JP2006094651A - Overcurrent protection circuit for active antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an overcurrent protection circuit capable of overcurrent protection while maintaining the operation of a receiver without interrupting current supply to an antenna even if a current exceeds a determined value. <P>SOLUTION: This overcurrent protection circuit, used in an active antenna, includes: a first transistor whose emitter is connected to a power supply; a first resistance element inserted in between the emitter and the base of the first transistor; a second transistor in which the base of the first transistor is connected to the emitter and the collector of the first transistor is connected to the base; a second resistance element inserted in between the base and the ground of the second transistor; and a chalk coil inserted in between the collector of the second transistor and an antenna element. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an overcurrent protection circuit for an antenna, and more particularly to an overcurrent protection circuit for an active antenna used in a GPS receiver.

Conventionally, active antennas have been widely used in GPS receivers, and for example, the one shown in FIG. 2 is generally employed.
For example, as shown in FIG. 2, a configuration is basically provided in which a choke coil L1 is inserted and connected between the antenna element ANT and the power source Vcc.

  Here, the choke coil L1 is used to prevent the AC signal from the antenna element ANT from flowing into the DC power source Vcc side, and it is common to select an element value that becomes AC high impedance. It is.

  By the way, in an active antenna having such a configuration, for example, the antenna element ANT is short-circuited to the ground due to connection failure caused by repeated attachment / detachment of the antenna element or accumulation of dust and dirt under humid conditions. There is a problem that a large excess current flows.

In order to solve such a problem, for example, Japanese Patent Application Laid-Open No. 6-6248 discloses a car radio active antenna antenna provided with an overcurrent protection circuit.
That is, when the overcurrent protection circuit exceeds a predetermined current value, the transistor disposed in the current path is cut off, and the current supply to the antenna is cut off.
JP-A-6-6248

As described above, the conventional overcurrent protection circuit achieves the object by cutting off the current supply to the antenna when the current exceeds a predetermined value, but the fact that the current is cut off means that the receiver is cut off. This means that the function stops. That is, there arises a problem that it cannot be used as a receiver until the cause is resolved.
An object of the present invention is to provide an overcurrent protection circuit capable of performing overcurrent protection while maintaining the operation of a receiver without interrupting the current supply to the antenna even if the current exceeds a predetermined value. Is.

The present invention relates to an overcurrent protection circuit for an active antenna, a first transistor having an emitter connected to a power source, and a first resistance element inserted and connected between the emitter and base of the first transistor And a second transistor having the base of the first transistor connected to the emitter and the collector of the first transistor connected to the base, and being inserted between the base of the second transistor and the ground. And a second resistance element, and a choke coil inserted and connected between the collector of the second transistor and the antenna element,
Further, when the maximum allowable value of the flowing current is Imax when the antenna terminal and the ground are short-circuited, the first transistor operates normally when a current of Imax flows through the first resistance element. And the resistance value of the second resistance element is set to
A GPS receiver is configured by using an active antenna provided with these overcurrent protection circuits.

  The overcurrent protection circuit according to the present invention has an advantage that overcurrent protection can be performed while maintaining the operation of the receiver.

Hereinafter, the present invention will be described in detail based on examples.
FIG. 1 is a circuit diagram showing an embodiment of an overcurrent protection circuit according to the present invention.
As shown in the figure, the overcurrent protection circuit includes two transistors Q1 and Q2, two resistors R1 and R2, and a choke coil L1.
Here, the emitter of the first transistor Q1 is connected to the power source Vcc, the first resistor element R1 is inserted and connected between the emitter and the base, and the base is connected to the emitter of the second transistor Q2. The collector is connected to the base of the second transistor Q2.
Furthermore, the base of the second transistor Q2 is grounded via the second resistance element R2, and the collector is connected to the antenna element ANT via the choke coil L1.

  Each element value is selected as shown in the individual parts table on the right side of the circuit diagram of FIG. Each element value is for applying this overcurrent protection circuit to an active antenna for a GPS receiver, and the reception frequency at this time is 1575.42 MHz.

The operation principle of this circuit will be described below.
First, the maximum allowable value Imax of the current that flows when the antenna element ANT is short-circuited to the ground is set to 50 mA.

As is well known, the first transistor Q1 is turned ON / OFF by the voltage across the first resistor R1.
In the present invention, the first resistor R1 is set so that the first transistor Q1 operates when a current of 50 mA which is the maximum allowable value of current flows through the first resistor R1.

  The second resistor R2 controls the collector current of the first transistor Q1. If the second resistor R2 is increased to 10kΩ here, it will be difficult for Q2 to operate. Conversely, if R2 is decreased to 50Ω, current exceeding the collector allowable current value of Q1 may flow and the transistor may be damaged. Therefore, 5.1kΩ is the optimum value.

  The second transistor Q2 is preferably a transistor with a large collector loss so that it can withstand even at high temperatures.

1 is a circuit diagram showing an embodiment of an overcurrent protection circuit according to the present invention. It is a circuit diagram of the conventional overcurrent protection circuit.

Explanation of symbols

Q1, Q2 ... transistor
R1, R2 ... resistance
L1 ... Choke coil
ANT ・ ・ ・ Antenna element

Claims (3)

An overcurrent protection circuit for an active antenna,
A first transistor having an emitter connected to a power source; a first resistance element inserted and connected between the emitter and base of the first transistor; and a base of the first transistor connected to the emitter; A second transistor in which the collector of the first transistor is connected to a base; a second resistance element inserted and connected between the base of the second transistor and the ground; and a collector of the second transistor And an overcurrent protection circuit for an active antenna, comprising: a choke coil inserted and connected between the antenna element and the antenna element.   When the maximum allowable value of the current flowing when the antenna terminal and the ground are short-circuited is Imax, the second transistor is set so that the first transistor operates normally when a current of Imax flows through the first resistance element. 2. The overcurrent protection circuit for an active antenna according to claim 1, wherein a resistance value of the resistance element is set. A GPS receiver using an active antenna provided with the overcurrent protection circuit according to claim 1.

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