KR101533878B1 - DC-DC Switching supply system with analog bypass function for preventing inductor saturation - Google Patents

Abstract

The present invention relates to a DC-DC switching converter capable of overcoming a phenomenon in which the operable power is lowered due to an obstacle of reduction in inductor saturation current generated by using a small-sized inductor in a DC-DC switching converter, The feedback loop has two switching loops, a switching-loop and a bypass-loop. The switching loop and the bypass feedback loop are automatically switched according to the saturation current detection condition of the inductor. The loop does not have any activation signal for selection of the feedback loop, with the system obtaining the feedback control right. It also includes a structure that delivers the maximum operable power in the inductor and can deliver power that the inductor does not supply to the output without going through the inductor for excess power beyond the saturation point of the inductor.

Description

[0001] The present invention relates to a bypass system having an inductor saturation prevention function in a DC-DC switching converter,

The present invention relates to a DC-DC switching converter applicable to small-sized mobile devices, and to an analog bypass including a DC-DC switching converter.

Efforts are being made to create a more compact, lightweight, and portable device that can handle the complex functions of today's mobile devices. In terms of energy management, efforts are being made to maximize the efficiency and increase the operating time of the battery. DC-DC switching converters are used in several energy-efficient ways.

Accordingly, an inductor (Inductor), which is an indispensable component, is used as an energy storage component in a DC-DC switching converter, and an inductor having a large size is inevitably used so that saturation does not occur in a portion where a required power is large .

For example, when the inductance is saturated due to the large power input to the inductor, the magnetic field storage capability of the inductor is significantly reduced, and the input power is mostly represented by heat loss, Loss occurs. In addition, when the inductor is saturated, the current ripple generated in the inductor becomes very large, and the output voltage ripple also becomes large. In Korean Patent Publication No. 1020070005006, the LDO is inserted between the DC- Efforts have been made to reduce ripple at the output voltage even if saturated.

However, since the above technique does not eliminate the energy loss generated in the saturated inductor, the energy efficiency in the saturation region of the inductor greatly deteriorates.

In order to prevent such a phenomenon, the saturation level of the inductor must be raised and the size of the inductor must be increased in order to raise the saturation level. As a result, the occupied area of the component becomes large.

There is a US patent application entitled " US2012 / 0105032 ", which is designed to solve this problem. The technique is to bypass the excess power before the inductor is saturated, Technology, and the saturation of the inductor is not caused, so that the above-described technical problem can be avoided.

However, the provided US2012 / 0105032 technique is a very complicated and difficult to configure technology including a digital processing technique, and it is difficult for a technician working in the same kind to implement it. Thus, there is a need to provide a technique that is simple in construction, bypasses input power above a saturation level of the inductor, and bypasses excess input power while maintaining DC-DC switching conversion at maximum power acceptable in the inductor.

Korean Patent Publication No. 1020070005006: Voltage Regulator, Method Performed by Hybrid Regulator, and Hybrid Voltage Regulator. United States Patent US2012 / 0105032: System and method for providing active current assistant with a bypass circuit for a switcher circuit.

The DC-DC switching converter of the present invention is a DC-DC switching converter that overcomes a phenomenon in which operable power is lowered due to a hindrance of reduction in inductor saturation current generated when a small size inductor is used, To a bypass control technique of a switching converter.

The present invention has a switching-loop, the switching-loop having a DC-DC switching converter, the DC-DC switching converter having switch means, a switch driver for driving or stopping the switch, And a first reference voltage source (VB1) for controlling the switching-loop, and includes a PWM driver, inductor current detection means for monitoring the inductor current, and a saturation current sensing unit do.

The present invention also includes a bypass-loop, wherein the bypass-loop includes a -2 error amplifier, a -2 reference voltage source (VB2), and a variable current source (Ivar).

The present invention is characterized in that a first reference voltage source (VB1), which is an input of the first error amplifier, and a second reference voltage source (VB1), which is an input of the first error amplifier, The second reference voltage source VB2, which is the input of the second reference voltage source VB2, does not have the same level and is configured to have a constant difference.

According to the present invention, in a DC-DC switching converter using a small-sized inductor, a DC-DC converter which bypasses excess power beyond the saturation current of the inductor, maintains a stable output voltage, The present invention can provide a switching converter. In contrast to the prior art, the present invention requires only a small amount of components and does not require a function block such as a digital calculator or a digital to analog converter (D / A) have.

1 is a detailed configuration diagram according to the present invention;
2 shows an example of a buck converter for explaining the present invention.
3 is a representative view of a prior art.
4 is a graph showing an error amplifier signal and a switch driving signal generation of a PWM generator in a buck converter.
5 is a graph showing the change in the output voltage when the amount of current of the required load exceeds the saturation level of the inductor, but the switching of the inductor is stopped so as not to exceed the saturation level of the inductor.
6 is a graph showing the relationship between the output voltage and the inductor current when the load current rises and the saturation level of the inductor is exceeded in the buck converter.
FIG. 7 is a graph showing the change in output voltage generated when the switching-loop and the bypass-loop exchange control in the detailed configuration of FIG.

The present invention is directed to a DC-DC switching converter, and the general operation of the switching converter is not described in the context of the present invention.

Before describing the details of the present invention, it will be described in detail what kind of technology has been used and what problems have been found in order to solve the above problems in the prior art.

In the DC-DC switching converter, the problem of using a small-sized inductor is as described above.

As described above, a technique for bypassing excess of the inductor by more than the saturation current to avoid it is known from USP US2012 / 0105032 (System and method for providing an analog bypass for a switcher circuit) The drawing is shown in Fig.

3A, SWITCHER 120 is a DC-DC switching unit, and when a saturation signal ILIMIT of an inductor is generated, it is regarded that the saturation current flows in inductor 130.

The ACB CONTROL 180 of FIG. 3A analyzes the I_LIMIT signal to calculate the amount of current to be bypassed from the input to the output, outputs the calculated value as a digital signal, and outputs a current DAC (Digital) of the ACTIVE CURRENT 190 function unit to Analog Converter) receives the digital signals M-bit and N-bit, and bypasses the current 195 corresponding to the digital signal without going through an inductor.

FIG. 3B is a detailed block diagram of the prior art, which is quite complex and shows that there are quite a number of input variables for calculating the current to be diverted.

In order to maintain the stability of the feedback loop of the DC-DC converter, a high speed digital calculation is required and the bypass current 195 to be supplied to the output 150 of FIG. 3 (A) A current sink type current source is also required to control the ripple of the output 150. It is understood that there is a difficult problem in maintaining the stability of the feedback loop and the stable state of the feedback loop It is necessary to have a considerable computation speed.

The conditions for how to supply current should be bypassed, but it does not imply a method to maximize the inductor switching current, which is the factor to maximize energy efficiency.

In the above-described conventional technique, it is expected that a considerable scale digital calculator and two current-type DACs that pull or pull down the current will occupy a large portion of the silicon chip area.

The advantages of the present invention are as described above, and a detailed embodiment thereof is shown in Fig.

FIG. 2 is a general buck-converter. FIG. 1 includes FIG. 2. Problems to be solved by the present invention will be described with reference to FIG.

The structure in which the inductor 224 is saturated in the buck-converter of FIG. 2 and prohibits switching from the saturation point is generally applied, and what change from the saturation point of the inductor 224 is shown in FIGS. 4, 5 The graph of FIG.

It is assumed that the IL graph of Figure 4A is the average current of the inductor 224 and that the inductor current means 219 also detects the average current of the inductor (generally a peak current detector is used, Average current).

Assuming that the average currents of the inductors 224 corresponding to the request of the load 226 are ILa1 and ILa2 in Fig. 4A, the error voltage 231 of the error amplifier 210, as shown in Fig. 4B, EV1 and EV2 are generated corresponding to the inductor current and are compared with the sawtooth signal at the PWM generator 211 and the times at which the inductor 224 is supplied with power from the input 214 are switched- It should be noted that the on-time should be known by the same kind of engineers.

If the inductor 224 saturates above the ILa1 value and the saturation current sensing unit 212 depicted in FIG. 2 senses this value and stops switching, then after the current of the inductor exceeds the saturation point, A signal ENB (Fig. 4 (E)) for stopping the operation is generated. The ENB (FIG. 4 (E)) controls the switch driver 213 at the time when the inductor 224 is saturated to prohibit switching. If this process is repeated periodically, the inductor 224 will not supply the current required by the load, so the specified output voltage 215 level will not maintain a constant value and will have some random low value. Of course.

FIG. 5 is a graph showing the transition of the output voltage 215 at the time when the inductor 224 is saturated in the buck-converter of FIG. 2 described above. The output voltage remains at the specified VB1 216 value until the current IL of the inductor 224 is kept below the saturation level Isat of the inductor 224, From the point in time when the inductor needs to be higher than the saturation level (Isat) of the inductor, the output voltage converges to an arbitrary value VOT which is lower than the prescribed output voltage VB1 due to a power shortage from the input. This is a natural process as it protects the inductor and prevents excessive energy loss.

A graph comprehensively expressing the above description is shown in Fig. 6 (A) shows a state in which the maximum current limit level ILavg of the inductor 224 and the current ILoad required in the load 226 change as shown in Fig. 6 (A) And the change in the voltage Vout (215).

If the output of the DC-DC switching converter can be kept in operation near a prescribed position in a situation where the above-described inductor is out of saturation point, the device using the output voltage is normally operational, It will be a great help from the standpoint. A conceptual approach is needed to implement this, and can be found in Figure 6 (A). In the buck converter of FIG. 2, after the inductor 224 is saturated, since the load does not receive power at the input by the difference between the requested current ILoad and ILavg, the output voltage Vout ) Will decrease, and the prescribed output voltage will be maintained only if the difference is supplied from the input. If the inductor is able to deliver the maximum power that it can continuously operate, it will be able to maintain its energy efficiency. 1 is described and posted as a method for achieving the above two conditions, maintaining the first output voltage, and maximizing the power transfer of the second inductor.

1 is a detailed diagram according to the present invention. The bypass-loop that bypasses the insufficient power after the inductor 124 is saturated is connected to the second -2 error amplifier 121 and the second -2 reference voltage source VB2 122 And a variable current source Ivar (123).

1, the switching-loop includes an inductor 124, a comparator 125, an inductor current detector 119, a saturation current sensing unit 112, a saturation current sensing unit 118, An error amplifier 110, a PWM generator 111, and a switch driver 113. The configuration of the switching-loop has been described in the description of FIG. 2, and description thereof will not be repeated.

According to the present invention, in order to realize maintenance of the output voltage and maintenance of maximum power transfer of the inductor switching after the inductor 124 is saturated, the first reference voltage source VB1 116 and the first reference voltage source VB1 -2 reference voltage source VB2 122 is set to a different value.

If the first reference voltage source VB1 and the second reference voltage source VB2 have the same value, the two feedback loops are activated at all times, resulting in a leaning toward the strong feedback loop in accordance with the time-varying conditions. In the worst case, there are two conditions. One is the bypass-loop operation. The second is that the bypass-loop and the switching-loop operate at the same time, Lt; / RTI >

If the two reference voltage sources VB1 116 and VB2 122 are set differently, there is no case in which two loops are simultaneously activated in the two feedback loops. A method of determining the voltage of the voltage sources VB1 116 and VB2 122 basically varies according to the output voltage requirements of the DC-DC switching converter.

The value of VB1 116 is a value that satisfies the prescribed or required center output voltage Vout and VB2 122 determines between the upper limit value and the lower limit value of the prescribed or required output voltage Vout.

In order to maintain the switching of the inductor 124 at 100% in a normal operation in which the inductor 124 is not saturated, the operation of the bypass-loop must be limited. As a method, the -2nd reference voltage source VB2 122 is set to be lower or higher than the voltage of the output voltage Vout 115 so that the output Vbyp signal of the -2 error amplifier 121 causes the current of the variable current source Ivar 123 to become "0".

The fact that the variable current source Ivar 123 is "0" means that the value of the Ivar 123 corresponding to the state in which the output Vbyp of the -2 error amplifier has the upper limit or the lower limit is "0" Therefore, since the Ivar 123 performs a function of transmitting power or current to the output Vout 115 in response to the Vbap signal, it can be implemented as a variable resistor instead of a current source type. Therefore, it is preferable to express it by the variable impedance means something to do.

In order to easily understand the process of activating only one of the two feedback loops according to the current level of the inductor 124, the two voltage sources are assumed to be VB1 > VB2 condition for convenience.

Output voltage Vout 115 is equal to VB1 116 and the switching-loop is active while VB2 122 is at a voltage level that deviates from Vout 115 Value, so the bypass-loop can not be activated.

When the inductor 124 current increases and passes the saturation point, the output voltage Vout 115 becomes lower than the prescribed voltage VB1 116 in response to the shortage of the input power. In this case, the output Verr 131 of the -1 error amplifier 110 outputs a wider ON-state to the switch driver so that the inductor 124 can supply more power as the output voltage Vout (115) TIME 128 signal but the saturation current sensing unit 112 detects the saturation current state and generates the ENB 129 to stop the switching so that a constant ON-Time 128 signal is generated and the inductor 124 maintain a maximum switching current that is not saturated.

The output voltage Vout 115 is lower than VB1 116 because the inductor 124 is supplied with a current smaller than the required load current ILoad in a state where the current of the inductor 124 is maintained at a constant current level at the saturation point Value is as described above.

The output voltage Vout 115 reaches VB2 122 at an arbitrary time as the output voltage Vout 115 becomes lower than the predetermined level VB1 116 due to insufficient supply power from the inductor 124 and the switching power transmission of the inductor 124 reaches the maximum value VB2 122 and Vout 115 are equal to each other and the bypass-loop is activated and the rest of the power to be supplied to the load is passed through the variable current source Ivar 123 to bypass the inductor 124.

The process of returning the current of the inductor 124 from the saturated state to the normal state is as follows. If the current of the inductor 124 is below the saturation point while the load current ILoad decreases while the value of the Vout 115 is maintained in the same state as the VB2 122 in the state where the bypass-loop is present, The current supplied from the load 124 becomes more than the current required for the load. At that point, Vout 115 becomes higher than VB2 122, the bypass-loop goes into an inactive state, the switching-loop becomes active, and Vout 115 becomes equal to VB1.

FIG. 7 is a graph showing a form of an output voltage of a step in which the current of the inductor is saturated at the time of the saturation in the detailed embodiment of FIG. 7, when the inductor current IL is lower than the saturation level Isat of the inductor, the output voltage Vout is equal to VB1 and when the inductor current IL is higher than the saturation level Isat of the inductor, same. The response in the section in which the feedback control is transited has a very natural response because the selection of the two feedback loops described above is not activated by the forced selection signal and naturally gains control of the feedback loop, Which is difficult to attain.

As described above, the present invention includes a switching-loop and a bypass-loop to prevent the inductor from saturating and to maintain the stable output by bypassing the inductor and providing the remaining power not supplied by the inductor to the output, DC-to-DC switching converters that always switch to the maximum current that the inductor can accept.

Smaller mobile products emphasize thinness and light portability while integrating functions in a very compact manner. Such pursuits are a significant burden on component manufacturers, and many investments and research are required to meet those needs. The present invention provides a DC-DC switching converter capable of reducing the size of an inductor used in a DC-DC switching converter in particular and maintaining the output voltage at a high energy efficiency while suppressing saturation of the inductor .

Figure 1-114 VIN (Input)
Figure 1-115 Vout (output)
1-110 1st-order error amplifier
Figs. 1-121 -2 error amplifier
FIG.
1-122 second reference voltage source
1-119 Inductor current detection means
Figure 1-111 PWM generator
1-112: Saturated current sensing unit
FIG.

Claims (1)

DC-DC switching systems that prevent and bypass inductor saturation are:
There is a switching loop and a bypass loop,
The switching loop comprising: There is a first switch between the inductor and the power supply Vin and a second switch between the inductor and the ground and between the common node of the first switch and the second switch and the output Vout, Wherein the first comparator has an output Vout and a first reference voltage and the switch driver controls the first switch and the second switch, Wherein the PWM generator generates a PWM under the control of the first comparator and has a current sensing part for detecting the current of the inductor,
The bypass loop comprising: There is a second comparator between the power supply Vin and the output Vout having a variable impedance under the control of the second comparator and having an output Vout and a second reference voltage as inputs,
Wherein the first reference voltage of the switching loop and the second reference voltage of the bypass loop have different values and the switching operation of the inductor is always maintained.

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