JPH0314830Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field of the invention] This invention adjusts the output of the transmitter according to the ambient temperature, etc.
The present invention relates to a transmission power lower limit setting circuit that automatically reduces transmission power.

[Prior art and its problems]

Conventionally, there has been a circuit as shown in FIG. 6 as such a transmission power lower limit setting circuit.

In the figure, 1 is a transmitter consisting of a drive stage 2 and an output stage 3, 4 is a directional coupler, and the detection signal is a traveling wave. 5 is a high frequency input terminal, 6
is the antenna terminal.

Q ₁ and Q ₂ are transistors forming a differential amplifier, Q ₃
is a transistor that controls the power supply current of the drive stage 2 and is a variable current element.

The base of Q ₁ is a resistor R ₁ and a temperature sensing element (thermistor)
It is connected to the power supply line +B via TH ₁ and grounded via resistor R ₂ .

Detected by directional coupler 4, diode
When the transmission output increases, the traveling wave voltage rectified and converted to direct current by D ₁ and capacitor C becomes a negative signal corresponding to the amount, and controls the base potential of Q ₂ .

Q ₁ and Q ₂ are based on the base potential of Q ₁ , and the difference is
It outputs to the collector of _Q2 , controls the base current of variable current element _Q3 , lowers the power supply voltage of drive stage 2 of transmitter 1, and lowers the output power.

Here, if the temperature of TH ₁ rises due to ambient temperature etc., it has a negative temperature coefficient, so
The reference voltage of Q ₁ increases.

As a result, the collector current of _Q2 decreases, causing the collector current of _Q3 to decrease. Therefore, the power supply voltage of the drive stage 2 is lowered and the transmission output is reduced.

However, since the conventional lower limit setting circuit is configured as described above, when temperature detection is performed using the internal temperature of the output stage heatsink, etc., the time constant of temperature change becomes extremely large, resulting in poor feedback. The loop has become unstable. Another drawback was that the transmission output was cut off at a certain temperature, and the output appeared again after a time constant had elapsed.

Alternatively, even if the transmission output does not stop, it becomes a very small value and cannot be put to practical use until the time constant elapses.

[Purpose of invention]

The purpose of the present invention is to overcome the drawbacks of the conventional lower limit setting circuit described above, and to prevent the transmitter from disconnecting by allowing a predetermined current to flow regardless of whether the variable current element is disconnected. Our goal is to provide the following.

Hereinafter, the present invention will be specifically explained with reference to the drawings.

〔Example〕

FIG. 1 is a block diagram of a transmission power lower limit setting circuit according to an embodiment of the present invention, in which 11 is a detection circuit;
12 is a comparison circuit, 13 is a variable current element, R ₁₀₀ is a transmission power lower limit setting resistor, TH ₁₀ is a temperature sensing element, and R ₁₀ is a reference voltage setting resistor.

FIG. 2 is an example of a practical circuit diagram. What is important here is that the transistor, which is a variable current element,
In parallel with Q ₃ , a transmission power lower limit setting resistor R ₁₀₀ is connected between its emitter and collector.

In FIG. 1, the output of the detection circuit 11 is connected to the inverting input (-) of the comparator circuit 12, and the reference voltage generated by the resistor R ₁₀ and the temperature sensing element TH ₁₀ is connected to the non-inverting input (+). A voltage is input to the control terminal of the variable current element 13, and the transmitter (not shown)
control to keep the output constant.

Here, the temperature sensing element TH ₁₀ has temperature characteristics as shown in Figure 3, and the temperature at the point of sudden change is
T ₁ almost coincides with the start point of output reduction as the temperature of the circuit increases.

Now, if the temperature rises due to mismatching of the transmitter's load and reaches the above-mentioned temperature _T1 , the circuit lowers the control output of the variable current element 13 so that the transmission output decreases.

At this time, since the thermal time constant is large, the transmission power is reduced excessively, and the variable current element 13 is turned off.

However, since the resistor R ₁₀₀ is connected in parallel with element 13, the drop stops at a predetermined value, and the lower limit of the transmitted output can be determined.

As a result, the transmitter's heat generation is suppressed, and the temperature-sensitive element
TH ₁₀ begins to operate to increase the transmission output, exhibits long-period damped oscillation characteristics, and finally becomes constant at a certain value.

Further, in FIG. 2, the traveling wave is detected by the directional coupler 4, negatively detected by the diode _D1 , and smoothed by the capacitor C.

At this time, the base of transistor Q ₂ is resistor R ₄ ,
It is biased to a predetermined value by a series circuit of R ₅ and diode D ₁ , and the collector current of transistor Q ₂ is adjusted so that the negative detection output almost matches the base bias voltage of transistor Q ₁ at a predetermined transmission output. change and control transistor _Q3 .

Here, if the temperature sensing element TH ₁ is attached to the transmitter's heatsink and the transmitter generates abnormal heat, the temperature sensing element TH ₁ has a negative temperature coefficient, so the base of the transistor Q ₁ Increase current. Then, due to the characteristics of the differential multiplier, the transistor
The collector current of Q ₂ decreases, and the base current of transistor Q ₃ decreases. As a result, drive stage 2
The power supply voltage decreases, and the transmission output decreases.

However, the temperature of the radiator does not stop rising instantly due to thermal resistance, but has a certain time constant. During this time constant, the loop containing the temperature sensitive element TH ₁ reduces the transmitted output, but due to the resistor R ₁₀₀ connected between the emitter and collector of the transistor Q ₃ , the supply voltage of the drive stage 2 does not fall below a predetermined value, and operates to eliminate transmission interruptions during temperature loop transient phenomena.

At this time, the value of the resistor R ₁₀₀ is determined by the drop in the power supply voltage of drive stage 2 due to the resistor R ₁₀₀ , as shown in the TH characteristic diagram.
The radiator temperature is set to be below _T1 .

FIG. 4 is a circuit diagram showing an example of using the circuit of the present invention for manual switching of transmission output, and shows a transistor
Switch SW and resistor in base bias circuit of _Q1
R ₁₀₁ is connected in series.

By manually switching the switch SW,
This turns transistor Q ₁ "on" and thus causes transistor Q ₃ to operate in succession, reducing the transmit output to the lower limit setting.

In addition, instead of the transmission power lower limit setting resistor R ₁₀₀ , as shown in Fig. 5, a parallel circuit of a transistor Q ₁₀ and a semi-fixed volume VR ₁₀ is connected between the emitter and collector of the variable current element Q ₃ . You can. In this case, the lower limit transmission power value can be adjusted within a certain range, which is more preferable.

Further, when the temperature sensing element TH ₁ has a positive temperature coefficient, the same effect as in the above embodiment can be obtained by connecting the temperature sensing element TH ₁ between the base of the transistor Q ₁ and the ground.

[Effects of the invention] As explained above, in the present invention, since the current setting means is connected in parallel with the variable current element,
The following effects can be achieved.

When the temperature rises, the transmitter output will not be cut off temporarily.

Switching the transmitter output is also easy.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a transmission power lower limit setting circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram thereof.
Figure 3 is a graph of the temperature vs. resistance value characteristics of the temperature sensing element.
FIG. 4 is a circuit diagram of a main part of a manual switching circuit, FIG. 5 is a circuit diagram of another embodiment of the current setting means, and FIG. 6 is a circuit diagram of a conventional transmission power lower limit setting circuit. DESCRIPTION OF SYMBOLS 1... Transmitter, 2... Drive stage, 3... Output stage, 4... Directional coupler, 11... Detection circuit, 1
2...Comparison circuit, _Q1 , _Q2 ...Differential amplifier, 13,
Q ₃ ... Variable current element, R ₁₀₀ ... Current setting resistor,
TH ₁ , TH ₁₀ ... Temperature sensing element.

Claims (1)

[Scope of utility model registration request] A detection section that detects a voltage according to the output, a reference voltage setting section that includes a temperature sensing element, a comparison section that compares the detected voltage and the reference voltage, and an output of the transmitter that controls the current using the output of the comparison section. 1. A transmission power lower limit setting circuit comprising an output control section for controlling a transmission power lower limit setting circuit, characterized in that a current setting means is connected in parallel with a variable current element of the output control section.