KR20130014970A

KR20130014970A - Over voltage protection circuit

Info

Publication number: KR20130014970A
Application number: KR1020110076753A
Authority: KR
Inventors: 한재현
Original assignee: 엘지이노텍 주식회사
Priority date: 2011-08-01
Filing date: 2011-08-01
Publication date: 2013-02-12

Abstract

PURPOSE: An overvoltage protection circuit is provided to be applied to a power supply with a multiple output terminal by satisfying various load voltages according to the change of a zener voltage of a zener diode. CONSTITUTION: A transformer(T1) transforms an input voltage to an output voltage required for a load. A rectifying diode(D1) rectifies the voltage transformed in the transformer. A smoothing condenser(C1) smoothes the voltage rectified by the rectifying diode. A conductive state of a zener diode is controlled according to the level of the rectified and smoothed output voltage. A first switching device is electrically connected to a second switching device.

Description

Over voltage protection circuit

The present invention relates to an overvoltage protection circuit that protects the output stage circuit from overvoltage.

In general, a power supply refers to a circuit that converts an input voltage to a voltage of a desired level at a plurality of output terminals and outputs the voltage, and prevents a malfunction and damage of a load (for example, home appliance, industrial equipment, etc.) coupled to the output terminal. The overvoltage protection circuit is adopted for this purpose.

By connecting a microcomputer with a conventional overvoltage protection circuit to the output terminal of the power supply, the voltage of the output terminal is measured, and when it is detected that a voltage higher than a predetermined reference voltage is output, the microcomputer stops the operation of the power supply. It is designed to protect the circuit.

However, such an overvoltage protection circuit of a conventional power supply uses a microcomputer to cut off the circuit when an overvoltage is detected at the output of the power supply, thereby increasing the load to be processed by the microcomputer.

In this case, the load of the microcomputer is further increased in a circuit using multiple multi-output stages having a large number of output stages of the power supply, and a structural problem in which the economic burden of using a high-speed and expensive microcomputer is increased for this purpose. have.

The present invention provides an overvoltage protection circuit of a power supply which can protect a circuit from an overvoltage applied to an output end of a power supply even with a simple circuit configuration.

An overvoltage protection circuit according to an embodiment of the present invention includes a transformer for transforming an input voltage into an output voltage required by a load; A rectifier diode for rectifying the voltage transformed by the transformer; A smoothing capacitor for smoothing the voltage rectified by the rectifying diode; A Zener diode whose conduction state is controlled according to the level of the rectified and smoothed output voltage in the rectifying diode and the smoothing capacitor; And first and second switching devices that are turned on and electrically connected to each other when the output voltage level applied to the zener diode is equal to or higher than the zener voltage of the zener diode.

According to the present invention, by using a simple overvoltage protection circuit composed of a switching element such as a Zener diode and a FET to protect the load from overvoltage, the circuit can be easily configured and the protection circuit can be configured at a low cost.

In addition, as the zener voltage of the zener diode is changed, various load voltages can be satisfied, and thus, all the power supplies having multiple output stages can be applied.

1 is a circuit diagram illustrating an output terminal of an LED driver to which an overvoltage protection circuit according to an embodiment of the present invention is applied.
2 is a view showing a simulation waveform of the voltage applied to each node in the overvoltage protection circuit according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The details of other embodiments are included in the detailed description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and how to accomplish them, will become apparent by reference to the embodiments described in detail below with reference to the accompanying drawings. Like reference numerals refer to like elements throughout.

1 is a circuit diagram illustrating an output terminal of an LED driver to which an overvoltage protection circuit according to an exemplary embodiment of the present invention is applied.

Referring to FIG. 1, at least one transformer T1 for boosting or reducing the input voltage input from the input terminal to a voltage level required by a load of a subsequent stage, and a rectifying diode for rectifying the output voltage transformed by the transformer T1. (D1), the smoothing capacitor (C1) smoothing the output voltage rectified by the rectifying diode (D1), and the level of the output voltage DC-directed by the rectifying diode (D1) and the smoothing capacitor (C1). In accordance with the overvoltage protection circuit 100 to control the output voltage is supplied to the load.

Here, the overvoltage protection circuit 100 receives an output voltage, which is DC, by the rectifying diode D1 and the smoothing capacitor C1, as a cathode, and the output voltage input to the cathode is a preset Zener voltage ( First and second switching elements (turned on by the zener diode ZD1 conducted when the voltage is equal to or higher than the breakdown voltage) and the zener voltage excess conducted through the zener diode ZD1 to pass the output voltage to ground. Q1 and Q2 and a load resistor R9 for regulating the voltage across the switching element Q1 through the zener diode ZD1. At this time, it is preferable that the zener diode ZD1 sets the zener voltage to be equal to or similar to the voltage level required by the loads R7 and R8.

In addition, the first and second switching elements Q1 and Q2 may use ordinary switching transistors, and switching FETs may be used in a circuit requiring a high voltage.

The first and second switching elements Q1 and Q2 may be electrically connected, the first switching element Q1 may be an npn transistor, and the second switching element Q2 may be formed as a pnp transistor. have. A connection resistor R4 may be formed at the base end of the first switching element Q1 and the emitter end of the second switching element Q2.

A first base resistor R2 may be connected to a base end of the first switching element Q1, and a second base resistor R3 may be connected to a base end of the second switching element Q2. The first and second base resistors R2 and R3 may be formed in consideration of operating voltages of the first and second switching elements Q1 and Q2.

In addition, a first collector resistor R1 may be connected to the collector terminal of the first switching element Q1. The first collector resistor R1 operates as a current limiting resistor. That is, when a current flows from the collector of the first switching element Q1 to the emitter, if there is no current resistance resistance, the resistance value decreases so that the positive electrode and the ground of the input power supply pass through the first switching element Q1. Since the current is directly connected, excessive current flows, which may deteriorate the reliability of the first switching element Q1, thereby forming the first collector resistor R1 to limit the current flowing through the first switching element Q1. .

Referring to the operation of one embodiment and another embodiment of the present invention having such a configuration as follows.

The input voltage is converted into a voltage level required by the load by the turns ratio of the primary winding and the secondary winding of the transformer T1 and output. For example, when the winding ratio of the primary winding and the secondary winding is 2: 1, if the input voltage is 24 [V], 12 [V] is output to the secondary winding side of the transformer T1.

The voltage transformed by the transformer T1 is rectified by the rectifying diode D1, smoothed by the smoothing capacitor C1, and converted into a DC voltage.

Subsequently, the rectified and smoothed voltage in the rectifying diode D1 and the smoothing capacitor C1 is applied to the cathode of the zener diode ZD1, and at this time, the voltage level applied to the cathode of the zener diode ZD1 becomes When the zener diode ZD1 is less than or equal to the Zener voltage of ZD1, the Zener diode ZD1 is not conductive, and therefore, no voltage is applied to the first switching element Q1, so that the first switching element Q1 is turned off.

Therefore, the voltage rectified and smoothed in the rectifying diode D1 and the smoothing capacitor C1 is normally supplied to the loads R7 and R8.

On the other hand, when the voltage induced on the secondary winding side of the transformer T1 is overvoltage due to system instability and instability of the input voltage, rectification and smoothing are performed in the rectifying diode D1 and the smoothing capacitor C1. The voltage is applied to the cathode of the zener diode ZD1.

At this time, since the input voltage is an overvoltage, the voltage rectified and smoothed in the rectifying diode D1 and the smoothing capacitor C1 also becomes an overvoltage, and when the voltage exceeds the zener voltage of the zener diode ZD1, the zener diode ZD1 Is conducting.

When the zener diode ZD1 is turned on, a voltage exceeding the zener voltage of the zener diode ZD1 is applied to the load resistor R9 and the first switching element Q1, whereby the first switching element Q1 is Is turned on.

When the first switching device Q1 is turned on, the second switching device Q2 is also turned on to operate. At this time, the emitter resistor R5 and the load resistors R7 and R8 of the second switching element Q2 are connected in parallel, and the voltage applied to the load resistor R8 is increased.

2 is a diagram illustrating a simulation waveform of a voltage applied to each node in an overvoltage protection circuit according to an embodiment of the present invention. The a node is green, the b node is red, the c node is yellow, and the d node is blue.

The voltage rectified and smoothed by the rectifying diode D1 and the smoothing capacitor C1 is output to the point t1 through the cathode of the zener diode ZD1.

In the present embodiment, a case where the input voltage in the normal operation state is 14.5v and the preset zener voltage (breakdown voltage) level is 15v will be described as an example.

Since the output voltage input to the cathode is equal to or lower than a preset zener voltage (breakdown voltage) level, the zener diode ZD1 is not conductive. Accordingly, the voltage applied to the node a is maintained at 0V.

Since the zener diode ZD1 is not conducting, the first switching element Q1 and the second switching element Q2 do not operate, and thus R1, R3, and R5 are not recognized and are detected at the b and c nodes. The voltage is equal to 14.5v.

When the resistance ratio of the load resistors R7 and R8 is set to 10: 1, the voltage detected at the point d is divided according to the resistance ratios of the load resistors R7 and R8 so that the voltage applied to R8 is 14.5, which is an input voltage. v has a value of 1.3v.

In addition, since the output voltage inputted to the cathode is equal to or less than a preset zener voltage (breakdown voltage) level, the circuit operates normally. The d node between the load resistors R7 and R8 has a load resistance at an input voltage of 14.5v. A constant voltage is applied according to the voltage distribution of R7 and R8.

For example, in the case where t1 has passed, for example, when the input voltage is 22v, without the overvoltage protection circuit 100, since the input voltage 22v is directly input to the load resistor, the reliability of the device may deteriorate.

An output voltage input to the cathode is input at a predetermined zener voltage (breakdown voltage) level or higher, and a voltage above the breakdown voltage of the zener diode ZD1 is applied to the load resistor R9.

That is, since the input voltage in the normal operation state is 14.5v and the zener voltage of the zener diode ZD1 is 15v, the output voltage 22v input to the cathode is equal to or higher than the preset zener voltage (breakdown voltage) level. A voltage of 7v is applied to node a.

The first switching element Q1 is turned on by the voltage applied at the node a. For example, when the input voltage is AC power and the period is 3 ms, the voltage rectified and smoothed by the rectifying diode D1 and the smoothing capacitor C1 decreases with time, and accordingly, The voltage detected at each node also decreases over time.

The a and c nodes are reduced in the same width with a difference of 15v which is a zener voltage of the zener diode ZD1.

The voltage at node b is a voltage at which the first switching element Q1 and the second switching element Q2 are turned on. The emitter resistor R5 is connected in parallel with the load resistors R7 and R8. Will be reduced in width.

As shown in FIG. 2, the voltage detected by the overvoltage protection circuit 100 at the load resistance R8 is varied within 1.3v to 6v.

Therefore, the voltage difference rectified and smoothed by the rectifying diode D1 and the smoothing capacitor C1 is alleviated by the first and second switching elements Q1 and Q2 so that the load malfunctions due to overvoltage. Destruction is prevented.

As shown in the drawing, the reduction width of the voltage is alleviated by the first and second switching elements Q1 and Q2 to supply a more stable voltage.

The overvoltage protection circuit 100 may be separately installed and used for each output terminal of the multiple multi output terminals.

In addition, each device value may be set to a resistance value such that the operating voltage is sufficiently applied by checking a protection level when an actual circuit is applied.

As described above, the present invention relates to an overvoltage protection circuit 150 applied to an output terminal of an LED driver. Output stage circuit can be protected.

Features, structures, effects, and the like described in the above embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to only one embodiment. Furthermore, the features, structures, effects, and the like illustrated in each embodiment may be combined or modified with respect to other embodiments by those skilled in the art to which the embodiments belong. Therefore, it should be understood that the present invention is not limited to these combinations and modifications.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be understood that various modifications and applications are possible. For example, each component specifically shown in the embodiments can be modified and implemented. It is to be understood that all changes and modifications that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

A transformer for transforming an input voltage into an output voltage required by a load;
A rectifier diode for rectifying the voltage transformed by the transformer;
A smoothing capacitor for smoothing the voltage rectified by the rectifying diode;
A zener diode whose conduction state is controlled according to the level of the rectified and smoothed output voltage in the rectifying diode and the smoothing capacitor; And
And first and second switching elements which are turned on and electrically connected to each other when the output voltage level applied to the zener diode is equal to or higher than the zener voltage of the zener diode.

The method of claim 1,
And a load resistor for regulating the voltage across the switching element through the zener diode.

The method of claim 1,
And the first switching element is an npn transistor and the second switching element is a pnp transistor.

The method of claim 1,
And the first switching element and the second switching element include a base resistor.

The method of claim 1,
And the second switching element comprises an emitter resistor.

The method of claim 3,
And a connection resistor formed between the base end of the first switching element and the collector end of the second switching element.

The method according to claim 6,
And the connection resistance is connected between the base resistance of the first switching element and the base end of the first switching element.