KR20080017697A - Protection circuit - Google Patents

Abstract

A protection circuit is provided to sense short-circuit of a minus output voltage line smoothly by changing a feedback voltage when the output line for generating a minus voltage is short-circuited. In a power supply unit for generating a voltage with various amplitudes required in a product, a feedback voltage generation unit generates a feedback voltage by sensing normal operation of an output voltage. A short-circuit sensing unit controls the feedback voltage, by being operated by a difference between a minus output voltage and a reference voltage. The reference voltage is a plus output voltage.

Description

Protection circuit

1 shows an exemplary view of a protection circuit according to the prior art,

2 shows an exemplary view of a protection circuit according to the present invention.

Explanation of symbols on the main parts of the drawings

50: trance 51: SCR

52, 56, 57, 58: resistor 53: transistor

54 diode 55 photo transistor

60: PWM IC

The present invention relates to a protection circuit, and more particularly, to a protection circuit for blocking a short line to prevent safety accidents when a short circuit occurs in the output line.

All electronic and communication equipment uses a power supply such as a switching mode power supply (hereinafter referred to as SMPS). The power supply device generates DC power of various sizes required in the product. To this end, the power supply device inputs an external AC power and generates a DC power of various sizes required by the product by using a transformer such as a transformer.

The transformer is configured to input a voltage obtained by rectifying an external AC power source to the primary side, and generate secondary voltages of various magnitudes using the primary side voltage. Therefore, when various sizes of voltage are required in the product, the secondary winding ratio of the transformer is controlled to provide multiple terminals on the secondary side, and a voltage having a desired magnitude is generated from each terminal.

The SMPS with a transformer operating in this manner needs to protect the transformer from the overvoltage and the overcurrent. If overvoltage and overcurrent occur on the secondary side of the transformer, the control circuit configured to receive DC voltage from the transformer is in a state of receiving overvoltage and overcurrent, and the control circuit is caused by overvoltage and overcurrent higher than the rated voltage. Malfunction or circuit breakage.

On the other hand, the transition from the existing analog electronics to digital electronics, the digital electronics, the high-definition, high sound quality, and the like, the IC design used in the digital electronics requires a high-density process technology. In addition, high speed data processing is accompanied by high density processing technology in digital electronic devices. In other words, as the speed of the CPU is increased, high-speed data processing is required for signal processing. Therefore, various circuit elements are configured to enable high-speed switching for high-speed data processing, and the same also applies to various elements used in the SMPS power supply. Digital electronics also have a much higher current compared to conventional products. Therefore, since digital electronic devices use high-speed switching and high current, an overcurrent condition occurs in the SMPS, a power supply device, which causes damage to the product and further fatal injury.

In the conventional protection circuit, as shown in FIG. 1, the PWM control circuit 20 for switching the voltage supplied to the primary coil 25a of the transformer 25 is connected. The PWM control circuit 20 switches the voltage supplied to the primary coil 25a of the transformer 25 by PWM control.

The secondary side of the transformer 25 is composed of a coil 25b having a plurality of output terminals. Output terminals connected to the secondary coil of the transformer 25 have different turns ratios and output voltages of different magnitudes. As such, the voltage generated at the secondary side of the transformer 25 is supplied to various control circuits in the product through an output line connected to the output terminal.

In order to monitor the short circuit of the supply line to which the secondary-side generated voltage of the transformer 25 is supplied, the conventional protection circuit feeds back the secondary-side voltage of the transformer 25. That is, as shown, when a short occurs in the output line of the transformer 25, the divided voltage V1 of the feedback line falls. When the feedback voltage V1 falls, the cathode voltage V2 of the switching element SCR 21 rises.

When the cathode voltage V2 of the switching element 21 rises, the current Ic of the photo transistor 22 falls, and the photo transistor 22 is turned off. When the photo transistor 22 is turned off, the feedback voltage V3 of the PWM IC 20 rises, and the overcurrent protection circuit OCP in the PWM IC which senses the voltage operates to operate the transformer 25. The voltage supply to the furnace will be cut off.

The conventional protection circuit which operates as mentioned above may not respond correctly to a short circuit occurrence. Therefore, the conventional protection circuit is configured to connect the diode 24 between the feedback line and the output line of the transformer 25 in order to increase the accuracy of the short circuit occurs, so that an effective response to the short circuit is made.

However, in the conventional protection circuit having the above-described short circuit detection, the short circuit detection can be performed only for the occurrence of a short of the positive (+) output voltage line. This is because the protection circuit is configured to lower the feedback voltage V1 when a short circuit occurs.

That is, in the case where a positive voltage of about 5.3 volts is normally generated in the output line, the feedback voltage V1 may be maintained at a predetermined value or more (the turn-on voltage of the SCR), thereby turning on the SCR 21. Done. However, when a short occurs in the output line, the potential of the output line drops to ground, and the feedback voltage V1 also drops. At this time, the SCR 21 is switched to the off state to detect the occurrence of a short circuit.

Such operation control is possible because the generated voltage of the output line is a positive voltage. Therefore, in normal operation, the feedback voltage V1 remains above a certain value (turn-on voltage of SCR), and in the event of a short circuit, the feedback voltage (V1) falls below a certain value (turn-on voltage of SCR) and a short circuit occurs. Detection can be made.

However, in the case where the generated voltage of the output line is a negative voltage, the feedback voltage V1 always has a predetermined value or less as the configuration of the protection circuit as described above. Therefore, in the conventional protection circuit, the short-circuit monitoring is smoothly performed on the positive (+) voltage among the output voltages of the transformer 25, and when the short-circuit occurs, effective blocking can be achieved. However, in the conventional protection circuit, the short-circuit monitoring was not performed for the negative (-) voltage among the output voltages of the transformer 25. Furthermore, due to the directionality of the diode 24, a problem arises in which the diode 24 plays no role with respect to the negative voltage.

Accordingly, an object of the present invention is to provide a protection circuit that allows accurate control of occurrence of a short circuit on a secondary negative output line of a transformer.

A protection circuit according to the present invention for achieving the above object, the power supply for generating a voltage of various sizes required by the product, the feedback voltage generating means for generating a feedback voltage for detecting the normal operation of the output voltage; And short-circuit detection means operated by the difference between the negative output voltage and the reference voltage to control the feedback voltage.

The reference voltage of the present invention is characterized by using a positive output voltage.

The short circuit detecting means of the present invention comprises: a first output line for outputting a negative output voltage; A second output line for outputting a positive output voltage; A voltage divider connected between the first and second output lines; And a switching device operated by the voltage distributed by the voltage divider to control the feedback voltage.

The negative output voltage of the present invention is characterized in that it is relatively larger than the positive output voltage.

The voltage divider of the present invention is characterized by using a resistor.

The switching element of the present invention is characterized by using a transistor.

The transistor of the present invention is characterized in that the feedback voltage is lowered to the ground potential during the turn-on operation.

The feedback voltage generating means of the present invention includes: a voltage divider for voltage-sharing a positive output voltage; A switching element operated by the divided voltage of the voltage divider; It characterized in that it comprises a feedback voltage generator for generating a feedback voltage by the operation of the switching device.

The feedback voltage generator of the present invention is characterized by using a photo transistor.

The switching device of the present invention is characterized by using SCR.

The present invention may further include a diode connected between the distribution voltage output line of the voltage divider and the output line of the power supply device.

In addition, the protection circuit according to the present invention for achieving the above object, the power supply for generating a voltage of various sizes required by the product, the output line for outputting a positive voltage; Feedback voltage generating means for voltage-dividing the positive voltage to generate a feedback voltage; First switching means for switching operation based on the feedback voltage generated by the feedback voltage generating means; PWM switching means for cutting off the supply voltage of the power supply by the operation of the first switching means; An output line for outputting a negative voltage; Voltage dividing means for receiving the negative output voltage and the positive output voltage and dividing the voltage; And second switching means for switching the feedback voltage to control the feedback voltage.

Hereinafter, a protection circuit according to the present invention will be described in detail with reference to the accompanying drawings.

2 shows an exemplary diagram of a protection circuit according to an embodiment of the present invention.

The protection circuit of the present invention shown is divided into a primary side and a secondary side around the transformer 50.

The primary coil 50a of the transformer 50 is provided with a PWM IC 60 for PWM switching control of the voltage supplied to the transformer 50. The PWM IC 60 is configured to cut off the primary side supply voltage of the transformer 50 when a short circuit occurs, based on the secondary side feedback voltage V3 of the transformer 50.

A plurality of output lines L1, L2, ... are formed in the secondary coil 50b of the transformer 50. The output line L1 of the secondary coil 50b of the transformer 50 finally generates -12 volt output, and the output line L2 finally generates 5.3 volt output, which is provided on the secondary side of the transformer. Supply power to the control circuit (not shown). In order to generate the −12 volt and 5.3 volt voltages, a rectifier circuit or the like is provided on the secondary side of the transformer 50. In addition, although the output line L1 shows a -12 volt output in FIG. 2, the -12 volt output is the final output voltage. Similarly, a 5.3 volt output is shown in output line L2, but the 5.3 volt output is the final output voltage. Since the output voltage of the transformer for generating the final output voltage is regulated by the secondary winding ratio of the transformer, the magnitude of the final output voltage is not important.

The configuration for monitoring the short circuit of the output line for generating a voltage on the secondary side of the transformer 50 having the above configuration is made as follows.

Output line (L1) and plus (+) voltage outputting -12 volts voltage of transformer (50) to monitor the short circuit of the output line outputting negative (-) power on the secondary side of transformer (50). The voltage distribution resistors 52 and 53 are connected between the output lines L2.

And an NPN type transistor 53 configured to turn on or turn off by the voltage divided by the resistors 52, 53 is configured to control the feedback voltage V1 of the protection circuit. The transistor 53 is a switching element that switches by the voltage divided by the resistors 52 and 53. Therefore, the switching device is a switching device that is on / off operation by a distribution voltage of a predetermined size or more, and can be configured to control the feedback voltage during the switching operation, so other elements than the NPN transistor 53 (PNP transistor, etc.) Also available.

At this time, the turn-on condition of the switching element 53 is based on the potential of the output line L1 that outputs a negative voltage. That is, when the output line L1 outputting a negative voltage normally outputs -12 volts, the output line L1 does not have a positive voltage enabling the turn-on of the switching element 53. However, when the output line L1 that outputs a negative voltage is shorted and rises to the ground potential, the output line L1 has a positive voltage state that enables the turn-on of the switching element 53.

As described above, in order to satisfy the turn-on condition of the switching element 53, in the present invention, a reference voltage V5 having a positive voltage is used as a reference voltage for determining the turn-on voltage of the switching element 53. I use it. That is, the reference voltage V5 plays a decisive role of converting the voltage V4 into a positive voltage state when a short circuit of a negative output line occurs.

The feedback voltage V1 is a voltage divided by voltage distribution resistors 57 and 58 connected in series between the output line L2 and the ground. The feedback voltage V1 controls the gate terminal of the SCR 51 which is a switching element to control the on / off operation of the SCR 51.

The SCR 51 controls the current flow of the light emitting device of the phototransistor 55. Therefore, when the SCR 51 is turned on, the phototransistor 55 is operated to lower the feedback voltage V3 of the PWM IC 60. However, when the SCR 51 is turned off, the phototransistor 55 does not operate and the feedback voltage V3 of the PWM IC 60 is increased.

Therefore, when -12 volt power is normally output from the negative voltage output line L1, -12 volts flows in the line L3, and about +5.3 volts flows in the line L4. The voltage is distributed by the distribution resistors 52 and 53 to apply a low logic signal to the base terminal of the transistor 53.

At this time, the NPN transistor 53 is turned off by the low logic signal, and does not affect the feedback voltage V1 of the protection circuit. The PWM IC 60 is provided with a normal feedback voltage V3.

However, if a short circuit occurs in the output line L1, the voltage of the output lines L1 and L3 rises to near 0 volts. Normally, about +5.3 volts is applied to the line L4. At this time, the distribution voltage V4 is in a high logic state under the influence of the reference voltage V5, and the transistor 53 is turned on by the signal. When the transistor 53 is turned on, the feedback voltage V1 of the protection circuit also has a ground potential.

The operation lowers the gate voltage of the SCR 51 so that the SCR 51 is in an off state. In connection with this, the voltage V2 is raised. The elevated voltage V2 controls the photo transistor 55 in the off state. The feedback voltage V3 of the PWM IC is raised.

When the feedback voltage V3 of the PWM IC 60 rises, the overcurrent protection circuit OCP operates in the PWM IC 60 to control the short circuit to supply voltage to the primary side of the transformer 50. Is blocked.

Next, an operation for monitoring a short circuit in the supply line of the positive voltage generated on the secondary side of the transformer 50 will be described.

As shown, when a short occurs in the positive voltage output line L2 of the transformer 50, the divided voltage V1 of the feedback line falls. When the feedback voltage V1 falls, the SCR 51 is turned off while the cathode voltage V2 of the switching element SCR 51 rises.

When the cathode voltage V2 of the switching element 51 rises, the current Ic of the photo transistor 55 falls, and the photo transistor 55 is turned off. When the photo transistor 55 is turned off, the feedback voltage V3 of the PWM IC 60 increases, and an overcurrent protection circuit OCP in the PWM IC which senses the voltage operates to operate the transformer 50. The voltage supply to the furnace will be cut off.

In addition, when +5.3 volts is normally output from the positive voltage output line L2 of the transformer 50, the distribution voltage V1 of the feedback line is a constant value (a voltage capable of turning on the SCR). Keeping the above, the SCR 51 is turned on.

When the SCR 51 is turned on, a current path of the photo transistor 55 is formed, the photo transistor 55 is turned on, and the on-operated photo transistor 55 of the PWM IC 60 is turned on. The feedback voltage V3 is lowered.

As described above, the protection circuit according to the present invention is characterized in that the short circuit detection can be performed for both the positive voltage (+) and the negative voltage (−) which are the secondary voltages of the transformer. To this end, the protection circuit of the present invention is configured such that a change in the feedback voltage V1 occurs when a short occurs in an output line that generates a negative voltage. The detection of the output line short generation of the negative voltage is performed by the operation of the switching element that is switched by comparing the output voltage of the negative output line and the reference voltage.

The above-described preferred embodiment of the present invention has been disclosed for the purpose of illustration, and may be applied to the case of detecting a short generation of a negative output voltage line in an SMPS power supply. Therefore, those skilled in the art will be able to improve, change, substitute or add other embodiments within the technical spirit and scope of the present invention disclosed in the appended claims.

The protection circuit according to the present invention described above is characterized in that the short circuit detection can be performed for both the positive voltage (+) and the negative voltage (-) which are the secondary voltages of the transformer. To this end, the protection circuit of the present invention, when a short occurs in the output line generating a negative voltage, the change in the feedback voltage (V1) is generated, so that the short-circuit detection of the negative output voltage line is made smooth. By the control as described above, the present invention can obtain the effect of preventing the occurrence of safety and the prolongation of life for the product by taking appropriate measures and prevention for short circuit occurrence.

Claims (13)

In the power supply for generating a voltage of various sizes required by the product, Feedback voltage generating means for generating a feedback voltage for detecting normal operation of the output voltage; And And a short-circuit detecting means operating by the difference between the negative output voltage and the reference voltage to control the feedback voltage. The method of claim 1, The reference voltage is a protective circuit, characterized in that the use of a positive output voltage. The method of claim 2, The short circuit detection means, A first output line for outputting a negative output voltage; A second output line for outputting a positive output voltage; A voltage divider connected between the first and second output lines; And a switching element operated by the voltage distributed by the voltage divider to control the feedback voltage. The method of claim 3, wherein And the negative output voltage is relatively larger than the positive output voltage. The method of claim 3, wherein And said voltage divider uses a resistor. The method of claim 3, wherein The switching element is a protective circuit, characterized in that using a transistor. The method of claim 6, And the transistor lowers the feedback voltage to ground potential during a turn-on operation. The method of claim 1, The feedback voltage generating means, A voltage division unit for voltage division of the positive output voltage; A switching element operated by the divided voltage of the voltage divider; And a feedback voltage generator for generating a feedback voltage by the operation of the switching device. The method of claim 8, And the feedback voltage generator uses a photo transistor. The method of claim 8, And said voltage divider uses a resistor. The method of claim 8, The switching device is a protection circuit, characterized in that using the SCR. The method of claim 8, And a diode connected between the divided voltage output line of the voltage divider and an output line of the power supply device. In the power supply for generating a voltage of various sizes required by the product, An output line for outputting a positive voltage; Feedback voltage generating means for voltage-dividing the positive voltage to generate a feedback voltage; First switching means for switching operation based on the feedback voltage generated by the feedback voltage generating means; PWM switching means for cutting off the supply voltage of the power supply by the operation of the first switching means; An output line for outputting a negative voltage; Voltage dividing means for receiving the negative output voltage and the positive output voltage and dividing the voltage; And a second switching means for switching the feedback voltage to control the feedback voltage.

Images