common power source is used without separating the power supplied to the main power amplifier, the circuit may be configured as described in the drawings and claims to implement a high efficiency power supply.

Description

Switching mode power supply with high efficiency

The present invention relates to a switching mode power supply, and more particularly, to a switching mode power supply capable of operating at a high switching frequency by preventing oscillation that may occur in a circuit.

In Switching Mode Power Supply (SMPS), there is an attempt to reduce the energy loss caused by the resistance of the coil by reducing the size of the transformer by increasing the switching frequency (fs) as much as possible and reducing the number of turns of the coil. According to the configuration, oscillation occurs even if the switching frequency is only 100 KHz or more. Due to such oscillation noise, the switching waveform is distorted, and there is a problem in that a constant voltage output cannot be obtained.

The technical problem to be achieved by the present invention is to provide a power supply that can obtain a high efficiency without generating oscillation even if the switching frequency in the circuit configuration of the switching mode power supply.

1 is a block diagram showing a schematic configuration of a switched mode power supply (SMPS).

FIG. 2 is a circuit diagram showing the configuration of the input rectifier 11 shown in FIG.

FIG. 3 is a circuit diagram showing the configuration of the DC / DC converters 12, 13, and 14 shown in FIG.

4 is an example of configuration diagram of the PWM control circuit 31 shown in FIG.

5A and 5B show an example of the output voltage feedback circuit constituting the error amplifier 41 shown in FIG.

Figure 6 shows a circuit according to the prior art as compared to the circuit of Figure 3, an embodiment of the present invention.

Power supply according to the present invention for achieving the above object,

A switching unit which is turned on or off according to a predetermined switching signal; A power conversion unit connected to an input DC power source and the switching unit to supply power to the secondary winding by intermitting power supplied to the primary winding by turning on and off the switching unit; A detector for detecting a current flowing in the primary winding of the power converter according to an on / off operation of the switching unit and feeding it back to the controller; A controller configured to receive an output DC power supply and generate the switching signal according to an error signal comparing the same with a reference signal and a detection signal output from the detection unit; And a rectifier connected to the secondary winding of the power converter to convert AC power into DC power and output the DC power.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

FIG. 1 is a block diagram illustrating a schematic configuration of a switching mode power supply (SMPS), and illustrates a basic operation principle of the SMPS according to functions. When AC power is input to the input rectifier 11, DC power is generated and output to the switching circuit 12. The switching circuit 12 operates at a predetermined frequency to chop the input DC voltage into a square wave of high frequency. The square wave signal is applied to the power transformer 13, stepped down to a predetermined value according to the coil turns ratio, and rectified and filtered by the output rectifier 14 to output the required DC voltage. The output signal of the output rectifier 14 is detected and fed back to the switching circuit 12. The switching circuit 12 compares the voltage of the output signal with a reference voltage and turns on / off the switching circuit 12 according to the error signal. Adjust the off time (PWM control). In Fig. 1, the AC input voltage signal is converted into a DC voltage signal by the input rectifier 11, applied to the switching circuit 12 and the power TRF 13, and the output rectifier 14 is a converter for rectifying a high frequency square wave. It acts as a (converter).

FIG. 2 is a circuit diagram showing the configuration of the input rectifier 11 shown in FIG. The AC input stage constitutes a low pass filter composed of a varistor (Z ₁ ), a capacitor (C), and an inductor (L ₁ , L ₂ ), and eliminates spark or high frequency noise when commercial AC power is input to the input power. Therefore, heat loss due to noise can be prevented. The diode D ₁ determines the flow of current according to the phase of the AC power source, and the switch S ₁ is a selection switch according to the AC input voltage 110V or 220V. The rectifier D ₂ outputs a DC voltage by the forward direction of the diode and the charge charge action of the capacitor. The rectified DC voltage is 80V when the input AC voltage is 100V to 220V. Slightly lowered to ~ 150.

3 is a circuit diagram illustrating a configuration of the DC / DC converter shown in FIG. 1. The input DC power supply V _in is an output voltage of the input rectifier 11 of FIG. 1, and includes a PWM control circuit 31, a switching transistor Q ₁ , a current detector 33, and a magnetic bias circuit 35. 1 corresponds to the switching circuit 12 of FIG. 1, and the transformer T ₁ corresponds to the power transformer 13 of FIG. 1, and the circuits 37, a, and b connected to the secondary winding of the transformer T ₁ . c corresponds to the output rectifier 14 of FIG. In the flyback converter shown in this embodiment, one input power supply V _in is commonly supplied to the PWM control circuit 31, which is an oscillator, and a transistor Q ₁ connected to an output terminal, but a high switching frequency (for example, 650 KHz or more) is provided. ) Does not cause parasitic oscillation, so the required output can be obtained.

In the embodiment of the present invention shown in FIG. 3, the transistor Q ₁ operates as a switching element that is turned on or off in accordance with the switching signal output from the PWM control circuit 31. The transformer T ₁ , which is a power conversion unit, is connected to the primary winding N _p between the input DC power supply V _in and the switching unit. Power the windings. The input current detector 33 detects a current flowing in the primary winding of the power converter T ₁ according to the on / off operation of the switching element (transistor Q ₁ ) and returns it to the PWM control circuit 31. The PWM control circuit 31 receives the output direct current power supply (+ FB) and detects an input signal that is changed according to an error signal and an input voltage V _{in that} are compared with the reference signal through the input current detector 33. The amount of current flowing in the primary winding is controlled by controlling the on / off duration of the switching signal SW _out according to the voltage level. In addition, the rectifiers 37a, b, and c are connected to the secondary windings of the power transformer T ₁ to convert AC power into DC power to obtain one or more constant voltage outputs.

In the present embodiment, the circuit for the switching operation is composed of a switching signal generation PWM control circuit 31, a transistor Q ₁ , a voltage step-down transformer T ₁ and a current sensing transformer T ₂ . The transistor Q ₁ is turned on / off by the square wave SW _out generated from the PWM control circuit 31. When the transistor Q ₁ is turned on, the current is charged in the primary winding of the transformer T ₁ , and when the transistor Q ₁ is turned off, the current charged in the primary winding is transferred to the secondary winding, so that the transformer ( Voltage is induced across the secondary winding according to the turns ratio of T ₁ ).

On the other hand, the source (source) terminal and the minus of the transistor (Q ₁₎ (-) is the input current detecting section 33 between the terminal connected to the transistor a signal generated according to the current time (Q ₁₎ is turned on the PWM control circuit ( 31). The input current detector 33 senses a change in the input side current due to a change in current or a change in output load (load) caused by a potential change _{in the} input voltage V _in , and returns it to the PWM control circuit 31. In order to compensate for the phenomenon caused by the same current variation, the PWM control circuit 31 controls the switching operation according to the sensing signal.

The input current detector 33 detects a change in the current Ipp according to a change in the input voltage V _in or a change in the output voltage, converts it into a voltage signal, and then returns it to the PWM control circuit 31. The PWM control circuit 31 adjusts the pulse interval of the positive phase of the switching signal SW _out by reflecting the variation of the input voltage V _in or the variation of the output voltage, so that the output voltage is constant. Control it to If the current I _pp is increased, the current sensing voltage detected by the input current detector 33 and fed back to the PWM control circuit 31 is increased, and the PWM control circuit 31 is based on the current sensing voltage. _pp ) adjusts the pulse interval of the switching signal SW _out to be controlled in the decreasing direction.

When the transistor Q ₁ is turned on, current is induced in the secondary winding by the current flowing in the primary winding of the current-coupling transformer T ₂ . The resistor R1 converts the current induced in the transformer T ₂ into a voltage signal, and the voltage applied to the sensing terminal SENSE is determined by adjusting the resistance value of the variable resistor R ₂ . The capacitors C ₂ and C ₃ are used for ripple and noise removal, and the diode D ₂ converts and rectifies the detected square wave signal into a DC signal. Current-coupling Fran spokes Murray (T ₂₎ is the power source (+) according to the primary side and the secondary side separated of the transformer (T ₂₎ in sensing the variation of the current flowing through the primary winding of the transformer (T ₁₎ The poles are separated from each other to enable a circuit configuration that switches at high frequencies.

The ratio of the primary winding to the secondary winding of the transformer T ₂ is preferably about 1:50 to 200. For example, for low power consumption of less than 10 watts, the primary winding of transformer T ₂ is once when the continuius current (I _PDC ) flowing in the primary coil of main transformer T ₁ is 1.0 A or less. The secondary winding is preferably 100 times. The core of the transformer T ₂ is preferably made of the same material as the core of the main transformer T ₁ .

When the (+) poles of the power supply power supply and the switching control power supply are in common, oscillation is likely to occur due to a high frequency clock signal generated by the PWM control circuit 31 or a switching operation by the switching element Q ₁ . In this circuit, both power supplies have a common (-) pole but have positive (+) poles separated by the configuration of the transformer T ₂ included in the input current detection unit 33, thereby enabling stable high frequency switching. In particular, the circuit of this embodiment is useful for low power (e.g., 10 Watt) converter devices.

The PWM control circuit 31 receives the output voltage (+ FB) of the converter and receives the sensing voltage SENSE generated by the input side current, and the square wave pulse for the on / off operation of the switching element Q ₁ . Generates. A detailed configuration thereof will be described with reference to FIG. 4.

The magnetic bias circuit 35 supplies the operating power to the output of the switching signal SW _out in the PWM control circuit 31. The voltage induced by the auxiliary winding N _FB on the primary side of the power transformer T ₁ is applied to the Vcc terminal of the PWM control circuit 31 via the diode D1. Here, the capacitor C ₁ is for removing ripple. The input power supply V _in supplies power to elements in the PWM control circuit 31 other than the switching output section.

On the other hand, in selecting the transistor Q ₁ , it is necessary to consider the following points. First, it is desirable to make the input gate capacitance of the transistor low (e.g., 350pF) and the internal resistance (R _{DS (on)} ) to low (e.g., 3 ohms or less), thereby reducing power loss. .

The process of designing the main transformer (T ₁ ) is as follows. The peak current I _PP and the direct current I _PDC (continuous current) flowing in the primary coil are expressed as follows.

The inductance Lp of the primary coil and the size of the core are determined as follows.

The actual core size is larger than (AeAc x 1.5).

The number of turns Np of the primary coil is

The air gap (l _g )

The number of turns N _s1 of the first output V _out1 of the secondary coil and the number of turns of the gate voltage N _G1 of the transistor Q5 are as follows.

The number of turns N _s2 and N _s3 of the second and third outputs V _out1 and V _out3 of the secondary coil

Output rectifiers 37a, b, and c are connected to the secondary winding of the power transformer T ₁ . Basically, the output side of the power transformer T ₁ includes a rectifying element and a ripple removing capacitor. When the output current is low (e.g. 0.5A or less), it is preferable to use a diode for rectification, and when the output current is high, it is preferable to use a MOFET transistor (preferably R _{DS (on)} = 0.02 ohm or less). This can minimize power losses. The power loss in the case of diode and transistor as rectification device is as follows.

On the other hand, the RC snubber circuit in the output sections 37a, b, and c in FIG. 3 is considered. A resonance circuit is formed by the junction inductance of the leakage inductance of the primary coil Lp of the high-frequency power transformer T ₁ and the rectifying diode. This tuning circuit causes a transient overvoltage ringing phenomenon in the transient state. Ringing can have amplitudes that are loud enough to cause noise in the turn-off period and destroy the diode in severe cases. RC snubber circuitry suppresses this ringing to a safe amplitude. The second or third output rectifiers 37b and c of FIG. 3 have a snubber circuit, which may be connected to both ends of the rectifying diode or to the second winding of the power transformer T ₁ . have.

In the first output rectifier 37a of FIG. 3, the transistor Q ₅ used as the rectifying element is preferably a field effect transistor FET, and the power transformer (Q ₁ ) is turned on by the on-off operation of the switching element Q ₁ . The voltage induced on the secondary winding side of T ₁ ) is converted into a direct current, and the capacitor (C _o1 ) is a device for suppressing pulsation to smooth the ripple to generate a constant voltage output (V _out1 ). Filter capacitors C _o1 , C _o2 , and C _o3 used in the output rectifier can prevent ripple noise even when the capacity is 1/10 as compared with the conventional art.

The RC element, consisting of a resistor (R ₅ ) and a capacitor (C ₅ ), has a leakage inductance (L _T ) of the primary coil (Lp) of the power transformer (T ₁ ) and a gate input capacitance (C _GS ) of the transistor (Q ₅ ). Is a first snubber circuit for preventing oscillation ringing caused by an oscillation ring. An RC element composed of a resistor (R ₇ ) and a capacitor (C ₇ ) includes a leakage inductance of a primary coil (Lp) and a transistor of a power transformer (T ₁ ). A second snubber circuit for preventing oscillation ringing due to capacitance (C _oss ) between the drain and the source of (Q ₅ ).

In the first output rectifier 37a, a transistor can be used instead of a diode as a rectifying element to greatly reduce power loss, thereby increasing efficiency. Therefore, the present invention is also suitable for high current and has a snubber circuit for preventing ringing phenomenon, thereby solving the problem of ringing by oscillation.

A design process of the snubber circuit shown in FIG. 3 will be described. The snubber resistors R ₅ and R ₇ can be obtained as follows.

The snubber capacitances C ₅ and C ₇ can be found as follows.

Output capacitors (electrolytic capacitors) C _o1 , C _o2 and C _o3 used to reduce the ripple of the output voltage can be designed as follows.

in reality This is preferred. However, according to the prior art, since the output ripple is larger than the present embodiment, it should be about x 10,000. Therefore, the capacity of the output capacitor used in this embodiment can be reduced.

An RC snubber circuit connected to the rectifying diode can also be obtained using the above equation. Here, CJ is the junction capacitance of the diode.

The circuit according to the prior art is shown in FIG. 6 as opposed to the circuit of FIG. 3, which is an embodiment of the present invention, and the basic configurations are substantially the same. The PWM control circuit 61 of FIG. 6 corresponds to the PWM control circuit 31 of FIG. 3, the transformer T ₁ of FIG. 6 corresponds to the transformer T ₁ of FIG. 3, and the magnetic bias circuit of FIG. 6. 65 is a switching transistor (Q ₁₎ of the response and, Figure 6 a self-bias circuit 35 of Figure 3 corresponds to the switching transistor (Q ₁₎ of Figure 3, all of which are substantially the same function with each other. However, although the current feedback part 63 of FIG. 6 corresponds to the current feedback part 33 of FIG. 3, the structure is completely different. In addition, the output rectifiers 67a and b connected to the secondary side of the transformer T ₁ are composed of rectifying diodes D ₁ and D ₂ and capacitors C _o1 and C _o2 .

According to FIG. 6, it can be seen that the current flowing through the transistor Q ₁ is detected by the resistor R _cs and fed back to the PWM control circuit 61. The change in the current flowing between the drain and the source of the transistor Q ₁ is detected by the change in the input voltage and / or the output load, and fed back to the PWM control circuit. For example, when the input voltage is high, the PWM control circuit can keep the output voltage constant by reducing the amplitude of the positive phase in the switching mode to reduce the current to suppress the rise of the output voltage.

Embodiments of the present invention and the prior art are fundamentally different in the current sensing method. Due to such differences, the present invention works well at switching frequencies above 500 KHz and the power loss caused by the coupler is almost negligible. However, according to the related art, a voltage drop (V _Drp = I _PDC x R _CS ) occurs in the resistor RDS, and the power loss (P _Loss = R _CS x I _PDC ² ) caused by the resistor is very high, and the switching frequency is also high. Could not be greatly increased.

In this embodiment, if the coil winding directions of the primary side and the secondary side of the current sensing transformer T ₂ are shown in the drawing, in the case of low power (10 watts), it works well even if the switching frequency is increased to 1 MHz. It could be confirmed as. In this embodiment, since the number of turns of the primary winding of the transformer T ₂ is one time, the resistance of the coil can be almost neglected, resulting in almost no power loss.

FIG. 4 illustrates a current-mode control method as an example of the configuration diagram of the PWM control circuit 31 shown in FIG. Current-mode converters use an inner loop to adjust the error signal with respect to the input peak current. The power supply Vcc induced by the auxiliary winding NFB on the primary side of the power transformer T ₁ supplies the power to the amplifier 45 which outputs the switching signal SW _out , and the clock generator 43 and the flip line. Circuits such as the flop 44, the error amplifier 51, the comparator 52, and the like are supplied with operating power from an input power source V _in applied through the regulator 47.

The error amplifier 41 compares and amplifies the output signal + FB and the reference voltage V _ref , and the error signal is input to the comparator 42. When the switching element is turned on, the peak current flowing through the primary winding of the power transformer is sensed and converted into a voltage, and then the sensing signal SENSE is input to the comparator 42. The comparator 42 compares the detection signal SENSE according to the peak switch current with an error signal associated with the output signal and inputs the RS flip-flop (latch) 44. The clock generator 43 generates a clock signal which is a square wave signal corresponding to the switching frequency fs, and the RS flip-flop 44 receives the output of the comparator 42 and the clock signal to drive on / off of the switching element. To generate a switching signal SW _out . The switching signal turns on / off a switching element (usually a transistor) connected at the rear end according to its logic level.

The main output voltage (+ FB) fed back from the final output stage is compared with the reference voltage (V _ref ) in the error amplifier 41, and the signal SENSE fed back by sensing the input current is the reference voltage (1.2) in the comparator 42. Is compared with V) and the result is inputted to the flip flop 44. In the flip-flop 44, the switching signal SW _out is generated by increasing or decreasing the phase (or width) of the clock signal generated by the oscillator 43 according to the output signal of the comparator 42 to change the input voltage and the load. As a result, the current flowing through the transformer T ₁ may be increased or decreased to keep the output voltage at the final output terminal constant. That is, the switching signal SW _out becomes a pulse width modulated signal whose duty cycle is changed according to the output voltage and the input current.

If there are several output voltages, adjust the voltage of the other output based on the highest output voltage. That is, the output voltage must be kept constant even if the input voltage or the load varies within a certain range, and therefore the main output voltage (+ FB) must be fed back to the PWM control circuit 31 as well as the feedback by the input current detector 33. . By such a configuration, the stable phase of the converter circuit can be enhanced and a high frequency high efficiency SMPS can be realized.

5A and 5B show an example of an output voltage feedback circuit constituting the error amplifier 41 shown in FIG.

5A shows a constant gain between frequencies f1 and f2, the circuit parameters of bias resistor R _bias , capacitance C ₁ , C ₂ , gain AV, cutoff frequency f ₁ , f ₂ , and switching The frequency f _s is represented by the following equation.

FIG. 5B is an improvement in the transient response characteristics compared to the circuit of FIG. 5A. The circuit parameters include bias resistors R _bias , capacitances C ₁ , C ₂ , C ₃ , and C ₄ , and gains AV ₁ and AV ₂ . , The cutoff frequencies f ₁ , f ₂ and f ₃ , f ₄ and the switching frequency f _s are expressed by the following equation.

Next, the efficiency (Equation 1) of the converter circuit diagram shown in Figure 3 is calculated as follows.

Assume that the output power P _out for the three outputs is

Then, the total output power is as follows.

The continuous current I _PDC flowing in the primary coil of the power transformer T ₁ is as follows. Here, the switching frequency (f _s ) is 650 KHz, the input minimum voltage (V _{in (min)} ) is 160Vdc, the input maximum voltage (V _{in (max)} ) is 240Vdc, the maximum pulse phase (D _max ) = 0.45 It shall be

The total power loss is calculated as follows. Here, the copper resistance of the primary coil of the power converter is 0.4 ohm, the resistance R _{DS (on)} between the drain and the source when the switching transistor Q ₁ is _on is 1.5 ohm, and the drain and the source when the rectification transistor Q5 is on. Assume that the resistance R _{DS (on)} of the liver is 0.02 ohm and the forward voltage V _F of the rectifying diodes D8 and D9 is 0.3V.

Therefore, the efficiency of the converter is as follows.

The above-described configuration of the converter can be used as a drive circuit (drive amplifier) of a power converter that requires high power, and is particularly useful for various inverters or converter circuits used in battery chargers, DC motor drive devices, and the like. In addition, the converter according to the present invention is also suitable as a driving circuit for a low voltage / high power power supply device, such as a notebook computer, and in particular, a battery charger or a built-in uninterruptible battery for a portable radio, a TV, a computer, as well as a mobile phone or a video wireless phone. It can be widely applied as a basic circuit of a power supply (UPS) or the like.

As described above, according to the power supply according to the present invention, if the circuit is configured such that the power supplied to the switching frequency oscillation unit of the PWM control circuit and the power supplied to the main power amplifier for amplifying and converting the switching signal are separately supplied, the switching is performed. The oscillation caused by the oscillation unit is not transmitted to the output stage and high efficiency can be achieved. In the present invention, even if a common power source is used without separating the two power sources, the circuit can be configured as described in the drawings and claims. The power supply of can be implemented.

The conventional SMPS is only 65% to 75% of the efficiency, but in the present invention can operate in a high frequency switching mode can exhibit an efficiency of more than 90%, especially when applied to the DC motor for the air compressor size of the motor Is reduced and the torque (rotational power) of the motor is increased, thereby saving further electric energy.

Claims (5)

A switching unit which is turned on or off according to a predetermined switching signal; A power conversion unit connected to an input DC power source and the switching unit to supply power to the secondary winding by intermitting power supplied to the primary winding by turning on and off the switching unit; A detector for detecting a current flowing in the primary winding of the power converter according to an on / off operation of the switching unit and feeding it back to the controller; A controller configured to receive an output DC power supply and generate the switching signal according to an error signal comparing the same with a reference signal and a detection signal output from the detection unit; And And a rectifier connected to the secondary winding of the power converter to convert AC power into DC power. The method of claim 1, wherein the detection unit It is connected between the negative pole of the input DC power supply and the switching unit, the power flowing in the primary winding of the power conversion unit according to the on-off of the switching unit is supplied to the primary winding and converted to a predetermined ratio to the secondary winding A current-coupled converter for supplying power; And And a signal generator for generating a sensing signal input to the controller from power induced in the secondary winding of the current-coupling converter. The method of claim 1, wherein the rectifying unit A transistor having a gate terminal and a source terminal connected to both ends of the secondary winding of the power converter and having an output terminal drawn from the drain terminal; And A first snubber circuit for preventing a ringing phenomenon caused by a leakage capacitance and a gate capacitance between the gate terminal and the source terminal and a leakage inductance between the drain terminal and the source terminal and the capacitance between the drain and the source terminal And a snubber portion including at least one of second snubber circuits for preventing ringing from occurring. The method of claim 1, wherein the rectifying unit A rectifier diode is connected to the secondary winding of the power converter, And a snubber circuit connected to both ends of the diode or both ends of the secondary winding of the power converter in order to prevent ringing caused by leakage inductance of the power converter and junction capacitance of the diode. The method of claim 1, The detection unit is connected between the ground of the input DC power supply and the switching unit, the current-coupling converter that receives the power flowing in the primary winding of the power conversion unit and converts it to a predetermined ratio to supply power to the secondary winding Including; The control unit receives a sensing signal generated from the power induced in the secondary winding of the current-coupling converter, receives an output DC power feedback and compares the switching signal with a reference signal and the switching signal according to the sensing signal. Power supply, characterized in that generated.