JP2598793Y2 - 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 chopper control type switching power supply for converting AC power into appropriate DC or AC, and more particularly to a starting circuit for starting a switching operation in response to application of an AC input. Regarding improvement.

[0002]

2. Description of the Related Art FIG. 1 shows a configuration example of a typical conventional switching power supply. In this power supply device, a noise filter 2 is provided on an input line connecting an AC power supply 1 such as a commercial power supply, and an AC input passing through the noise filter 2 is transmitted from two rectifier diodes D3 and D4 and two smoothing capacitors C3 and C4. The DC voltage is converted by a voltage doubler rectifier circuit, and the rectified output is applied to a chopper circuit including a primary winding 3 a of a transformer 3 and a switching element 4. The switching element 4 is driven by a switching signal from the controller 5 and switches the rectified output at a high frequency to flow to the primary winding 3a of the transformer 3. The high frequency power induced in the secondary winding 3b of the transformer 3 is converted into a stable direct current by the rectifying and smoothing circuit 6.

The controller 5 is a pulse width modulation type switching control circuit having a well-known configuration, and is commercially available in the form of an IC. Although not shown,
The rectifying / smoothing circuit 6 is provided with an error amplifying circuit for detecting a DC output voltage and calculating a deviation from a target voltage, and feeds back the error signal to the controller 5 via a photocoupler. The controller 5 changes the pulse width of the drive signal of the switching element 4 according to the feedback signal, and stabilizes the DC output voltage to a high degree irrespective of load fluctuations and input voltage fluctuations. This is the operation of a general AC / DC converter.

An operating power supply for the switching controller 5 itself, which is formed as an IC, is obtained from the AC input side at the time of startup, but uses stable power from the winding 3c of the transformer 3 in a steady operation state. That is, the output of the transformer winding 3c is rectified by the diode D5, smoothed by the capacitor C5, and applied with a DC voltage limited by the Zener diode Z1 to the power supply terminal Vcc of the controller 5. This is the power supply circuit for steady operation. As a starting circuit, a series circuit of a rectifier diode D6 and a resistor R2 is connected between the input side of the voltage doubler rectifier circuit and the power supply terminal Vcc of the controller 5, and when an AC input from the AC power supply 1 is applied. The AC input is rectified by a diode D6 to charge a smoothing capacitor C5 through a resistor R2, thereby supplying operating power to the controller 5. When the controller 5 is activated by this activation circuit and switching of the chopper circuit is started, the transformer winding 3c, the diode D5, and the capacitor C
The power of the controller 5 is supplied from the system 5.

[0005]

As is well known, the controller 5 has a function of stopping the switching of the switching element 4 when an abnormality such as an overvoltage or an overcurrent occurs (referred to as latch-up). . When the switching is stopped due to the latch-up, the output of the transformer 3 is lost, so that the operating power is not supplied from the system of the transformer winding 3c and the diode D5 to the controller 5, and the capacitor C5 is supplied from the AC input side via the diode D6 and the resistor R2. Is maintained.

In order to release the latch-up and restart the controller 5, the AC power supply 1 is once disconnected, the voltage of the power supply terminal Vcc of the controller 5 is reduced to a specified value (referred to as a latch release voltage), and then the AC power supply 1 is restarted. Restart by applying AC input from

However, in the conventional apparatus shown in FIG. 1, even if the AC power supply 1 is disconnected to release the latch-up, it takes a very long time for the voltage of the power supply terminal Vcc of the controller 5 to drop to the above-mentioned latch release voltage. As a result, there is a problem that the waiting time from the latch-up to the point at which restart is possible is long.

The cause of this problem is as follows. A connection point between the two capacitors C3 and C4 of the voltage doubler rectifier circuit is connected to an AC input line, and a noise filter 2 is connected to the AC input line. Therefore, even if the AC power supply 1 is disconnected, a large-capacity smoothing capacitor C
4 is connected to the diode D via the noise filter 2
6, applied to the system of the resistor R2, the power supply V of the controller 5
The voltage of the capacitor C5 that provides cc is maintained at or above the latch release voltage for a long time. This problem does not occur without the noise filter 2, but the noise filter 2 is almost indispensable in this type of switching power supply device so that the high-frequency switching signal component of the chopper circuit does not leak to the AC power supply side.

The present invention has been made in view of the above-described conventional problems, and has as its object the purpose of the present invention in a switching power supply device including a noise filter and a voltage doubler rectifier circuit, when a switching controller latches up. To release the latch and restart immediately with very little waiting time.

[0010]

Therefore, according to the present invention, a noise filter inserted into an AC input line, a voltage doubler rectifier circuit for voltage doubler rectifying the AC input passing through the noise filter, and a switching signal from a switching controller are provided. A chopper circuit that receives and operates, switches the output of the voltage doubler rectifier circuit at a high frequency, and a starter circuit that rectifies an AC input on the input side of the voltage doubler rectifier circuit with a diode and applies the rectified power to a power supply terminal of the switching controller. And a zener diode that is intermittently turned on in synchronization with the input only when the AC input is applied, is connected in series with the rectifier diode of the starting circuit.

[0011]

Even if the Zener diode is connected in series to the starting circuit, the Zener diode is intermittently turned on in synchronization with the AC input when an AC input is applied, and a voltage required for starting the switching controller is obtained. To the power supply terminal. However, in a state where the AC input is disconnected, the Zener diode does not turn on even if the capacitor voltage of the voltage doubler rectifier circuit flows into the starter circuit via the noise filter. Therefore, the power supply terminal voltage of the controller falls to or below the latch release voltage in a short time.

[0012]

FIG. 2 shows an embodiment in which the conventional switching power supply shown in FIG. 1 is improved by this invention. In the conventional configuration of FIG. 1, a Zener diode 7 is connected in series between a rectifier diode D6 and a resistor R2 of a start circuit, and FIG. 1 and FIG. 2 are the same in other configurations. is there.

In FIG. 2, a Zener diode 7 functions as a clip circuit. That is, when the AC input is applied, a voltage obtained by subtracting (clipping) the Zener voltage of the Zener diode 7 from the pulsating voltage obtained by rectifying the AC input by the diode D6 is applied to the resistor R2. Although the voltage applied to the resistor R2 is lower than that of the conventional circuit shown in FIG. 1, a sufficient voltage can be obtained as the operating voltage of the controller 5, and the controller 5 is activated in response to application of an AC input. The function of the circuit is not impaired at all.

If the controller 5 latches up for some reason from the steady state of operation of the apparatus, once the AC power supply 1 is disconnected, the capacitor C of the voltage doubler rectifier circuit is disconnected.
4 wraps around the diode D6 side of the starting circuit via the noise filter 2, but the Zener diode 7 does not turn on with this wraparound voltage, and therefore the controller 5
The power supply voltage Vcc (the voltage of the capacitor C5) drops rapidly and falls below the latch release voltage in a short time. Thereafter, when the AC power supply 1 is connected again, the power supply voltage Vcc required for starting is applied to the controller 5 via the diode D6, the Zener diode 7, and the resistor R2, and the switching operation of the chopper circuit is restarted. Transformer winding 3 if normal operation
The power supply Vcc of the controller 5 is supplied from the side c.

[0015]

As described above in detail, according to the present invention, the Zener diode is turned on intermittently in synchronization with the AC input when AC input is applied, and is necessary for starting the switching controller. Voltage can be led to the power supply terminal, and in a state where the AC input is cut off, the Zener diode does not turn on even if the capacitor voltage of the voltage doubler rectifier circuit sneaks into the starting circuit via the noise filter. . Therefore, the power supply terminal voltage of the controller falls to or below the latch release voltage in a short time, and the waiting time before the restart becomes possible is much shorter than in the past.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a conventional switching power supply device.

FIG. 2 is a schematic block diagram of an embodiment in which the conventional device of FIG. 1 is improved by the present invention.

[Explanation of symbols]

 2 Noise filter 4 Switching element 5 Switching controller 7 Zener diode D3, D4 Diode of voltage doubler rectifier circuit C3, C4 Capacitor of voltage doubler rectifier circuit D6 Diode of starter circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H02M 3/28 H02M 1/12 H02M 7/10

Claims (1)

(57) [Scope of request for utility model registration] 1. A noise filter inserted into an AC input line, a voltage doubler rectifier circuit that doubles voltage rectifies an AC input that has passed through the noise filter, and operates by receiving a switching signal from a switching controller. A switching power supply device comprising: a chopper circuit that switches an output of a circuit at a high frequency; and a startup circuit that rectifies an AC input on an input side of the voltage doubler rectifier circuit with a diode and applies the rectified AC input to a power supply terminal of the switching controller. A switching power supply device, characterized in that a zener diode that is intermittently turned on in synchronization with an input only when the AC input is applied is connected in series with a rectifier diode of a starting circuit.