JP2002315320A - Switching power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply unit capable of attaining positive starting with a rise in cost restrained. SOLUTION: This power supply unit consists of a main circuit 2, comprising a rectifying and smoothing circuit 10 which converts AC voltage VAC into DC voltage VDC, and a switching circuit 20 which develops output voltage V0 by switching the DC voltage VDC; an auxiliary rectifying circuit 33 which outputs pulsating voltage by rectifying the AC voltage VAC inputted via capacitors 31, 32; a capacitor 34 which smoothes the pulsating voltage and develops a DC starting power supply VCC; a main control circuit 4, which operates and controls the main circuit 2 by inputting the DC starting power supply VCC; a switching means 36, which is arranged between the capacitor 34 and the main control circuit 4, and controls supply and interruption of the DC starting power supply VCC to the main control circuit 4; and a control circuit 37 for starting, which supplies the DC starting power supply VCC to the main control circuit 4 by driving the switching means 36, when the DC starting power supply VCC reaches a first predetermined voltage, immediately after input of the AC voltage VAC.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply for switching an AC voltage to convert it into a DC voltage.

[0002]

2. Description of the Related Art A power supply device 51 shown in FIG. 3 is conventionally known as a switching power supply device for generating a DC voltage by switching an AC voltage input from an AC power supply. The power supply device 51 includes a main circuit 2, a start-up power generation circuit 53, and a main control circuit 4.

The main circuit 2 includes a first rectifying / smoothing circuit 10 and a switching circuit 20. In this case, the first rectifying / smoothing circuit 10 includes a rectifying diode, a smoothing capacitor, and the like (not shown). . The switching circuit 20 includes a transformer 21 having a primary winding 21a, a secondary winding 21b, and an auxiliary winding 21c, and a DC voltage VDC which is connected in series to the primary winding 21a and receives a drive signal SDV.
Main switching element (for example, FET) 2 for switching
2, a diode 23 for rectifying an AC voltage induced in the secondary winding 21b to generate a pulsating voltage, and a smoothing capacitor 24 for smoothing the pulsating voltage generated by the diode 23 to generate an output voltage VO. A diode 2 for rectifying an AC voltage induced in the auxiliary winding 21c to generate a pulsating voltage
5 and a smoothing capacitor 26 for smoothing the pulsating voltage generated by the diode 25 to generate the auxiliary power supply VSO.

[0004] The starting power supply generating circuit 53 includes first and second power supply circuits.
, An auxiliary rectifier circuit 33 and a smoothing capacitor 34 to generate a DC starting power supply VCC. In this case, the first and second capacitors 31, 32
Has one end connected to each of the AC lines LA and LB of the AC power supply PS. The auxiliary rectifier circuit 33 is constituted by a diode (not shown) combined in a bridge form, and the respective lines LC and LD on the input side are connected to the other ends of the first and second capacitors 31 and 32, respectively. Have been. The smoothing capacitor 34 includes an auxiliary rectifier circuit 33
Is connected between the respective lines LE and LF on the output side of.

The main control circuit 4 operates by inputting the DC starting power supply VCC generated by the starting power supply generating circuit 53 to generate a drive signal SDV. Specifically, the main control circuit 4 controls the DC power supply
3 operates when the voltage is higher than a predetermined voltage (starting voltage) VST (see FIG. 2) higher than the operation assurance voltage VGU. At that time, the output voltage VO is detected and the detected output voltage VO is set in advance. The drive signal S is set to the target voltage.
The pulse width of DV is PWM controlled.

In the power supply device 51, when the supply of the AC voltage VAC from the AC power supply PS is started, the first rectifying and smoothing circuit 10 generates a DC voltage VDC by full-wave rectifying and smoothing the AC voltage VAC. I do. The auxiliary rectifier circuit 33 rectifies the AC voltage VAC input via the first and second capacitors 31 and 32 to generate a pulsating voltage, and the smoothing capacitor 34 is generated by the auxiliary rectifier circuit 33. The generated pulsating voltage is smoothed to generate a DC starting power supply VCC. On the other hand, the main control circuit 4 starts at a time t2 at which the DC starting power supply VCC indicated by the broken line A in FIG. 2 exceeds the starting voltage VST. Drive signal SDV is applied to main switch element 22
Is output periodically. In this case, the main switch element 22
Shifts to the ON state when the drive signal SDV is output from the main control circuit 4, and switches the DC voltage VDC.
At this time, the switching operation is performed by the main switch element 22 so that the secondary winding 21 of the transformer 21 is
AC voltage is induced in the auxiliary winding b and the auxiliary winding 21c. Next, the diode 23 rectifies the induced AC voltage, and the smoothing capacitor 24 smoothes the output of the diode 23. The output voltage VO is generated by the above operation. At the same time, the diode 25 rectifies the induced AC voltage, and the smoothing capacitor 26 smoothes the output of the diode 25 to generate the auxiliary power supply VSO and outputs it to the main control circuit 4. Therefore, although the voltage value of the DC starting power supply VCC drops momentarily, the auxiliary power supply VSO is supplied after time t2, so that the main control circuit 4 continues to operate mainly using the auxiliary power supply VSO as the operating power supply. .

[0007]

However, the conventional power supply device 51 has the following problems. That is, in the power supply device 51, the smoothing capacitor 34 and the main control circuit 4 are connected to the lines LE and LF on the respective output sides of the auxiliary rectifier circuit 33. Therefore, when the power supply device 51 is started, the DC power generated by the auxiliary rectifier circuit 33 is stored in the smoothing capacitor 34 and consumed by the main control circuit 4. Therefore, the smoothing capacitor 34
Since the charging voltage (that is, the DC starting power supply VCC) rises slowly as shown by the waveform A shown by the broken line in FIG. 2, the DC starting power supply VCC starts after the supply of the AC voltage VAC is started.
Until the voltage reaches the starting voltage VST of the main control circuit 4 (t
2) longer. For this reason, there is a problem in that the time until the start of generation of the output voltage VO by the power supply device 51 becomes long. Further, due to the gradual rise of the DC starting power supply VCC, the main control circuit 4 may not be reliably started depending on the circuit configuration of the main control circuit 4. In such a case, the output voltage VO of the power supply device 51 may be reduced. A problem arises in that the generation of the data is not started indefinitely. On the other hand, by increasing the capacity of the first and second capacitors 31 and 32, the amount of energy generated by the auxiliary rectifier circuit 33 is increased, thereby improving the rising characteristics of the DC starting power supply VCC. . However,
When this configuration is employed, the startup power supply generation circuit 53 is increased with the increase in the size of the first and second capacitors 31 and 32.
In addition to the increase in the size of the power supply device 51 and the size of the power supply device 51, the cost of the power supply device 51 increases due to an increase in the component price of the first and second capacitors 31 and 32.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and has as its main object to provide a switching power supply device that can be reliably started while suppressing an increase in cost.

[0009]

According to a first aspect of the present invention, there is provided a switching power supply device comprising: a first rectifying / smoothing circuit for converting an input AC voltage into a DC voltage; A main circuit including a switching circuit that generates an output voltage; an auxiliary rectifier circuit that rectifies the AC voltage input through first and second capacitors to output a pulsating voltage; A switching power supply device comprising: a smoothing capacitor that generates a DC startup power supply by smoothing; and a main control circuit that operates by inputting the DC startup power supply and controls the main circuit. A switch unit disposed between the main control circuit and controlling supply and stop of supply of the DC starting power supply to the main control circuit; and When the DC starting power supply reaches a first predetermined voltage immediately after the input of the voltage, the control means for driving the switch means to supply the DC starting power supply to the main control circuit. Features.

The switching power supply according to claim 2 is
2. The switching power supply device according to claim 1, further comprising a voltage clamp element connected in parallel to the smoothing capacitor to limit the DC starting power supply to a second predetermined voltage that is higher than the first predetermined voltage. It is characterized by.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a switching power supply according to the present invention will be described below with reference to the accompanying drawings. The conventional switching power supply 51
The same components as those described above are denoted by the same reference numerals, and redundant description is omitted, and redundant description of the same operation is also omitted.

First, the configuration of the power supply 1 will be described with reference to FIG. The power supply device 1 is a flyback type switching power supply device, and includes a main circuit 2, a start-up power supply generation circuit 3, and a main control circuit 4. Are configured identically. Therefore, the configuration and operation of the startup power supply generation circuit 3 will be mainly described below.

The starting power supply generating circuit 3 includes a first capacitor 31, a second capacitor 32, an auxiliary rectifying circuit 33, a smoothing capacitor 34, a voltage clamp element 35, a switch element (switch means) 36, and a starting control circuit 37. And a DC starting power supply VCC for starting the main control circuit 4. In this case, the first and second capacitors 31, 32
Has one end connected to each of the AC lines LA and LB of the AC power supply PS. The auxiliary rectifier circuit 33 is composed of diodes combined in a bridge form, and its input lines LC and LD are connected to the other ends of the first and second capacitors 31 and 32, respectively. The smoothing capacitor 34 is connected between the lines LE and LF on the output side of the auxiliary rectifier circuit 33. Voltage clamp element 35
Is composed of, for example, a Zener diode, and is connected in parallel to the smoothing capacitor 34. Further, the voltage clamp element 35 shifts to the conductive state when the DC starting power supply VCC applied to both ends exceeds the element-specific clamping voltage VCL, and in this case, the DC starting power supply VCC falls below the clamp voltage VCL. Voltage. That is, the voltage clamp element 35 prevents abnormal rise of the DC starting power supply VCC. In this case, the clamp voltage VCL of the voltage clamp element 35 corresponds to a second predetermined voltage in the present invention, and is set slightly higher than a reference voltage VREF described later, as shown in FIG.

The switching element 36 includes a smoothing capacitor 34
(And the voltage clamp element 35) and the main control circuit 4 are connected in series between lines LE. Further, the switch element 36 is formed of, for example, a switching element such as an FET or a transistor, or a relay, and has a drive signal SON
Is turned on when you are inputting,
DC starting power supply V generated by starting power generation circuit 3
CC is supplied to the main control circuit 4. On the other hand, when the input of the drive signal SON is stopped, the switch element 36 shifts to the off state, and at that time, the supply of the DC starting power supply VCC to the main control circuit 4 is stopped. The start-up control circuit 37 is composed of, for example, a zener diode and a comparator (each not shown). The start-up control circuit 37 detects the voltage of the DC start-up power supply VCC whose voltage gradually increases immediately after the start of the supply of the AC power supply PS, and detects the voltage. The voltage of the DC starting power supply VCC is compared with an internally generated reference voltage (first predetermined voltage) VREF. Output. The reference voltage VREF is adjusted to an arbitrary voltage higher than the operation guarantee voltage VGU of the start-up power supply generation circuit 53 by voltage adjusting means (for example, a variable resistor) not shown. Also,
The reference voltage VREF is preferably a voltage higher than the start voltage VST, but may be the same voltage as the start voltage VST or a lower voltage as long as the voltage is higher than the operation guarantee voltage VGU.

Next, the operation of the power supply device 1 will be described.

In the power supply device 1, when the supply of the AC voltage VAC from the AC power supply PS is started, the first rectifying / smoothing circuit 10 of the main circuit 2 performs full-wave rectification and smoothing of the AC voltage VAC, thereby obtaining a DC voltage. A voltage VDC is generated. In the start-up power supply generation circuit 3, the auxiliary rectifier circuit 33 rectifies the AC voltage VAC input via the first and second capacitors 31, 32 to generate a pulsating voltage, and the smoothing capacitor 3
4 smoothes the pulsating voltage generated by the auxiliary rectifier circuit 33 to generate a DC starting power supply VCC. At this time, the startup control circuit 37 detects the voltage of the DC startup power supply VCC,
The detected voltage is compared with the reference voltage VREF. In this case, at the start of the supply of the AC voltage VAC from the AC power supply PS, the voltage of the DC starting power supply VCC is lower than the reference voltage VREF, so the starting control circuit 37 outputs the drive signal SON and outputs the switching element 36 is kept off. Therefore, the load of the starting power supply generating circuit 3 at this time is mainly only the smoothing capacitor 34. Therefore, the voltage value of the DC starting power supply VCC is changed to the DC starting power supply It rises sharply compared to VCC.

Thereafter, the DC starting power supply VCC is changed to the reference voltage VRE.
At time point F (time t1 in the figure), the activation control circuit 37 outputs a drive signal SON to the switch element 36. At this time, the switch element 36 shifts to the ON state, whereby the supply of the DC starting power supply VCC to the main control circuit 4 is started. In this case, since the DC starting power supply VCC is input to the main control circuit 4 and consumed, the DC starting power supply VCC drops temporarily. However, since the smoothing capacitor 34 is charged to the reference voltage VREF higher than the starting voltage VST in the main control circuit 4, the DC starting power supply VCC is maintained at a voltage higher than the starting voltage VST. Therefore, the main control circuit 4
Starts in a short time and reliably from the start of the supply of the AC voltage VAC by the AC power supply PS.

Thereafter, the main control circuit 4 periodically outputs a drive signal SDV having a pulse width corresponding to the detected output voltage VO to the main switch element 22 after time t1. In this case, when the drive signal SDV is input from the main control circuit 4, the main switch element 22 shifts to the ON state and switches the DC voltage VDC. At this time, the switching operation is performed by the main switch element 22, so that the secondary winding 21 b and the auxiliary winding 2
An AC voltage is induced at 1c. Next, the diode 23 rectifies the induced AC voltage, and the smoothing capacitor 24 smoothes the output of the diode 23. The output voltage VO is generated by the above operation. At the same time, the diode 25 rectifies the induced AC voltage,
6 generates the auxiliary power supply VSO by smoothing the output of the diode 25 and outputs it to the main control circuit 4. As a result, although the voltage value of the DC starting power supply VCC decreases instantaneously at time t1 with the activation of the main control circuit 4, it maintains a voltage higher than the operation guarantee voltage VGU, and after time t1 (DC starting Since the auxiliary power supply VSO is supplied at the time when the power supply VCC temporarily drops and then rises), the main control circuit 4
Once activated, the operating state is reliably maintained, mainly using the auxiliary power supply VSO as the operating power supply.

As described above, in the power supply device 1, at the time when the supply of the AC voltage VAC from the AC power supply PS is started, the switch element 36 is maintained in the off state, and the DC power supply from the start-up power generation circuit 3 to the main control circuit 4 By stopping the supply of the power supply VCC, the smoothing capacitor 34 is rapidly (in a short time) charged to a voltage exceeding the starting voltage VST. When the voltage of the DC starting power supply VCC reaches the reference voltage VREF, the switch element 36 is turned on, and the main control circuit 4 supplies the DC starting power supply VCC as starting power.
Is supplied. By the above processing, according to the power supply device 1, the main control circuit 4 can be started in a short time and reliably, and as a result, the output voltage VO can be generated quickly and reliably.

The power supply device according to the present invention is not limited to the configuration of the power supply device 1 described above, and can be appropriately changed.
For example, if the switching circuit 20 is a forward type AC / D
It can also be constituted by a C converter. Further, the present invention can be applied to a non-insulated chopper type power supply device.

[0021]

As described above, according to the switching power supply device of the first aspect, the start-up control circuit maintains the switch means in the off state at the time of starting the supply of the AC voltage to switch the main control circuit. The supply of the DC starting power supply is stopped to rapidly charge the smoothing capacitor, and when the voltage of the DC starting power supply reaches the first predetermined voltage, the switch means is driven to supply the DC starting power supply to the main control circuit. By
As a result, the main control circuit can be started in a short time and reliably, so that the output voltage can be quickly and reliably generated.

According to the second aspect of the present invention, the switching power supply apparatus further comprises a voltage clamp element connected in parallel to the smoothing capacitor to limit the DC starting power supply to a second predetermined voltage or less. Since an abnormal rise can be prevented, an adverse effect on the main control circuit due to the abnormal rise of the DC starting power supply can be reliably prevented. Therefore, the durability of the power supply device can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply device 1 according to an embodiment of the present invention.

FIG. 2 is a voltage waveform diagram of a DC starting power supply VCC for explaining operations of the power supply device 1 and the power supply device 51.

FIG. 3 is a circuit diagram of a conventional power supply device 51.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 power supply device 2 main circuit 3 start-up power generation circuit 4 main control circuit 10 first rectifying and smoothing circuit 20 switching circuit 31 first capacitor 32 second capacitor 33 auxiliary rectifying circuit 34 smoothing capacitor 35 voltage clamp element 36 switch element 37 Start-up control circuit SDV, SON Drive signal VAC AC voltage VDC DC voltage VCC DC start-up power supply VO output voltage VREF reference voltage

Claims (2)

[Claims] 1. A main circuit comprising: a first rectifying and smoothing circuit for converting an input AC voltage into a DC voltage; and a switching circuit for generating an output voltage by switching the DC voltage; and a first and a second circuit. An auxiliary rectifier circuit that rectifies the AC voltage input through the capacitor and outputs a pulsating voltage, a smoothing capacitor that generates the DC starting power by smoothing the pulsating voltage, and inputs the DC starting power. And a main control circuit operable to control the main circuit, wherein the main control circuit is disposed between the smoothing capacitor and the main control circuit, and the main control circuit of the DC starting power supply. Switch means for controlling supply and supply stop to the power supply, and when the DC starting power supply reaches a first predetermined voltage immediately after the input of the AC voltage, Switching power supply device is characterized in that a start-up control circuit drives the switching means to supply the direct current startup power to the main control circuit. 2. A voltage clamp element, which is connected in parallel to said smoothing capacitor and limits said DC starting power supply to a voltage equal to or lower than a second predetermined voltage higher than said first predetermined voltage. Item 2. The switching power supply device according to Item 1.