JPS59154807A - Overload preventing circuit for high frequency amplifier or the like - Google Patents

Abstract

PURPOSE:To obtain a stable overload preventing circuit by interrupting a power supply circuit when a power value extracted by a progressive wave component extracting circuit and a reflected wave component extracting circuit and a high frequency power calculated by a supply power exceed a set value. CONSTITUTION:The high frequency power 2 applied from an exciting device of a pre-stage is amplified by a trnasistor (TR) 1 and reaches an output terminal 5 through a tuning circuit 4. The high frequency output of the progressive power extracting device 6 and the reflected wave power extracting device 7 is converted into a DC voltage at detectors 8, 9 and applied to an adder 12 via a coupling resistor 11. The DC voltage drop of a resistor 10 corresponding to the power supply input power is applied to the adder 12 via the coupler 11. A value adding the reflected wave power to the power supply input power and subtrated by the propressive wave power therefrom is outputted from the adder 12. This value is the power loss in the TR1, and when the loss exceeds the set value of a voltage adjuster 14, a relay 15 is operated and the power supply circuit is interrupted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention protects against true overload operation of high frequency amplifiers or high frequency oscillators.

Generally, in such cases, when the corresponding input power (input current if the power supply voltage is constant) and reflected power from the load exceed set values, the power supply is shut off or the excitation high-frequency power is reduced. We have adopted protection circuits such as

However, the power that actually damages the high-frequency amplifier or high-frequency oscillator is the power supply input power minus the high-frequency output power, and within the range where the applied power supply voltage and current have enough margin, the power supply input power increases. However, if the high frequency output power increases further, the amount of power that would cause damage will decrease and it will be safe.

However, in conventional protection circuits, individual set values are set for the power supply voltage, power supply current (anode current or collector current, etc.), and reflected wave power, and the operation is stopped when any of them exceeds the set value. Ta. At this time, if the power supply voltage, power supply current, etc. are set to the maximum values of the standard, even if they are within the safe range, a situation will occur in which the dangerous power is exceeded due to a decrease in the high frequency output power. In order to protect against this, if the set values related to the power supply are lowered, an overprotection state will occur where the operation will be cut off even if the high frequency output power is within the safe operating range due to the increase.

This is true in cases where the load is stable, such as in communication equipment, but in industrial applications, the load generally fluctuates rapidly, so
An appropriate overload prevention circuit that can safely output as much high-frequency power as possible is desired.

The high frequency output power of a high frequency amplifier or the like is the difference between the traveling high frequency power flowing between the high frequency amplifier and the load circuit and the reflected wave power from the load circuit. Therefore, the power obtained by subtracting the traveling wave high frequency power Wf to the load from the power supply input power Wp and adding the reflected wave high frequency power Wr from the load is the power loss 1 in the amplifier.

Wl=Wp-(Wf-Wr)'=Wp-Wf+Wr,
(1) Based on this principle, the present invention measures safety by interrupting the circuit when the actual power loss of the high-frequency amplifier or high-frequency oscillator exceeds a set value.

FIG. 1 shows a schematic diagram of one embodiment of the invention. In this example, a transistor is used in the output stage, so a stabilized power supply voltage is used. Therefore, the power input power of the output transistor is proportional to the collector current or emitter current.

A high frequency power 2 is applied to the base of the transistor 1 from an exciter in the previous stage, and a power supply voltage is received from a constant voltage power supply line 3.

The high frequency output power amplified by the transistor 1 reaches the output terminal 5 through the tuning circuit 4 and is applied to the load, but a traveling wave power extractor 6 and a reflected wave power extractor 7 are inserted between them. Wave components and reflected wave components from the load are extracted. Ordinary directional couplers may be used for these extractors. The high-frequency outputs of both extractors are converted into DC voltage by detectors 8 and 9, and then added to adder 12 via coupling resistor 11. At this time, only the detector for the traveling wave component changes the polarity. This is reversed and a negative voltage is applied to the adder.

On the other hand, the power input to transistor 1 is as described above.
Since it is proportional to the collector or emitter current, the DC voltage drop across the resistor 10 inserted into this circuit corresponds to the power input to the power supply. This voltage is also applied to the adder 12 via the coupling resistor 11. Adder 1
If the value of the coupling resistor 11 is set appropriately, the voltage applied to 2 can be made to correspond to the power supply input power wp, the traveling wave component Wf of the output high-frequency signal, and the reflected wave component Wr multiplied by the same ratio. , as in equation (1) above, the output voltage of the adder 12 is determined by the voltage loss W1 in the output transistor l.
It will be equivalent to .

The output voltage of the adder 12 is applied to one input terminal of the differential amplifier 13, while the output variable voltage of the voltage regulator 14 is applied to the other input terminal of the differential amplifier. Therefore, by changing the output voltage level of the voltage regulator 14, the level of power loss -1 for operating the relay 15 connected to the output of the differential amplifier 13 can be adjusted.

When the relay 15 operates, its contacts 16 are opened.

In the circuit shown in FIG. 1, the power supply voltage Vcc of the output transistor l is protected at this time by being cut off by opening the relay contact 16, but the high frequency excitation power from the previous stage is cut off by the relay contact 16. It's okay. Alternatively, it is possible to make it easier to restart by controlling both of them to a low level without completely shutting them off.

In Fig. 1, 17 is a high frequency bypass capacitor;
18 is a power supply voltage supply terminal.

Next, an example of how much improvement can be achieved when the method of the present invention is adopted will be described. Now consider a conventional system in which a power supply voltage of 100V is applied to the collector of the final stage transistor, the collector current is limited to 1.5A, and the reflected wave power is set to 10W. The input power is 100 when
If X 1.5 = 150W and efficiency is 50%, high frequency output power Wo = 150 X 0.5 = 75W-
There is t'. When the reflected wave power Wr is 10 W, the traveling wave power Wf is Wf = Wo + Wr = 85 W, and the reflection coefficient is 1 r l = Ia = B / 85
'=<0.343-7'? It pressure standing wave ratio VSWR=
(1+lrI)/(1-1rI)=
2. oaa tonal.

At this time, assume that the load circuit is adjusted to improve the VSWR to 1.2. With the improvement of VSWR, the efficiency has naturally increased to 60.
%, the collector current remains at 1.5 A, and the high frequency output is 75 x (0,6/0.5
) = 90W. At this time, the reflected wave power Wr has a reflection coefficient 1rl of VSWR = 1.2 to 1r l =
(1,2-1) / (1,2+1)', o, 0
91;j: Te decreases, and l r l 2=Wr/Wf
=Wr/ (Wo+Wr) =0.0083, so W
r=Wo/ (1/ l r I2-1) =90/
(110,0083-1) = 0.75W, i.e. I
Although it is sufficiently small compared to the OW limit, Ic=1.
Due to the 5A limit, the high frequency output Wo is 90W, and the collector loss W+ is W+ = 150-90 = 60W, which is 75W compared to the case of VSWR = 2.044.
-60W = 15W Although the weight has been reduced by 15W, it means that you will not be able to demonstrate your full potential by that much.

If the method of the present invention is adopted in such a case, the voltage Ep corresponding to 150 W of input power of the power supply is set to 1.5 V, the voltage Ef corresponding to 100 W of traveling wave power is set to -IV, and the voltage Er corresponding to reflected wave power of 100 W is set to 1.5 V. When the magnification of the adder divider is adjusted so that the voltage becomes 1V and the voltage is added as shown in FIG. 2, the output voltage Ea of the adder becomes Ea=Ep+Er-Ef, (2). In the above calculation example, power supply input power 111p = 15
OW, reflected wave power Wr=10W, traveling wave power 11if8
High frequency output power at 5W -o = Wf -Wr = 75
W, the corresponding voltages are Ep=1
．． 5V, Er-0, IV, Ef = 0.85V, Ea = 1.5 + 0.1-0.85 = 0°? 5V
becomes. This is the voltage corresponding to the power loss of the transistor according to equation (1).

Assuming that the maximum loss of this transistor is 75W,
The voltage corresponding to this value is 0. ? It becomes 5V.

Therefore, the reference voltage applied to the differential amplifier 13, that is, the regulator 1
If the output voltage level Eb of 4 is set to the same level, when the loss voltage of the transistor exceeds 75W, the output current of the differential amplifier will flow, operating the relay 15,
This protects the transistor by stopping its operation.

In this state, if the VSWR of the load is matched to 1.2, the efficiency increases from 50% to 60% as described above.

At this time, assuming that the power loss in the transistor -1 is constant, the power supply input power in the case of improvement is -p', and Wf-
High frequency output type car compatible with Wr-Wo 〇'--f'-
Wr' has the following relationship.

w+=wp-102 wp'--0' However, Wo/Wp= 0.5, Wo'/Wp'-0,
8, so WI=Wp (1-Wo/Wp) -0,5Wp=W
p'(1-Wo'/Wp') -0,4Wp' Therefore, Wp'=WpX 0.510.4 =WpX1.25
That is, if the losses in the transistors are made equal, the system of the present invention can increase the power input by 25% and, as a result, the high frequency output power can also be increased by 25%. At this time,
The power input is 150W x 1.25 = 187.5W, and the high frequency output power is 187.5W x 0.6 =
112.5W, which is 112.5W compared to the conventional method.
．． An increase of 5-90 = 22.5W is obtained. That is, since the overload prevention circuit of the present invention limits the internal loss of the transistor that really requires protection, it is possible to always exert sufficient power against changes in load.

Since transistors have weaker overload resistance than electron tubes, the present invention is particularly advantageous for semiconductor circuits, but it goes without saying that it is also effective for electron tube circuits. Further, the present invention is particularly effective for industrial applications where load fluctuations are significant.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram schematically showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram of the adder operation thereof. ■ is an output transistor, 2 is a high frequency power, 3 is a power supply line, 4 is a tuning circuit, 5 is an output terminal, 6 is a traveling wave component extraction circuit, 7 is a reflected wave component extraction circuit, 8 and 9 are detectors,
10 is a transistor current detection resistor, 11 is a coupling resistor, 12 is an adder, 13 is a differential amplifier, 14 is a voltage regulator, 15 is a relay, 16 is a relay contact, 17 is a high frequency bypass capacitor, 18 is a power supply supply terminal.

Claims (1)

[Claims] (1) A traveling wave component extraction circuit and a reflected wave component extraction circuit are placed between the high frequency amplifier or high frequency oscillator and the load circuit, and the traveling wave component is extracted from the voltage corresponding to the input power supply power of the high frequency amplifier or high frequency oscillator. When the voltage corresponding to the traveling wave power extracted by the extraction circuit is subtracted, and the voltage corresponding to the reflected wave power extracted by the reflected wave component extraction circuit is added, and the total value exceeds a preset value,
An overload prevention circuit for a high frequency amplifier or the like, characterized in that it is configured to cut off or control the corresponding power supply circuit or high frequency excitation power.