JPH08340670A - Dc/dc converter - Google Patents

Abstract

PURPOSE: To switch the operation mode of a DC/DC converter which has a heavy load mode and a light load mode securely with small current consumption. CONSTITUTION: A comparator 13b monitors a coil current and, if the current value is lowered to zero, outputs an 'H' level signal. A counter 22 receives the reverse signal of the output of the comparator 13b through its CK terminal and increments the counted value every time the falling edge is detected. If a 2-bit counter 24 is counted up to '2' by pulse signals for the control of a coil current in a heavy load mode before the falling edge of the output of the comparator 13b is received, the counter 24 resets the counter 22. If the counter 22 is counted up to '4' without reset, the counter 22 outputs a pulse. If a latch circuit 23 receives the pulse from the counter 22, the latch circuit 23 switches the operation mode of a DC/DC converter from a heavy load mode to a light load mode.

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 that switches an operation mode according to a load.

[0002]

2. Description of the Related Art A DC / DC converter is a device that converts a certain direct current input voltage into a different direct current voltage and outputs it, and is used for various purposes. This output voltage needs to be stable at a predetermined value determined in advance, and in consideration of the case of being mounted on a mobile terminal or the like, it is required to reduce its power consumption as much as possible.

FIG. 9 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 V _out and the coil current calculation signal (mode switching signal), and outputs a switch control signal based on these received signals. When this 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 a switch control signal according to the mode. Is output.

The switching element 102 performs switching according to a switch control signal output from the switching signal generation circuit 101. For example, when the output voltage V _out decreases, the switching element 102 is turned on, the current flowing through the switching element 102 is caused to flow to the output side through the coil L, and power is supplied to the capacitor C and the output side to output the output voltage V. Increase _out .

The operation mode of the DC / DC converter is switched according to the current I _LD flowing through the connected load. Since this load current I _LD can be regarded as the average value of the coil current I _L , the average value of the coil current I _L is calculated as follows and output as a coil current calculation signal (mode switching signal). That is, the voltage value across the resistor R _sense through which the coil current I _L flows is impedance-converted via the buffer 103, and the converted signal is averaged by the integrating circuit 104. In this averaging process, the timer 10
5 is used, and the integral value of the 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 the comparison result as a coil current calculation signal (mode switching signal).

The switching signal generation circuit 101 switches the operation mode as necessary according to the coil current calculation signal (mode switching signal) and switches so as to supply the necessary load current I _LD while keeping the output voltage constant. A switch control signal for controlling the on / off state of the element 102 is output.

[0007]

As described above, since the coil current calculation signal (mode switching signal) is generated,
That is, in order to detect the load current, the buffer 10
3, integrating circuit 104, timer 105, comparator 10
A large number of circuit blocks such as 6 are required. For this reason, the scale of the circuit for detecting the load current becomes large and the current consumption thereof is also large. Further, the buffer 103, the integrator circuit 104, and the comparator 106 are required to always supply a bias current, which consumes current constantly, which hinders the power consumption reduction of the DC / DC converter. That is, in the conventional DC / DC converter, the consumption current 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 thereof is to provide a DC / DC converter which detects a load current with a small current consumption and surely switches modes.

[0009]

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

The DC / DC converter according to claims 1 and 2 operates when the bottom value of the coil current that changes according to the control in the heavy load mode reaches a predetermined current value (for example, 0) a predetermined number of times. Switch the mode from heavy load mode to light load mode. Further, in the process of detecting that the value of the coil current has reached the predetermined current value and counting the number of times of detection, when the bottom value of the coil current becomes larger than the predetermined current value, the count value is set to Reset.

The DC / DC converters according to claims 3 and 4 have each means shown in FIG. The comparison means 1 is
For example, a comparator, which compares a coil current that changes according to the control in the heavy load mode with a preset predetermined current value (for example, 0), and outputs a detection signal when the coil current reaches the predetermined current value. The counting means 2 counts the number of detection signals output by the comparing means 1. The control means 3 switches the operation mode of the DC / DC converter from the heavy load mode to the light load mode when the count value of the counting means 2 reaches a predetermined number of times. In the light load mode, the control means 3 determines the coil current by controlling the on / off state of the switch unit according to the control in the light load mode, for example. The reset means 4 is
The counter means 2 is reset when the bottom value of the coil current that changes according to the control in the heavy load mode becomes larger than the predetermined current value. During the period when the DC / DC converter is operating in the heavy load mode, the coil is usually Although the current is large, when the load current decreases, the coil current also decreases, and the value reaches a preset predetermined current value (for example, 0). The coil current has, for example, a ramp waveform (a waveform in which the current linearly increases and reaches a peak, and then linearly decreases and reaches a bottom value), and fluctuates in a predetermined cycle. Therefore, when the load current decreases and the coil current reaches a level where the coil current reaches the predetermined current value, the coil current value and the predetermined current value repeatedly cross each other.

The comparison means 1 outputs a detection signal each time the above two values cross, the counter means 2 counts the number of the detection signals, and when the count value reaches a predetermined number, the operation mode is set. Switch from heavy load mode to light load mode. That is, when the state in which the coil current is sufficiently small continues for a certain period, the operation mode is switched from the heavy load mode to the light load mode.

On the other hand, even when the coil current is reduced to a sufficiently small state, if the state does not continue for a certain period, the resetting means 4 resets the counting means 2 (count value), so that the operation mode is I can't switch. Therefore, the mode switching does not occur when the coil current value instantaneously decreases or due to noise.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows the DC / DC of one embodiment of the present invention.
It is a block diagram of a DC converter. DC / DC shown in FIG.
Converter converts the DC input voltage V _in to an output voltage V _out. In addition, this DC / DC converter has two operation modes: a heavy load mode, which is an operation mode when the consumption current of the connected load is large, and a light load mode, which is an operation mode when the consumption current of the connected load is small. And has its operation mode automatically switched according to the load current.

The switching element 11 is a power MOS transistor and performs on / off operation according to the gate potential. Then, the input voltage V _in to the one terminal is applied, a cathode and a coil L of the diode D is connected to the other terminal. The anode of the diode D is grounded. The other end of the coil L is connected to the output terminal via the resistor R _sense . The output terminal is grounded via the capacitor C.

The reference voltage V _ref is applied to the + input of the comparator 12, and the comparison voltage V _{1 obtained by} dividing the output voltage V _out by the resistors R ₁ and R ₂ is applied to the − input of the comparator 12. Then, the comparison result is output to the light load control circuit 15.

The comparators 13a and 13b include a resistor R
Monitor the voltage across _sense . Where resistance R
_The current flowing through the _sense is the coil current I flowing through the coil L.
_Since it is _L , the comparators 13a and 13b are
The coil current I _L on the primary side of the C / DC converter will be monitored. The comparator 13a has a coil current I
_L is compared with a preset comparison level I _LP (I _LP > 0), and when the coil current I _L exceeds the comparison level I _LP , the “H” level is output. On the other hand, the comparator 13b compares the coil current I _L with a preset comparison level I _LB (I _LB = 0 in this case), and when the coil current I _L drops to 0, the "H" level is reached. Is output. The outputs of the comparators 13a and 13b are transferred to the light load control circuit 15 and used as one condition for the control in the light load mode.

PWM control circuit (heavy load control circuit) 14
Outputs a pulse signal for controlling the output voltage V _out so as to maintain a constant value. For example, when the output voltage V _out drops, the duty of the pulse signal is once increased and the coil current I _L is increased to output the output voltage V _out . After the output voltage V _out is recovered, the duty of the pulse signal is restored. The output signal of the PWM control circuit 14 is input to the A terminal of the selector 16 and the mode switching control circuit 20, and the inverted signal thereof is input to the A terminal of the selector 17.

The light load control circuit 15 includes a comparator 1
It receives the output signals of 2, 13a and 13b and produces a control signal according to the output voltage V _out and the coil current I _L. The output signal of the light load control circuit 15 is the selector 16
Is input to the B terminal of the selector 17, and the inverted signal thereof is input to the B terminal of the selector 17.

The selectors 16 and 17 select and output one of the signals input to the A terminal or the B terminal according to the select signal notified from the mode switching control circuit 20. That is, the selectors 16 and 17 are
When the select signal is "H" level, the signal input to the A terminal is selected, and when it is "L" level, the signal input to the B terminal is selected. In FIG. 2, when the select signal is at “H” level, it is shown as “A select”, and when it is at “L” level, it is shown as “B select”. The output signal of the selector 16 is input to the S terminal (set terminal) of the flip-flop 18, and the output signal of the selector 17 is input to the R terminal (reset terminal) of the flip-flop 18.

The flip-flop 18 outputs an ON signal in the set state and an OFF signal in the reset state. The driver 19 drives the switching element 11 into an ON state when receiving the ON signal, and turns the switching element 11 into an OFF state when receiving the OFF signal.

The mode switching control circuit 20 is a DC / DC
This is a circuit for instructing switching of the operation mode of the converter, and transfers a select signal to the selectors 16 and 17. The mode switching control circuit 20 includes a comparator 13
Based on b and the output signal of the PWM control circuit 14, it is determined whether to switch from the heavy load mode to the light load mode. When switching from the heavy load mode to the light load mode, the select signal is changed from the “H” level to the “L” level.

As described above, when the selectors 16 and 17 receive the "L" level as the select signal, they respectively select and output the signal input to the B terminal. That is, when the select signal changes from the “H” level to the “L” level, the selectors 16 and 17 select the output signal of the light load control circuit 15, and the switching element 11 is selected.
Is driven by the selected signal, DC /
The DC converter will now operate in the light load mode.

When switching the operation mode of the DC / DC converter from the heavy load mode to the light load mode, the PWM
It is also possible to stop the oscillation of an oscillator for generating the output pulse of the control circuit 14 (this oscillator is not shown, but is incorporated in the PWM control circuit 14, for example). In addition, the mode switching control circuit 20 uses the DC / DC
Control for switching the operation mode of the converter from the light load mode to the heavy load mode is also performed, but the description thereof is omitted here.

FIG. 3 is a circuit diagram of the mode switching control circuit 20 and its peripheral portion. As described above, the comparator 13b monitors the coil current I _L by receiving the potential across the resistor R _sense at each input terminal.
The comparator 13b may, when the coil current I _L flows from the input side to the output side outputs "L" level, when the coil current I _L is flowing to the input side from 0 or the output side "H" Output level.

By the way, when the operation mode is switched according to the load current, a method of directly detecting the load current may be considered, but for that 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 lowered, which is not preferable. Therefore, in this embodiment, the load current is estimated using the resistance (that is, the resistance R _sense ) provided on the input side (primary side) of the capacitor C. The resistor R _sense uses a resistor used for the purpose of overcurrent protection or keeping the output voltage constant. Therefore, it is not necessary to newly provide a resistor for detecting the load current, and the efficiency of the DC / DC converter is not reduced.

The counter 22 receives the output signal of the comparator 13b inverted by the inverter 21, and when the falling edge of the signal is detected, the counter 22 sets the count value to 1
Just count up. Then, when the count value becomes “n (natural number)”, a pulse is output. In this embodiment, n = 4. The counter 22 is a DC
The / DC converter is reset when the operation mode is switched from the light load mode to the heavy load mode.

Upon receiving the pulse from the counter 22, the latch circuit 23 holds and outputs the "L" level until the operation mode of the DC / DC converter is switched from the light load mode to the heavy load mode. The output of the latch circuit 23 is transferred to the selectors 16 and 17 as a select signal.

The 2-bit counter 24 receives the output signal of the PWM control circuit 14 at its clock terminal and increments the count value by 1 each time the falling edge of the signal is detected. The 2-bit counter 24 outputs "H" when the count value becomes 2. When the output of the 2-bit counter 24 becomes "H" level, the counter 22 is reset. The 2-bit counter 24 is reset when the output of the comparator 13b becomes "H" level.

Next, the operation of the DC / DC converter of this embodiment will be described with reference to the time chart. FIG.
[Fig. 6] is a time chart explaining the operation mode switching from the heavy load mode to the light load mode. It is to be noted that the symbols (1) to (3) in the figure are signals at corresponding points in FIG.

Before time T1, the load current is large and DC
The / DC converter is operating in the heavy load mode. Here, it is assumed that the counter value of the counter 22 is 0.
In the heavy load mode, the coil current I _L has a ramp waveform. That is, the waveform of the coil current I _L is formed by the ramp-up during the ON state of the switching element 11 and the ramp-down during the OFF state of the switching element 11, and its cycle depends on the operating frequency of the PWM control circuit 14. Decided.

While the load current is large to some extent, the coil current I _L always fluctuates to a value larger than zero. Therefore,
The output of the comparator 13b remains at "L" level, and since the falling edge is not input to the CK terminal of the counter 22, the count value of the counter 22 remains "0".

In the above state, when the load current becomes smaller, the output voltage V _out changes accordingly. On the other hand, the PWM control circuit 14 changes the duty of the output pulse so as to keep the output voltage V _out at a constant value. For example, when the output voltage V _out rises, the PWM control circuit 14 once reduces the duty of the output pulse to reduce the average value of the coil current I _L. If the output voltage V _out returns to the preset value by this, the duty is returned to V _out / V _in .

FIG. 5 is a diagram showing how the coil current I _L decreases. When the load current decreases, the PWM control circuit 14 controls the duty of the output pulse so as to keep the output voltage V _out at a constant value, and as shown in FIGS. 5 (a) to 5 (c), the coil current _IL Decrease the average value of. When the load current decreases to a predetermined current value, the bottom value of the coil current I _L becomes 0, as shown in FIG. 5 (c).

If the load current becomes smaller, the average value of the coil current I _L needs to be made smaller. In this case, as shown in FIG. 5 (d), there is a period in which the coil current I _L does not flow. become. In this way, in a state where the coil current I _L does not flow and the power supply cycle is discontinuous, the efficiency in the heavy load mode decreases. Therefore, the DC / DC converter of the present embodiment operates in the heavy load mode when the load current (coil current I _L ) is larger than the state shown in FIG. It is configured to operate by switching to the load mode.

[0036] Here, the coil current I _L in the state shown in FIG. 5 (c), when the peak value I _P, can represent the average value I _P / 2. The average value of the coil current is
Since it can be regarded as the load current, when the mode switching is performed based on the load current, the condition for switching from the heavy load mode to the light load mode can be determined by setting the current value I _P.

Returning to FIG. When the coil current I _L gradually decreases and its bottom value becomes 0 at time T1, the output of the comparator 13b becomes “H” level, and the falling edge is input to the CK terminal of the counter 22. The count value of the counter 22 is 0 to 1 depending on this falling edge.
Is counted up.

After time T1, each time the bottom value of the coil current I _L becomes 0, the output of the comparator 13b becomes "H".
The level becomes a level, and as a result, the counter 22 is sequentially incremented.

On the other hand, the 2-bit counter 24 indicates the time T1.
After that, the count value is incremented each time the falling edge of the output signal of the PWM control circuit 14 is detected,
When the output of the comparator 13b becomes "H" level, it is immediately reset, so that the count value is 0 or 1. Therefore, the output of the 2-bit counter 24 is "L".
The level remains as it is, and the counter 22 is not reset and is sequentially incremented each time the falling edge is received at the CK terminal.

At time T2, when the count value of the counter 22 becomes "4", the counter 22 is latched by the latch circuit 23.
Pulse is output to. Upon receiving this pulse, the latch circuit 23 changes its output from “H” level to “L”.
After changing to the level, the “L” level is continuously output until it is reset. This output signal is transferred to the selectors 16 and 17 as a select signal.

Upon receiving the "L" level as the select signal, the selectors 16 and 17 select and output the signal input to the B terminal, that is, the signal generated by the light load control circuit 15, respectively. Therefore, the switching element 11 is on / off controlled by the signal generated by the light load control circuit 15, and the DC / DC converter shifts to the light load mode operation.

As described above, during the operation in the heavy load mode, the coil current I _L decreases due to the decrease of the load current, and when the counter 22 receives the falling edge a predetermined number of times (4 times), DC / The DC converter considers that the load current has become sufficiently small and switches the operation mode from the heavy load mode to the light load mode.

FIG. 6 is a time chart for explaining the operation when the count value is reset in the heavy load mode. Similar to the operation after time T1 described in FIG. 4,
The comparator 13b outputs a pulse, and the count value of the counter 22 is counted up as "0""1""2". Here, it is assumed that the load current increases after time T3. In this case, the DC / DC converter changes the output of the PWM control circuit 14 so as to keep the output voltage at a constant value and increases the coil current I _L. Then, the coil current I _L is always a value larger than 0. That is, the bottom value of the coil current I _L will not drop to zero. Therefore, after time T3, the comparator 13b
No longer outputs a pulse, and the count value of the counter 22 remains 2.

Since the output of the comparator 13b does not become "H" level after time T3, the 2-bit counter 24
Will not be reset. However, since the 2-bit counter 24 receives the falling edge of the output signal of the PWM control circuit 14, it counts up. When the count value of the 2-bit counter 24 becomes 2 at time T4, the output of the 2-bit counter 24 becomes "H" level. The counter 22 is reset when the output of the 2-bit counter 24 becomes "H" level.

As described above, in the heavy load mode, even if the bottom value of the coil current I _L becomes 0 and the counter 22 starts counting up, the coil current I _L falls within a predetermined period.
If is increased, the counter 22 is reset. Thus, for example, even though not actually decrease the coil current I _L is sufficiently, when the noise component or the like of the coil current I _L had increments the count value of the counter 22, the count value Can be reset. That is, according to the method of this embodiment, it is possible to prevent erroneous mode switching due to noise or other factors.

FIG. 7 shows a DC / D according to another embodiment of the present invention.
It is a block diagram of a C converter. 7, the same reference numerals as those used in FIG. 3 indicate the same parts. The difference between the two embodiments is that in the configuration of FIG.
The offset voltage V _OS is applied to the-terminal of b.

FIG. 8 is a diagram showing the input / output of the comparator 13b. When the offset voltage V _OS is applied as in the above configuration, the coil current I _L becomes 0 as shown in FIG.
In this state, the input of the comparator 13b has the potential (V ₊ ) at the + terminal higher than the potential (V ₋ ) at the − terminal by the offset voltage V _OS . In other words, the comparator 1
3b input potential difference (in FIG. 8, the comparator 13
When the input potential difference of b is V13 = V ₋₋ V ₊ ) 0, the value I _m of the coil current I _L becomes a value larger than 0. Therefore, when the coil current I _L decreases below I _m , the output of the comparator 13b becomes "H" level.

With such a structure, the coil current I _L
When the bottom value of 0 becomes 0, the comparator 1
Since the width of the pulse output by 3b becomes wider, the counter 2
2 can certainly detect the falling edge of the pulse.

Further, in the above configuration, as shown in FIG. 8 (b), when the bottom value of the coil current I _L decreases below I _m , the output of the comparator 13b becomes "H" level,
The pulse generated at that time is counted by the counter 22. Then, according to this count value, DC / D
The converter operating mode is switched. in this case,
The average value of the peak value and the bottom value of the coil current I _L shown in the figure serves as a standard for switching the operation mode. In this way, the switching point of the operation mode can be determined by setting the offset voltage V _OS (current value I _m ).

In the above embodiment, the PWM control method is adopted as the heavy load mode, but the present invention is not limited to this. Further, although the step-down DC / DC converter has been described as an example, the present invention is not limited to this configuration and can be applied to, for example, a step-up DC / DC converter and an inverting DC / DC converter. .

[0051]

In the DC / DC converter, the load current is detected by using the resistor provided in advance on the primary side of the capacitor of the output section, so that the consumption current does not increase. Further, when the operation mode is switched according to the load current, the means for judging whether or not the load current has reached this switching point is composed of a circuit with low current consumption.
The efficiency of the entire DC / DC converter is improved.

When it is determined whether or not the operation mode needs to be switched, the mode switching is performed assuming that the load current has reached the switching point only when a predetermined condition continues to occur. It is possible to prevent erroneous mode switching due to noise or the like. Further, the condition for switching the operation mode can be easily set to a desired value.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a means of the present invention.

FIG. 2 is a configuration diagram of a DC / DC converter according to an embodiment of the present invention.

FIG. 3 is a circuit diagram of a mode switching control circuit and its peripheral portion.

FIG. 4 is a time chart (No. 1) for explaining the operation of the DC / DC converter.

FIG. 5 is a diagram showing how the coil current I _L decreases.

FIG. 6 is a time chart (No. 2) for explaining the operation of the DC / DC converter.

FIG. 7 is a configuration diagram of a DC / DC converter according to another embodiment of the present invention.

FIG. 8 is a diagram for explaining the operation of the DC / DC converter shown in FIG.

FIG. 9 is a block diagram of an example of a conventional DC / DC converter.

[Explanation of symbols]

 1 Comparing Means 2 Counting Means 3 Control Means 4 Reset Means 11 Switching Elements 12 Comparators 13a, 13b Comparators 14 PWM Control Circuits (Heavy Load Control Circuits) 15 Light Load Control Circuits 16, 17 Selectors 18 Flip Flops 19 Drivers 20 Mode Switching Control circuit 21 Inverter 22 Counter 23 Latch circuit 24 2-bit counter

Claims (4)

[Claims] 1. A DC / DC converter which has at least a heavy load mode and a light load mode as an operation mode for supplying a current to a load, and which changes a coil current according to a method corresponding to each operation mode to control an output, The operation mode is switched to the light load mode when the value of the coil current that changes according to the control in the heavy load mode reaches the predetermined current value a predetermined number of times.
C / DC converter. 2. When the bottom value of the coil current becomes larger than the predetermined current value in the process of detecting that the value of the coil current has reached the predetermined current value and counting the number of times of detection. The DC / DC converter according to claim 1, wherein the count value is reset. 3. A DC / DC converter that has at least a heavy load mode and a light load mode as operation modes for supplying a current to a load, and changes a coil current according to a method corresponding to each operation mode to control an output, A comparison unit that compares the coil current that changes according to the control in the heavy load mode with a preset predetermined current value, and outputs a detection signal when the coil current reaches the predetermined current value, and the comparison unit outputs the detection signal. A DC / DC converter comprising: counting means for counting the number of detection signals; and control means for switching the operation mode to the light load mode when the count value of the counting means reaches a predetermined number. 4. A reset means for resetting the counter means when the bottom value of the coil current changing according to the control in the heavy load mode becomes larger than the predetermined current value. The described DC / DC converter.