CN108462395B - Switching power supply device - Google Patents
Switching power supply device Download PDFInfo
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- CN108462395B CN108462395B CN201711171500.1A CN201711171500A CN108462395B CN 108462395 B CN108462395 B CN 108462395B CN 201711171500 A CN201711171500 A CN 201711171500A CN 108462395 B CN108462395 B CN 108462395B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
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- Dc-Dc Converters (AREA)
Abstract
The invention provides a switching power supply device which can obtain peak power even if the input voltage is low. The switching power supply device includes: an on/off control signal forming circuit (24) for forming an on/off control signal for controlling the output voltage to be constant on the basis of the output voltage detected by the output voltage detection means (6) and supplying the on/off control signal to the switching element (3); and a correction current detection signal generation unit (40a) which, in response to a signal indicating the on start time of the switching element in the on/off control signal generation circuit, generates a 1 st correction signal having a constant value during a period in which the duty ratio is smaller than a predetermined value from the on start time of the switching element, generates a 2 nd correction signal that increases with the elapse of time from the value of the 1 st correction signal during a period in which the duty ratio is equal to or greater than the predetermined value, and generates a correction current detection signal by sequentially subtracting the 1 st correction signal and the 2 nd correction signal from the current detection signal.
Description
Technical Field
The present invention relates to a switching power supply device such as a DC-DC converter.
Background
As shown in fig. 8, the conventional switching power supply device includes a switching element 3, an output rectifying/smoothing circuit 4, an output voltage detection circuit 6, a control unit 7, a control power supply rectifying/smoothing circuit 8, a control power supply circuit 9, and a current detection resistor 10. The transformer 2 has a primary winding N1, a secondary winding N2, and a tertiary winding (control power supply winding) N3.
The output rectifying/smoothing circuit 4 includes a rectifying diode 4a and a smoothing capacitor 4b, and the smoothing capacitor 4b is connected in parallel to the secondary winding N2 via the rectifying diode 4 a. The control power supply rectifying/smoothing circuit 8 has a rectifying diode 8a and a smoothing capacitor 8b, and supplies a dc voltage to the control unit 7 via the control power supply circuit 9 after the switching element 3 starts an on/off operation.
The control power supply circuit 9 is connected to the control power supply rectifying/smoothing circuit 8 and the control unit 7. The control power supply circuit 9 drives the control unit 7 with the voltage of the 1 st dc power supply terminal 1a before the third coil N3 obtains the voltage. After the tertiary winding N3 receives the voltage, the control unit 7 controls the voltage of the power supply rectifying/smoothing circuit 8 to drive the motor. The output voltage detection circuit 6 detects an output voltage, and has a secondary-side part 22 and a primary-side part 23. The secondary-side portion 22 is constituted by a series circuit of a light emitting diode 22a and a zener diode 22 b. The primary-side portion 23 is constituted by a phototransistor 23a and a capacitor 23b optically coupled to the light emitting diode 22 a.
As shown in fig. 9, the control section 7 has an on/off control signal forming circuit 24, an overcurrent protection circuit 25, and a low-pass filter 26. In the on/off control signal forming circuit 24, one end of the resistor 27 is connected to the dc power supply terminal 27a, and the other end is connected to the collector of the phototransistor 23a via the 4 th terminal 18. A connection point P1 between the resistor 27 and the phototransistor 23a is connected to the negative input terminal of the feedback comparator 28, and the low-pass filter 26 is connected to the positive input terminal of the feedback comparator 28 via the correction circuit 42. The low-pass filter 26 is connected to one end of the current detection resistor 10 via the 3 rd terminal 17. The feedback comparator 28 compares the correction current detection signal with the voltage V1 of the phototransistor 23a, and outputs a trigger signal indicating the end of the on period of the switching element 3.
When the amplitude of the correction current detection signal at the positive input terminal of the feedback comparator 28 reaches the voltage V1 at the negative input terminal, a high-level pulse is generated from the output terminal of the feedback comparator 28, OR the circuit (OR circuit) 29 outputs a high-level pulse. The output terminal of the or circuit 29 is connected to the reset terminal R of the RS flip-flop 30, and when the or circuit 29 outputs a high-level pulse, the RS flip-flop 30 is reset. The set terminal S of the RS flip-flop 30 is connected to the clock generator 31. When the clock signal is generated from the clock generator 31, the RS flip-flop 30 is triggered to be set. Q of RS flip-flop 30-The inverting output terminal is shown low when in the set state. One input terminal of the NOR circuit (NOR circuit) 32 is connected to the inverting output terminal of the RS flip-flop 30, and the other input terminal of the NOR circuit 32 is connected to the clock generator 31.
The current detection resistor 10 corresponds to a current detection means, is connected in series with the switching element 3, detects a current flowing through the switching element 3, and obtains a current detection signal as a voltage proportional to the current. The overcurrent protection circuit 25 has an overcurrent detection comparator 35, an overcurrent reference voltage source 36, and a correction current detection signal generation unit 40. The overcurrent detection comparator 35 has a positive input terminal connected to the low-pass filter 26 via the correction circuit 42, and an output terminal connected to the or circuit 29. When the correction current detection signal from the correction circuit 42 exceeds the overcurrent reference voltage Vr which is the overcurrent threshold of the overcurrent reference voltage source 36, a trigger signal is generated from the overcurrent detection comparator 35, and the trigger signal is supplied to the reset terminal R of the RS flip-flop 30 via the or circuit 29. The RS flip-flop 30 is reset and the switching element 3 is turned off. The overcurrent reference voltage Vr is set not to cross the correction current detection signal when the load 21 is in the normal state, and is set to cross the correction current detection signal when the load 21 is in the short-circuit state or the low impedance state.
The correction current detection signal generation unit 40 suppresses the fluctuation of the maximum output current due to the fluctuation of the input voltage Vin, and includes a ramp voltage generation circuit 41 and a correction circuit 42. The ramp voltage generation circuit 41 generates a ramp voltage V2 composed of a triangular wave voltage in synchronization with the clock signal from the clock generator 31. The ramp voltage generation circuit 41 continuously generates a positive ramp voltage Va having a positive slope and then continuously generates a negative ramp voltage Vb having a negative slope in response to the clock signal in a period later than the end time of the maximum on period of the switching element 3 from the on start time of the switching element 3.
The correction circuit 42 forms a correction current detection signal V4 corresponding to a value obtained by subtracting the correction voltage V2 from the current detection signal V3 of the low-pass filter 26, and sends the correction signal V4 to the feedback comparator 28 and the overcurrent detection comparator 35. As shown in fig. 10, the correction circuit 42 has a voltage conversion resistor Ra, a current conversion resistor Rb, 1 st and 2 nd control elements Q1, Q2, 3 rd control element Q3, 4 th and 5 th control elements Q4, Q5, and 1 st and 2 nd constant current source circuits 45, 46. One end of the voltage conversion resistor Ra is connected to the low-pass filter 26, and the other end is connected to the output line 47 of the correction current detection signal V4. When the value of the current I5 flowing through the voltage conversion resistor Ra changes, the inter-terminal voltage V5 of the voltage conversion resistor Ra changes. The current I5 flowing through the voltage conversion resistor Ra increases with the passage of the on-time of the switching element 3. Therefore, the amplitude difference (i.e., the voltage V5) between the current detection signal V3 and the correction current detection signal V4 increases with the passage of the on-time. The current detection signal V3, the correction current detection signal V4, and the voltage V5 of the voltage conversion resistor Ra have a relationship of V4 — V3-V5, and therefore the voltage conversion resistor Ra functions as a subtractor. The voltage V5 is a correction voltage or correction signal.
Sources as the 1 st main electrodes of the 1 st and 2 nd control elements Q1, Q2 in fig. 10 are connected to the dc power supply terminal 43, respectively, and gates as control electrodes of the 1 st and 2 nd control elements Q1, Q2 are connected in common with each other and to a drain as the 2 nd main electrode of the 1 st control element Q1. The drain of the 1 st control element Q1 is connected to the collector of the 3 rd control element Q3. The emitter of the 3 rd control element Q3 is connected to the ground terminal 44 via the current-converting resistor Rb. The base of the 3 rd control element Q3 is connected to the output line 41a of the ramp voltage generating circuit 41. The drain of the 2 nd control element Q2 is connected to the drain of the 4 th control element Q4. The source of the 4 th control element Q4 is connected to the ground terminal 44 via the 1 st constant current source circuit 45. The gates of the 4 th and 5 th control elements Q4, Q5 are commonly connected to each other and to the drain of the 4 th control element Q4. The source of the 5 th control element Q5 is connected to the ground terminal 44 via the 2 nd constant current source circuit 46, and the drain of the 5 th control element Q5 is connected to the other end of the voltage conversion resistor Ra.
The 1 st and 2 nd constant current source circuits 45, 46 limit the correction voltage V5 to be higher than a prescribed value. That is, the 1 st and 2 nd constant current source circuits 45 and 46 limit the correction current I5 corresponding to the leakage current of the 5 th control element Q5 to be larger than the predetermined current values I3 and I4. The predetermined current value I3 of the 1 st constant current source circuit 45 is set to be the same as the predetermined current value I4 of the 2 nd constant current source circuit 46.
According to this switching power supply device, when a clock signal for turning on the switching element 3 is generated, the ramp voltage V2 is generated in synchronization therewith. The ramp voltage V2 is applied to the base of the 3 rd control element Q3. Thereby, the ramp voltage V2 is converted into the impedance of the 3 rd control element Q3, and the impedance of the 3 rd control element Q3 changes in inverse proportion to the ramp voltage V2. As a result, the 1 st current I1 proportional to the ramp voltage V2 flows through the current conversion resistor Rb.
A 2 nd current I2 equal to the 1 st current I1 flows through the drain of the 2 nd control element Q2. When the 2 nd current I2 proportional to the ramp voltage V2 flows through the drain of the 2 nd control element Q2, the current I5 corresponding to the 2 nd current I2 also flows through the drain of the 5 th control element Q5. The current I5 of the 5 th control element Q5 flows in proportion to the ramp voltage V2 until the predetermined current value I4 of the 2 nd constant current source circuit 46 becomes I3, but is limited to the predetermined current value I4 becomes I3. The correction current I5 flows through a path of the 1 st dc power supply terminal 1a, the primary winding N1, the switching element 3, the low-pass filter 26, the voltage conversion resistor Ra, the 5 th control element Q5, the 2 nd constant current source circuit 46, and the ground terminal 44. Therefore, the inter-terminal voltage V5 of the voltage conversion resistor Ra is I5 × Ra. The correction current detection signal V4 output from the correction circuit 42 is a value (V3-V5) obtained by subtracting the correction voltage V5 from the current detection signal V3 from the low-pass filter 26. The correction voltage V5 increases with the passage of time during the on period Ton of the switching element 3.
In this way, in the input correction voltage characteristic of the conventional overcurrent protection circuit 25, the correction voltage V5 has a smaller value as the on duty is smaller, and the correction voltage V5 has a larger value as the on duty is larger.
Patent document 1: japanese patent No. 5169135
However, when the on duty ratio is increased to obtain the peak power at a low input voltage or when the switching frequency is increased to obtain the peak power, a sub-harmonic phenomenon occurs, and the peak power cannot be obtained. The subharmonic phenomenon is explained with reference to fig. 11. When the switching element 3 is turned on by the clock signal at time t0, the drain current Id linearly increases. If the ramp voltage V2, which linearly increases from zero, is applied to the base of the 3 rd control element Q3, the correction current detection signal V4 also linearly increases from zero.
When the switching element 3 is turned off at time t1, the leakage current Id becomes zero, but a current flows through the secondary coil N2. The secondary coil current linearly decreases, but at time t2 before the current becomes zero, the switching element 3 is turned on, and therefore the secondary coil N2 is not reset. Therefore, the drain current Id is linearly increased by superimposing a direct current component. The current detection signal V3 proportional to the drain current Id is also linearly increased by being superimposed with a direct current component. The ramp voltage V2 increases linearly from zero. Since the voltage V4 is V3-V5, the voltage V4 is linearly increased by superimposing a direct current component.
Next, when the switching element 3 is turned off at time t3, the leakage current Id becomes zero, but the secondary coil current linearly decreases. When the switching element 3 is turned on at time t4 before the current becomes zero, the overcurrent protection operation is performed, and therefore the drain current Id is a narrow pulse. The secondary coil current gradually decreases to zero at time t5, and the transformer 2 is reset. Since the state returns to the state at the time T0 at the time T6, the period T1 is repeated from the time T0 to the time T6. The drain current Id does not flow during the period t3 to t6, and therefore peak power cannot be obtained.
Disclosure of Invention
The present invention addresses the problem of providing a switching power supply device that: the peak power can be obtained even when the input voltage is low and the switching frequency is increased.
The switching power supply device of the present invention is characterized by comprising: a transformer having a primary coil and a secondary coil; a switching element that is connected to a dc power supply via the primary winding of the transformer and is turned on/off; an output voltage detection unit that detects an output voltage on the secondary coil side of the transformer; an on/off control signal forming circuit that forms an on/off control signal for controlling the output voltage to be constant in accordance with the output voltage of the output voltage detecting unit and supplies the on/off control signal to the switching element; a current detection unit that detects a current flowing through the switching element and outputs a current detection signal; a correction current detection signal generation unit that generates a 1 st correction signal having a constant value during a period in which a duty ratio is smaller than a predetermined value from an on start time of the switching element in response to a signal indicating the on start time of the switching element in the on/off control signal generation circuit, generates a 2 nd correction signal that increases with time from a value of the 1 st correction signal during a period in which the duty ratio is equal to or greater than the predetermined value, and sequentially subtracts the 1 st correction signal and the 2 nd correction signal from the current detection signal to generate a correction current detection signal; and a comparison unit that compares the correction current detection signal with an overcurrent threshold indicating an overcurrent level of the current flowing through the switching element, and outputs a signal for turning off the switching element to the on/off control signal forming circuit when the correction current detection signal reaches the overcurrent threshold.
The switching power supply device of the present invention is characterized by comprising: a transformer having a primary coil and a secondary coil; a switching element that is connected to a dc power supply via the primary winding of the transformer and is turned on/off; an output voltage detection unit that detects an output voltage on the secondary coil side of the transformer; an on/off control signal forming circuit that forms an on/off control signal for controlling the output voltage to be constant in accordance with the output voltage of the output voltage detecting unit and supplies the on/off control signal to the switching element; a current detection unit that detects a current flowing through the switching element and outputs a current detection signal; a correction current detection signal generation unit that responds to a signal indicating a conduction start timing of the switching element in the on/off control signal formation circuit and, when an input voltage is less than a predetermined voltage, a 1 st correction signal having a constant value is formed during a period from a conduction start timing of the switching element when a duty ratio is smaller than a predetermined value, forming a 2 nd correction signal that increases with the elapse of time from the value of the 1 st correction signal during a period in which the duty ratio is equal to or greater than the predetermined value, and generating a corrected current detection signal by sequentially subtracting the 1 st correction signal and the 2 nd correction signal from the current detection signal, forming a 3 rd correction signal that increases with the passage of time from zero when the input voltage is equal to or greater than the predetermined voltage, and generating a corrected current detection signal by subtracting the 3 rd correction signal from the current detection signal; and a comparison unit that compares the correction current detection signal with an overcurrent threshold indicating an overcurrent level of the current flowing through the switching element, and outputs a signal for turning off the switching element to the on/off control signal forming circuit when the correction current detection signal reaches the overcurrent threshold.
Effects of the invention
According to the present invention, the correction current detection signal generation means generates the 1 st correction signal having a constant value while the duty ratio is smaller than the predetermined value from the on start time of the switching element, and generates the correction current detection signal by subtracting the 1 st correction signal from the current detection signal. That is, since the constant correction amount is subtracted while the duty ratio is smaller than the predetermined value, the correction current detection signal is reduced.
Therefore, even if the dc component is superimposed, the overcurrent protection operation does not occur when the switching element is turned on, and thus the sub-harmonic phenomenon does not occur. Therefore, the following switching power supply device can be provided: the peak power can be obtained even when the input voltage is low and the switching frequency is increased.
Drawings
Fig. 1 is a circuit diagram showing a switching power supply device of embodiment 1 of the present invention.
Fig. 2 is a detailed circuit diagram of the control unit shown in fig. 1.
Fig. 3 is a detailed circuit diagram of the addition operator and the correction circuit shown in fig. 2.
Fig. 4 is a diagram showing an enlarged waveform of each part of the switching power supply device of embodiment 1.
Fig. 5 is a detailed circuit diagram of a control unit provided in the switching power supply device according to embodiment 2 of the present invention.
Fig. 6 is a detailed circuit diagram of the adder, the switch, and the correction circuit shown in fig. 5.
Fig. 7 is a detailed circuit diagram of a control unit provided in the switching power supply device according to embodiment 3 of the present invention.
Fig. 8 is a circuit diagram showing a conventional switching power supply device.
Fig. 9 is a detailed circuit diagram of the control unit shown in fig. 8.
Fig. 10 is a detailed circuit diagram of the correction circuit shown in fig. 9.
Fig. 11 is a diagram showing an amplified waveform of each part of the harmonic phenomenon in the conventional switching power supply device.
Description of the reference symbols
1a, 1 b: 1 st and 2 nd DC power supply terminals; 2: a transformer; 3: a switching element; 4: an output rectifying smoothing circuit; 6: an output voltage detection circuit; 7: a control unit; 10: a current detection resistor; 14: an integrated circuit; 24: an on/off control signal forming circuit; 25: an overcurrent protection circuit; 35: an overcurrent detection comparator; 36: an overcurrent reference voltage source; 40. 40a, 40b, 40 c: a correction current detection signal generation unit; 41: a ramp voltage generating circuit; 42. 42a, 42b, 42 c: a correction circuit; 51. 51a, 51 b: an addition operator; 52: a duty ratio detection circuit; 53: an input voltage monitoring circuit; SW: a switch; ra: a voltage conversion resistor; v3: a current detection signal; v4: correcting the current detection signal; v5: correcting the voltage; i5: correcting the current; vr 1: a reference voltage source; d1, D2: and a diode.
Detailed Description
Next, several embodiments of the switching power supply device of the present invention will be described with reference to the drawings.
[ example 1 ]
The switching power supply device of embodiment 1 shown in fig. 1 is characterized by being provided with a control unit 7a instead of the control unit 7 of the conventional switching power supply device shown in fig. 8. In fig. 1, the same reference numerals are given to the same portions as those in fig. 8, and the description thereof will be omitted.
As shown in fig. 2, the control unit 7a shown in fig. 1 differs from the conventional control unit 7 shown in fig. 8 in the structure of the corrected current detection signal generation means 40 a. The correction current detection signal generation unit 40a has a ramp voltage generation circuit 41, a reference voltage source Vr1, an addition operator 51, and a correction circuit 42 a.
The correction current detection signal generation unit 40a generates a 1 st correction signal having a constant value in a period in which a duty ratio is smaller than a predetermined value from the on start timing of the switching element 3 in response to a signal indicating the on start timing of the switching element 3 in the on/off control signal generation circuit 24, generates a 2 nd correction signal that increases with the elapse of time from the value of the 1 st correction signal in a period in which the duty ratio is equal to or larger than the predetermined value, and sequentially subtracts the 1 st correction signal and the 2 nd correction signal from the current detection signal to generate a correction current detection signal.
The ramp voltage generating circuit 41 has the same configuration as that shown in fig. 9, and therefore, the description thereof is omitted. The reference voltage source Vr1 generates a reference voltage and supplies the reference voltage to the adder 51.
The adder 51 outputs the reference voltage from the reference voltage source Vr1 to the correction circuit 42a while the on duty is smaller than a predetermined value (for example, 10%). The adder 51 outputs a superimposed voltage obtained by superimposing the ramp voltage V2 from the ramp voltage generation circuit 41 on the reference voltage to the correction circuit 42a while the on duty is equal to or larger than a predetermined value (for example, 10%).
The correction circuit 42a creates a 1 st correction signal based on the reference voltage from the adder 51, creates a 2 nd correction signal proportional to the ramp voltage with a dc component superimposed thereon based on the superimposed voltage from the adder 51, and generates a corrected current detection signal by sequentially subtracting the 1 st correction signal and the 2 nd correction signal from the current detection signal of the current detection unit 10. That is, the correction circuit 42a subtracts the voltage V2a from the adder 51 from the voltage V3 from the low-pass filter 26, and outputs the subtracted voltage as a correction voltage V4 a.
Fig. 3 is a detailed circuit diagram of the adder 51 and the correction circuit 42a shown in fig. 2. As shown in fig. 3, the adder 51 includes a diode D1 and a diode D2, wherein the anode of the diode D1 is connected to the output line 41a of the ramp voltage generation circuit 41, the cathode thereof is connected to the base of the 3 rd control element Q3, the anode of the diode D2 is connected to the positive terminal of the reference voltage source Vr1, and the cathode thereof is connected to the base of the 3 rd control element Q3.
Next, the operation of the switching power supply device of example 1 configured as described above will be described with reference to a timing chart shown in fig. 4.
First, at time t0, switching element 3 is turned on. In the adder 51, the ramp voltage V2 from the ramp voltage generation circuit 41 is applied to the diode D1, and the reference voltage from the reference voltage source Vr1 is applied to the diode D2. At time t0 to t01 (the period in which the on duty is smaller than the predetermined value), since the reference voltage Vr1 is higher than the ramp voltage V2, the diode D2 is turned on and the diode D1 is turned off.
Accordingly, the reference voltage Vr1 is applied to the base of the 3 rd control element Q3. Thereby, the 1 st correction signal proportional to the reference voltage Vr1 is created in the correction circuit 42 a. Therefore, the correction current detection signal V4 output from the correction circuit 42a is a value obtained by subtracting the 1 st correction signal from the current detection signal V3 from the low-pass filter 26.
Next, at time t01 to t11 (during a period in which the on duty is equal to or greater than a predetermined value), since the ramp voltage V2 is higher than the reference voltage Vr1, the diode D1 is turned on, and the diode D2 is turned off. Therefore, a superimposed voltage obtained by superimposing the ramp voltage V2 on the reference voltage Vr1 is applied to the base of the 3 rd control element Q3.
Thereby, the 2 nd correction signal proportional to the superimposed voltage is created in the correction circuit 42 a. Therefore, the correction current detection signal V4 output from the correction circuit 42a is a value obtained by subtracting the 2 nd correction signal from the current detection signal V3 from the low-pass filter 26.
Next, when the switching element 3 is turned off from time t11 to t12, the secondary coil current flows. The processing after the time t12 is the same as the processing from the time t0 to t 12.
As described above, according to the switching power supply device of embodiment 1, the corrected current detection signal generation unit 40a forms the 1 st correction signal having a constant value during a period in which the duty ratio is smaller than a predetermined value from the on start time of the switching element 3, and subtracts the 1 st correction signal from the current detection signal to generate the corrected current detection signal. That is, since the constant correction amount is subtracted while the duty ratio is smaller than the predetermined value, the correction current detection signal is reduced.
Therefore, even if the dc component is superimposed, the overcurrent protection operation does not occur when the switching element 3 is turned on, and thus the sub-harmonic phenomenon does not occur. Therefore, the following switching power supply device can be provided: even low input voltages can result in peak power. That is, the input voltage range can be expanded.
[ example 2 ]
Fig. 5 is a detailed circuit diagram of the control unit 7b provided in the switching power supply device of embodiment 2. Fig. 6 is a detailed circuit diagram of the adder 51a, the switch SW, and the correction circuit 42b shown in fig. 5. The correction current detection signal generation unit 40b included in the control unit 7b includes a ramp voltage generation circuit 41, a reference voltage source Vr1, an adder 51a, a switch SW connected to the reference voltage source Vr1 and the adder 51a, and a correction circuit 42 b.
The control unit 7b further includes a duty detection circuit 52, and the duty detection circuit 52 detects the duty, turns on the switch SW when the duty is smaller than a predetermined value, and turns off the switch SW when the duty is equal to or larger than the predetermined value.
Specifically, the duty detection circuit 52 is connected to an output terminal of the nor circuit 32, and receives a gate signal (gate signal) for turning on and off the switching element 3, integrates the gate signal, and compares an integrated value obtained by integrating the gate signal with a threshold corresponding to the predetermined value (the duty ratio is, for example, 10%).
When the integrated value is smaller than the threshold value, the duty detection circuit 52 turns on the switch SW for a period in which the duty ratio is smaller than a predetermined value. Accordingly, the reference voltage Vr1 is applied to the base of the 3 rd control element Q3. Thereby, the 1 st correction signal proportional to the reference voltage Vr1 is created in the correction circuit 42 b. Therefore, the correction current detection signal V4 output from the correction circuit 42b is a value obtained by subtracting the 1 st correction signal from the current detection signal V3 from the low-pass filter 26.
Next, when the integrated value is equal to or greater than the threshold value, the duty detection circuit 52 turns off the switch SW for a period in which the duty ratio is equal to or greater than a predetermined value. That is, when the switch SW is turned off, the ramp voltage V2 is the same voltage as the reference voltage Vr 1. Therefore, a superimposed voltage obtained by superimposing the ramp voltage V2 on the reference voltage Vr1 is applied to the base of the 3 rd control element Q3.
Thereby, the 2 nd correction signal proportional to the superimposed voltage is created in the correction circuit 42 b. Therefore, the corrected current detection signal V4 output from the correction circuit 42b is a value obtained by subtracting the 2 nd correction signal from the current detection signal V3 from the low-pass filter 26. Therefore, the same effects as those of the switching power supply device of embodiment 1 can be obtained also in the switching power supply device of embodiment 2.
Further, in the switching power supply device of embodiment 1, the predetermined value of the on duty ratio is determined based on the reference voltage value of the reference voltage source Vr1, but in the switching power supply device of embodiment 2, the predetermined value of the on duty ratio can be determined by the duty detection circuit 52.
[ example 3 ]
Fig. 7 is a detailed circuit diagram of the control unit 7c provided in the switching power supply device according to embodiment 3 of the present invention. The correction current detection signal generation unit 40c included in the control unit 7c includes a ramp voltage generation circuit 41, a reference voltage source Vr1, an adder 51b, a switch SW connected to the reference voltage source Vr1 and the adder 51b, and a correction circuit 42 c.
The correction current detection signal generation unit 40c generates a correction current detection signal by sequentially subtracting the 1 st correction signal and the 2 nd correction signal from the current detection signal in response to a signal indicating the on start timing of the switching element 3 in the on/off control signal generation circuit 24, and when the input voltage is lower than the predetermined voltage, forming a 1 st correction signal having a constant value during a period in which the duty ratio is lower than a predetermined value from the on start timing of the switching element 3, forming a 2 nd correction signal that increases with the elapse of time from the value of the 1 st correction signal during a period in which the duty ratio is equal to or higher than the predetermined value.
When the input voltage is equal to or higher than the predetermined voltage, the corrected current detection signal generation unit 40c generates a 3 rd correction signal that increases with the passage of time from zero, and subtracts the 3 rd correction signal from the current detection signal to generate a corrected current detection signal.
The adder 51b outputs the reference voltage from the reference voltage source Vr1 while the duty ratio is smaller than the predetermined value when the input voltage is smaller than the predetermined voltage value, outputs a superimposed voltage obtained by superimposing the ramp voltage of the ramp voltage generation circuit 41 on the reference voltage while the duty ratio is equal to or larger than the predetermined value, and outputs the ramp voltage when the input voltage is equal to or larger than the predetermined voltage value. The switch SW is connected to the reference voltage source Vr1 and the adder 51 b.
The correction circuit 42c creates a 1 st correction signal from the reference voltage from the adder 51b, creates a 2 nd correction signal from the superimposed voltage, and sequentially subtracts the 1 st correction signal and the 2 nd correction signal from the current detection signal to generate a corrected current detection signal. The correction circuit 42c creates a 3 rd correction signal proportional to the ramp voltage from the ramp voltage V2 from the ramp voltage generation circuit 41, and subtracts the 3 rd correction signal from the current detection signal to generate a corrected current detection signal.
The control unit 7c includes an input voltage monitoring circuit 53, and the input voltage monitoring circuit 53 monitors the input voltage, turns on the switch SW when the input voltage Vin is smaller than a predetermined voltage value, and turns off the switch SW when the input voltage Vin is equal to or greater than the predetermined voltage value.
In the switching power supply device of embodiment 3 configured as described above, the input voltage monitoring circuit 53 monitors the input voltage, and turns on the switch SW when the input voltage Vin is smaller than a predetermined voltage value. Then, the adder 51b outputs the reference voltage from the reference voltage source Vr1 while the duty ratio is smaller than the predetermined value, and outputs the superimposed voltage obtained by superimposing the ramp voltage of the ramp voltage generation circuit 41 on the reference voltage while the duty ratio is equal to or larger than the predetermined value.
The correction circuit 42c creates a 1 st correction signal from the reference voltage from the adder 51b, creates a 2 nd correction signal from the superimposed voltage, and sequentially subtracts the 1 st correction signal and the 2 nd correction signal from the current detection signal to generate a corrected current detection signal.
Therefore, the same effects as those of the switching power supply device of embodiment 1 can be obtained.
Next, the input voltage monitoring circuit 53 monitors the input voltage, and turns off the switch SW when the input voltage Vin is equal to or greater than a predetermined voltage value. Then, the adder 51b outputs a ramp voltage that increases with time from zero when the input voltage is equal to or greater than a predetermined voltage value.
The correction circuit 42c creates a 3 rd correction signal proportional to the ramp voltage from the ramp voltage, and subtracts the 3 rd correction signal from the current detection signal to generate a corrected current detection signal.
That is, when the input voltage is high, the duty ratio is narrow, and the subharmonic phenomenon does not occur, so that it is not necessary to subtract the 1 st correction signal from the correction current detection signal.
Claims (5)
1. A switching power supply device characterized by comprising:
a transformer having a primary coil and a secondary coil;
a switching element that is connected to a dc power supply via the primary winding of the transformer and is turned on/off;
an output voltage detection unit that detects an output voltage on the secondary coil side of the transformer;
an on/off control signal forming circuit that forms an on/off control signal for controlling the output voltage to be constant in accordance with the output voltage of the output voltage detecting unit and supplies the on/off control signal to the switching element;
a current detection unit that detects a current flowing through the switching element and outputs a current detection signal;
a correction current detection signal generation unit that generates a 1 st correction signal having a constant value during a period in which a duty ratio is smaller than a predetermined value from an on start time of the switching element in response to a signal indicating the on start time of the switching element in the on/off control signal generation circuit, generates a 2 nd correction signal that increases with time from a value of the 1 st correction signal during a period in which the duty ratio is equal to or greater than the predetermined value, and sequentially subtracts the 1 st correction signal and the 2 nd correction signal from the current detection signal to generate a correction current detection signal; and
a comparison unit that compares the correction current detection signal with an overcurrent threshold indicating an overcurrent level of the current flowing through the switching element, and outputs a signal for turning off the switching element to the on/off control signal forming circuit when the correction current detection signal reaches the overcurrent threshold.
2. Switching power supply unit according to claim 1,
the correction current detection signal generation unit has:
a ramp voltage generation circuit that generates a ramp voltage in synchronization with a conduction start time of the switching element and continues the generation of the ramp voltage until a time after an end time of a maximum conduction period of the switching element;
a reference voltage source that generates a reference voltage;
an adder that outputs the reference voltage from the reference voltage source while the duty ratio is smaller than a predetermined value, and outputs a superimposed voltage obtained by superimposing the ramp voltage of the ramp voltage generation circuit on the reference voltage while the duty ratio is equal to or larger than the predetermined value; and
and a correction circuit that creates the 1 st correction signal from the reference voltage from the adder, creates the 2 nd correction signal proportional to the ramp voltage with a direct current component superimposed thereon from the superimposed voltage, and generates a corrected current detection signal by sequentially subtracting the 1 st correction signal and the 2 nd correction signal from the current detection signal of the current detection means.
3. Switching power supply unit according to claim 1,
the correction current detection signal generation unit has:
a ramp voltage generation circuit that generates a ramp voltage in synchronization with a conduction start time of the switching element and continues the generation of the ramp voltage until a time after an end time of a maximum conduction period of the switching element;
a reference voltage source that generates a reference voltage;
an adder that outputs the reference voltage from the reference voltage source while the duty ratio is smaller than a predetermined value, and outputs a superimposed voltage obtained by superimposing the ramp voltage of the ramp voltage generation circuit on the reference voltage while the duty ratio is equal to or larger than the predetermined value;
a switch connected to the reference voltage source and the adder; and
a correction circuit that creates the 1 st correction signal based on the reference voltage from the adder, creates the 2 nd correction signal proportional to the ramp voltage with a direct current component superimposed based on the superimposed voltage, and generates a corrected current detection signal by sequentially subtracting the 1 st correction signal and the 2 nd correction signal from the current detection signal of the current detection means,
the switching power supply device further includes a duty detection circuit that detects the duty, and turns on the switch when the duty is smaller than a predetermined value, and turns off the switch when the duty is equal to or larger than the predetermined value.
4. A switching power supply device characterized by comprising:
a transformer having a primary coil and a secondary coil;
a switching element that is connected to a dc power supply via the primary winding of the transformer and is turned on/off;
an output voltage detection unit that detects an output voltage on the secondary coil side of the transformer;
an on/off control signal forming circuit that forms an on/off control signal for controlling the output voltage to be constant in accordance with the output voltage of the output voltage detecting unit and supplies the on/off control signal to the switching element;
a current detection unit that detects a current flowing through the switching element and outputs a current detection signal;
a correction current detection signal generation unit that responds to a signal indicating a conduction start timing of the switching element in the on/off control signal formation circuit and, when an input voltage is less than a predetermined voltage, a 1 st correction signal having a constant value is formed during a period from a conduction start timing of the switching element when a duty ratio is smaller than a predetermined value, forming a 2 nd correction signal that increases with the elapse of time from the value of the 1 st correction signal during a period in which the duty ratio is equal to or greater than the predetermined value, and generating a corrected current detection signal by sequentially subtracting the 1 st correction signal and the 2 nd correction signal from the current detection signal, forming a 3 rd correction signal that increases with the passage of time from zero when the input voltage is equal to or greater than the predetermined voltage, and generating a corrected current detection signal by subtracting the 3 rd correction signal from the current detection signal; and
a comparison unit that compares the correction current detection signal with an overcurrent threshold indicating an overcurrent level of the current flowing through the switching element, and outputs a signal for turning off the switching element to the on/off control signal forming circuit when the correction current detection signal reaches the overcurrent threshold.
5. Switching power supply unit according to claim 4,
the correction current detection signal generation unit has:
a ramp voltage generation circuit that generates a ramp voltage in synchronization with a conduction start time of the switching element and continues the generation of the ramp voltage until a time after an end time of a maximum conduction period of the switching element;
a reference voltage source that generates a reference voltage;
an adder that outputs the reference voltage from the reference voltage source during a period in which the duty ratio is smaller than a predetermined value when the input voltage is smaller than a predetermined voltage value, outputs a superimposed voltage obtained by superimposing the ramp voltage of the ramp voltage generation circuit on the reference voltage during a period in which the duty ratio is equal to or larger than the predetermined value, and outputs the ramp voltage when the input voltage is equal to or larger than a predetermined voltage value;
a switch connected to the reference voltage source and the adder; and
a correction circuit that creates the 1 st correction signal from the reference voltage from the addition operator, creates the 2 nd correction signal from the superimposed voltage, creates the 3 rd correction signal proportional to the ramp voltage from the ramp voltage,
the switching power supply device further includes a voltage monitoring circuit that monitors an input voltage input to the switching power supply device, turns on the switch when the input voltage is smaller than a predetermined voltage value, and turns off the switch when the input voltage is equal to or greater than the predetermined voltage value.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2017027926A JP6436177B2 (en) | 2017-02-17 | 2017-02-17 | Switching power supply |
| JP2017-027926 | 2017-02-17 |
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| Publication Number | Publication Date |
|---|---|
| CN108462395A CN108462395A (en) | 2018-08-28 |
| CN108462395B true CN108462395B (en) | 2020-06-09 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN201711171500.1A Active CN108462395B (en) | 2017-02-17 | 2017-11-22 | Switching power supply device |
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| CN (1) | CN108462395B (en) |
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| CN114285251B (en) * | 2021-12-24 | 2024-05-17 | 西安理工大学 | Circuit for improving load capacity of switching power supply |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1369953A (en) * | 2001-01-31 | 2002-09-18 | 松下电器产业株式会社 | Switching mains |
| CN101557166A (en) * | 2008-04-11 | 2009-10-14 | 株式会社瑞萨科技 | Power supply apparatus and semiconductor integrated circuit device |
| JP2016158398A (en) * | 2015-02-25 | 2016-09-01 | ミツミ電機株式会社 | Semiconductor device for power supply control |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2004040856A (en) * | 2002-06-28 | 2004-02-05 | Fuji Electric Holdings Co Ltd | Switching power supply |
| JP5169135B2 (en) * | 2007-10-22 | 2013-03-27 | サンケン電気株式会社 | Switching power supply |
-
2017
- 2017-02-17 JP JP2017027926A patent/JP6436177B2/en active Active
- 2017-11-22 CN CN201711171500.1A patent/CN108462395B/en active Active
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1369953A (en) * | 2001-01-31 | 2002-09-18 | 松下电器产业株式会社 | Switching mains |
| CN101557166A (en) * | 2008-04-11 | 2009-10-14 | 株式会社瑞萨科技 | Power supply apparatus and semiconductor integrated circuit device |
| JP2016158398A (en) * | 2015-02-25 | 2016-09-01 | ミツミ電機株式会社 | Semiconductor device for power supply control |
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| Publication number | Publication date |
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| JP6436177B2 (en) | 2018-12-12 |
| JP2018133957A (en) | 2018-08-23 |
| CN108462395A (en) | 2018-08-28 |
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