KR100283510B1 - Secondary Side Protection Circuit of Switched-Mode Power Supplies - Google Patents

Abstract

An internal bias 30 providing a reference voltage; A positive voltage protection unit 10 connected to the internal bias and the + 5V signal line, comparing the voltage input from the + 5V signal line and the internal bias and outputting a result; An input terminal is connected to the internal bias and the -5V signal line, and the negative voltage protection unit 20 compares the voltage input from the -5V signal line and the internal bias and outputs the result, and the positive voltage protection unit and the negative voltage An OR terminal connected to an output terminal of the protection unit and configured to logically output a signal input from the positive voltage protection unit and the negative voltage protection unit; An SCR gate driver unit 50 connected to an output terminal of the OR gate, for converting a signal input from the OR gate to a voltage level capable of driving the gate of the thyristor; A thyristor (SCR) which is connected to a gate of the SCR gate driver and protects the system by shorting the + 12V signal line with ground in accordance with a signal input from the SCR gate driver; A secondary protection circuit of a switching mode power supply having an effect of improving the temperature characteristics of a detection voltage and the stability of a system, etc., in which a circuit composed of individual elements can be integrated.

Description

Secondary Side Protection Circuit of Switched-Mode Power Supplies

1 is a detailed circuit diagram of a secondary side protection circuit of a conventional switching mode power supply,

2 is a block circuit diagram of a secondary side protection circuit of a switched mode power supply according to an embodiment of the present invention,

3 is a detailed circuit diagram of the secondary side protection circuit of the switched mode power supply according to the embodiment of the present invention,

4 is a diagram showing the voltage change state of the gate terminal of the thyristor for the + 5V signal,

5 is a diagram showing the voltage change state of the gate terminal of the thyristor for the -5V signal.

* Explanation of symbols for main parts of the drawings

10: positive voltage protection unit 20: negative voltage protection unit

30: internal bias 40: ora gate

50: SCR Gate Driver

The present invention relates to a secondary side protection circuit of a switching mode power supply (SMPS), and more specifically, to an integrated circuit of a circuit composed of individual elements, the temperature characteristics of the detection voltage and the system A secondary side protection circuit of a switched mode power supply having improved stability of the present invention.

The switching mode power supply typically maintains a stable output voltage by adjusting the driving time of the switching transistor connected to the primary coil of the transformer by an integrated circuit (PIC) according to the variation of the output voltage. It is configured to be obtained. That is, when the output voltage is lowered, the driving frequency of the switching transistor is increased by the pulse width modulation IC, and the output voltage is increased. On the contrary, when the output voltage is increased, the driving frequency of the switching transistor is decreased by the pulse width modulation IC. As the output voltage is lowered, the output voltage is always kept constant regardless of the load variation.

This is because switching mode power supplies can transmit a lot of power even if the transformer size is small because of the above-mentioned operating characteristics. Therefore, the size and volume of the switching mode power supply can be reduced and the power transmission efficiency is high. Increasingly, the range of use is expanding.

In addition, the switching mode power supply is becoming more and more complicated in functionality by requiring the functions required for the stable operation of the system in addition to the requirements for miniaturization, light weight, high efficiency, high reliability.

For this reason, a circuit for improving the power factor is required on the primary side (input) of the switched mode power supply, and a function for improving the power factor of the entire system, and a protection function and stable constant voltage generation on the secondary side (output) There is a need for a power good signal generation function for detecting and transmitting a stable state of a circuit, particularly an output voltage, to prevent a microprocessor or the like from malfunctioning.

As the primary-side control IC of the switched-mode power supply, there is a ML4824 from Micro-Linear, which incorporates only PFC (Power Factor Correction) in the current-mode PWM control IC. There is no product that can perform various functions with one IC component.

Hereinafter, a conventional switching mode power supply will be described with reference to the accompanying drawings.

1 is a detailed circuit diagram of a secondary side protection circuit of a conventional switching mode power supply.

As shown in FIG. 1, the structure of the secondary side protection circuit of the conventional switching mode power supply includes resistors R1 and R2 having one terminal connected to the + 5V signal line and the -5V signal line, respectively, and the other terminal connected to each other. ) And a capacitor Q1 having a base terminal connected to a connection point of the resistors R1 and R2 and a collector terminal connected to a + 5V signal line, and a capacitor connected between the base terminal of the transistor Q1 and ground. (C1), a zener diode D1 having a cathode terminal connected to the collector terminal of the transistor Q1 and an anode terminal connected to the emitter terminal, and between the emitter terminal of the transistor Q1 and ground, respectively. The thyristor (SCR) has a resistor (C2) and a capacitor (C2) connected to the emitter terminal of the transistor (Q1), a gate terminal connected to the + 12V signal line, and an anode connected to the + 12V signal line. )

With the above configuration, the operation of the secondary side protection circuit of the conventional switched mode power supply is as follows.

1. Positive voltage protection function

+ 5V signal, a Zener diode (D1) a voltage (V _D1) and the thyristors of (D1) the gate of the-current signal to the gate of the anode-to-voltage (V _BE) to a voltage the moment thyristors (SCR) beyond combined Is approved. As a result, the + 12V signal line is shorted to ground while the thyristor SCR is turned on, thereby protecting the system.

2. Negative voltage protection function

The voltage input to the base terminal of the transistor Q1 is set by the resistor R1 connected to the + 5V signal line and the resistor R2 connected to the -5V signal line. In this case, the moment when the -5V signal exceeds -2.5V, that is, the voltage input to the base terminal of transistor Q1 is the gate of the base-emitter voltage V _BE and transistor DCR of transistor Q1. At the instant when the inter-anode voltage V _BE becomes greater than the sum of the voltages, the thyristors SCR are driven. When the thyristor SCR is driven, the + 12V signal line is shorted to ground to protect the system.

However, the secondary side protection circuit of the conventional switching mode power supply as described above,

1. As a separate element on a circuit board becomes difficult to arrange, there is a disadvantage that the power supply is complicated and the reliability is lowered.

2. In the case of the positive voltage protection function, the zener diode D1 is directly connected to the gate terminal of the thyristor (SCR) and driven to obtain stable operation. Has the disadvantage of requiring a capacitor (C2) element,

3. Even in the case of the negative voltage protection function, there is a disadvantage that a resistor (R3) and a capacitor (C1, C2) elements are required to obtain stable operation.

4. Since the detection point is sensitive to the change of the base-emitter voltage V _BE of the transistor Q1 and the voltage V _D1 of the zener diode D1 when the temperature changes, the predetermined detection point is shaken. There is a problem that setting of a detection point is difficult.

Therefore, the object of the present invention is to solve the above-mentioned disadvantages and problems,

1. Minimize external device by accommodating all necessary functions in one IC chip

2. Reduction of the number of parts in the overall circuit configuration and the use of a high reliability IC can increase the circuit reliability, and also simplify the FP takeout of the printed circuit board.

3. By using a comparator with sufficient hysteresis, the circuit can be operated stably without the resistor and capacitor elements required for the existing stability.

4. By making and using bandgap voltage that is less affected by temperature change inside the IC, it is less influenced by the temperature change of the system, and by using a comparator that can set the exact detection point, the protection function can be operated stably. A secondary side protection circuit of a switched mode power supply is provided.

As a means for achieving the above object, the configuration of the present invention, the internal bias for providing a reference voltage, the input terminal is connected to the internal bias and the + 5V signal line, the voltage input from the + 5V signal line and the internal bias is compared A positive voltage protection unit for outputting the result, a negative voltage protection unit for connecting an input terminal to the internal bias and the -5V signal line, comparing the voltage input from the -5V signal line and the internal bias, and outputting the result; An input terminal is connected to an output terminal of the positive voltage protection unit and the negative voltage protection unit, and an OR terminal for outputting a logic sum of the signals input from the positive voltage protection unit and the negative voltage protection unit, and an input terminal at the output terminal of the OA gate. Is connected, and the signal input from the OR gate is converted into a voltage level capable of driving the gate of the thyristor. The gate is connected to the SCR gate driver unit, the driver unit for the SCR gate, made of a + 12V signal line in accordance with a signal inputted from the gate driver part to a SCR thyristor for protecting the system by a short to ground.

With the above configuration, the most preferred embodiment which can be easily carried out by those skilled in the art with reference to the present invention will be described in detail with reference to the accompanying drawings.

2 is a block circuit diagram of the secondary side protection circuit of the switching mode power supply according to the embodiment of the present invention, and FIG. 3 is a detailed circuit diagram of the secondary side protection circuit of the switching mode power supply according to the embodiment of the present invention.

As shown in FIG. 2 and FIG. 3, the configuration of the secondary side protection circuit of the switched mode power supply according to the embodiment of the present invention includes an internal bias 30, an internal bias 30, and a + 5V signal line. A positive voltage protection unit 10 connected thereto, a negative voltage protection unit 20 having an input terminal connected to the internal bias 30 and a -5V signal line, a positive voltage protection unit 10 and a negative voltage protection unit 20 The gate is connected to an OR gate 40 having an input terminal connected to an output terminal of the SCR gate driver, an SCR gate driver unit 50 having an input terminal connected to an output terminal of the OR gate 40, and an SCR gate driver unit 50. And a thyristor (SCR) having an anode connected to a + 12V signal line.

The configuration of the positive voltage protection unit 10 described above is non-inverted at the connection point of the distribution resistor pairs R6 and R7 connected in series between the + 5V signal line and the ground and the distribution resistor pairs R6 and R7 described above. The comparator COMP2 has an input terminal connected thereto and an inverting input terminal connected to the internal bias 30.

The configuration of the negative voltage protection unit 20 is a connection point of the distribution resistor pairs R4 and R5 connected in series between the -5V signal line and the + 5V signal line and the distribution resistor pairs R4 and R6. The non-inverting input terminal is connected to the comparator COMP1 connected to the inverting input terminal to the internal bias 30.

The internal bias 30 is made of a battery, and the OR gate 40 is configured to wire-or cut the output terminal of the positive voltage protection unit 10 and the output terminal of the negative voltage protection unit 20.

The SCR gate driver unit 50 includes a transistor Q2 having a base terminal connected to an output terminal of the OR gate 40 and a collector terminal connected to a Vcc signal line, and a collector at an output terminal of the OR gate 40. A transistor Q3 having a terminal connected thereto and a base terminal connected to the emitter terminal of the transistor Q2, and a resistor R8 connected between the base terminal and the emitter terminal of the transistor Q3.

With the above configuration, the operation of the secondary side protection circuit of the switched mode power supply according to the embodiment of the present invention is as follows.

The overall operation of the circuit shown in FIGS. 3 and 4 detects abnormalities in the system's output voltages (+ 5V, -5V), and in the event of an abnormality, turns on transistors Q2 and Q3 to It is designed to protect the system by driving the thyristor (SCR) by shorting the + 12V signal line to ground by flowing a current of about 50mA through the gate terminal of the Lister (SCR).

The + 5V signal is divided by the voltage distribution of the resistor pairs R6 and R7 of the positive voltage protection part 10 and output to the comparator COMP2.

The comparator COMP2 of the positive voltage protection part 10 divides the voltage inputted by the resistor pairs R6 and R7 to the input voltage of 1.28 V, which is the voltage of the internal bias 30, and its hysteresis voltage V _BE . By comparing the voltages, the transistors Q2 and Q3 of the SCR gate driver 50 are turned on by outputting a high state signal when the + 5V signal exceeds about 6V.

Thus, the positive voltage protection function is achieved by turning on the transistors Q2 and Q3 of the SCR gate driver section 50 at the moment when the + 5V signal of the system exceeds 6V.

The -5V signal is divided by the voltage distribution of the resistor pairs R4 and R5 of the negative voltage protection unit 20 and output to the comparator COMP1.

The comparator COMP1 of the negative voltage protection unit 20 divides the voltage inputted by the resistor pairs R4 and R5 into the input voltage of 1.28 V, which is the voltage of the internal bias 30, and its hysteresis voltage V _BE . By comparing the sum voltage, the transistors Q2 and Q3 of the SCR gate driver unit 50 are turned on by outputting a high state signal at the moment when the above -5V signal exceeds about -2.5V.

Thus, the negative voltage protection function is achieved by turning on the transistors Q2 and Q3 of the SCR gate driver section 50 at the moment when the -5V signal of the system exceeds -2.5V.

In this case, the resistor R5 may be provided outside the integrated circuit in the pair of resistor resistors R4 and R5 so that the user can change the detection voltage point by varying the distribution resistor ratio.

Even when only one signal among the output signals of the positive voltage protection unit 10 and the negative voltage protection unit 20 becomes high, the transistors Q2 and Q3 of the SCR gate driver unit 50 are turned on, and the thyristor ( A high state signal is output to the gate terminal of the SCR so that the + 12V output signal of the system is shorted to the ground line, thereby protecting the system.

FIG. 4 illustrates a state in which the voltage applied to the gate terminal of the thyristor SCR is changed according to the voltage change of the + 5V signal, thereby turning on and off the thyristor SCR.

FIG. 5 shows a state in which the voltage applied to the gate terminal of the thyristor SCR is changed according to the voltage change of the -5 V signal, thereby turning on and turning off the thyristor SCR.

As shown in FIG. 4 and FIG. 5, it can be seen that the thyristors SCR has hysteresis characteristics as operating characteristics. In the embodiment of the present invention, the thyristors are utilized by using the hysteresis characteristics of the comparators COMP1 and COMP2. (SCR) was able to take a stable operation.

As described above, in the embodiment of the present invention, the secondary side protection of the switching mode power supply which can integrate the circuit composed of the individual elements and has the effect of improving the temperature characteristics of the detected voltage and the stability of the system. A circuit can be provided. This effect of the invention can be used in the field of power supply.

Claims (6)

An internal bias providing a reference voltage, an input terminal connected to the internal bias and a + 5V signal line, and a positive voltage protection unit for comparing the voltage input from the + 5V signal line and the internal bias and outputting a result; An input terminal is connected to the bias and -5V signal lines, and a negative voltage protection unit for comparing the voltage input from the -5V signal line and the internal bias and outputting the result, and an input terminal at the output terminals of the positive voltage protection unit and the negative voltage protection unit. A thyristor connected to an OR gate configured to logically output a signal input from the positive voltage protection unit and the negative voltage protection unit, and an input terminal connected to an output terminal of the OR gate; A SCR gate driver unit for converting the gate of the gate to a voltage level capable of driving the gate and outputting the gate; The gate is connected, the secondary protection circuit of a + 12V signal line in accordance with a signal inputted from the above-described SCR gate driver unit switched mode power supply, characterized in that comprising a thyristor for protecting the system by a short to ground. The non-inverting input terminal of claim 1, wherein the positive voltage protection unit and the negative voltage protection unit are connected to a distribution resistor pair connected in series between a + 5V signal line and ground, and a connection point of the distribution resistor pair. And a comparator having an inverting input terminal connected to an internal bias. The switching mode of claim 2, wherein the negative voltage protection unit installs one resistor outside the integrated circuit in the distribution resistor pair so that the user can change the detection voltage point by changing the distribution resistance ratio. Secondary side protection circuit of the power supply. 3. The secondary side protection circuit of a switched mode power supply according to claim 2, wherein the comparator has an appropriate hysteresis characteristic so as to be less affected by noise. 2. The base circuit of claim 1, wherein the SCR gate driver comprises a first transistor having a collector terminal connected to a Vcc signal line, a base terminal connected to an emitter terminal of the first transistor, and a base of the first transistor. And a second transistor having a collector terminal connected to the terminal, and a resistor connected between the base terminal and the emitter terminal of the second transistor. The secondary side protection circuit of a switching mode power supply according to claim 1, wherein the oar gate has a configuration in which the output terminals of the positive voltage protection unit and the negative voltage protection unit are wired orally.