JP3097493B2 - DC / DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC converter, and more particularly to a DC / DC converter for switching an operation mode according to a load.
It relates to a C / DC converter.

[0002]

2. Description of the Related Art A DC / DC converter is a device for converting a certain DC input voltage into a different DC voltage and outputting the same, and is used for various purposes. This output voltage must be stable at a predetermined value, and in consideration of the case where it is mounted on a portable terminal or the like, it is required that its power consumption be reduced as much as possible.

FIG. 6 is a schematic configuration diagram of an example of a conventional DC / DC converter. DC / DC converter shown in the figure, converts the input voltage V _in to an output voltage V _out. The switching signal generation circuit 101 receives the output voltage _Vout and the coil current calculation signal (mode switching signal) as feedback signals, and outputs a control signal based on the received signals. When the DC / DC converter has two operation modes, a light load mode and a heavy load mode, the switching signal generation circuit 101 switches the operation mode according to the received signal, and outputs a control signal corresponding to the mode. Output.

[0004] The switching element 102 performs switching according to a control signal output from the switching signal generation circuit 101. For example, when the output voltage _Vout decreases, the switching element 102 is turned on, the current flowing through the switching element 102 flows to the output side via the coil L, and power is supplied to the capacitor C and the output side to output the output voltage Vout. raise _out .

[0005] The operation mode of the DC / DC converter is switched according to the current I _LD flowing through the connected load. The load current I _LD, so can be regarded as the mean value of the coil current I _L, the mean value of the coil current I _L is calculated as follows and outputs it as the coil current calculation signal (mode switching signal). That is, the voltage value at both ends of the resistor R _sense through which the coil current I _L flows is subjected to impedance conversion via the buffer 103, and the converted signal is averaged by the integration circuit 104. In this averaging process, the timer 1
05 is used, and an integrated value in a period according to the switching frequency (operating frequency) of the switching element 102, the peak-to-peak voltage of the output signal of the buffer 103, and the like is obtained. Then, the comparator 106 compares the integrated value with the reference voltage, and outputs a result of the comparison as a coil current calculation signal (mode switching signal).

The switching signal generation circuit 101 switches the operation mode as needed in accordance with the coil current calculation signal (mode switching signal), and performs switching so as to supply a required load current I _LD while keeping the output voltage constant. A signal for controlling the on / off state of the element 102 is output.

[0007]

As described above, in order to generate the coil current calculation signal (mode switching signal), which is one of the feedback signals, that is, to detect the load current, the buffer 103 needs to be integrated. Since many circuit blocks such as the circuit 104, the timer 105, and the comparator 106 are required, the circuit scale becomes large and the current consumption is large. Also, the buffer 103 and the integration circuit 104
In addition, the bias current needs to be always supplied to the comparator 106, and the current is always consumed. Therefore, the reduction of the power consumption of the DC / DC converter is prevented. That is, in the conventional DC / DC converter, the current consumption of the circuit for monitoring the load current is large, and the conversion efficiency of the DC / DC converter is reduced.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide a DC / DC converter which detects a load current with a small current consumption and switches an operation mode.

[0009]

A DC / DC converter of the present invention has at least two operation modes for supplying power to a load, a light load mode and a heavy load mode, and outputs an output according to a method corresponding to each operation mode. It is assumed that the control is performed. The light load mode is an operation mode when the current flowing through the connected load is small, and the heavy load mode is an operation mode when the current flowing through the load is large.

The DC / DC converter according to the first and second aspects switches the operation mode from the light load mode to the heavy load mode when the power supply cycle in the light load mode is executed a predetermined number of times. In the process of counting the number of executions of the power supply cycle, when the cycle is stopped, the count value is reset.

The DC / DC converter according to the third and fourth aspects has the following means. The comparing means is, for example, a comparator, and compares the output voltage with a predetermined voltage set in advance. The counting means refers to the comparison result of the comparing means, and when the output voltage is lower than the predetermined voltage,
The number of power supply cycle executions in the light load mode is counted. The control means switches the operation mode from the light load mode to the heavy load mode when the count value of the counting means reaches a predetermined number. The reset unit refers to the comparison result of the comparison unit and resets the count value of the counting unit when the output voltage is higher than the predetermined voltage.

[0012]

When the load current increases while the DC / DC converter is operating in the light load mode, the output voltage decreases. When the output voltage falls below a predetermined value, the comparing means recognizes the fact and starts a power supply cycle to recover the voltage drop. Then, when the power supply cycle is executed, the counting means increments the count value.

When the power supply cycle is completed, referring to the comparing means, if the output voltage has not recovered to the predetermined value, the next cycle is executed. At this time, the counting means increments the count value. When the count value thus increases and reaches the predetermined number, the operation mode is switched from the light load mode to the heavy load mode.

On the other hand, even when the output voltage falls below the predetermined value and a power supply cycle is started, if the output voltage recovers to the predetermined value before the count value reaches the predetermined number, the reset means resets the count value. Since the operation is reset, the operation mode is not switched. That is, when the power supply cycle is continuously executed a predetermined number of times, it is determined that more power supply is necessary, and the mode is switched from the light load mode to the heavy load mode. Therefore, the mode switching does not occur when the output voltage drops momentarily or due to noise or the like.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a DC / D of one embodiment of the present invention.
It is a block diagram of a C converter. DC / DC converter shown in the figure, converts the DC input voltage V _in to an output voltage V _out. This DC / DC converter has two operation modes, a heavy load mode which is an operation mode when the current consumption of the connected load is large, and a light load mode which is an operation mode when the current consumption of the connected load is small. And automatically switches its operation mode according to the load current.

The switching element 1 is a power MOS transistor, and performs an on / off operation according to the gate potential. The coupled input voltage V _in to one terminal, a cathode and a coil L of the diode D to the other terminal
Is connected. The anode of the diode D is grounded. The other end of the coil L is connected to an output terminal via a resistor R _sense . The output terminal is grounded via a capacitor.

The comparator 2 has its - reference voltage V _ref is applied to the input, the + the input comparison voltages V ₁ obtained by dividing the output voltage V _out by a resistor R ₁ and R ₂ are applied. This comparison voltages V ₁ is proportional to the output voltage V _out, the comparator 2 determines whether substantially the output voltage V _out reaches a predetermined value to drive the load. Then, the comparison result is output to AND circuits 5 and 6.

The comparator 3 monitors the voltage across the resistor R _sense . Resistor R at + terminal of comparator 3
The input side of the _sense is connected, and the output side of the resistor R _sense is connected to the-terminal. The current flowing through the resistor R _sense is
Since the current is the coil current I _L flowing through the coil _L , the comparator 3 determines the coil current I _L on the primary side of the DC / DC converter.
_L will be monitored. The comparison level of the comparator 3 is converted into a coil current and set as I _LP . Therefore, the output is determined according to the magnitude relationship between the coil currents I _L and I _LP . This output is transferred to the B terminal of the selector 8. The comparison level I _LP is set using the offset voltage V _S1 .

The comparator 4, like the comparator 3, monitors the voltage across the resistor R _sense . However, the input side of the resistor R _sense is connected to the − terminal of the comparator 4, and the output side of the resistor R _sense is connected to the + terminal.
The comparison level of the comparator 4 is 0 in terms of the coil current.
(Actually, as will be described later, a value slightly larger than 0 is set). Then, an output is determined according to the value of the coil current I _L , and this output is transferred to AND circuits 5 and 6. The comparison level of the comparator 4 is set using the offset voltage V _S2 .

When the operation mode is switched in accordance with the load current, a method of directly detecting the load current is conceivable. For this purpose, it is necessary to provide a resistor on the output side of the capacitor C, and the efficiency of the entire DC / DC converter is increased. Is not preferred. For this reason, in the present embodiment, the load current is estimated using the resistor R provided on the input side (primary side) of the capacitor C. This resistance R
_{The sense} uses what has been used for the purpose of overcurrent protection or keeping the output voltage constant.

The AND circuit 5 receives the inverted signal of the output of the comparator 4 and the inverted signal of the output of the comparator 2 and transfers their logical product to the B terminal of the selector 7 and the clock terminal CK of the counter 12. This logical product indicates that the coil current I _L becomes 0 and the comparison voltage V ₁ becomes the reference voltage V _ref.
The level becomes “H” when the temperature is lower than the above. AND circuit 6
Receives the output of the comparator 4 and the output of the comparator 2 and transfers their logical product to the clear terminal CL of the counter 12. The logical product, a coil current I _L becomes 0, and becomes "H" level when the comparison voltage V ₁ is higher than the reference voltage V _ref.

The selectors 7 and 8 select and output one of the signals input to the A terminal or the B terminal according to the A select signal (heavy load mode) and the B select signal (light load mode), respectively. The output signal of the selector 7 is input to the S terminal (set terminal) of the flip-flop 10, and the output signal of the selector 8 is
0 is input to the R terminal (reset terminal).

The PWM control circuit (heavy load control circuit) 9
The pulse signal based on the output voltage _Vout is output. That is, for example, when the output voltage V _out decreases,
A signal with a large pulse duty is output. The output signal of the PWM control circuit 9 is input to the A terminal of the selector 7 and its inverted signal is input to the A terminal of the selector 8.

The flip-flop 10 outputs an ON signal when in the set state, and outputs an OFF signal when in the reset state. The driver 11 drives the switching element 1 to the ON state when receiving the ON signal, and turns the switching element 1 to the OFF state when receiving the OFF signal.

The counter 12 receives the output signal of the AND circuit 5 at the clock terminal CK, and receives the output signal of the AND circuit 6 at the clear terminal CL. And the clear terminal CL
During the period when the signal state of the clock terminal C is at the “L” level.
Every time a rising edge is detected at K, the count value is incremented. When the signal state of the clear terminal CL becomes “H” level, the count value is cleared to 0. And
When the count value becomes “n (natural number)”, a pulse is output to the latch circuit 13. In this example,
Let n = 4.

When receiving a pulse (rising edge) from the counter 12, the latch circuit 13 outputs an "H" level until it is reset. This reset signal is a B select signal output by the mode switching control circuit 20,
The detection of the rising edge of the signal resets the latch circuit 13 to output the "L" level. The output of the latch circuit 13 is transferred to the selectors 7 and 8 and the mode switching control circuit 20 as an A select signal.

The A select signal is a signal for instructing switching from the light load mode to the heavy load mode, and is at the "L" level in the light load mode and at the "H" level in the heavy load mode. The mode is switched by setting the A select signal to the “H” level.
The output signals of the PWM control circuit 9 are selected and output to the selectors 7 and 8, and the switching element 1 is driven by the selected signals.

The mode switching control circuit 20 instructs the mode switching from the heavy load mode to the light load mode based on the coil current _{IL and the} like, although the connection lines thereof are not particularly shown. The trigger for mode switching, for example, a case where the average value of the coil current I _L is smaller than a predetermined value. When switching the operation mode from the heavy load mode to the light load mode, the mode switching control circuit 20 sets the B select signal to the “H” level and outputs it to the selectors 7 and 8. Then, according to the B select signal,
Each of the selectors 7 and 8 selects a signal of the B terminal, and the switching element 1 is driven by the selected signal. The B select signal is at "L" level in the heavy load mode, and is at "H" level in the light load mode.

The operation of the DC / DC converter having the above configuration will be described. In the light load mode, the selectors 7 and 8 each select and output a signal input to the B terminal. In this state, when the output voltage _Vout is higher than a predetermined voltage (reference value) for driving the load, the output of the comparator 2 becomes "H" level, and the switching element 1 is turned off by the signal. Therefore, the DC / DC converter does not supply current to the load. On the other hand, the output voltage V _out is lower period than the reference value, and supplies a current to the load while on-off controlling the switching element 1 a value of the coil current I _L as a feedback signal. If the output voltage _Vout cannot be recovered even when the current supply in the light load mode is continued, as will be described in detail later, the operation mode of the DC / DC converter is switched to the heavy load mode to increase the current. The supply increases the output voltage V _out .

Next, the operation of the DC / DC converter of this embodiment will be described in detail with reference to a time chart. FIG. 2 is a time chart for explaining the operation mode switching from the light load mode to the heavy load mode. Note that the symbols “〜” in FIG. 3 indicate signals at corresponding points in FIG.

Before time T ₁ , the output voltage V _out is higher than the reference value, and the comparison voltage V ₁ is higher than the reference voltage V _ref . Therefore, the output of comparator 2 is at "H" level. In this state, DC / DC
Since the converter does not need to supply current to the load, the coil current _IL is zero. Here, the operation of the comparators 3 and 4 for detecting the coil current _IL will be described with reference to FIG.

Since the offset voltage V _S1 is applied so as to give a negative potential to its + terminal, the comparator 3 outputs an “L” level when the coil current _IL is 0. When the coil current I _L increases and its value becomes I _LP , the voltage across the resistor R _sense becomes the offset voltage V _S1 , and the output of the comparator 3 is inverted from “L” to “H”. Because of the output inversion, the switching element 1 is turned off. Thereafter, the coil current _IL starts to decrease.
When the value becomes smaller than I _LP , the output of the comparator 3 is again inverted from “H” to “L”.

Since the offset voltage V _S2 is applied so that a positive potential is applied to its + terminal, the comparator 4 outputs an “H” level when the coil current _IL is 0. Coil current I _L increases and the value is I _LB,
The voltage across the resistor R _sense becomes the offset voltage V _S2 , and the output of the comparator 3 is inverted from “H” to “L”. Then, when the coil current I _L decreases and its value becomes smaller than I _LB , the output of the comparator 3 is again inverted from “L” to “H”. In this embodiment, the current value I _{LB is set} to 0
It is set to a value slightly larger than. Accordingly, the comparator 3 may be considered to be substantially the coil current I _L outputs "H" level when zero.

As described above, when the coil current _IL is 0, the output of the comparator 4 is at the "H" level.
Before ₁ the output of the AND circuit 6 is at "H" level,
The count value of the counter 12 is reset to “0”.

[0035] period DC / DC converter is operating in light load mode, the load current is increased, at time T _1, the output voltage V _out is smaller than the reference value, the output of the comparator 2 is "L" Therefore, the output of the AND circuit 6 also becomes "L" level, and the counter is released from the reset state. That is, thereafter, the state becomes such that the count operation can be performed.

At this time, the output of the AND circuit 5 once becomes "H" level, and the count value of the counter 12 is incremented from "0" to "1" by its rising edge. In addition, when the output of the AND circuit 5 becomes “H” level, the state of the flip-flop 10 becomes “set”, so that the switching element 1 is turned on. When the switching element 1 is turned on and the coil current _IL increases (ramp-up), the output of the comparator 4 goes low, and the output of the AND circuit 5 also goes low.

At time T ₂ , the coil current I _L becomes I _LP
, The output of the comparator 3 once becomes “H” level as described with reference to FIG.
This signal resets the state of the flip-flop 10
And the switching element 1 is turned off. The switching element 1 is turned off, the coil current I _L begins to decrease (ramp down), firstly, the comparator 3
Output becomes "L" level. Then, at time T _3, the coil current I _L becomes zero (smaller than the current value I _LB), the output of the comparator 4 becomes "H" level. In this way, the power supply cycles of one cycle at a time T ₁ through T ₃ is completed.

When one power supply cycle is completed,
At time T _3, checks whether the output voltage V _out with reference to the output of the comparator 2 is recovering the reference value.
Here, the output voltage V _out has not recovered to the reference value,
The output of the comparator 2 remains at the “L” level. Thus, at time T _3, the output of the comparator 4 becomes "H" level, the output of the AND circuit 5 becomes "H" level, "2 by the rising edge of this signal from the count value of the counter 12 is" 1 " Is incremented.

The operation from time T _{3 to} time T ₄ corresponds to time T ₁
Is the same as one period of the power supply cycle in through T _3, it is determined whether it is necessary to perform the following cycle when the cycle end (time T _4), the comparator 2
Since the output of the is "L" level, further executes the following cycle at time T ₄ through T _5. Then, the time T _{4 to} T ₅
When the cycle is executed, the count value is “2”.
Is incremented to “3”.

As described above, when the output voltage _Vout decreases in the light load mode, the power supply cycle is repeated until the output voltage _Vout recovers to the reference value, and the count value of the counter 12 is increased each time the cycle is executed. Incremented.

[0041] The above cycle is repeated at time T _5, the output voltage V _out even more when determined not to restore the reference value next power supply cycle is executed, at this time, the count value of the counter 12 It becomes "4". When the count value of the counter 12 becomes “4”, the output changes from “L” level to “H” level, and the latch circuit 13 detects a rising edge of the signal. And
The latch circuit 13 changes the output to the “H” level, and thereafter keeps that state until reset by a signal from the mode switching control circuit 20. This output signal is transferred to selectors 7 and 8 and mode switching control circuit 20 as an A select signal.

When receiving the "H" level as the A select signal, the mode switching control circuit 20 changes the B select signal from the "H" level to the "L" level and transfers it to the selectors 7, 8 and the latch circuit 13. . On the other hand, the selectors 7 and 8 receive the “H” level as the A select signal from the latch circuit 13 and
Receives the “L” level as the B select signal from
The signal input to each A terminal, that is, PWM
A signal generated by the control circuit (heavy load control circuit) 9 is selected and output. Therefore, the switching element 1 is turned on / off by the signal generated by the PWM control circuit 9, and the DC / DC converter shifts to the operation in the heavy load mode.

As described above, during operation in the light load mode, the output voltage _Vout decreases due to an increase in load current or the like, and the power supply cycle is repeated a predetermined number of times (four times) in order to recover the reduced voltage. When executed continuously, DC /
The DC converter automatically switches its operation mode from the light load mode to the heavy load mode.

FIG. 4 is a time chart for explaining the operation when the count value is reset in the light load mode. Similar to the time T ₁ after the operation described in FIG. 2,
The count value of the counter 12 is incremented to “0”, “1”, and “2”. Here, after the second count value power supply cycle is initiated at time T ₆ becomes "2", at time T _7, the output voltage V _out to recover the reference value, the output of the comparator 2 is "H Level. In this state, at time T _8, when the second cycle has been completed, by referring to the output of the comparator 2 determines whether it is necessary to next cycle. Since the output of the comparator 2 is the "H" level, the next cycle will not run and, at time T ₈ is the output of the comparator 4 the coil current I _L is 0 also "H", the AND circuit The output of the counter 6 becomes "H" level, the count value of the counter 12 is cleared, and returns to "0". Therefore, the operation mode of the DC / DC converter remains in the light load mode.

As described above, in the light load mode, even when the count-up is started due to the output voltage V _out falling below the reference value, the value is maintained within the predetermined time (within four power supply cycle periods). When the value is restored, the count value of the counter 12 is reset. For this reason, for example, when the count value is incremented due to the output voltage _Vout dropping below the reference value due to a momentary drop of the output voltage _Vout or noise or the like, the count value can be reset. That is, according to the method of the present embodiment, erroneous mode switching due to noise or other factors can be prevented.

By the way, while the DC / DC converter is operating in the heavy load mode, the B select signal is "L".
Fixed to level. Although not particularly shown, the counter 12 is in a reset state during a period when the B select signal is at the “L” level, that is, while the counter 12 is operating in the heavy load mode, and the count value remains 0. It is. When the operation mode of the DC / DC converter switches from the heavy load mode to the light load mode, the mode switching control circuit 20 changes the B select signal from the “L” level to the “H” level, but the latch circuit 13 ,
The signal is reset by the rising edge at that time, and its output, that is, the A select signal is set to the “L” level.
Thus, when the mode is switched from the heavy load mode to the light load mode, the output (A select signal) of the latch circuit 13 is automatically switched.

FIG. 5 shows the power supply cycle and the coil current I.
It is a figure showing the relation of the average value of _L. Here, the peak value of the coil current I _L is I _LP (comparison level of the comparator 3).
And the bottom value is 0 (comparison level I _{LB of} comparator 4)
It is.

In the DC / DC converter of this embodiment, the mode is switched when the count value of the counter 12 is continuously incremented and becomes "4". In other words, it can be said that the configuration is such that the average value of the coil current I _L during the four power supply cycle period times (monitoring time) is monitored, and the mode is switched when the average value reaches a predetermined value. That is, for example, at any monitoring time, power is supplied to the load side at its first cycle, when in the second to fourth cycles and is not supplied, the average coil current I _L in the monitoring time The value is I _LP / 8. On the other hand, the first to fourth
Power on the load side in every cycle period when the supplied average value of the coil current I _L in the monitoring time is I _LP / 2 of. And the coil current I _L
Is switched from the light load mode to the heavy load mode when the average value of _ILP becomes I _LP / 2. This current value I _LP
/ 2 is the maximum current that can be supplied in the light load mode.

By the way, the average value of the coil current I _L can be regarded as the load current. Therefore, it can be said that the DC / DC converter of the present embodiment is configured to switch its operation mode to the heavy load mode when the load current reaches the maximum supply current in the light load mode. Further, the waveform of the coil current I _L, the coil L, the input voltage V _in, so determined by comparing the level I _LP of the output voltage V _out and a comparator 3, by setting the I _LP, the light-load mode to the heavy load mode Can be determined.

[0050] In the above embodiment, the count value of the counter 12 is configured to perform mode switching when it is "4", by increasing the value, long period to obtain an average value of the coil current I _L Therefore, the accuracy is increased.

As described above, in the DC / DC converter of the present embodiment, the circuit for obtaining the load current is composed of low-current-consumption circuits such as comparators, gate circuits, counter circuits, and latch circuits. , The current consumption of the entire DC / DC converter is reduced, and the conversion efficiency is improved.
In particular, the present embodiment is intended for operation in a light load mode in which the load current is small, and reducing the ratio of the current consumption to the load current has a great effect on improving the conversion efficiency.

In the above embodiment, the step-down DC
Although the present invention has been described using a DC / DC converter, the present invention is not limited to this configuration.
The present invention is also applicable to a DC / DC converter and an inverting DC / DC converter.

[0053]

Since the means for calculating the load current is constituted by a circuit consuming less current, the current consumption of the entire DC / DC converter can be reduced. Further, since it is determined whether or not the mode switching is necessary using the logic signal binarized by the comparator without using the integrating circuit or the like, the current consumption can be reduced. Further, the circuit for processing the above logic signal has a small scale, and the area occupied by the chip can be reduced.

When it is determined whether or not the operation mode needs to be switched, the switching is performed only when the predetermined condition occurs n times consecutively. Therefore, it is possible to prevent erroneous mode switching due to noise or the like. Can be. Further, the condition for switching the operation mode can be easily set to a desired value.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a DC / DC converter according to an embodiment of the present invention.

FIG. 2 is a time chart (part 1) for explaining the operation of the DC / DC converter.

FIG. 3 is a diagram illustrating the operation of a comparator for detecting coil current.

FIG. 4 is a time chart (part 2) for explaining the operation of the DC / DC converter.

FIG. 5 is a diagram illustrating a coil current at the time of mode switching.

FIG. 6 is a configuration diagram of an example of a conventional DC / DC converter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Switching element 2-4 Comparator 5, 6 AND circuit 7, 8 Selector 9 PWM control circuit (control circuit for heavy load) 10 Flip-flop 11 Driver 12 Counter 13 Latch circuit 20 Mode switching control circuit

Claims (1)

(57) [Claims] An operation mode for supplying power to a load includes a light load mode and a heavy load mode, and the switching means is driven according to a method corresponding to each operation mode .
DC to control the output voltage by controlling the coil current
In the DC / DC converter, in the light load mode, the predetermined voltage to be held by the output voltage is set.
When the pressure is higher than the pressure, the switching means is in the off state.
And the output voltage is higher than the predetermined voltage to be held.
If the coil current becomes zero,
Start by turning on the above switching means
The coil current increases and the preset current
The above switching method is triggered by exceeding the upper limit.
Turning the stage off reduces its coil current
Power supply cycle ends when it returns to zero
An operation mode to be, the heavy load mode is determined based on the output voltage de
A pulse signal having a duty value is generated and the pulse
An operation mode in which the switching means is controlled according to a signal.
An over-de, comparing means for comparing a predetermined voltage set in advance and the output voltage, when the output voltage is lower than the predetermined voltage, the number of times the power supply cycle in the light load mode is executed continuously Counting means for counting, and the comparing means when the output voltage is higher than the predetermined voltage.
Is determined, the count value of the above counting means
And resetting means for resetting, when the count value of said counting means reaches a predetermined number, DC / DC converter, characterized in that it comprises a control means for switching the operation mode from the light load mode to the heavy load mode, the.