JP3664012B2 - Switching power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention repetitively opens and closes a semiconductor switch element connected via at least inductive means such as a transformer or a reactor between input DC power sources serving as energy sources by a PWM-controlled drive pulse, thereby providing a stabilized DC power source. A so-called switching power supply as a power supply that is generated and supplied to the outside,
In particular, the snubber capacitor that protects the semiconductor switch element from the surge voltage generated when the semiconductor switch element is turned off minimizes the switching loss of the semiconductor switch element caused by discharging the semiconductor switch element when it is turned on. The present invention relates to a switching power supply device that improves the efficiency of the device.
In the following drawings, the same reference numerals denote the same or corresponding parts.
[0002]
[Prior art]
FIG. 6 shows an example of a circuit configuration of a conventional switching power supply apparatus using a flyback transformer 12. In the figure, 8 is a semiconductor switch element (simply abbreviated as a switch element) made of an N-channel MOSFET, and 5 is a constant DC supply voltage while detecting the DC voltage supplied to the external load 15 by the switching power supply device. The power supply control circuit is a control circuit for driving the switch element 8 on / off with a PWM output 7 as a drive pulse controlled by PWM (pulse width modulation).
[0003]
In the power supply control circuit 5, 3 is an oscillator that oscillates and outputs an oscillation wave (in this case, a triangular wave) to be described later using the oscillation capacitor 2, 4 is an oscillation output of the oscillator 3, and this switching power supply device This is a PWM control unit that receives the output voltage detection input 6 as a detected value of the DC voltage supplied to the load 15 and generates a PWM output 7 for driving the switch element 8 on / off.
[0004]
With this configuration, the switch element 8 has a duty ratio in which the input DC power source 1 is set to the frequency of the oscillator 3 and the DC output voltage on the secondary winding 11 side of the flyback transformer 12, and hence the output voltage detection input 6 is constant. That is, it is intermittently applied by the ON ratio = ON period / (ON period + OFF period) and applied to the primary winding 10 of the transformer 12.
Since the secondary winding 11 of the transformer 12 has a polarity voltage corresponding to the direction of maintaining the current that has been flowing through the primary winding 10 until the switching element 8 is turned off, the diode 13 is turned on. This voltage is smoothed by the capacitor 14 and supplied to the external load 15 as the output voltage of the switching power supply device.
[0005]
By the way, the capacitor 9 connected in parallel to the switch element 8 is called a snubber capacitor, and suppresses a surge voltage generated when the switch element 8 is turned off and a noise associated therewith.
FIG. 7 shows an example of the operation waveform of each part of FIG. 7A shows a voltage waveform of the oscillation capacitor 2 as an output waveform of the oscillator 3 in the power supply control circuit 5, and FIG. 7B shows a gate drive pulse applied to the switch element 8 by the power supply control circuit 5. PWM output 7 (this signal 7 is also a signal indicating the ON / OFF state of the switch element 8 at the same time), and FIG. 7C shows the snubber voltage as the voltage across the snubber capacitor 9.
[0006]
In the power supply control circuit 5, the frequency at which the switching element 8 is repeatedly turned on / off is determined by the oscillator 3 using charging / discharging of the oscillation capacitor 2.
FIG. 8 shows an example of the basic circuit configuration of the oscillator 3. In the figure, 36 is a constant voltage internal power source, 27 is a constant current source for charging the oscillation capacitor 2 (a resistor 28 may be used in place of the constant current source 27), and 29 is a discharge of the capacitor 2. Constant current source (which may be replaced by the resistor 30), 34 is a comparator having hysteresis, 35 is a reference voltage switched between the upper limit value VU and the lower limit value VL, and 33 is Inverter elements 31 and 32 that invert the output of the comparator 34 and give it to the switch 31 are switches composed of transistors that are alternately opened and closed by the output of the comparator 34.
[0007]
Next, the operation of FIG. 8 will be described with reference to FIG. Assume that the switch 31 is closed and the 32 is open by the output of the comparator 34. At this time, the reference voltage 35 input to the comparator 34 is the upper limit value VU. The oscillation capacitor 2 is charged via the constant current source 27 (or from the internal power supply 36 via the resistor 28), and the voltage of the capacitor 2 rises.
[0008]
When the voltage of the capacitor 2 eventually reaches the upper limit value VU, the output of the comparator 34 is inverted, the switch 31 is opened, 32 is closed, and the reference voltage 35 is switched to the lower limit value VL. As a result, the capacitor 2 is discharged via the constant current source 29 (or to the ground potential via the resistor 30), and the voltage of the capacitor 2 drops.
Thereafter, when the voltage of the capacitor 2 reaches the lower limit value VL, the output of the comparator 34 is inverted again, the switch 31 is closed and 32 is opened, and the reference voltage 35 is switched to the upper limit value VU.
[0009]
By repeating such charging and discharging operations, a triangular wave oscillation waveform shown in FIG. 7A is generated, and this oscillation wave, that is, the voltage across the oscillation capacitor 2 is used as the output of the oscillator 3 as a PWM control unit 4. Sent to. Then, the switch element 8 is repeatedly turned on / off in synchronization with the oscillation period Tosc consisting of the charging period Tc and the discharging period Tdc.
In the PWM control unit 4, as shown in FIG. 7, b), the deviation voltage between the output voltage detection input 6 and the reference value of the switching power supply output voltage corresponding to the detection input 6 is set to zero. A PWM output 7 having a pulse width with a variable ON period Ton is generated and output.
[0010]
In this case, the beginning of the on period Ton is set to the start point of the charging period Tc (in other words, the end point of the discharge period Tdc). The end of the on period Ton varies depending on the control of the output voltage of the switching power supply device. In the present apparatus, however, the discharge element Tdc is always turned off for the purpose of protection in the event of an abnormality (dead time). Therefore, the maximum on period Ton max is set to be equal to the charging period Tc.
[0011]
Therefore, the on-period Ton is always increased within the maximum on-period Ton max, so that the on-period Ton increases when the output voltage of the switching power supply device is too low compared to the reference value. When the voltage is going to rise too much compared to the reference value, the ON period Ton is controlled to decrease.
[0012]
[Problems to be solved by the invention]
As described above, FIG. 7C shows an example of the voltage across the snubber capacitor 9 in the switching power supply device of FIG. That is, after the switch element 8 is turned off, when the transformer 12 finishes releasing energy to the secondary side, LC resonance is generated by the inductance of the transformer 12 and the snubber capacitor 9 and the voltage oscillates.
[0013]
During this vibration, the switch element 8 is turned on (turned on). At this time, the snubber capacitor 9 discharges all the stored energy corresponding to the voltage between both ends as the switching loss of the switch element 8.
The turn-on timing is determined by the oscillator 3 of the power supply control circuit 5 and is independent of voltage oscillation. Therefore, it often turns on when the voltage of the snubber capacitor 9 is large. In this case, the loss of the switch element 8 becomes very large, and the presence of the snubber capacitor 9 is effective in suppressing the surge voltage and noise. However, on the other hand, there is a problem that the heat generation of the switch element 8 is increased and the efficiency of the switching power supply device is lowered.
[0014]
Therefore, the present invention can minimize the loss of the switch element 8 due to the snubber capacitor 9 by turning on the switch element 8 when the voltage is always the lowest during the oscillation of the voltage of the snubber capacitor 9 described above. An object of the present invention is to provide a switching power supply device that can be used.
[0015]
[Means for Solving the Problems]
In order to solve the above problem, in the switching power supply device according to claim 1,
An oscillation capacitor (2) that is repeatedly charged to a predetermined minimum voltage (lower limit value VL) after being charged to a predetermined maximum voltage (maximum value VM);
Connected in series with inductive means consisting of a transformer (12) or a reactor (18) between input DC power sources (input voltage 1) and in parallel with a snubber capacitor (9), and for each period of charging and discharging of the oscillation capacitor A semiconductor switching element (8) that is turned on / off so that the time when the voltage of the oscillation capacitor reaches the minimum voltage is set as an on time;
The semiconductor switch is configured so that a DC power source having a predetermined voltage to be supplied to an external load is generated (at both ends of the smoothing capacitor 14) using energy released from the inductive means when the semiconductor switch element is turned off. In the switching power supply apparatus in which the ratio between the on period and the off period of the element is controlled (by the PWM control unit 4),
An auxiliary winding (16) is provided in the inductive means, and a voltage generated in the auxiliary winding during the off period of the semiconductor switch element is applied to the oscillation capacitor via a diode (17) to induce the oscillation capacitor to the induction Charging to the highest voltage for a period until the resonance operation by the power means and the snubber capacitor starts ,
At least during this charging period, a discharge power source comprising a constant current source (29) or a constant voltage source (ground potential) having a predetermined resistance (30) in series is connected to the oscillation capacitor,
The time until the voltage of the oscillation capacitor drops from the highest voltage to the lowest voltage via the discharge power source after the end of the charging period (voltage fall time TF) is the voltage oscillation due to the resonant operation of the inductive means and the snubber capacitor. The period is set to ½.
[0016]
Further, in the switching power supply device according to claim 2, in the switching power supply device according to claim 1, the auxiliary winding is also used for generating a power supply (such as the control circuit power supply 22) in the switching power supply apparatus. To be.
The operation of the present invention is as follows. That is, an auxiliary winding is provided in an inductive means such as a transformer 12 or a reactor whose current is interrupted by the switch element 8, and the oscillation capacitor is pulled up by a voltage generated when the switch element 8 is turned off.
[0017]
The time for the voltage of the oscillation capacitor to fall from the maximum value after pull-up charging to the lower limit value by the discharge power supply is ½ of the period of voltage oscillation (LC resonance) caused by the inductive means and the snubber capacitor 9. By doing so, the oscillation voltage of the snubber capacitor 9 is also minimized when the voltage of the oscillation capacitor reaches the lower limit as the point of time when the switch element 8 is turned on (turned on).
[0018]
Thereby, switching loss and heat generation due to the discharge of the snubber capacitor 9 when the switch element 8 is turned on are reduced, and the efficiency of the switching power supply device is improved.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a circuit configuration of a main part of a switching power supply device as a first embodiment of the present invention. FIG. 1 corresponds to FIG. FIG. 3 is a circuit diagram showing the principle of the oscillator 3 shown in FIG. 1. FIG. 3 corresponds to FIG.
In FIG. 1, an auxiliary winding 16 is added to the transformer 12 with respect to FIG. 6, and the voltage of the auxiliary winding 16 is applied to the oscillation capacitor 2 via a diode 17 as shown in FIG. The internal configuration of the oscillator 3 in FIG. 3 is the same as that in FIG.
[0020]
FIG. 2 shows operation waveforms of respective parts in FIG. Next, the operation of the main part of FIGS. 1 and 3 will be described with reference to FIG. The auxiliary winding 16 is connected so that the polarity of the oscillation capacitor 2 is charged when the switch element 8 is turned off, in other words, the positive polarity portion of the voltage shown in FIG.
When the voltage of the auxiliary winding 16 is applied to the oscillation capacitor 2 and the switch element 8 is turned off, the voltage of the oscillation capacitor 2 as the output voltage of the oscillator 3 is supplied from the constant current source 27 (or through the resistor 28). From the time t1 when the voltage of the auxiliary winding 16 exceeds the conventional rising curve due to charging (from the power source 36), the voltage of the auxiliary winding 16 is further pulled up during the pull-up period Tpu shown in FIG. .
[0021]
When the voltage of the oscillation capacitor 2 reaches the upper limit value VU of the reference voltage 35 input to the comparator 34 in FIG. 3 at the time t2 during the rise, the output of the comparator 34 is inverted and the switch 31 in FIG. 3 is opened. , 32 are closed, and a constant current source 29 (or a ground potential via a resistor 30) is connected to the capacitor 2 as a power source for discharge.
[0022]
However, after that, as shown in FIG. 2, c), the voltage of the capacitor 2 does not drop due to the pull-up of the auxiliary winding 16 within the period in which the transformer 12 is releasing energy to the secondary side until the time point t3. . Note that the maximum value VM (flat portion) of the voltage of the oscillation capacitor 2 is the voltage of the secondary winding 11 in a conductive state at this time, that is, the voltage of the secondary smoothing capacitor 14, and accordingly, the external load from the switching power supply device. 15 is proportional to the constant-voltage controlled output DC voltage supplied to 15, and is practically constant.
[0023]
When the transformer 12 finishes releasing energy to the secondary side at the time t3, the oscillation of the voltage of the snubber capacitor 9 starts. Then, the voltage of the auxiliary winding 16 also decreases due to vibration. Therefore, the auxiliary winding 16 is separated from the oscillation capacitor 2 by the diode 17, and the voltage of the capacitor 2 starts to decrease due to the above-described discharge power supply.
[0024]
In this way, when the voltage of the oscillation capacitor 2 reaches the lower limit value VL of the reference voltage 35 input to the comparator 34 at time t4, the output of the comparator 34 is inverted again, and the oscillation capacitor 2 is charged with the above-described charging. Is connected to the power source, and the switch element 8 is turned on at the same time.
In the present invention, from the time t3 when the pull-up of the auxiliary winding 16 is removed by adjusting the capacity of the oscillation capacitor 2 or the like to the time t4 when the switch element 8 is turned on (in other words, the oscillation capacitor 2 is driven by the discharge power supply). The voltage fall time TF (until the voltage drops from the maximum value VM to the lower limit value VL) is made to coincide with a half cycle of voltage oscillation due to LC resonance of the snubber capacitor 9.
[0025]
Then, the oscillation voltage of the snubber capacitor 9 is also minimized at the time point t4, and the switch element 8 is turned on at this time point. Therefore, the turn-on loss (switching loss) of the switch element 8 due to the discharge of the snubber capacitor 9 can be minimized. become.
The period of this voltage oscillation is determined by the inductance L and capacitance C of the circuit such as the transformer 12 and the snubber capacitor 9 and does not depend on the input voltage or load. Therefore, even if the input or load changes, this effect does not change.
[0026]
FIG. 4 shows a circuit configuration of a main part as a second embodiment of the present invention. In the figure, a reactor 18 is used instead of the transformer 12 of FIG. 1, and the switching power supply device is configured in a boost chopper system. The auxiliary winding 16 is wound around the reactor 18. As described above, the present invention can also be implemented in a switching power supply apparatus that does not use a transformer.
[0027]
FIG. 5 shows a circuit configuration of a main part as a third embodiment of the present invention. In this example, the commercial power supply 19 is rectified via a diode bridge circuit 20 and smoothed via a capacitor 21 to obtain an input DC voltage of the switching power supply.
As in the case of FIG. 5, when the input DC voltage of the switching power supply device is generally high, the power supply 22 of the power supply control circuit 5 is generated using the auxiliary winding of the transformer 12. Therefore, in this embodiment, the auxiliary winding for generating the power source 22 is also used as the auxiliary winding 16 used in the present invention.
[0028]
That is, the power supply 22 of the power supply control circuit 5 is produced by rectifying the voltage of the auxiliary winding 16 through the diode 23 and smoothing it through the capacitor 24. On the other hand, the voltage of the auxiliary winding 16 is applied to the oscillation capacitor 2 through the diode 17 and the resistor 25 in order to implement the present invention. A Zener diode 26 is inserted in parallel with the oscillation capacitor 2.
[0029]
Although the resistor 25 and the Zener diode 26 are not originally necessary for this operation, the resistor 25 and the Zener diode 26 oscillate from the auxiliary winding 16 in order to use the power supply control circuit 5 for generating power and the auxiliary winding 16 for the present invention. It is used for protection so that the voltage applied to the capacitor 2 does not exceed the rated voltage of the oscillator 3.
[0030]
【The invention's effect】
In synchronization with charging / discharging of the oscillation capacitor in which charging / discharging is repeated between a predetermined maximum voltage and a minimum voltage, the time when the voltage of the oscillation capacitor reaches the minimum voltage is set as the ON time point.
The semiconductor switch element connected in series with the inductive means consisting of a transformer or a reactor between the input DC power supplies and in parallel with the snubber capacitor is turned on / off by PWM control,
In the switching power supply apparatus for supplying a DC power supply of a predetermined voltage to an external load using energy released from the inductive means when the semiconductor switch element is turned off,
An inductive means is provided with an auxiliary winding, and a voltage generated in the auxiliary winding during the off period of the semiconductor switch element is applied to the oscillation capacitor via a diode to charge the oscillation capacitor to the maximum voltage,
At least during this charging period, a discharge power source consisting of a constant current source or a constant voltage source having a predetermined resistance in series is connected to the oscillation capacitor,
Since the time until the voltage of the oscillation capacitor drops from the highest voltage to the lowest voltage via the discharge power source is set to ½ of the period of voltage oscillation caused by the inductive means and the snubber capacitor,
The voltage of the snubber capacitor when the semiconductor switch element is turned on is minimized, the switching loss of the semiconductor switch element due to the discharge of the snubber capacitor is minimized, the heat generation of the semiconductor switch element is reduced, and the efficiency of the switching power supply device is improved. Can do.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a main part as a first embodiment of the present invention. FIG. 2 is an operation waveform diagram of each part of FIG. 1. FIG. FIG. 4 is a circuit diagram showing a configuration of a main part as a second embodiment of the present invention. FIG. 5 is a circuit diagram showing a configuration of a main part as a third embodiment of the present invention. 1 is a conventional circuit diagram corresponding to FIG. 1. FIG. 7 is an operation waveform diagram of each part of FIG. 6. FIG. 8 is a circuit diagram showing the fundamental configuration of the oscillator part of FIG.
DESCRIPTION OF SYMBOLS 1 Input voltage 2 Oscillation capacitor | condenser 3 Oscillator 4 PWM control part 5 Power supply control circuit 6 Output voltage detection input 7 PWM output 8 Semiconductor switch element (switch element)
9 Snubber capacitor 10 Primary winding 11 Secondary winding 12 Transformer 13 Diode 14 Smoothing capacitor 15 Load 16 Auxiliary winding 17 Diode 18 Reactor 19 Commercial power supply 20 Diode bridge circuit 21 Smoothing capacitor 22 Control circuit power supply 23 Diode 24 Smoothing Capacitor 25 Resistor 26 Zener diode 27 Constant current source 28 Resistor 29 Constant current source 30 Resistor 31 and 32 Switch 33 Inverter 34 Comparator 35 Reference voltage 36 Internal power supply VU Upper limit of reference voltage VL Lower limit of reference voltage VM Voltage of oscillation capacitor Maximum value TF Oscillation capacitor voltage fall time

Claims (1)

An oscillation capacitor that is repeatedly charged to a predetermined minimum voltage after being charged to a predetermined maximum voltage;
When inductive means consisting of a transformer or a reactor is connected in series between the input DC power supply and in parallel with the snubber capacitor, and the voltage of the oscillation capacitor reaches the minimum voltage every charge / discharge period of the oscillation capacitor A semiconductor switch element that is turned on / off so that
An on period and an off period of the semiconductor switch element are generated so that a DC power source having a predetermined voltage to be supplied to an external load is generated using energy released from the inductive means when the semiconductor switch element is turned off. In the switching power supply in which the ratio is controlled,
An auxiliary winding is provided in the inductive means, and a voltage generated in the auxiliary winding during an off period of the semiconductor switch element is applied to the oscillation capacitor via a diode, and the oscillation capacitor is formed by the inductive means and the snubber capacitor. Charge to the highest voltage for the period until LC resonance starts ,
At least during this charging period, a discharge power source consisting of a constant current source or a constant voltage source having a predetermined resistance in series is connected to the oscillation capacitor,
The time until the voltage of the oscillation capacitor drops from the highest voltage to the lowest voltage via the discharge power source after the end of the charging period is ½ of the period of voltage oscillation due to LC resonance of the inductive means and the snubber capacitor. A switching power supply device characterized by that.

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