JP3654282B2 - Switching power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a switching power supply apparatus comprising a magnetic element that receives an input voltage and induces an output voltage to supply power to a load device, a switching means connected to the magnetic element, and an on / off control means for turning on and off the switching means. It is about.
[0002]
[Prior art]
FIG. 5 shows a configuration diagram of a current control type flyback converter which is an example of a conventional switching power supply device.
In the figure, an input power source Vin, a primary winding N1 of a transformer T1, which is a magnetic element, a switching means Q1, and a current detection resistor R1 are connected in series.
[0003]
The secondary winding N2 of the transformer T1 is connected to the diode D1, is further connected to the capacitor C1, becomes the output voltage Vo, and is further connected to a load device (not shown).
The auxiliary winding N3 of the transformer T1 is connected to the diode D2, further connected to the capacitor C2, serves as the power source Vcc, and is further connected to the on / off control means 10 and the like.
[0004]
The output voltage Vo is connected to the photocoupler OC1 through the resistor R2, and is connected to the error amplifier U2 through the resistor R3. Further, a reference voltage Vref, a capacitor C3, and a photocoupler OC1 are connected to the error amplifier U2.
[0005]
The on / off control means 10 is connected to the photocoupler OC1 via the voltage feedback signal VFB, connected to the filter F via the current detection signal CS, connected to the switching means Q1 via the drive signal OUT, and via the power supply Vcc. To the capacitor C2.
[0006]
The internal circuit of the on / off control means 10 will be described in detail. The voltage feedback signal VFB is pulled up by the current source U13, divided by the resistor R11 and the resistor R10 via the diode D10, and then connected to the negative input of the comparator U11. Further, the Zener diode D11 is connected to the negative input of the comparator U11. The current detection signal CS is connected to the positive input of the comparator U11. The output of the oscillator U10 is connected to the input of the set of the flip-flop U12, the output of the comparator U11 is connected to the reset input of the flip-flop U12, and the output of the flip-flop U12 is connected to the drive signal OUT.
[0007]
Next, the operation of each part will be described. The on / off control means 10 turns on / off the switching means Q1 according to the drive signal OUT, and applies the input voltage Vin to the primary winding N1 of the transformer T1. The voltage induced in the secondary winding N2 of the transformer T1 is rectified by the diode D1, smoothed by the capacitor C1, becomes the output voltage Vo, and becomes the voltage of the load device (not shown). The load current Io supplies power to a load device (not shown). The voltage induced in the auxiliary winding N3 of the transformer T1 is rectified by the diode D2, smoothed by the capacitor C2, becomes the power source Vcc, and supplies power to the on / off control means 10 and the like.
[0008]
There is a correlation between the output voltage Vo and the power supply Vcc. When the output voltage Vo increases, the power supply Vcc also increases, and when the output voltage Vo decreases, the power supply Vcc also decreases.
[0009]
Further, when the ratio of time between ON and OFF (duty ratio) increases, the output voltage Vo and the power supply Vcc increase, and when the ratio of time between ON and OFF (duty ratio) decreases, the output voltage Vo and the power supply Vcc. Will decline.
[0010]
The error amplifier U2 amplifies the difference between the output voltage Vo and the reference voltage Vref, and feeds it back to the on / off control means 10 as a voltage feedback signal VFB via the photocoupler OC1. Capacitor C3 and resistor R3 change the frequency response characteristics of the feedback. The resistor R2 changes the feedback gain.
[0011]
A voltage proportional to the current of the switching means Q1 is generated in the current detection resistor R1. This voltage becomes the current detection signal CS of the on / off control means 10 via the filter F.
[0012]
When the negative input based on the voltage feedback signal VFB and the positive input based on the current detection signal CS are equal, the comparator U11 resets the flip-flop U12, sets the drive signal OUT to Low, and turns off the switching means Q1. To do.
[0013]
The oscillator U10 operates at a constant operating frequency fs, and sets the flip-flop U12 at regular intervals. When the flip-flop U12 is set, the drive signal OUT becomes High, and the switching means Q1 is turned on.
[0014]
When the switching means Q1 is turned on, the current of the switching means Q1 increases linearly, the voltage generated in the resistor R1 increases linearly, the current detection signal CS increases linearly, and the positive input of the comparator U11 is When it increases linearly and its value reaches the value of the negative input of the comparator U11, the comparator U11 resets the flip-flop U12, sets the drive signal OUT to Low, and turns off the switching means Q1.
[0015]
The overall operation of the conventional example of FIG. 5 in the steady state will be described.
When the output voltage Vo is lower than the reference voltage Vref, the output of the error amplifier U2 increases, the current of the photodiode of the photocoupler OC1 decreases, the current of the phototransistor of the photocoupler OC1 decreases, and the voltage feedback signal VFB is The negative input of the comparator U11 increases, the time until the positive input of the comparator U11 reaches the negative input value of the comparator U11 increases, the ON period of the switching means Q1 increases, and the ON and OFF The time ratio (duty ratio) increases and the output voltage Vo increases.
[0016]
When the output voltage Vo is higher than the reference voltage Vref, the output of the error amplifier U2 decreases, the current of the photodiode of the photocoupler OC1 increases, the current of the phototransistor of the photocoupler OC1 increases, and the voltage feedback signal VFB is Decreases, the negative input of the comparator U11 decreases, the time until the positive input of the comparator U11 reaches the value of the negative input of the comparator U11 decreases, the ON period of the switching means Q1 decreases, and the ON and OFF states The time ratio (duty ratio) decreases, and the output voltage Vo decreases.
Thus, the output voltage Vo and the reference voltage Vref are equal.
[0017]
In the slight fluctuation of the output voltage Vo, the time constant of the capacitor C3 and the resistor R3 removes the high frequency component. Then, the output of the error amplifier U2 varies in its low frequency component, the photodiode current of the photocoupler OC1 varies in the low frequency component, the current of the phototransistor in the photocoupler OC1 varies in the low frequency component, and voltage feedback. The signal VFB varies with the low frequency component, the negative input of the comparator U11 varies with the low frequency component, and the time until the positive input of the comparator U11 reaches the value of the negative input of the comparator U11 varies with the low frequency component. The on period of the means Q1 varies with a low frequency component, the ratio of time between on and off (duty ratio) varies with the low frequency component, and the output voltage Vo varies with the low frequency component.
[0018]
Therefore, the time constant of the capacitor C3 and the resistor R3 is dominant in the response characteristics of the switching power supply device. Further, since the band of the filter F is set to three times or more of the band determined by the time constant of the capacitor C3 and the resistor R3, the band of the filter F does not affect the response characteristics of the switching power supply device.
In such a minute fluctuation of the output voltage Vo, the error amplifier U2 and the photocoupler OC1 operate in an active state.
[0019]
Next, the step response operation in the conventional example of FIG. 5 will be described. The load current Io changes sharply from the light load Iol to the heavy load Ioh at time t0.
At time t0, an increase in a steep change in the load current Io flows through the capacitor C1. The electric charge of the capacitor C1 is discharged, and the output voltage Vo decreases. Further, when the parasitic elements (equivalent series resistance and equivalent series inductance) inside the capacitor C1 are large, the output voltage Vo is greatly reduced.
[0020]
When the output voltage Vo decreases, the ratio of the ON / OFF time (duty ratio) increases and the feedback acts so that the output voltage Vo increases as in the description of the operation in the steady state described above.
However, in such a step response, the output voltage Vo greatly decreases, so that immediately after time t0, the error amplifier U2 is saturated and the photocoupler OC1 is turned off.
[0021]
Specifically, at time t0, the output voltage Vo decreases, the output of the error amplifier U2 is saturated at high, the photodiode of the photocoupler OC1 is turned off, the phototransistor of the photocoupler OC1 is turned off, and the voltage feedback signal VFB is Saturated at high, the negative input of the comparator U11 is clamped by the Zener diode D11, the time until the positive input of the comparator U11 reaches the negative input value of the comparator U11 is maximized, and the ON period of the switching means Q1 is maximized. The ratio of time between ON and OFF (duty ratio) becomes maximum, and the output voltage Vo increases.
[0022]
The Zener diode D11 limits the upper limit of the negative input of the comparator U11, limits the maximum value of the time until the positive input of the comparator U11 reaches the value of the negative input of the comparator U11, and sets the maximum during the ON period of the switching means Q1. Limits the value and limits the time ratio (duty ratio) between on and off. Further, the linear increase of the current detection signal CS is limited, the linear increase of the voltage generated in the resistor R1 is limited, the linear increase of the current of the switching means Q1 is limited, and thus the current of the switching means Q1 is limited. Limit the peak value of.
[0023]
The restriction of the ON period in the switching means Q1 and the restriction of the peak value of the current in the switching means Q1 suppress the magnetic saturation of the transformer T1.
[0024]
The operation will be described in detail with reference to FIG. FIG. 6 is a characteristic diagram for explaining the operation of the conventional example of FIG. In the figure, Io is a load current, Vo is an output voltage, and Id is a drain current of the switching means Q1.
[0025]
The load current Io sharply increases from the light load Iol to the heavy load Ioh at time t0. The output voltage Vo decreases steeply by ΔVo at time t0, and rises to a steady output voltage Vo (= Vref) over a period of time Td.
[0026]
The drain current Id of the switching means Q1 has a peak value idl when the load is light Iol, and idh when the load is heavy Ioh. Further, after time t0, the peak value is limited to it for a while.
[0027]
When the peak values are idl and idh, as described above, the error amplifier U2 operates in an active state, and the time constant of the capacitor C3 and the resistor R3 has a dominant influence on the response characteristics of the switching power supply device.
[0028]
When the peak value is “ith”, as described above, the output of the error amplifier U2 is saturated at “high” and limits the ON period of the switching means Q1. The response characteristics of the switching power supply device are affected by the filter F, the exciting inductance of the transformer T1, the capacitor C1, and the on / off time ratio (duty ratio). The time constant between the capacitor C3 and the resistor R3 is not affected.
[0029]
In the characteristic diagram of FIG. 6, when the peak value of the drain current of the switching means Q1 is isth, the on / off control means 10 limits the ratio of time (duty ratio) between on and off to about 50%. When the peak values are idl and idh, the ratio of time between on and off (duty ratio) is about 33%.
[0030]
After the period Td, when the output voltage Vo rises to the reference voltage Vref, the error amplifier U2 becomes active, the output decreases, the photodiode of the photocoupler OC1 becomes active, the current increases, and the photocoupler OC1. The phototransistor becomes active and the current increases, the voltage feedback signal VFB becomes active and decreases, the negative input of the comparator U11 decreases, and the positive input of the comparator U11 becomes the value of the negative input of the comparator U11. The time until it reaches is reduced, the ON period of the switching means Q1 is reduced, the ratio of time between ON and OFF (duty ratio) is reduced, and the output voltage Vo is reduced. In this way, the output voltage Vo and the reference voltage Vref are equal.
[0031]
On the other hand, the conventional switching power supply device includes an output voltage detection circuit that detects at a slow detection response speed, an upper limit voltage detection circuit that detects at a fast detection response speed, and a lower limit voltage detection circuit that detects at a fast detection response speed. The response characteristic is improved (for example, see Patent Document 1).
[0032]
[Patent Document 1]
Japanese Patent No. 3294211
[0033]
[Problems to be solved by the invention]
However, such a switching power supply device has a problem that a step response from a light load to a heavy load is slow.
[0034]
Specifically, the switching power supply device has a characteristic that the response becomes faster when the ratio of time between on and off (duty ratio) increases, but immediately after the step response from light load to heavy load, Since the time ratio (duty ratio) is limited, the response becomes slow.
[0035]
An object of the present invention is to solve the above-described problems and to provide a switching power supply device having suitable response characteristics.
[0036]
[Means for Solving the Problems]
  The present invention which achieves such an object is as follows.
(1) In a switching power supply apparatus comprising: a magnetic element that receives an input voltage and induces an output voltage to supply power to a load device; a switching means that is connected to the magnetic element; and an on / off control means that turns the switching means on and off The magnetic elementAuxiliary winding N3Operating frequency modulation means for increasing the on / off operating frequency of the switching means based on the voltage drop induced inThe auxiliary winding N3 is connected to the on / off control means and the operating frequency modulation means via a diode D2 and a capacitor C2, and the internal circuit of the on / off control means has a negative input between the output voltage and the reference voltage Vref. A comparator U11 for connecting a voltage feedback signal VFB based on the difference and connecting a current detection signal CS based on the current of the switching means to a positive input, an output of an oscillator oscillating at the operating frequency connected to a set input, and the reset input to the reset input And a flip-flop U12 for connecting the output of the comparator U11 and connecting the drive signal of the switching means to the output.The switching power supply device characterized by the above-mentioned.
(2)The on / off control means and the operating frequency modulation means are formed by a common integrated circuit element.It is characterized byClaim 1Switching power supply.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to FIG. FIG. 1 is a block diagram showing an embodiment of a switching power supply device according to the present invention. In addition, the same code | symbol is attached | subjected to the same element as the prior art example of FIG. 5, and description is abbreviate | omitted.
[0038]
A feature of the embodiment of FIG. 1 is that the operating frequency modulation means 20 for increasing the on / off operating frequency of the switching means Q1 based on a decrease in the value of the power supply Vcc based on the voltage induced in the auxiliary winding N3 of the transformer T1 which is a magnetic element. Is to provide.
[0039]
The operating frequency modulation means 20 includes a comparator U20 and a reference voltage Vr1. In the comparator U20, the negative input terminal is connected to the power supply Vcc, the positive input terminal is connected to the reference voltage Vr1, and the operating frequency modulation signal Fm is output. The operating frequency modulation signal Fm is connected to an oscillator U10 inside the on / off control means 10.
[0040]
The on / off control means 10 and the operating frequency modulation means 20 may be formed of a common integrated circuit element or may be formed of independent circuit elements. In the case of forming with a common integrated circuit element, the switching power supply device can be formed simply and in a small size.
[0041]
The value of the reference voltage Vr1 is set lower than the value of the power supply Vcc at the steady output voltage Vo (= Vref).
[0042]
If the voltage feedback signal VFB (output of the comparator U20) is Low, the oscillator U10 inside the on / off control means 10 oscillates at the same operating frequency fs as in the conventional example of FIG. 5, and the voltage feedback signal VFB (output of the comparator U20). If is high, it oscillates at a higher operating frequency fsh than the conventional example of FIG.
[0043]
The operation of the embodiment of FIG. 1 will be described. Since the operation in the steady state is the same as that of the conventional example of FIG. At this time, the output of the comparator U20 is Low.
[0044]
The operation of the step response in the embodiment of FIG. 1 will be described. The load current Io changes sharply from the light load Iol to the heavy load Ioh at time t0, the output voltage Vo decreases, the power supply Vcc also decreases, and the error amplifier U2 is saturated, as in the conventional example of FIG. Thus, the on / off control means 10 limits the peak value of the current of the switching means Q1 to ish.
[0045]
Thus, when the power supply Vcc is lower than the reference voltage Vr1, the output of the comparator U20 becomes High, and the oscillator U10 oscillates at a high operating frequency fsh.
[0046]
The operation will be described in detail with reference to FIG. FIG. 2 is a characteristic diagram for explaining the operation of the conventional example of FIG. The same elements as those in the characteristic diagram of FIG.
[0047]
At time t0, the output voltage Vo decreases steeply by ΔVo = ΔVo1 + ΔVo2, and increases by ΔVo1 over a period of time Td1, and then increases by ΔVo2 over a period of time Td2. In other words, the voltage rises to the steady output voltage Vo (= Vref) almost taking the period Td = Td1 + Td2.
[0048]
In the period Td1, the power supply Vcc becomes smaller than the reference voltage Vr1, the output of the comparator U20 becomes High, the oscillator U10 oscillates at a high operating frequency fsh, and the switching means Q1 turns on and off at a high operating frequency fsh.
[0049]
In the period Td2, the power supply Vcc becomes larger than the reference voltage Vr1, the output of the comparator U20 becomes Low, the oscillator U10 oscillates at the operating frequency fs, and the switching means Q1 turns on and off at the operating frequency fs.
[0050]
In the period Td1 and the period Td2, the on / off control unit 10 limits the peak value of the drain current Id of the switching unit Q1 to both, and suppresses the magnetic saturation of the transformer T1. Here, the linear increase rate (current gradient) of the drain current Id of the switching means Q1 does not change and is the same. Similarly to the conventional example of FIG. 5, the response characteristics of the switching power supply device are affected by the filter F, the exciting inductance of the transformer T1, the capacitor C1, and the time ratio (duty ratio) between on and off.
[0051]
As a result, the ratio of on / off time (duty ratio) in the period Td1 is larger than the ratio of on / off time (duty ratio) in the period Td2, and the low-frequency component also increases. In the characteristic diagram of FIG. 2, the ratio of on / off time (duty ratio) in the period Td1 is about 66%, which is more than about 50% of the ratio of on / off (duty ratio) in the period Td2. growing.
[0052]
In addition, the response of the switching power supply device in the period Td1 is faster than the response in the period Td2 because the ratio of time between ON and OFF (duty ratio) is increased.
[0053]
Then, when the output voltage Vo rises and the power supply Vcc rises to the reference voltage Vr1, the output of the comparator U20 becomes Low, the oscillator U10 oscillates at the operating frequency fs, and the switching means Q1 turns on and off at the operating frequency fs. The period Td1 ends and becomes the period Td2. After the period Td2, the operation is the same as in the conventional example of FIG.
[0054]
As described above, the response of the embodiment of FIG. 1 is faster than the response of the conventional example of FIG. Specifically, in the period Td1, since the ratio of time between on and off (duty ratio) increases, the response becomes faster.
[0055]
In the above-described example, the operating frequency is changed in two stages by the comparator U20. However, the operating frequency may be changed more than two stages. Moreover, you may change continuously.
[0056]
In the above example, the operating frequency is modulated based on the decrease in the value of the power supply Vcc based on the voltage induced in the auxiliary winding N3 of the transformer T1, which is a magnetic element. However, separately from this, the output voltage Vo is decreased. Based on this, the operating frequency may be modulated. Since the output voltage Vo and the power supply Vcc have a correlation, they operate similarly.
[0057]
Furthermore, in the above example, the current detection signal CS is a value based on the current of the switching means Q1, but separately from this, the current of the primary winding N1 of the transformer T1 or the primary winding of the transformer T1. It may be a value based on the current of the line N2 or the current of the diode D1.
[0058]
In the above example, the current control type flyback converter is used. However, a voltage control method may be used, and other converter methods such as a forward converter may be used.
[0059]
FIG. 3 is a block diagram showing another embodiment of the switching power supply device according to the present invention. This figure shows a configuration diagram of a voltage-controlled forward converter. Note that the same elements as those in the embodiment of FIG.
[0060]
The feature of the embodiment of FIG. 3 resides in that an operating frequency modulation means 30 for increasing the on / off operating frequency of the switching means Q1 based on a notice signal S of a response from a load device (not shown) is provided.
[0061]
In the figure, an input power source Vin, a primary winding N1 of a transformer T2, which is a magnetic element, a switching means Q1, and a current detection resistor R1 are connected in series. The secondary winding N2 of the transformer T2 is connected to the diode D3 and the diode D4, is further connected to the inductor L1 and the capacitor C1, becomes the output voltage Vo, and is further connected to a load device (not shown). The load current Io supplies power to a load device (not shown).
[0062]
The internal circuit of the on / off control means 40 will be described in detail. The operating frequency modulation signal Fm is connected to the oscillator U33, and the ramp output from the oscillator U33 is connected to the positive input of the PWM comparator U31. The voltage feedback signal VFB is pulled up by the current source U32 and connected to the negative input of the PWM comparator U31. The current detection signal CS is connected to the positive input of the overcurrent comparator U30. The reference voltage Vr2 is connected to the negative input of the overcurrent comparator U30. The output of the PWM comparator U31 and the output of the overcurrent comparator U30 are connected to the logic circuit U34. The output of the logic circuit U34 is connected to the drive signal OUT. The value of the reference voltage Vr2 is set higher than the value of the current detection signal CS when the steady output voltage Vo (= Vref).
[0063]
The operating frequency modulation means 30 includes a comparator U40, a reference voltage Vr3, a photocoupler OC2, and a resistor R4. In the comparator U40, its positive input is connected to the response warning signal S from the load device (not shown), its negative input is connected to the reference voltage Vr3, and its output is connected to the photodiode of the photocoupler OC2. In the photocoupler OC2, the photodiode is connected to the output voltage Vo via the resistor R4, and the phototransistor is connected to the operating frequency modulation signal Fm.
[0064]
The notice signal S of a response from a load device (not shown) is a notice of a change in the load current Io from the load device to the switching power supply device at time t1 prior to the step response at time t0.
[0065]
This will be described in detail with reference to FIG. FIG. 4 is a characteristic diagram for explaining the operation of the conventional example of FIG. The same elements as those in the characteristic diagram of FIG. In the figure, S is a notice signal of response from a load device (not shown). At time t1 prior to time t0 when the load current Io changes, the response notice signal S from the load device (not shown) changes from High to Low.
[0066]
Also, in the figure, when the response notice signal S from the load device (not shown) is High, the signal oscillates at the same operating frequency fs as in the conventional example of FIG. 5 and the response from the load device (not shown). When the notice signal S is low, the signal oscillates at an operating frequency fsh higher than that of the conventional example of FIG.
[0067]
Next, the operation of each part in the embodiment of FIG. 3 will be described. Description of the same components as those in the embodiment of FIG. 1 is omitted. The on / off control means 40 turns on / off the switching means Q1 according to the drive signal OUT, and applies the input voltage Vin to the primary winding N1 of the transformer T2. The voltage induced in the secondary winding N2 of the transformer T2 is rectified by the diode D3 and the diode D4, smoothed by the inductor L1 and the capacitor C1, becomes the output voltage Vo, and becomes the voltage of the load device (not shown).
[0068]
As in the embodiment of FIG. 1, in the voltage-controlled forward converter of FIG. 3, the output voltage Vo rises as the time ratio (duty ratio) of on and off increases, and the time of on and off. When the ratio (duty ratio) decreases, the output voltage Vo decreases.
[0069]
When the positive input based on the current detection signal CS becomes equal to the reference voltage Vr2, the overcurrent comparator U30 resets the logic circuit U34, sets the drive signal OUT to Low, and turns off the switching means Q1. Further, the linear increase of the current detection signal CS is limited, the linear increase of the voltage generated in the resistor R1 is limited, the linear increase of the current of the switching means Q1 is limited, and thus the current of the switching means Q1 is limited. Limit the peak value of. Limiting the current peak value in the switching means Q1 suppresses magnetic saturation of the transformer T2.
[0070]
If the operating frequency modulation signal Fm (output of the photocoupler OC2) is High, the oscillator U33 inside the on / off control means 40 oscillates at the same operating frequency fs as in the conventional example of FIG. 5, and the operating frequency modulation signal Fm (photocoupler) If the output (OC2) is Low, oscillation occurs at a higher operating frequency fsh than in the conventional example of FIG.
[0071]
The PWM comparator U31 performs pulse width modulation on the voltage feedback signal VFB using the lamp output from the oscillator U33. Specifically, the pulse width is narrowed when the voltage feedback signal VFB decreases, and the pulse width is widened when the voltage feedback signal VFB increases. Then, the logic circuit U34 is subjected to pulse width modulation, the drive signal is subjected to pulse width modulation, and the switching means Q1 is turned on and off.
[0072]
The overall operation in the steady state of the embodiment of FIG. 3 will be described.
When the output voltage Vo is lower than the reference voltage Vref, the output of the error amplifier U2 increases, the current of the photodiode of the photocoupler OC1 decreases, the current of the phototransistor of the photocoupler OC1 decreases, and the voltage feedback signal VFB is The negative input of the PWM comparator U31 increases, the pulse width of the output of the PWM comparator U31 increases, the time ratio (duty ratio) between ON and OFF increases, and the output voltage Vo increases.
[0073]
When the output voltage Vo is higher than the reference voltage Vref, the output of the error amplifier U2 decreases, the current of the photodiode of the photocoupler OC1 increases, the current of the phototransistor of the photocoupler OC1 increases, and the voltage feedback signal VFB is The negative input of the PWM comparator U31 decreases, the pulse width of the output of the PWM comparator U31 decreases, the time ratio (duty ratio) between ON and OFF decreases, and the output voltage Vo decreases.
[0074]
Thus, the output voltage Vo and the reference voltage Vref are equal. At this time, the peak value of the current in the switching means Q1 is low, the voltage generated in the resistor R1 is low, the current detection signal CS is low, the positive input of the overcurrent comparator U30 is low, and the output of the overcurrent comparator U30 is always low. is there. Further, the response characteristics of the switching power supply device in the embodiment of FIG. 3 are dominated by the time constant of the capacitor C3 and the resistor R3, as in the embodiment of FIG.
[0075]
Next, the step response operation in the embodiment of FIG. 3 will be described in detail with reference to the characteristic diagram of FIG. Description of the same components as those in the embodiment of FIGS. 1 and 2 is omitted. When the notice signal S of the response from the load device (not shown) changes from High to Low at time t1 prior to the step response at time t0, the output of the comparator U40 is saturated at Low, and the photocoupler OC2 photo The diode is saturated when turned on, the phototransistor of the photocoupler OC2 is saturated when turned on, the operating frequency modulation signal Fm becomes Low, the oscillator U10 inside the on / off control means 40 oscillates at a high operating frequency fsh, and the switching means Q1 is high. Turns on and off at operating frequency fsh.
[0076]
Thus, the load current Io changes sharply from the light load Iol to the heavy load Ioh at time t0. The subsequent operation is the same as that of the embodiment of FIGS. From the above, the response of the embodiment of FIG. 3 is similar to the response of the embodiment of FIG.
[0077]
After that, when the period Td1 ends and the notice signal S of the response from the load device (not shown) changes from Low to High, the output of the comparator U40 is saturated at High and the photodiode of the photocoupler OC2 is turned off. Then, the phototransistor of the photocoupler OC2 is turned off, the operating frequency modulation signal Fm becomes High, the oscillator U10 inside the on / off control means 40 oscillates at the operating frequency fs, and the switching means Q1 turns on and off at the operating frequency fs.
[0078]
In this way, in the embodiment of FIG. 3, a suitable response characteristic can be obtained as in the embodiment of FIG.
[0079]
Further, since the switching means Q1 can increase the operating frequency prior to the step response of the load current Io, even if the operating frequency modulation signal Fm or the like is delayed, the step response time t0 of the load current Io is surely obtained. Before, the operating frequency of the switching means Q1 can be increased. Therefore, a suitable response characteristic can be obtained stably.
[0080]
Further, if the timing (period Td1) at which the response notice signal S from the load device (not shown) changes from Low to High is increased, the period Td2 is decreased, and a more suitable response is obtained. However, if the period from time t1 to time t0 and the period Td1 are excessively increased, the period during which the switching power supply device operates at a high operating frequency fsh increases and loss increases. Define a suitable value.
[0081]
In the above-described example, the operating frequency is modulated based on the response notice signal S from the load device (not shown). Alternatively, the operating frequency may be modulated based on the decrease in the output voltage Vo. Specifically, in FIG. 3, the positive input S of the comparator U40 is connected to the output voltage Vo.
[0082]
【The invention's effect】
As is apparent from the above description, according to the present invention, it is possible to provide a switching power supply device having suitable response characteristics in a step response from a light load to a heavy load. In addition, the switching power supply device can be easily formed at a low cost and in a small size.
[0083]
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an embodiment of the present invention.
FIG. 2 is a characteristic diagram for explaining the operation of the embodiment of FIG. 1;
FIG. 3 is a block diagram showing another embodiment of the present invention.
4 is a characteristic diagram for explaining the operation of the embodiment of FIG. 3; FIG.
FIG. 5 is a configuration of a conventional switching power supply device.
6 is a characteristic diagram for explaining the operation of the conventional example of FIG. 5;
[Explanation of symbols]
10, 40 ON / OFF control means
20, 30 Operating frequency modulation means
Q1 Switching means
Vin input voltage
Vo output voltage
Vcc power supply
Vref, Vr1, Vr2, Vr3 reference voltage
T1, T2 transformer
S Notification signal from the load device
OUT drive signal
CS current detection signal
VFB voltage feedback signal
Fm Operating frequency modulation signal

Claims (2)

In a switching power supply device comprising: a magnetic element that receives an input voltage and induces an output voltage to supply power to a load device; a switching means that is connected to the magnetic element; and an on / off control means that turns the switching means on and off.
An operating frequency modulation means for increasing the on / off operating frequency of the switching means based on a decrease in voltage induced in the auxiliary winding N3 of the magnetic element ;
The auxiliary winding N3 is connected to the on / off control means and the operating frequency modulation means via a diode D2 and a capacitor C2.
The internal circuit of the on / off control means connects a voltage feedback signal VFB based on the difference between the output voltage and the reference voltage Vref to a negative input and a current detection signal CS based on the current of the switching means to a positive input. And a flip-flop U12 that connects the output of the oscillator that oscillates at the operating frequency to the set input, connects the output of the comparator U11 to the reset input, and connects the drive signal of the switching means to the output. > A switching power supply characterized by that. 2. The switching power supply device according to claim 1, wherein the on / off control means and the operating frequency modulation means are formed by a common integrated circuit element .

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