JP2020141480A - Surge protection circuit - Google Patents

Abstract

To provide a surge protection circuit having sufficient protection performance while reducing the number of semiconductor elements used.SOLUTION: In a sink apparatus 1, a surge protection circuit 12 includes: a surge protection element R1 interposed in series in a DDC (Display Data Channel) communication line for an electronic apparatus to communicate with another electronic apparatus; and a bypass circuit 121 for detecting connection of the other electronic apparatus to the DDC communication line and bypassing the surge protection element. Since the surge protection element is bypassed when the other electronic apparatus is connected and "float" of a Lo level voltage from a ground voltage is suppressed, a surge protection element with a large resistance value can be used and sufficient surge protection can be achieved with few semiconductor elements.SELECTED DRAWING: Figure 2

Description

The present invention relates to a surge protection circuit provided in a communication line of an electronic device or the like.

HDMI (registered trademark) (High-Definition Multimedia Interface) is used as a communication standard for interconnecting video transmitting devices such as personal computers, game consoles, and hard disk recorders with video receiving devices such as monitor displays and televisions. There is.

In addition, a mobile terminal is connected to an in-vehicle device to output contents such as video and music stored in the mobile terminal from the display or speaker of the in-vehicle device. At this time, the in-vehicle device and the mobile terminal are used. HDMI may also be used for the connection.

FIG. 1 is a schematic diagram of a connection between devices by HDMI. Using a communication cable 4 and a connector 3, a source device 2 (a device for transmitting video or the like; a personal computer, a game machine, a mobile terminal, etc.) and a sink device 1 (a device for transmitting video or the like) and a sink device 1 ( A device that receives video or the like, a monitor display, a television, an in-vehicle device, etc.) is connected, and communication is performed between the communication units 101 and 201 of the receiver 10 of the sink device 1 and the transmitter 20 of the source device 2, respectively. It is said.

Here, the DDC (Display Data Channel) is a communication line that mutually communicates information related to display settings between the sink device 1 and the source device 2, and communicates in both directions with one data line. The output circuits of units 101 and 201 are connected to an open collector (open drain), and the DDC communication line is pulled up to a power supply voltage V0 (example: + 5V) by pull-up resistors Rp1, Rp2 and the like.

HPD (Hot Plug Detector) and + V are communication lines for transmitting a connection detection signal for the source device 2 to detect the presence / absence of connection of the sink device 1, and the source device 2 is a power supply voltage output to + V by itself. By looping back V0 in the sink device 1 and detecting it in the HPD, it is possible to detect that the sink device 1 is connected.

Further, the sink device 1 can also detect the presence or absence of the connection of the source device 2 by detecting the power supply voltage V0 output by the source device 2 by the + V detection unit 102, and the video output setting of the sink device 1 is changed. At that time, the HPD control unit 103 temporarily opens the SW to make the source device 2 recognize that the connection of the sink device 1 has been disconnected, thereby prompting the reconnection.

HDMI also includes communication lines such as TMDS (Transition Minimized Differential Signaling) for transmitting video and audio, and CEC (Consumer Electricals Control) used for control between devices, but illustration and description are omitted. ..

When the source device 2 is not connected to the connector 3 of the sink device 1 (open state), the DDC communication line of the sink device 1 is mainly affected by a surge such as static electricity (ESD) applied from the outside through the connector 3. In order to prevent the internal circuit of the receiver 10 and the like from being destroyed, a surge protection circuit 11 composed of a diode D1, a Zener diode ZD, varistor Va1, Va2, and a protection resistor R1 is provided.

The diode D1 is provided between the DDC communication line and the ground, and clamps the negative surge applied to the connector 3 to a substantially ground voltage (example: 0V).

The Zener diode ZD is provided between the DDC communication line and the ground, and clamps the positive surge applied to the connector 3 to a predetermined Zener voltage (eg + 15V).

Varistors Va1 and Va2 are non-linear resistance elements that have the property that the electrical resistance is large when the voltage difference between both terminals is small, but the electrical resistance suddenly decreases when the voltage difference is larger than a certain level, and DDC communication. The positive and negative surges provided between the wire and the ground and applied to the connector 3 are clamped to a predetermined ON voltage (eg, 30 V each for positive and negative).

The protection resistor R1 is inserted in series between the connector 3 of the DDC communication line and the receiver 10, and when a surge is applied to the connector 3, the internal circuit of the receiver 10 or the like is limited by limiting the current flowing into the receiver 10 or the like. To protect.

Here, in FIG. 3 of Patent Document 1, a clamp diode is inserted not only between the input terminal and the ground but also between the input terminal and the power supply voltage VCS to clamp the positive surge to the substantially power supply voltage VCS. A surge protection circuit is described. The one corresponding to the clamp diode between the input terminal and the power supply voltage VCS is shown by a broken line in FIG. 1 (A in the figure).

However, since the DDC communication line is pulled up by the pull-up resistors Rp1 and Rp2 as described above, when the diode is inserted at the position A, for example, the power of the source device 2 is turned on and the sink device 1 is turned on. When the power supply is OFF, the power supply voltage V0 of the source device 2 flows into the sink device 1 via the pull-up resistor Rp1 and the diode, so that the DDC communication line is actually positive. A diode cannot be inserted between the power supply voltage V0 and the power supply voltage V0 as a countermeasure against the surge.

It is effective to increase the value of the protection resistor R1 in order to increase the resistance to surge, but the Lo level voltage VLo when transmitting data from the sink device 1 to the source device 2 is the pull-up resistors Rp1 and Rp2. Since it is determined by the voltage division ratio between the parallel combined resistor Rpp and the protection resistor R1, if the value of the protection resistor R1 is increased, the "float" of the Lo level voltage from the ground voltage becomes large. Therefore, the protection resistor R1 cannot be increased as a countermeasure against surge.

As described above, the conventional surge protection circuit 11 is sufficient due to restrictions such as the inability to insert a diode that clamps a positive surge between the communication line and the power supply voltage V0 and the inability to increase the value of the protection resistor R1. In order to have surge protection performance, it is necessary to use many semiconductor elements (Zener diode ZD, varistor Va1, Va2) in combination, which has caused an increase in cost.

Japanese Unexamined Patent Publication No. 2010-73913

An object of the present invention is to provide a surge protection circuit having sufficient protection performance while reducing the number of semiconductor elements used.

In order to achieve the above object, the surge protection circuit according to the first embodiment of the present invention is provided on a communication line of an electronic device for connecting to another electronic device and communicating with the other electronic device. A bypass that bypasses the surge protection element by detecting that a surge protection element interposed in series with the communication line and another electronic device are connected to the communication line. It is equipped with a circuit.

Further, the surge protection circuit according to another embodiment of the present invention is the surge protection circuit according to the first embodiment, and the bypass circuit receives a connection detection signal from another electronic device connected to the communication line. By detecting, the surge protection element is bypassed.

Further, in the surge protection circuit according to another embodiment of the present invention, the surge protection element is a resistor or a diode.

According to the present invention, since the bypass circuit detects that another electronic device is connected and bypasses the protection element, it suppresses "floating" of the Lo level voltage of the communication line from the ground voltage and other devices. When an electronic device is not connected, the protective element is effective, and sufficient protection can be provided against surges such as static electricity (ESD) applied from the outside.

It is a figure which shows the outline of the communication interface part of the electronic device provided with the conventional surge protection circuit. It is a figure which shows the outline of the communication interface part of the electronic device provided with the surge protection circuit which concerns on 1st Embodiment of this invention. It is a figure explaining the operation of the surge protection circuit which concerns on 1st Embodiment of this invention. It is a figure explaining the signal waveform of each part of the communication interface of the electronic device provided with the surge protection circuit which concerns on 1st Embodiment of this invention. It is a figure which shows the outline of the communication interface part of the electronic device provided with the surge protection circuit which concerns on 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are designated by the same reference numerals and the description thereof will not be repeated.

<1. First Embodiment>
FIG. 2 shows an outline of a communication interface portion of an electronic device provided with a surge protection circuit 12 according to the first embodiment of the present invention. Note that in FIG. 2, only the sink device 1 is shown, and the source device 2 is omitted.
<1-1. Configuration of surge protection circuit 12>

The surge protection circuit 12 in this embodiment is different from the conventional surge protection circuit 11 shown in FIG. 1 in that it includes a bypass circuit 121 instead of the diode D1, the Zener diode ZD, and the varistor Va2.

The bypass circuit 121 includes an NPN transistor Tr1 (hereinafter, simply referred to as Tr1), resistors R0, R2, and R3.

The protection resistor R1 is inserted in series between the connector 3 of the DDC communication line and the receiver 10.

The base of Tr1 is connected to the V0 communication line of the connector 3 via the resistor R3, and is also connected to the emitter via the resistor R2. The emitter is connected to the receiver 10 side of the protection resistor R1. The collector is connected to the connector 3 side of the protection resistor R1 via the resistor R0.

In the surge protection circuit 12 of the present embodiment, the protection resistor R1 mainly functions as a surge protection element.

The surge protection circuit 12 includes a varistor Va1, which protects the Tr1 when a surge exceeding the withstand voltage of the Tr1 is applied, and has a sufficient withstand voltage against the assumed surge magnitude. If a large Tr1 can be used, it may be deleted.
<1-2. Operation of surge protection circuit 12>

Hereinafter, the operation of the surge protection circuit 12 will be described with reference to FIGS. 3 and 4.

First, FIG. 3A shows a state in which neither the sink device 1 nor the source device 2 is transmitting data.

In this state, the transistors 101b and 201b of the output circuits of the communication units 101 and 201 are turned off, the input / output terminals 101a and 201a are open (high impedance), and the DDC communication line is set by the pull-up resistor Rp1 or the like. It is pulled up to the power supply voltage V0 (Hi level voltage, eg + 5V).

At this time, in the sink device 1, the protection resistor R1 and the series combined resistor of the resistors R2 and R3 function as a pull-up resistor. Further, since the base, emitter, and collector of Tr1 are all the same voltage at the power supply voltage V0, Tr1 is turned off.

Next, FIG. 3B shows a case where data is transmitted from the sink device 1 to the source device 2.

When data is transmitted (Lo level is transmitted) from the sink device 1, the transistor 101b of the output circuit of the communication unit 101 is turned on, and the input / output terminal 101a is short-circuited to the ground.

Then, the current I1 flows from the power supply voltage V0 to the input / output terminal 101a via the resistors R3 and R2, and when the voltage across the resistor R2 exceeds the ON voltage VBEon between the base and emitter of Tr1, the base and emitter of Tr1 Conducts between collectors and emitters at the same time.

By conducting between the collector and the emitter of Tr1, the protection resistor R1 is bypassed by the resistor R0, and the current I2 flows from the power supply voltage V0 to the input / output terminal 101a via the pull-up resistor Rp and the resistor R0.

At this time, the voltage (Lo level voltage) VLoB of the input / output terminal 201a of the communication unit 201 of the source device 2 is changed.

VLoB = V0 × R0 / (Rp1 + R0) (1)

Therefore, if the value of the resistor R0 is made sufficiently smaller than the pull-up resistor Rp1, the "floating" of the Lo level voltage from the ground voltage can be made sufficiently small (example: V0 = 5V, Assuming that Rp1 = 2kΩ and R0 = 100Ω, VLoB = 5V × 100Ω / (2kΩ + 100Ω) ≈ 0.24V).

Next, FIG. 3C shows a case where data is transmitted from the source device 2 to the sink device 1.

When data is transmitted (Lo level is transmitted) from the source device 2, the transistor 201b of the output circuit of the communication unit 201 is turned on, and the input / output terminal 201a is short-circuited to the ground.

Then, when the current I3 flows from the power supply voltage V0 to the input / output terminal 201a via the resistors R3, R2 and the protection resistor R1, the voltage difference across the resistor R2 exceeds the ON voltage VBEon between the base and emitter of Tr1. Conduction between the base and emitter of Tr1.

At the same time, the PN junction between the base and collector of Tr1 is also biased in the forward direction by the resistors R3 and R0, so that the base and collector of Tr1 are conducted and input from the power supply voltage V0 via the resistors R3 and R0. The current I4 flows into the output terminal 201a.

Since the value of the resistor R0 is set sufficiently smaller than the protection resistor R1, most of the current flowing through the resistor R3 flows through the resistor R0 (I4 >> I3, that is, bypassing the protection resistor R1), and Tr1 The base voltage of is almost determined by the voltage division ratio of the resistor R3 and the resistor R0.

Further, since the ON voltage VBCon between the base and collector is substantially equal to VBEon (VBCon≈VBEon), the collector and emitter of Tr1 are substantially the same voltage with respect to the base voltage.

Therefore, the voltage (Lo level voltage) VLoA of the input / output terminal 101a of the communication unit 101 at this time is, as is clear from FIG. 4C,.

VLoA ≒ (V0-VBCon) × R0 / (R3 + R0) (2)

If the value of the resistor R0 is made sufficiently smaller than that of the resistor R3, the "floating" of the Lo level voltage from the ground voltage can be made sufficiently small (example: V0 = 5V, VBCon). If = 0.7V, R3 = 47kΩ, and R0 = 100Ω, VLoA = (5V-0.7V) × 100Ω / (47kΩ + 100Ω) ≈ 0.01V).

FIG. 4 shows a simulation result of a signal waveform of each part in the surge protection circuit 12 according to the first embodiment.

FIG. 4A shows a signal waveform of the input / output terminal 201a of the communication unit 201 of the source device 2 when data is transmitted from the sink device 1. During the period when the input / output terminal 101a of the communication unit 101 of the sink device 1 is open (high impedance) (the period “B” in the figure), the signal is + 5V, which is equal to the power supply voltage V0.

On the other hand, during the period when the input / output terminal 101a is the ground voltage (0V) (the period "C" in the figure), the signal is almost 0V (about 0.2V), and the "Lo level voltage" from the ground voltage is ". It can be seen that "floating" does not occur (small enough).

Next, FIG. 4B shows the signal waveform of the input / output terminal 101a of the communication unit 101 of the sink device 1 when data is transmitted from the source device 2. During the period when the input / output terminal 201a of the communication unit 201 of the source device 2 is open (high impedance) (the period “D” in the figure), the signal is + 5V, which is equal to the power supply voltage V0.

On the other hand, during the period when the input / output terminal 101a is the ground voltage (0V) (the period “E” in the figure), the signal is almost 0V, and “floating” from the ground voltage of the Lo level voltage occurs. It turns out that there is no (small enough).

As described above, in the surge protection circuit 12 according to the first embodiment, even if the protection resistor R1 is set to a large value, the protection resistor R1 is bypassed by the bypass circuit 121 at the time of data transmission (at the time of Lo level transmission), so that Lo. The "float" of the level voltage from the ground voltage can be made sufficiently small.

When the source device 2 is not connected to the connector 3, the power supply voltage V0 is not supplied from the source device 2 to the base of Tr1 of the bypass circuit 121, so Tr1 is OFF (the collector and the emitter are cut off). Since the protection resistor R1 is effective without being bypassed, sufficient protection can be provided against surges such as static electricity (ESD) applied from the outside through the connector 3.

Further, except for the varistor Va1, the required semiconductor element is only one transistor Tr1, and it is not necessary to use many semiconductor elements for surge protection.

The values of the protection resistors R1, resistors R2, R3, and R0 can be set arbitrarily, but at least when data is transmitted from the source device 2, the input / output terminal 201a of the communication unit 201 has a ground voltage (0V). ), For example, it is necessary to satisfy the following conditions in order to turn on the base / emitter of Tr1.

V0 × R2 / (R1 + R2 + R3) ≧ VBEon (3)

Further, in the sink device 1, since the series combined resistance of the protection resistors R1, R2, and R3 functions as the pull-up resistance of the DDC communication line, this series combined resistance value is defined by the communication line standard. It can also be set to be substantially equal to the pull-up resistance value.
<2. Second embodiment>

FIG. 5 shows an outline of a communication interface portion of an electronic device provided with a surge protection circuit 13 according to a second embodiment of the present invention. Note that in FIG. 5, only the sink device 1 is shown, and the source device 2 is omitted.

<2-1. Configuration of surge protection circuit 13>
The first point shown in FIG. 2 is that the surge protection circuit 13 in the present embodiment includes a diode D2 in place of the protection resistor R1, a bypass circuit 131 in place of the bypass circuit 121, and a resistor R0'. It is different from the surge protection circuit 12 according to the embodiment of.

The bypass circuit 131 is different from the bypass circuit 121 in that the portion of the bypass circuit 121 where the resistor R0 is located is short-circuited, and is the same as the bypass circuit 121 except that.

The diode D2 is inserted in series with the DDC communication line so that the connector 3 side is the cathode and the receiver 10 side is the anode.

The collector of Tr1 is connected to the cathode of the diode D2, and the emitter is connected to the anode.

The resistor R0'is inserted in series between the connector 3 of the DDC communication line and the cathode of the diode D2.

In the surge protection circuit 13 of the present embodiment, the diode D2 mainly functions as a surge protection element.

The surge protection circuit 13 includes a varistor Va1, which is for protecting Tr1 and diode D2 when a surge exceeding the withstand voltage of Tr1 and diode D2 is applied, and the expected surge magnitude is increased. On the other hand, if Tr1 or diode D2 having a sufficiently large withstand voltage can be used, it may be deleted.
<2-2. Operation of surge protection circuit 13>

The operation of the surge protection circuit 13 is almost the same as that of the surge protection circuit 12. First, in a state where neither the sink device 1 nor the source device 2 is transmitting data, the DDC communication line has a power supply voltage V0 (Hi level voltage, eg + 5V) as described in the description of the first embodiment. It has been pulled up.

Next, when data is transmitted from the sink device 1 (Lo level is transmitted), the input / output terminal 101a of the communication unit 101 is short-circuited to the ground, so that the power supply voltage V0 is passed through the resistors R3 and R2. A current flows into the input / output terminal 101a, which causes the base and emitter of Tr1 to conduct, and at the same time, the collector and emitter conduct to bypass the diode D2.

At this time, the voltage (Lo level voltage) VLoB of the input / output terminal 201a of the communication unit 201 of the source device 2 is changed.

VLoB ≒ V0 × R0'/ (Rp1 + R0') (4)

Therefore, if the value of the resistor R0'is made sufficiently smaller than the pull-up resistor Rp1, the "floating" of the Lo level voltage from the ground voltage can be made sufficiently small (example: V0 = 5V). , Rp1 = 2kΩ, R0'= 100Ω, VLoB = 5V × 100Ω / (2kΩ + 100Ω) ≈ 0.24V).

Next, when data is transmitted from the source device 2 (Lo level is transmitted), the input / output terminal 201a of the communication unit 201 is short-circuited to the ground, so that the electric voltage V0 is passed through the resistors R3, R2 and the diode D2. A current flows into the input / output terminal 201a, which causes conduction between the base and emitter of Tr1.

At the same time, the PN junction between the base and collector of Tr1 is also biased in the forward direction by the resistors R3 and R0', so that the base and collector of Tr1 also conduct with each other.

Since the diode D2 is bypassed by this, the voltage (Lo level voltage) VLoA of the input / output terminal 101a of the communication unit 101 of the sink device 1 is the same as described in the description of the operation of the first embodiment.

VLoA ≒ (V0-VBCon) × R0'/ (R3 + R0') (5)

Therefore, if the value of the resistor R0'is made sufficiently smaller than that of the resistor R3, the "floating" of the Lo level voltage from the ground voltage can be made sufficiently small (example: V0 = 5V, VBCon =). Assuming 0.7V, R3 = 47kΩ, and R0'= 100Ω, VLoA = (5V-0.7V) × 100Ω / (47kΩ + 100Ω) ≈ 0.01V).

As described above, the surge protection circuit 13 according to the second embodiment uses the bypass circuit 131 to connect the diode D2 at the time of data transmission (at the time of Lo level transmission), similarly to the surge protection circuit 12 according to the first embodiment. Since it is bypassed, the "floating" of the Lo level voltage from the ground voltage can be sufficiently reduced.

Then, when the source device 2 is not connected to the connector 3, Tr1 of the bypass circuit 131 is turned off, so that the diode D2 is effective without being bypassed. Since the diode exhibits high insulation in the reverse direction, it is possible to provide more reliable protection against surges such as static electricity (ESD) applied from the outside through the connector 3.

Further, except for the varistor Va1, the required semiconductor elements are only one transistor Tr1 and one diode D2, and it is not necessary to use many semiconductor elements for surge protection.
<4. Others>

Although the embodiment of the present invention has been described above, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be appropriately modified and implemented within a range that does not deviate from the gist thereof.

Further, in the above, the surge protection circuit provided in the HDMI communication line has been described as an example, but the surge protection circuit of the present invention can also be applied to communication lines of other standards, for example, DVI (Digital Visual Interface). Needless to say, it can also be applied to communication lines of other open collector (open drain) output communication methods.

1 Sink equipment 2 Source equipment 3 Connector 4 Cable 10 Receiver 20 Transmitter 101, 201 Communication unit 11, 12, 13 Surge protection circuit 121, 131 Bypass circuit
R1 protection resistor D1, D2 diode Tr1 NPN transistor ZD Zener diode Va1, Va2 varistor

Claims (3)

A surge protection circuit provided on a communication line for connecting to another electronic device of an electronic device and communicating with the other electronic device.
A surge protection element interposed in series with the communication line,
A surge protection circuit including a bypass circuit that detects that another electronic device is connected to the communication line and bypasses the surge protection element. The surge protection circuit according to claim 1, wherein the bypass circuit bypasses the surge protection element by detecting a connection detection signal from another electronic device connected to the communication line. The surge protection circuit according to claim 1 or 2, wherein the surge protection element is a resistor or a diode.

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