JPS61210870A - Switching regulator - Google Patents

Abstract

PURPOSE:To protect a simple circuit from being overloaded, by detecting current through a switching transistor, and by contriving the detected voltage and the voltage from a transformer winding changing in proportion with DC input voltage, to be put together. CONSTITUTION:The conducting angle of a switching transistor 2 is controlled according to DC output. When the switching transistor 2 is ON, then voltage generated on a transformer winding N3 is in proportion with DC input voltage, and the voltage for feedback is provided by a diode 3, a resistance 4, and a resistance 6. Excess current is detected by a transistor 7, and when DC output is abnormally increased, current is conducted to the transistor 7.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention utilizes a so-called single-stone flyback method in which a switching element stores excitation energy in a transformer when it is on, and releases excitation energy when it is off to obtain an output. The present invention relates to switching regulators, and particularly to switching regulators that include current detection performance for use in overcurrent protection and the like.

[Conventional technology]

A conventional switching regulator includes a transformer having a first transformer winding and a second transformer winding, one end of which is connected to one end of a DC input, and a second transformer winding, and one end of which is connected to the other end of the first transformer winding. A switching element whose other end is connected to the other end of the DC input, and a rectifier connected to both ends of the second transformer winding to obtain a stabilized DC output by controlling opening and closing of the switching element. It is configured to include a smoothing circuit.

To detect current for overcurrent protection in such conventional switching regulators, it is necessary to insert a resistor into the DC output to directly detect the output current of the switching regulator, or to insert a resistor or current in series with the switching element. Only a transformer was installed to directly detect the current flowing through the switching element and send it to the overcurrent protection circuit.

[Problem that the invention seeks to solve]

However, in the case of the former type of current detection, when the DC output current is large, K requires a detection resistor with a large power or a small resistance value, which is difficult to select. Furthermore, even if an abnormal current flows in the stage before the DC output, such as the output rectifying and smoothing circuit of the switching regulator, it cannot be detected and damage increases.

On the other hand, in the case of the latter current detection, - When used in a stone-carved flyback type switching regulator, even if the same DC output current is obtained, if the DC input voltage changes greatly, the peak value of the current pulse will change greatly. 1. For example, if overcurrent protection is performed by detecting the peak value of a current pulse, the disadvantage is that the DC output current that is protected by the DC input will change significantly, so it is difficult to use the protective circuit when the DC input voltage is high. Even if provided, there was a drawback that a large load was placed on the output side of the switching regulator.

[Means for solving problems]

The switching regulator of the present invention includes: a first resistor having one end connected to one end of the DC input; a first transformer winding and a second transformer winding having one end connected to the other end of the DC input; is connected to the other end of the first resistor.
a transformer having a transformer winding, one end of which is connected to the first transformer winding;
a switching element connected to the other end of the transformer winding and whose other end is connected to the other end of the first resistor; and a switching element connected to both ends of the second transformer winding to control opening and closing of the switching element. a rectifying and smoothing circuit for obtaining a stabilized DC output; a series circuit comprising a diode and a second resistor connected in series, one end of which is connected to the other end of the third transformer winding; a third resistor with one end connected to the other end of the series circuit and the other end connected to the other end of the first resistor; and both ends connected to one end of the first resistor and one end of the third resistor. and a connected current detection element.

That is, the switching regulator of the present invention has the first
a transformer having a transformer winding and a second transformer winding, a switching element, a rectifying and smoothing circuit connected to the second transformer winding of the transformer, and a first transformer winding of the transformer.
A series circuit in which the transformer winding of the transformer and the switching element are connected in series is connected to one end of the non-stabilized DC input, and opening and closing of the switching element is controlled, thereby receiving the stabilized DC output from the rectifying and smoothing circuit. In the switching regulator obtained, a first resistor provided between the series circuit and the unregulated DC input, a third transformer winding further provided in the transformer, and the third transformer winding. a diode connected to one end of the line, and a second resistor connected between the other end of the diode and the terminal opposite to the DC input side of the first resistor. It consists of a series circuit of a third resistor, and in addition to the third winding! is connected to either terminal of the first resistor. and a current detection element connected to the connection terminal of the third resistor.

That is, in the switching regulator of the present invention, the first transformer winding of the transformer and the switching element are connected in series.
a first resistor provided between the line and one end of the DC input;
The first transformer winding of the transformer and W! A diode connected to one end of a third transformer winding, which is provided separately from the second transformer winding, and a diode? a series circuit of a second resistor and a third resistor provided between the other terminal and the terminal opposite to the DC input side of the resistor of il; This can be realized by a current detection circuit that extracts a voltage between the connection point of the third resistor and the DC input side terminal of the negative resistor. That is, the voltage appearing at the first resistor for detecting the current flowing through the switching element is added to the second resistor, which changes depending on the DC input voltage obtained by the third transformer winding of the transformer and the diode. This can be achieved by partially overlapping the resistors through the third resistor.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

The switching regulator shown in Fig. 1 consists of a rectifier circuit consisting of a transformer L including transformer windings N, N, a switching transistor 2, a diode 8, and a capacitor 9. It is a flyback type switching regulator, and further includes a transformer I NNs.

Diode 3. It includes resistors 4, 5, and 6 and is input between the Sakaki Tori paces to detect overcurrent.

Next, the operation of the switching regulator shown in FIG. 1 will be explained.

It is assumed that the conduction angle of the switching transistor 2 is controlled according to the DC output, and a constant voltage is obtained at the output. When switching transistor 2 is turned on, current flows through transformer winding N, and excitation energy is stored in transformer 1. Next, when switching transistor 2 is turned off, excitation energy is released from transformer winding N2 through diode 8, and capacitor 9 is charged. be done. The same current as that of the switching transistor 2 flows through the resistor 5, and the voltage generated across the resistor 5 is also proportional to this current.

Now, when a constant DC output is obtained and the DC input voltage increases, the conduction angle of the switching transistor 2 becomes tighter, and therefore the conduction angle of the diode 8 widens. The pulse voltage at both ends decreases. In other words, if current is detected from both ends of the resistor 5, the detected value will be greatly deviated by the DC input voltage even if it is a 4-DC output.

Therefore, when the switching transistor 2 is on, the voltage generated in the transformer winding NsK is proportional to the DC input voltage, and this voltage is transferred to the diode 3. If it is detected between the connection point of the resistors 4 and 6 and the (-) terminal of the DC input by feeding back through the resistor 4 and resistor 6, the deviation due to the DC input voltage will be corrected. Therefore, if each constant for this feedback is appropriately selected, if the DC output is constant for the pulse voltage 1, it can be made almost constant regardless of the DC input.

Transistor 7 is for detecting overcurrent,
When the DC output abnormally increases, the current detection voltage 11S increases and at a certain point, the transistor 7 becomes conductive and an overcurrent is detected.

In this way, the switching regulator shown in FIG. 1 can always perform overload protection against a constant DC output.

In the switching regulator shown in FIG. 1, a resistor 5 with a relatively small resistance value is used;
A resistor 6 having a sufficiently larger resistance value than the resistor 5 is selected depending on the amount of feedback.

The switching regulator of the present invention partially changes the embodiment shown in FIG.
Instead, use a series circuit of a diode and a resistor, or connect the terminal of the transformer winding N3 opposite to the terminal on the diode 3 side to the (-) terminal of the DC input, or connect the diode 30 cathode to the (-) terminal of the DC input. Of course, a capacitor can be provided between the transformer winding N3 and one end of the transformer winding N3.

〔Effect of the invention〕

The switching regulator of the present invention detects the current flowing through the switching transistor in a stone-carved flyback type switching regulator, and adds the voltage from the transformer winding, which changes in proportion to the DC input voltage, to the detected voltage. By using a method of feedback and superimposition, it is possible to detect a current that roughly corresponds to the DC output regardless of the DC input voltage with a simple circuit configuration, and it is possible to perform effective overload protection with a constant DC output. There is no need to provide a power margin for the circuit elements on the output side, and the cost can be reduced.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. l...Transformer, 2...Switching transistor, 3,8...Diode, 4.5
, 6...-Resistor, 7...Transistor,
9... Capacitor, N,, N,, N,...
...Transformer winding. Grass / [! I

Claims (1)

[Claims] a first resistor having one end connected to one end of the DC input; a first transformer winding and a second transformer winding having one end connected to the other end of the DC input; and a first resistor having one end connected to the other end of the DC input; a transformer having a third transformer winding connected to the other end;
a switching element having one end connected to the other end of the first transformer winding and the other end connected to the other end of the first resistor; and a switching element connected to both ends of the second transformer winding. A rectifying and smoothing circuit for obtaining a stabilized DC output by controlling opening and closing, a diode and a second resistor connected in series, one end of which was connected to the other end of the third transformer winding. a series circuit; a third resistor having one end connected to the other end of the series circuit and the other end connected to the other end of the first resistor; A switching regulator comprising: a current detection element connected to one end of a resistor.