JPH04125067A - Switching power source - Google Patents

Abstract

PURPOSE:To reduce in size and cost a conversion transformer by connecting one end of an input rectifying diode to an AC input line of the side in which a triac and a rush current preventing resistor are inserted, and connecting one end of a winding for other use to the other end of the diode. CONSTITUTION:When an AC power source is connected to electric lines A1, A2, an AC is applied to a bridge of diodes D1-D4 through a resistor R1, and a capacitor C1 is charged by the full-wave rectified voltage. Then, a voltage is generated at an auxiliary winding NA in response to its switching operation, and applied to a diode D5. Then, a forward voltage is applied from the winding NA to the diode D5 during a period in which the diodes D2, D4 of the rectifier are turned ON, the diode D5 is turned ON, and a capacitor C2 is charged through a resistor R2. A positive gate voltage is supplied to a triac 1, which is shifted to an ON state to short-circuit the resistor R1, thereby preventing power consumption of the resistor R1 during the switching operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching power supply, and more particularly to a switching power supply equipped with a circuit that prevents rush current from flowing into a capacitor of a rectifier circuit on the input side when AC power is turned on.

[Conventional technology]

In conventional switching power supplies of this type, for low power applications, a resistor or thermistor is inserted and connected on the AC input side to prevent excessive inrush current from flowing into the rectifier circuit capacitor when the power is turned on. There is. In the case of medium to high power applications, as shown in Figure 5, triac 1 is connected in parallel to resistor R1 for inrush current prevention. Immediately after the power is turned on, triac 1 is in the off state, so it is connected via resistor R1. When alternating current is connected to the rectifier circuit and the switching operation starts in response to this, a gate voltage is applied to triac 1 to turn it on, and both ends of resistor R1 are short-circuited.
The resistor R1 prevents unnecessary power consumption during operation.

In FIG. 5, electric wires A1 and A2 are for inputting AC power, and a resistor R1 for preventing rush current and a triac 1 are connected in parallel and inserted in the middle of one electric wire A1. The diodes D1 to D4 perform full-wave rectification of the input alternating current to charge the capacitor C1. Both ends of capacitor C1 are
It is connected to the primary winding Np of the transformer T via a switching circuit (SW) 2. The switching circuit 2 switches the current in the primary winding Np under the control of a signal generated by the auxiliary power supply 3 from the voltage generated in the auxiliary winding NA of the transformer T and a signal given from the control circuit 5.

Correspondingly, the voltage generated in the secondary winding Ns is rectified and smoothed by the rectifier circuit 4 to obtain a DC output. In response to this switching operation, the voltage generated in the bias winding NB of the transformer T is rectified by the diode D5, charges the capacitor C2 through the time constant setting and discharging resistors Rz and Rs, and charges the triac 1. is supplied as the gate voltage.

When AC power is applied to wires A, A2, capacitor C2
is being discharged through the resistor R3, and since the gate voltage of the triac 1 is zero, an alternating current is first applied to the rectifier circuit via the resistor R1. Therefore, it is possible to prevent an excessive rush current from flowing into the capacitor C1. Capacitor C1
When charged, a voltage is generated in the bias winding NB according to the switching operation, and as described above, the gate voltage is supplied to the triac 1, turning the triac 1 on and shorting the resistor R1.

[Problem to be solved by the invention]

In the conventional switching power supply mentioned above, the triac 1
A dedicated winding N is installed in the transformer T to supply the gate voltage of
Since B is provided, extra winding space and inter-winding insulating material must be added, leading to the problem that the transformer T becomes larger and more expensive.

SUMMARY OF THE INVENTION An object of the present invention is to provide a switching power supply capable of solving the above-mentioned problems and supplying a triac gate voltage without requiring an extra transformer winding.

[Means to solve the problem]

The switching power supply of the present invention includes an inrush current prevention circuit that includes a triac that is inserted and connected in the middle of one of two AC input lines and that operates to disconnect or disconnect in response to a gate voltage, and a resistor that is connected in parallel to the triac. an input rectifier circuit that has a rectifier diode connected at one end to the inrush current prevention circuit and charges an input capacitor by rectifying input alternating current; and a switching circuit that operates to disconnect current between both ends of the input capacitor. a transformer having a first winding connected through the transformer and a second winding that generates an induced voltage in response to current disconnection of the first winding; and one end connected to one end of the input capacitor. a bias capacitor whose one end is connected to the inrush current prevention circuit and whose other end is connected to the gate of the triac; and a gate bias circuit having a bias diode that rectifies the induced voltage and sends it to the bias capacitor.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. The difference from the conventional switching power supply (see Figure 5) (7) is that the transformer T does not have a bias winding (NB), and the gate voltage of the triac 1 is obtained from the auxiliary winding NA. . That is, the voltage of the auxiliary winding NA (or the output terminal of the auxiliary power supply 3) is rectified by the diode D5, and the capacitor C2 is charged through the resistors R2 and R3 to obtain the gate voltage of the triac I.

When AC power is applied to wires A+ and A2, triarch 1 is off, so AC is applied to the rectifier circuit (bridge circuit of diodes D1 to D4) via resistor R1, and the full-wave rectified voltage causes the capacitor to is charged. Therefore, it is possible to prevent an excessive rush current from flowing into the capacitor C1. When the capacitor C1 is charged, a voltage is generated in the auxiliary winding NA (or the output terminal of the auxiliary power supply 3) according to the switching operation, and is applied to the diode D5. Diode D2 of the rectifier circuit. When a forward voltage is applied from the auxiliary winding NA to the diode Ds during the period when DJ is in the on state, the diode D5 becomes in the on state,
Capacitor C2 is charged through resistor R2. While the input AC frequency is 50 or 60 hertz,
Since the switching frequency is on the order of kilohertz, capacitor C2 can be charged enough times to maintain the gate voltage of triac 1 during a switching operation. As a result, triac 1
A positive gate voltage is applied to the triac 1 to turn it on, shorting the resistor R1 and preventing power dissipation in the resistor R1 during switching operations.

FIG. 2 is a circuit diagram of a second embodiment of the invention.

In this embodiment, the switching power supply shown in FIG. 1 is modified so that a negative gate voltage is supplied to the triac 1. The cathode of a voltage regulator diode D is connected to the positive terminal of the primary winding N of the transformer T, and the auxiliary winding NA is AC coupled to the anode of the transformer T through a resistor R4 and a capacitor C4. A negative voltage is obtained at the 7th node. Furthermore, constant voltage diode D8
A capacitor C8 is connected in series with a diode D in the forward direction on both ends of the capacitor C8, and the capacitor C8 is charged with the negative voltage of the anode of the constant voltage diode D. During the period when diodes D, D3 of the rectifier circuit are on, diode D is on, charge is transferred from capacitor C1 to capacitor C2 through resistor R2, and a negative gate voltage is applied to triac 1, turning it on. can be done.

FIG. 3 is a circuit diagram of a third embodiment of the present invention.

In this embodiment, the transformer T has no auxiliary winding (NA).

The switching circuit (SW) 2 receives a control pulse given from the control circuit 15 via the pulse transformer PT, and performs on/off switching. The control circuit 15 operates using direct current obtained by rectifying and smoothing input alternating current by the rectifying circuit 14 of the auxiliary power source 13 as a power source. One end of the secondary winding of the pulse transformer PT is connected to the switching circuit 2 and the rectifier circuit (
to the connection point with the bridge circuit (bridge circuit of diodes D1 to D4),
The other end is connected to the control input end of the switch circuit (SW) 20 and to the diode D, respectively. Similarly to the embodiment shown in FIG. 1, in this embodiment, when a forward voltage is applied from the secondary side of the pulse transformer FT to the diode D during the ON period of the diodes D2 and D4 of the rectifier circuit. , diode D, is turned on and capacitor C2 is charged through resistor R2, allowing a positive gate voltage to be supplied to triac 1. In addition, auxiliary power supply 1
If 3 is a capacitor input type, inrush current can also be prevented.

In any of the embodiments described above, the circuit that rectifies the input AC is of the full-wave rectification type, and the triac 1 and the resistor R1 are connected to the electric wire A1. No matter where you insert it in A2,
The gate voltage for the triac 1 can be obtained without providing a dedicated winding in the transformer T for generating the gate voltage of the triac 1. Next, an embodiment will be described in which the rectifier circuit on the input side is of a voltage doubler rectifier type.

FIG. 4 is a circuit diagram of a fourth embodiment of the present invention.

The rectifier circuit on the input side is a diode D1. It has a voltage doubler rectification type configuration consisting of D + and capacitor C11r Cl□. The triac 1 and the resistor are inserted into the wire A1 on the side to which the diodes DI and D4 are connected. A primary winding Np of a transformer T is connected between both ends of the series-connected capacitors CIl and CI2 via a switching circuit 2, and a control circuit 16 is activated depending on the induced voltage of an auxiliary winding NA provided in the transformer T. The operation of the switching circuit 2 is controlled by the control signal generated by the switching circuit 2.

One end of the auxiliary winding NA is also connected to a diode D, and the other end is connected to the triac 1 and the capacitor C2 via a diode D4. Therefore, diode D
When a forward voltage is applied from the auxiliary winding NA to the diode D5 during the ON period of 4, the diode D5 turns on and charges the capacitor C2 through the resistor R2.
A positive gate voltage can be supplied to the triac 1.

In each of the above embodiments, one end of an input rectifying diode is connected to the AC input line on the side where the triac and inrush current prevention resistor are inserted, and one end is connected to the other end of this diode. If the circuit has a winding, one end of the capacitor is connected to the AC input line, and a rectified voltage induced in the winding for another purpose is applied to the other end of the capacitor to charge the capacitor and activate the triac. Can be used as a gate voltage supply source. Therefore, there is no need to provide a winding dedicated to the gate voltage.

〔Effect of the invention〕

As described above, according to the present invention, the gate voltage of the triac in the inrush current prevention circuit can be supplied without requiring an extra transformer winding, and the conversion transformer can be made smaller and cheaper than before.

[Brief explanation of drawings]

1 to 4 are circuit diagrams of embodiments of the present invention, and FIG. 5 is a circuit diagram of a conventional switching power supply. 1... Triac, 2... Switching circuit, 3.13... Auxiliary power supply, 4, 14...
... Rectifier circuit, 5.15.16 ... Control circuit, A 1. A2...Electric wire, R+ ~R
+ "'"'Resistance, C1~041011. CB・”
...Diode for capacitor %DI~D1..., T.
...Transformer, Np...-Next winding, Ns
...Secondary winding, NA...Auxiliary winding, N
n...Bias winding, PT...Pulse transformer. Agent patent attorney Shindai Uchihara! Mataya-style broom■ Kayakou

Claims (6)

[Claims] (1) An inrush current prevention circuit that includes a triac that is inserted and connected in the middle of one of two AC input lines and that disconnects and disconnects in response to a gate voltage, and a resistor that is connected in parallel to the triac, and the inrush current prevention circuit. an input rectifier circuit that has a rectifier diode connected to the circuit at one end and rectifies the input alternating current to charge the input capacitor; 1
a second winding that generates an induced voltage in response to current disconnection in the first winding; rectifying the induced voltage in the third winding through a bias capacitor whose one end is connected to the third winding supplying the circuit and the inrush current prevention circuit and whose other end is connected to the gate of the triac; and a gate bias circuit having a bias diode that sends the signal to the bias capacitor. (2) The switching power supply according to claim 1, wherein the third single wire is wound around the transformer in electromagnetic coupling with the first and second windings. (3) The gate bias circuit includes a negative voltage generating circuit that AC-couples the induced voltage of the third winding to a constant voltage diode connected to the other end of the input capacitor; Claim (1) further comprising a negative voltage rectifier circuit for rectifying and smoothing the voltage across the voltage, and the output voltage of the negative voltage rectifier circuit being connected to the bias diode.
Switching power supply listed. (4) The switching power supply according to claim 1, wherein the third winding is a winding of a pulse transformer provided separately from the transformer to transmit a pulse signal for connection/disconnection control to the switching circuit. (5) The switching power supply according to claim (1), wherein the input rectifier circuit is configured to full-wave rectify the input AC. (6) The switching power supply according to claim (1), wherein the input rectifier circuit is configured to voltage double rectify the input AC.