JP5109775B2 - Switching power supply - Google Patents

Description

  The present invention relates to a power source for improving a power factor which makes a stable DC power source from an AC power source and operates so that an input voltage and an input current are substantially in phase and similar.

This type of switching power supply
1) There are two systems: a critical mode control system for controlling the switching element to be turned on when the coil current becomes 0, and 2) a continuous current mode control system for controlling the coil current not to become 0.

Since the former current critical mode control method generally switches when the coil current is 0, the switching noise is low and it is advantageous for low noise. However, the stress applied to the coil and the diode is large and the load is large. It is unsuitable.
On the other hand, the latter current continuous mode control method has a larger switching noise than the current critical mode control method, but the current ripple is small, so that the stress applied to the coil and the diode is small, and it can be applied to applications where the load is large. is there.

In view of this, the critical mode control method is generally used for up to about 100 watts, and the continuous current mode control method is generally used for about 100 watts or more.
In addition, current critical mode control switching power supplies
There are two methods: A) a method for detecting the input rectified voltage, and B) a method for not detecting the input rectified voltage.

Here, as an example of the prior art, a switching power supply in a continuous current mode and a switching power supply in a current critical mode that does not detect the input rectified voltage in B) will be described. First, as an example of the former, refer to FIG. 9 disclosed in Patent Document 1, for example.
The switching power supply of FIG. 9 is an example of a boost converter that boosts an input rectified voltage and outputs a voltage higher than the input rectified voltage. Here, the input rectified voltage is a voltage obtained by full-wave rectifying an AC voltage by a rectifier circuit 2 including a diode bridge. The output voltage is a voltage across the capacitor 7 and is a DC voltage smoothed by the diode 6 and the output capacitor 7.

In the switching power supply, the current flowing through the inductor 4 is controlled by turning on and off the switching element 5 such as a MOSFET. The purpose of the control is
a) Improvement of power factor of AC input b) Stabilization of DC output voltage, and in order to achieve this, the waveform and amplitude of the current flowing in the inductor 4 are controlled as follows.

The inductor current waveform is controlled to be a similar full-wave rectified waveform with the same phase as the input rectified voltage, thereby improving the input power factor. The amplitude of the inductor current is
A) When the output voltage drops, the current amplitude is increased to increase the charge amount of the capacitor 7,
B) When the output voltage is lowered, the current amplitude is reduced to reduce the amount of charge, whereby the output voltage can be stabilized.

FIG. 9 will be described more specifically.
1) The output voltage error amplifier (also simply referred to as an error amplifier or amplifier) 26 outputs a signal Verr obtained by amplifying the error between the output voltage Vout and the reference voltage Vref to the multiplication circuit 23.
2) The multiplication circuit 23 multiplies the amplified error voltage Verr and the input rectified voltage detection value Vrec to generate a threshold signal Vth (the threshold signal Vth has the same phase as the input rectified voltage Vin) It is a full-wave rectified waveform and has an amplitude proportional to the error voltage Verr).
3) The current flowing through the inductor 4 is converted into the current detection signal Vi by the current detection resistor 13.
4) The current detection signal Vi is compared with the threshold signal Vth by the comparator 22, and when the current detection signal Vi exceeds the threshold signal Vth, the output of the comparator 22 becomes high level.
5) The output of the comparator 22 is input to the trigger input terminal of the monostable multivibrator 31.

6) The monostable multivibrator 31 keeps the output at the low level for a certain period from the trigger, and then changes the output to the high level.
7) The output of the monostable multivibrator 31 is input to the drive circuit 12.
8) The drive circuit 12 turns on the switching element 5 when the input is at a high level, and turns it off when the input is at a low level. That is, the switching element 5 is turned on after being turned off for a certain period.
9) While the switching element 5 is on, the current of the inductor 4 increases.
Thereafter, returning to 4), the current detection signal Vi increases as the inductor current increases, and when the threshold signal Vth is exceeded, the monostable multivibrator 31 is triggered.

The movement of the current flowing through the inductor can be summarized as follows.
a) When the switching element 5 is off (the output of the monostable multivibrator 31 is low level), the current of the inductor 4 gradually decreases.
b) The switching element 5 is turned on after a lapse of a certain time (the output of the monostable multivibrator 31 becomes high level). The switch-off time is set so that the current does not become 0 or less.

c) While the switching element 5 is on, the current of the inductor 4 gradually increases.
d) When the detected value of the inductor current reaches the threshold signal Vth, the switching element 5 is turned off.
With the above control, the peak value of the inductor current is controlled so as to coincide with the threshold signal Vth which is a full-wave rectified waveform in phase with the input rectified voltage Vin. As a result, the input power factor is improved.

Next, an example disclosed in Patent Document 2 will be described below with reference to FIG. 10 as a current critical mode control type switching power supply that does not detect an input rectified voltage.
1) The resistance voltage dividing circuit 11 divides the output voltage Vout and outputs it to the error amplifier 26.
2) The error amplifier 26 amplifies the error between the divided voltage and the reference voltage Vref, and outputs an error signal Verr. The error amplifier 26 responds only to a period longer than the commercial period.
3) When the switching element 5 is on, the current flowing through the inductor 4 increases at a constant rate. Along with this, the voltage Vaux of the inductor auxiliary winding becomes positive.
4) The CR series circuit 33 generates a drive voltage Vrs from the auxiliary winding voltage Vaux of the inductor. The drive voltage Vrs has a high level and a low level.

5) The ramp circuit 32 outputs the ramp voltage Vrmp while the drive voltage Vrs is at a high level. (This ramp voltage is, for example, a voltage that rises with a certain slope, shown as an internal signal in the timer circuit of FIGS. 2 and 4.)
6) The ramp voltage Vrmp is input to the positive terminal of the comparator 22, and the error voltage Verr is input to the negative terminal. When the ramp voltage Vrmp becomes larger than the error voltage Verr, the reset voltage Vreset is output. Here, the error voltage Verr fluctuates for a sufficiently long time compared to the commercial cycle. Therefore, the error voltage can be regarded as constant when viewed at the commercial cycle level. As a result, the time from when the drive voltage Vrs becomes high level and the ramp voltage starts to rise until the comparator 22 outputs the reset voltage (when viewed at the level of the commercial cycle) can be regarded as constant.

7) When the reset voltage Vreset is output, the drive voltage Vrs is fixed to the ground potential.
8) When the switching element 5 is off, the current flowing through the inductor 4 decreases at a constant rate. Along with this, the voltage Vaux of the inductor auxiliary winding becomes negative.
9) When the inductor current becomes 0, the auxiliary winding voltage Vaux is pushed up.
10) As a result, the drive voltage Vrs becomes positive, and the switching element 5 is turned on.
Thereafter, returning to 3), the above operation is repeated.

The movement of the current flowing through the inductor can be summarized as follows.
a) When the switching element 5 is off, the current of the inductor 4 gradually decreases.
b) When the inductor current becomes zero, the switching element 5 is turned off.
c) When the switching element 5 is on, the current of the inductor 4 gradually increases.
d) Since the on-time (when viewed at the level of the commercial cycle) is constant, the switching element 5 is turned off when a certain time elapses.

By the way, the current increment ΔIL while the switching element 5 is on is expressed by the following (1), where IL is a current flowing through the inductor, Vin is a full-wave rectified voltage, L is an inductance value, and Ton is an on-time of the switching element. ).
ΔIL = Ton · Vin / L (1)
Therefore, if the on-time is constant, the inductor current increment ΔIL is proportional to the input rectified voltage Vin. As a result, the current flowing through the inductor has a similar full-wave rectification waveform in phase with the input rectification voltage.

Japanese Patent Laid-Open No. 04-168975 JP 2002-320378 A

In the device described in Patent Document 1, the input rectified voltage Vin is detected, and the current of the inductor is controlled based on the detected voltage. In order to detect the input rectified voltage, a voltage dividing circuit using a direct current resistor is required, and power loss is generated by this resistor. In particular, during standby when the switching power supply is not operating, the loss due to the voltage dividing resistance becomes a magnitude that cannot be ignored.
On the other hand, in the thing of patent document 2, since the input rectification voltage Vin is not detected, said problem does not generate | occur | produce. However, since this method is a current critical method in which the switching element is turned on after the current flowing through the inductor becomes 0, ripple (current component that increases or decreases depending on the on / off state of the switching element) increases. As a result, there is a problem that the inductance must be increased and the apparatus becomes larger.

  Therefore, the problem to be solved by the present invention is to eliminate the need to detect the input rectified voltage and suppress the loss, and by adopting the current continuous mode method, the ripple is not increased and the enlargement of the apparatus is avoided. There is.

Before describing the embodiment, the principle will be described first.
In order to solve the above problems, the present invention employs a control method that operates in the continuous current mode and does not require detection of the input rectified voltage Vin. More specifically, the switching function and the main configuration are the same, and the waveform and amplitude of the current flowing through the inductor are controlled as follows.

I. Control of inductor current waveform 1) Turn on the switching element.
2) The on-time of the switching element is fixed, for example, as shown in FIG. 6 (or is changed with a long period so that it can be considered constant when viewed at the level of the commercial period). During this on-time, the inductor current increases monotonically.
3) After a certain time has elapsed, the switching element is turned off. The current Imax at the time of turn-off is detected.
4) While the switching element is off, the inductor current decreases monotonously.
5) A value obtained by multiplying the above Imax by a coefficient K (greater than 0 and less than 1) is set as a lower limit value Imin of the inductor current. When the inductor current decreases to the lower limit value, the switching element is turned on again.

The relationship of the inductor current when the above operation is repeated is as follows.
Imin = K · Imax (2)
Imax = Imin + ΔIL (3)
Here, ΔIL is expressed as the above equation (1).
Imax = Imin / K = {1 / (1-K)} (Ton · Vin / L)
Imin = K (Imin + ΔIL) = {K / (1-K)} ΔIL
= {K / (1-K)} (Ton · Vin / L) (4)
It is expressed as

Since the average value of the inductor current excluding the switching ripple component is an intermediate value between the peak current and the current lower limit value,
IL = (Imax + Imin) / 2
= [(1 + K) / {2 · (1-K)}] (Ton · Vin / L) (5)
As shown, the inductor current is proportional to Vin. That is, a full-wave rectified waveform having the same phase as the input rectified voltage Vin is obtained. Here, the ON time Ton of the switching element is constant.

I I. Inductor current amplitude Inductor current amplitude is
・ When the output voltage drops, increase the current amplitude to increase the charge amount of the capacitor 7,
-Conversely, when the output voltage rises, the current amplitude is reduced to reduce the amount of charge.
It is controlled as follows. As a result, the output voltage can be stabilized.

There are the following two methods for controlling the amplitude, both of which are advantageous for use in the present invention.
1) Adjust K in the above equation (5) according to the output voltage. However, the response time constant of the coefficient K is sufficiently long so that K can be considered constant in the commercial cycle.
2) The on-time Ton of the switching element is adjusted according to the output voltage. However, the response time constant of Ton is assumed to be sufficiently long so that Ton can be considered constant in the commercial cycle.

From the above consideration, the invention of claim 1 is a diode rectifier circuit that obtains a pulsating current output by full-wave rectification of an AC power supply, an inductor connected to the diode rectifier circuit, and switching that turns on and off the current flowing through the inductor. An element, a capacitor that smoothes the current supplied from the inductor and obtains a DC output, and a diode that rectifies the current flowing from the inductor to the capacitor, boosts the AC input voltage and generates a stable DC. At the same time, in the switching power supply with the function to improve the power factor of AC input,
An error amplifying means for amplifying and outputting an error between a detected DC output voltage and a set value; a current detecting means for detecting a current flowing through the inductor; and a holding means for holding a peak value of the detected current. The current limiting means for setting the lower limit value of the current flowing through the inductor according to the peak value, and the ON time determining means for determining the ON time of the switching element,
The switching element is turned on when a current flowing through the inductor becomes lower than a current lower limit value set in the current limiting means, and then the switching element is turned off when the ON time has elapsed.

  In the first aspect of the invention, the minimum current set value (set value of the current lower limit value) is adjusted based on the error by using a multiplier that multiplies the error and the peak value as the current limiting means. (Invention of Claim 2) In these inventions of Claim 1 or 2, a timer circuit for setting a time corresponding to the error is provided as the ON time determining means, and the ON time is determined based on the error. The time can be adjusted (invention of claim 3).

  According to the present invention, it is possible to provide power factor improving switching that operates in a current continuous mode in which the inductor current does not decrease to zero in each switching operation and that does not require detection of the rectified input voltage. As a result, the size can be reduced as compared with the conventional example to which the current critical mode control method is applied. Furthermore, since the resistance for detecting the rectified input voltage can be eliminated, the loss generated by this resistance can be eliminated, and the standby power can be reduced.

FIG. 1 is a block diagram showing an embodiment of the present invention, which is an example of a boost converter that boosts an input rectified voltage and outputs a voltage higher than the input rectified voltage.
FIG. 2 is an operation explanatory diagram of FIG. 1 and shows an inductor current, a peak hold circuit output, a multiplier circuit output, a comparator output, a timer circuit output, a drive signal to a switching element, a timer reset signal, a timer circuit internal signal, and the like. .

The configuration of the main circuit unit is as follows.
a) The AC voltage is full-wave rectified by a rectifier circuit 2 including a diode bridge.
b) A current is supplied to the capacitor 7 connected to the output terminal via the inductor 4 and the diode 6.
c) A smoothed DC voltage Vout is output.
d) The switching element 5 such as a MOSFET is connected between the inductor 4 and the diode 6.
e) The current flowing through the inductor 4 is controlled by turning on and off the switching element 5.

The on / off control of the switching element 5 is performed as follows (refer to FIG. 2 for the waveforms of the respective parts).
1) The output voltage Vout is divided to an appropriate voltage as an input signal to an error amplifier 26 described later by the resistance voltage dividing circuit 11.
2) The error amplifier 26 outputs a signal Verr obtained by amplifying the error between the divided voltage and the reference voltage Vref.
3) The current flowing through the inductor 4 is converted into a voltage signal by the current detection resistor 13 and input to the current detection circuit 28.
4) The current detection circuit 28 inputs the current detection signal Videt obtained by amplifying the voltage signal to the comparator 22 and the peak hold circuit 24.

5) The output Vreset of the timer circuit 25 is input to the trigger terminal of the peak hold circuit 24. This Vreset acts as a trigger signal for turning off the switching element 5, as will be described later. Therefore, the peak hold circuit 24 holds the inductor current Imax at the time of turn-off.
6) The output Vimax of the peak hold circuit 24 is input to the multiplier circuit 23.
7) The multiplier circuit 23 multiplies the output Verr of the error amplifier 26 and the output Vimax of the peak hold circuit 24, and inputs the result Vimin to the non-inverting terminal of the comparator 22. Here, the output Vimin of the multiplier circuit 23 acts as a signal that defines the lower limit value Imin of the inductor current.

8) The comparator 22 compares the detected value Videt of the inductor current with the multiplier output Vimin. When Videt becomes smaller than Vimin, the output of the comparator 22 becomes high level.
9) The output of the comparator 22 is input to a set input terminal of an RS (reset set) flip-flop circuit 21.
10) The (non-inverted) output Vgate 0 of the RS flip-flop circuit 21 is input to the gate of the switching element 5 via the drive circuit 12. When Vgate0 is at a high level, the switching element 5 is turned on.

11) The inverted output of the RS flip-flop circuit 21 is input to the reset signal input terminal of the timer circuit 25 as a timer reset signal. When the switching element 5 is in the off state, the reset of the timer is released.
12) The timer circuit 25 outputs a trigger voltage when a certain time has elapsed after reset release.
13) This timer output is input to the reset terminal of the RS flip-flop circuit 21. When the timer circuit 25 outputs a trigger signal, the output of the RS flip-flop circuit 21 becomes low level, and the switching element 5 is turned off.

The movement of the inductor current by the above control can be summarized as follows.
a) When the switching element 5 is off, the inductor current gradually decreases.
b) When the inductor current reaches the current lower limit value Imin set based on the peak value of the inductor current, the switching element 5 is turned on.
c) When the switching element 5 is on, the inductor current gradually increases.
d) When a certain time elapses after the turn-on, the switching element 5 is turned off.

Further, the output voltage Vout is controlled as follows.
B) When the output voltage Vout is higher than a predetermined value, the current lower limit value Imin is controlled to be small. As a result, the average current of the inductor is reduced and the output voltage Vout is reduced.
B) Conversely, when the output voltage Vout is lower than a predetermined value, the current lower limit value is controlled to be larger. As a result, the average current of the inductor increases and functions to increase the output voltage Vout.
The current amplitude adjustment method in FIG. 1 is illustrated in FIGS. 7 (a) and 7 (b). The difference between (a) and (b) in the figure is due to the difference in K value shown in the above equations (2) and (4).

FIG. 3 is a block diagram showing another embodiment of the present invention, and FIG. 4 is a waveform diagram of each part for explaining the operation of FIG.
This is also an example of a boost converter that boosts the input rectified voltage and outputs a voltage higher than the input rectified voltage. The configuration of the main circuit section is the same as in FIG. 1 and the waveform of each section is also the same as in FIG. 2, so the description thereof will be omitted. Only the differences from FIG.
7 ′) The multiplier circuit 23 multiplies the output Vimax of the peak hold circuit 24 by the current lower limit setting voltage, and inputs the result Vimin to the non-inverting terminal of the comparator 22. Here, the output Vimin of the multiplier circuit 23 acts as a signal that defines the lower limit value Imin of the inductor current.

12 ′) The output voltage signal Verr is input to the timer time setting voltage input terminal of the timer circuit 25.
12'-1) After the reset is released, the timer circuit 25 increases the internal lamp voltage at a constant rate.
12′-2) The ramp voltage is compared with Verr by a comparator, and when the ramp voltage becomes higher than Verr, a trigger voltage is output.

Further, the movement of the inductor current by the above control is as follows only in d).
d ′) After the turn-on, when the time determined according to the error of the output voltage elapses, the switching element 5 is turned off.
Further, the output voltage Vout is changed as follows.
B) When the output voltage Vout is higher than a predetermined value, the ON time of the switching element is controlled to be small. As a result, the average current of the inductor is reduced and the output voltage Vout is reduced.
B) Conversely, when the output voltage Vout is lower than a predetermined value, the on-time of the switching element is controlled to be longer. As a result, the average current of the inductor increases and functions to increase the output voltage Vout.
The current amplitude adjustment method in the case of FIG. 3 is shown in FIGS. 8 (a) and 8 (b).

Circuit diagram showing an embodiment of the present invention Waveform diagram of each part for explaining the operation of FIG. Circuit diagram showing another embodiment of the present invention Each part waveform diagram for explaining the operation of FIG. Circuit diagram showing the timer circuit used in FIGS. Explanatory drawing of the current control method by this invention Explanatory drawing of the current amplitude adjustment method in FIG. Explanatory drawing of the current amplitude adjustment method in FIG. Circuit diagram showing a conventional example using the continuous current mode control method Circuit diagram showing a conventional example using the current critical mode control method Explanatory drawing of the current control method in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... AC input terminal, 2 ... Rectifier circuit, 3 ... Input capacitor, 4 ... Inductor, 5 ... Switching element, 6 ... Diode, 7 ... Output capacitor, 8 ... DC output terminal, 11 ... Resistance voltage dividing circuit, 12 ... Switching Element drive circuit, 13 ... current detection resistor, 21 ... RS flip-flop, 22 ... comparator, 23 ... multiplication circuit, 24 ... peak hold circuit, 25 ... timer circuit, 26 ... output voltage error amplifier (amplifier or error amplifier), 28 ... current detection circuit, 31 ... monostable multivibrator, 32 ... ramp circuit, 33 ... CR series circuit.

Claims (3)

A diode rectifier circuit that obtains a pulsating output by full-wave rectifying an AC power supply, an inductor connected to the diode rectifier circuit, a switching element that turns on and off the current flowing through the inductor, and a current supplied from the inductor is smoothed And a diode that rectifies the current flowing from the inductor to the capacitor to generate a stable direct current by boosting the alternating current input voltage and to improve the power factor of the alternating current input. In the provided switching power supply,
An error amplifying means for amplifying and outputting an error between a detected DC output voltage and a set value; a current detecting means for detecting a current flowing through the inductor; and a holding means for holding a peak value of the detected current. The current limiting means for setting the lower limit value of the current flowing through the inductor according to the peak value, and the ON time determining means for determining the ON time of the switching element,
The switching element is turned on when a current flowing through the inductor becomes lower than a current lower limit value set in the current limiting means, and then the switching element is turned off when the ON time has elapsed. Power supply.   2. The minimum current set value (set value of a current lower limit value) is adjusted based on the error by using a multiplier that multiplies the error and a peak value as the current limiting means. Switching power supply described in   The switching power supply according to claim 1, wherein a timer circuit that sets a time according to the error is provided as the on-time determining unit, and the on-time is adjusted based on the error.

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