JP3507352B2 - Resonant switching power supply - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonance type switching power supply device having a wide output setting range.

[0002]

2. Description of the Related Art In a welding power source device, for example, when the rated welding current is 250 A, the minimum output is used up to 10 A or less. In other words, the power supply for welding has a very wide control range.

On the other hand, as the welding power source device, a PWM type switching regulator having advantages of small size, light weight and high power factor is often used. However, when the switching frequency is 20 kHz or less, there is no big problem.
When the frequency exceeds 00 kHz, the stray capacitance of the switching element affects the voltage waveform and the current waveform at both ends of the switching element at the time of switching on and off of the switching element, and the overlapping ratio becomes large. It becomes a loss and the loss increases. When the switching loss increases, the power conversion efficiency decreases and heat is generated. Therefore, a large radiator is required, which hinders downsizing of the power supply device.

In order to solve this problem, there is a resonance type switching power supply device shown in FIG. In FIG. 3, reference numeral 2 is a DC power supply, which is formed by rectifying a commercial AC power supply.
Reference numeral 4 is an inverter for converting the input DC voltage to high-frequency AC, and is composed of capacitors 6a and 6b connected in series between the outputs of the DC power supply 2 and switching elements 8a and 8b connected in series and alternately switched on and off. Has been done. The output of the inverter 4 is the capacitors 6a and 6
An output for outputting a high-frequency AC, a resonance inductance 10, a resonance capacitor 12, which are extracted from the connection point with b and the connection point with the switching elements 8a and 8b and are connected in series to the output of the inverter 4. Transformer 14 1
The secondary winding 14p is connected. 2 of output transformer 14
The secondary winding 14s is formed in a sensor tap shape, and output rectifiers 16a and 16b are connected to both ends of the secondary winding 14s to rectify the high frequency alternating current output from the output transformer 14. A smoothing reactor 18 and a capacitor 20 are provided at the outputs of the output rectifiers 16a and 16b to smooth the output rectified direct current, and the direct current output is supplied from the output terminals 22P and 22N to a load (not shown).

Reference numeral 26 is a current detector for detecting the output current flowing through the load. The detection signal detected by the current detector 26 and the setting signal of the reference power supply 30 for setting the output current are compared by the error amplifier 28. The error between the detection signal and the setting signal is amplified. The amplified signal is controlled by the switching control signal forming device 32, the switching elements 8a and 8b are switched, and the output current is controlled by a constant current.

The switching elements 8a and 8b are on / off controlled at a frequency lower than the resonance frequency of the series resonance circuit. During the period in which the first switching element 8a is on and the second switching element 8b is off, the current based on the series resonance causes the DC power supply 2, the first switching element 8a, the capacitor 12, the primary winding 14p, the reactor 10, the capacitor. It flows to the circuit composed of 6b. Immediately before switching of the first switching element 8a, a voltage having a polarity opposite to that shown in the figure is applied to the capacitor 12, gradually decreases toward 0 by the switching of the switching element 8a, and then charges to the polarity shown in the figure. Will be done. Capacitor 1
2, the current I flowing through the reactor 10 is
It has a maximum positive value when the voltage at becomes zero and then decreases. The charge of the capacitor 12 is discharged by the capacitor 12, the diode 9a, the capacitor 6a, and the reactor 1.
It is performed through the 0 and primary windings 14p. The same operation is performed during the ON period of the second switching element 8b.

[0007]

By the way, when the output setting is reduced, the switch control signals of FIGS. 5A and 5B are input to the switching elements 8a and 8b, respectively. This switch control signal has a controllable pulse width T3 and a fixed rest period T2, and when the load is used in a wide range such as a welding load, a limit occurs due to the switching speed, and the pulse width T3 However, there is a problem that the minimum output cannot be set.

[0008]

The invention according to claim 1 is
A direct current power source, and an inverter having at least one pair of switching elements connected in series with the direct current power source in parallel,
An output transformer provided at the output of the inverter, which is connected in series with a resonance reactor, a capacitor, and a load, an output rectifier that rectifies the output of the output transformer, and a current detector that detects the output current flowing through the load. An error amplifier that amplifies the error by comparing the detection signal of the current detector with a reference signal that sets the output current, and a switching that outputs a switching control signal that controls the switching element according to the error amplification signal. In a resonance type switching power supply device having a control signal forming device, a frequency change command device for forcibly turning off a part of the switching control signal when a reference signal for setting the output current drops to a predetermined value is provided. It is a thing.

That is, the inverter receives a DC voltage from a DC power supply and outputs a high frequency AC. The output of the inverter is provided with a series resonance circuit consisting of a reactor and a capacitor, and resonates at a frequency higher than the frequency of the inverter. The output of the inverter is transformed by the output transformer, rectified by the output rectifier, and the DC output is supplied to the load. In addition, the resonance frequency is set higher than the high frequency of the inverter by the reactor and the capacitor, and the switching loss of the switching element of the inverter is small.

Further, the current flowing through the load is detected by the current detector, and this command signal is compared with the reference signal for setting the output current by the error amplifier and error-amplified. The amplified signal switches the switching element of the inverter through the switching control signal forming device,
The output current is controlled by constant current. Then, when the reference signal for setting the output current drops to a predetermined value, a part of the switch control signal is forcibly turned off by the frequency conversion command device to lower the frequency. This expands the range of output settings.

A second aspect of the present invention is a frequency change command device for stopping the forced OFF of the switching control signal when the frequency change device reaches an audible frequency.

That is, since the switch control signal is forcibly turned off, the switching element does not drop to the audible frequency, and the output transformer or the like does not vibrate at the audible frequency, so that the generation of noise is suppressed. .

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to FIGS. 1 and 2 showing the embodiments thereof. 1 is different from FIG. 3 in that FIG. 1 forcibly turns off part of the switch control signal when the reference value of the reference power supply 30, that is, the set value of the output current falls below a predetermined value. The frequency change command device 36 is provided.

That is, 2 is a DC power supply, which is formed by rectifying a commercial AC power supply. Reference numeral 4 is an inverter for converting the input DC voltage to high-frequency AC, and is composed of capacitors 6a and 6b connected in series between the outputs of the DC power supply 2 and switching elements 8a and 8b connected in series and alternately switched on and off. Has been done. The output of the inverter 4 is taken out from the connection point between the capacitors 6a and 6b and the connection point between the switching elements 8a and 8b,
To the output of the inverter 4, the resonance inductance 10, the resonance capacitor 12, and the primary winding 14P of the transformer 14 that outputs a high frequency alternating current are connected in series. The secondary winding 14S of the output transformer 14 is formed in a center tap type, and output rectifiers 16a and 16b are connected to both ends of the secondary winding 14S to rectify the high frequency AC output from the output transformer 14. . Output rectifier 16
A smoothing reactor 18 and a capacitor 20 are provided at the outputs of a and 16b to smooth the output rectified direct current,
DC output is supplied to the load (not shown) from the output terminals 22P and 22N.

Reference numeral 26 is a current detector for detecting the output current flowing in the load. The detection signal detected by the current detector 26 and the reference signal of the reference power source 30 are compared by the error amplifier 28, and the detection signal and the reference signal are compared. The error with the signal is amplified. The amplified signal is controlled by the switching control signal forming circuit 32, the switching elements 8a and 8b are switched, and the output current is controlled by a constant current.

Further, the reference signal of the reference power source 30 is input to the frequency change command device 36. The frequency change command device 36 forces the switching control signal forming device 32 to partly turn off the switch control signal when the reference signal falls below a predetermined value.

Now, the switching elements 8a and 8b are on / off controlled at a frequency lower than the resonance frequency of the series resonance circuit. During the period when the first switching element 8a is on and the second switching element 8b is off, the current based on the series resonance causes the DC power supply 2, the first switching element 8a, the capacitor 12, the primary winding 14P, the reactor 10, the capacitor. It flows to the circuit composed of 6b. First switching element 8
Immediately before the switching of a, the voltage applied to the capacitor 12 is opposite to the polarity shown in the figure, and the switching element 8
It gradually decreases toward 0 due to the switching of a,
After that, it is charged to the polarity shown in the figure. Capacitor 12,
The current I flowing through the reactor 10 has a maximum positive value at the time when the voltage of the capacitor 12 becomes zero, and then decreases. The charge of the capacitor 12 is discharged by the capacitor 1
2, diode 9a, capacitor 6a, reactor 1
It is performed through the 0 and primary windings 14P. The same operation is performed during the ON period of the second switching element 8b.

When the output setting is reduced, no command signal is output from the frequency change command device 36 until the reference signal of the reference power source 30 reaches a predetermined value. Therefore, from the switch control signal forming circuit 32 to FIG.
The switch control signal shown in (a) is output.

When the reference signal reaches a predetermined value, the frequency change commanding device 36 forces the switch control signal forming device 32 to forcibly turn off the switch control signal indicated by the broken line as shown in FIG. 2B. Command. Therefore, the frequency drops. If the output setting is further reduced, the number of switch control signals that are forcibly turned off may be increased.

Further, the number of switch control signals forcibly turned off is increased, and when the frequency of the switching element drops to an audible frequency of ten and several kHz, the increase of the number of switch control signals forcibly turned off is stopped. Let As a result, it is possible to prevent generation of noise due to vibration of the output transformer or the like due to the oscillation frequency of the switching element.

The above-mentioned inverter is composed of a half bridge composed of a switching element and a capacitor.
The capacitor may be a switching element and may have a full bridge configuration.

[0022]

According to the first aspect of the present invention, the switching loss of the switching element can be reduced and the range of output setting can be widened, and the invention can be applied to a power source having a wide output setting range of the welding power source.

According to the second aspect of the invention, the switching element does not drop to an audible frequency, and the output transformer does not generate an audible vibration.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a resonant switching power supply device of the present invention.

FIG. 2 is a waveform diagram of a switch control signal applied to the switching element of FIG.

FIG. 3 is a block diagram of a conventional resonance type switching power supply device.

FIG. 4 is a waveform diagram of a switch control signal when a high output is set in FIG.

5 is a waveform diagram of a switch control signal when a low output is set in FIG.

[Explanation of symbols]

2 DC power supply 4 inverter 6a, 6b capacitors 8a, 8b switching element 10 Resonance reactor 12 Resonance capacitor 14 output transformer 26 Current detector 28 Error amplifier 32 switching control signal forming device 36 Frequency change command device

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-10-229673 (JP, A) JP-A-3-32467 (JP, A) JP-A-8-51774 (JP, A) JP-A-10- 277740 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02M 3/28 B23K 9/073

Claims (2)

(57) [Claims] 1. A DC power supply, an inverter having at least one pair of switching elements connected in series in parallel with the DC power supply, a series connected resonance reactor, a capacitor and a load provided at the output of the inverter. An output transformer connected, an output rectifier that rectifies the output of the output transformer, a current detector that detects the output current flowing in the load, a detection signal of the current detector, and a reference signal that sets the output current. In the resonance type switching power supply device having an error amplifier for error amplification and a switching control signal forming device for outputting a switching control signal for controlling the switching element according to the error amplification signal. When the reference signal to be set drops to a predetermined value, some of the above switching control signals are forcibly turned off. A resonance type switching power supply device comprising a frequency change command device. 2. The resonance type switching power supply device according to claim 1, wherein the frequency conversion command device is a frequency change command device that stops forced switching off of the switching control signal when an audible frequency is reached. .