JPH0717273Y2 - Inrush current limiting circuit for DC power supply - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a switching type DC power supply device.
The present invention relates to an inrush current limiting circuit that limits a large current generated when a system is started up, and particularly to an improvement in its operation and an improvement in loss.

<Prior Art> FIG. 5 is a configuration block diagram of a conventional DC power supply device having a rush current limiting function.

In the figure, 10 is an inrush current limiting circuit, which is configured by connecting a resistor R and a bidirectional switch element (triac) TS in parallel, and is connected in series with a rectifier circuit DB of a diode bridge (input AC Inserted in the current path from the power supply),
It is connected to the AC power supply ein. Reference numeral 20 is a transformer forming a switching power supply, Q1 is a switching element, and the DC voltage Ein from the rectifier circuit DB smoothed by the capacitor C is turned on / off and added to the primary winding n1.

30 is a rectifying / smoothing circuit for rectifying and smoothing an AC signal generated in the secondary winding n2 to obtain an output voltage Vout, 40 is an input voltage of the output voltage Vout, and an insulating transformer is provided so that this becomes a constant voltage corresponding to a predetermined reference voltage. A pulse width control circuit for controlling ON / OFF of the switching element Q1 via 41.

FIG. 6 is a waveform diagram for explaining the operation of this circuit. Initially, the triac TS is turned off, and when the power is turned on, the diode bridge rectifier circuit DB causes the current Iin (limited by the AC power source ein through the current limiting resistor R as shown in (a) to = Vin / R) flows.

The voltage across the capacitor C (corresponding to the voltage applied to the primary winding n1) Ein gradually increases as shown in (b), and when the converter starts operating, a predetermined voltage is generated in the winding n3. Triac TS is turned on and at this time t _O
Then, the input current Iin flows through the triac TS side, and the current is not limited by the resistor R. Therefore, the inrush current flows again at the time of t _O.

<Problems to be solved by the invention> As described above, in the conventional circuit, a constant current is required to turn on the triac, and since this current is affected by temperature and the like, a considerable margin is required. The value must be determined in anticipation, which causes a large power loss due to the resistance r, which causes a problem that the efficiency as a power source is reduced.

The present invention has been made in view of these points,
It is an object of the present invention to provide a circuit capable of effectively preventing a secondary inrush current generated when the inrush current limiting function is released without increasing power loss.

<Means for Solving the Problems> The present invention for achieving such an object is to rectify and smooth an input AC power supply, and turn on / off the DC voltage by a switching element.
A switching power supply (main converter) that turns off the voltage and applies it to the primary winding of the transformer and rectifies and smoothes the signal generated in the secondary winding to obtain a DC voltage. In a power supply device equipped with an inrush current limiting circuit that is inserted in the current path from the power supply to the switching power supply, a circuit that rectifies and smoothes the output generated in the winding provided in the transformer, and the output of this rectification and smoothing circuit to a constant current. And a constant current circuit for controlling the switching element to use the constant current from the constant current circuit.

<Operation> Each component of the present invention operates as follows.

At first, there is no output that occurs in the winding provided in the transformer,
Therefore, the output of the rectifying / smoothing circuit is zero, and the switch element such as a triac is off, and the inrush current limiting circuit prevents an excessive current from flowing when the power is turned on. When the voltage generated in the winding provided in the transformer gradually increases and the output of the rectifying and smoothing circuit becomes sufficiently large, the current supplied to the switch element also increases, and eventually the switch element turns on and the current limiting function is released. .

<Embodiment> An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a configuration block diagram of an embodiment of the present invention.
In this figure, the same parts as those in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted. A winding n3 is provided in the main transformer 20 that constitutes the switching power supply. 50 is a rectifying / smoothing circuit for rectifying and smoothing the signal generated in this winding, and 60 is a constant current circuit for making the output E3 of the rectifying / smoothing circuit 50 a constant current. Inrush current limiting circuit 10 triac
A constant current from the constant current circuit 60 is supplied to TR as a drive signal thereof.

FIG. 2 is a circuit diagram for explaining the operation of the constant current circuit 60. The resistor R1 and Zener diode ZD are connected in series to form a constant voltage circuit.
A constant Zener voltage VZ is obtained across ZD. Q2 is a transistor to which this Zener voltage VZ is applied. The voltage VR across the resistor R2 connected to the emitter of the transistor Q2 is expressed as VR = VZ-Vbe, where Vbe is the base-emitter voltage of the transistor Q2, and it becomes a constant voltage and is the current supplied to the triac TR. IS becomes a constant current.

According to the circuit configured as described above, when the power is turned on, the switching power supply starts to operate, the output of the winding n3 gradually increases, and the constant current circuit 60 can supply the constant current IS to the triac TR. Then, the TRIAC TR is surely turned on. While the constant current circuit 60 does not supply the constant current, the current does not flow to the triac TR side, so that no useless power loss occurs.

FIG. 3 is a connection diagram of a main part of a voltage detection circuit 70 which replaces the constant current circuit 60 connected to the rectifying / smoothing circuit 50 of FIG. 1 and a current control circuit 80 which controls a current by its output.
The voltage detection circuit 70 detects that the output voltage E3 of the rectifying / smoothing circuit 50 reaches a predetermined voltage, and the current control circuit 80 is configured to control the current supplied to the triac.

FIG. 4 is a diagram for explaining the operation of each of these circuits.

The voltage detection circuit 70 is composed of a series circuit of a Zener diode ZD1 and a resistor R3 and a transistor Q3.The series circuit of the Zener diode ZD1 and a resistor R3 turns off the Zener diode ZD1 when the output voltage E3 of the rectifying and smoothing circuit 50 is small. Then, in this state, the transistor Q3 is turned off.

The current control circuit 80 includes resistors R4, R5, R6 and a transistor Q4.
And is turned on when the transistor Q3 is turned off.

When the transistor Q4 is on, the current IT from the rectifying / smoothing circuit 50 passes through the resistor R6 and the transistor Q4 to the triac TR, and as shown in the portion of FIG.
The output voltage E3 gradually increases in proportion to the magnitude of the output voltage E3.

Then, when the output voltage E3 of the rectifying and smoothing circuit 50 gradually increases (this voltage is proportional to the output of the switching power supply), the Zener diode ZD1 turns on eventually,
Transistor Q3 also turns on. When the transistor Q3 turns on, the base current of the transistor Q4 flows to the transistor Q3 side as shown by the broken line, so the transistor Q4 turns off. Then, the current will be supplied to the triac TR through the resistors R6 and R5.
As shown in the portion of FIG. 4, the gradually increasing inclination angle becomes gentle.

In this embodiment, in FIG. 4, the zener voltage of the zener diode ZD1 and the values of the resistors R5 and R6 are set so that the value of becomes the current necessary to turn on the triac TR and the power loss is reduced. It will be decided.

In addition, in each of the above-described embodiments, the inrush current limiting circuit 10 is used.
Is inserted between the input AC power supply ein and the bridge rectification circuit DB, but it may be inserted and connected between the bridge rectification circuit DB and the switching power supply. In this case, SCR can be used as the switch element instead of the triac.

<Advantages of Device> As described in detail above, according to the present invention, the current supplied to the switch element used in the inrush current limiting circuit can be reduced or decreased, so that power loss can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of an embodiment of the present invention, FIG. 2 is a diagram for explaining the operation of the constant current circuit in FIG. 1,
FIG. 3 is a connection diagram of a voltage detection circuit and a current control circuit provided in place of the constant current circuit in FIG. 1, FIG. 4 is a diagram for explaining the operation, and FIG. 5 is an inrush current limiting function. FIG. 6 is a block diagram of a configuration of a conventional DC power supply device having the above, and FIG. 6 is a waveform diagram for explaining the operation of the circuit of FIG. 10 ... Inrush current limiting circuit 20 ... Main transformer, 30 ... Rectification smoothing circuit 40 ... Pulse width control circuit 50 ... Rectification smoothing circuit, 60 ... Constant current circuit 70 ... Voltage detection circuit

Claims (2)

[Scope of utility model registration request] 1. An input AC power supply is rectified and smoothed, a DC voltage thereof is turned on / off by a switching element to be applied to a primary winding of a transformer, and a signal generated in a secondary winding is rectified and smoothed to generate a DC voltage. In a power supply device equipped with a switching power supply to be obtained and a rush current limiting circuit in which a parallel circuit of a current limiting resistor and a switch element is inserted in the current path from the input AC power supply to the switching power supply, occurs in the winding provided in the transformer. A circuit for rectifying and smoothing the output and a constant current circuit for making the output of the rectifying and smoothing circuit a constant current are provided, and the constant current from the constant current circuit is used as a drive signal for the switch element. DC power supply inrush current limiting circuit. 2. An input AC power supply is rectified and smoothed, a DC voltage thereof is turned on / off by a switching element to be applied to a primary winding of a transformer, and a signal generated in a secondary winding is rectified and smoothed to generate a DC voltage. In a power supply device equipped with a switching power supply to be obtained and a rush current limiting circuit in which a parallel circuit of a current limiting resistor and a switch element is inserted in the current path from the input AC power supply to the switching power supply, occurs in the winding provided in the transformer. A circuit that rectifies and smoothes the output, a voltage detection circuit that detects when the output voltage of the rectification and smoothing circuit reaches a predetermined voltage, and a current that controls the current supplied to the switch element according to the output of the voltage detection circuit. Inrush current limiting circuit for DC power supply with control circuit.