JPH06103806B2 - Power amplifier protection circuit - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a power amplifier protection circuit that operates an amplification element in a safe operation region and prevents the amplification element from being destroyed.

[Prior art]

Conventionally, for protection of a power amplifier, for example, as shown in FIG. 4, a method of limiting a device current I _d to an operation limit (a is its limit straight line) by utilizing a drooping characteristic, or as shown in FIG. There is a method of utilizing the so-called "F" -shaped characteristic and limiting the element operating region by a straight line b which is the operation limit. 4 and 5
In the figure, p indicates a safe operation limit.

[Problems to be Solved by the Invention]

In the former method, as shown in FIG. 4, the shaded portion (c) is useless, and the shaded portion (d) exceeds the safe operation area limit, which is dangerous. Further, in the latter method, the hatched portion (e) becomes a dead area as shown in FIG. 5 due to the action of the protective function even within the safe operation area limit. Therefore, it is an object of the present invention to provide a protection circuit for a power amplifier that expands a safe operation area and reduces a waste area.

[Means for Solving the Problems]

That is, the protection circuit of the power amplifier according to the present invention is a constant current power amplifier (constant current amplifier 6), in which a voltage (element voltage V _ds ) between terminals of an amplifying element (MOS-FET 61, 62) installed at its output stage. Voltage detection means (detection amplifier 10)
And an arithmetic means (divider 12) which receives an output signal of the voltage detecting means as an input and generates an output representing a division result using the output signal as a denominator, and is installed in the preceding stage of the constant current power amplifier. When the input signal to the constant current power amplifier is the first input (A) and the calculation result of the calculation means is the second input (B), and the amplitude of the first input is smaller than the amplitude of the second input, The first input is input to the constant current power amplifier with the amplitude, and when the amplitude of the first input is larger than the amplitude of the second input, the first input is suppressed to the amplitude of the second input. After that, an output limiting unit (clipper circuit 4) for inputting to the constant current power amplifier and limiting the output of the power amplifier is provided.

[Action]

In the protection circuit of the power amplifier of the present invention, the power consumption of the amplifier element of the power amplifier is detected, and when the power consumption exceeds the safe operation area value of the amplifier element, the output of the power amplifier is limited to suppress the power amplifier. Always operate in the safe operation area. That is, since the protection circuit of this power amplifier is installed, the power amplifier can obtain the maximum output within its safe operation area. In this power amplifier protection circuit, the voltage between the terminals of the amplification element of the power amplifier is monitored, and the input signal to be input to the power amplifier is calculated using the voltage between the terminals and the coefficient set for the amplification element to be protected. Is determined. Therefore,
Since the instantaneous value of the power consumption of the amplifying element is limited so as not to exceed the limit value set for each element, the amplifying element is protected from destruction and it is possible to maximize the ability of the amplifying element. It will be possible.

【Example】

Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. FIG. 1 shows an embodiment of a protection circuit for a power amplifier according to the present invention. An input signal I _i to be amplified is applied to the input terminal 2, and this input signal I _i is applied to a constant current amplifier 6 as a power amplifier to be protected through a clipper circuit 4 provided as an output limiting means. At the final output stage of the constant current amplifier 6, MOS-FETs 61 and 62, which are transistors, are installed as amplification elements. In this embodiment, the MOS-FETs 61 and 62 constitute a push-pull amplifier, and when the input signal I _i is positive, the MOS-FET 61 is selective, and when the input signal I _i is negative, the MOS-FET 62 is selective. To work. The constant current amplifier 6 has an input / output characteristic in which the output current taken out from the output terminal 8 is proportional to the input voltage, and G indicates its conductance. The constant current amplifier 6 is provided with detection means for detecting the power consumption of the amplification element.
Between the drain and the source of the S-FET 61, the drain-source voltage, i.e., the sense amplifier 10 as a power detection means for detecting the element voltage is connected as a factor in power consumption, the device voltage V _ds of the MOS-FET 61 is To be detected. The detection amplifier 10, if the amplification gain and k _1, the power voltage k ₁
・ V _ds will be obtained. The output side of the detection amplifier 10 has a divider 12 as a calculation means for calculating the maximum value of the element current I _{d at} the element voltage V _ds .
Is installed. In the divider 12, the first input X has a coefficient k ₂ and the second input Y has an output voltage k _{1 from the} detection amplifier 10.
V _ds is added, the first input X is the numerator, the second input Y
The calculation (= X / Y) is performed with the denominator as the output, and the output Z is obtained as the calculation result. A clipper circuit 4 is installed in the front stage of the constant current amplifier 6 as an output limiting means for limiting the output of the constant current amplifier 6 according to the power consumption of the amplification element, and the output Z of the divider 12 is the clipper circuit 4. 4 to the second input B. When the input signal I _i to be amplified is set to the first input A of the clipper circuit 4, the clipper circuit 4 compares the amplitudes of the inputs A and B, and if the magnitude relationship between the two is A <B. Has a function of sending the input A to the output C and limiting the amplitude of the input A so that B = C when the magnitude relation between the amplitudes of the two is A> B. The output C of the clipper circuit 4 is added to the constant current amplifier 6 as an input to be amplified. Next, the operation of the protection circuit of this power amplifier will be described. First, when the input signal I _i is positive, when the input signal I _i is applied to the constant current amplifier 6 through the clipper circuit 4,
The MOS-FET 61 operates according to the input signal I _i . As a result,
A device voltage V _ds is generated between the drain and source of the MOS-FET 61 and detected by the detection amplifier 10. This sense amplifier 10
Due to the amplification gain k ₁ of the output voltage k ₁ · V _ds , which is the second input Y of the divider 12. In the divider 12, the first and second inputs X and Y are divided, and the output Z as the operation result is Becomes However, it is a coefficient given by k = k ₂ / k ₁ . That is, this output Z represents the maximum allowable value of the electron current I _{d at} the specific element voltage V _ds . This output Z is applied to the clipper circuit 4 and compared with the input signal I _i of the input A to obtain the magnitude relationship between the amplitudes of the two. That is, in the clipper circuit 4, when the magnitude relationship between the amplitudes of both is A <B, the input A is sent to the output C.
The input signal I _i is applied to the constant current amplifier 6 without being limited in amplitude. Also, the magnitude relationship between the two amplitudes is A>
In the case of B, the amplitude of the input A is limited so that B = C, and in this case, the input signal I _i is changed to the amplitude-suppressed input signal I _i ′ and applied to the constant current amplifier 6. . Since B = C when the amplitude is limited, from the element current I _d flowing from the MOS-FET 61 to the output terminal 8, That is, V _ds · I _d = k · G (3) holds. In the formula (3), V _ds · I _d is the power consumption P _d of the MOS-FET 61, and k · G is a constant. Therefore, by appropriately selecting k · G, as shown in FIG. And the instantaneous value of power consumption P _d
It is understood that it is possible to limit the safe operating area of the MOS-FET 61. This is a device voltage V _ds of the MOS-FET 61, detects the element current I _d flowing through the MOS-FET 61, power consumption V _ds · I _d constant value,
That is, when the value exceeds the safe operation region value, the amplitude of the input is limited so that it falls within the range of the constant value, and as a result, the output of the constant current amplifier 6 is limited. In the operating characteristics shown in FIG. 2, the maximum current I _{d max} and the maximum voltage V _{d max} can be limited by the conventional protection method. Therefore, according to the protection circuit of this power amplifier, the MOS
-The capability of FET61 can be fully utilized within the safe operation area. That is, by realizing an operation limiting circuit having the same condition as the limiting condition range of the amplifying element, it is possible to make maximum use of the capability of the element, and it is possible to handle large power with a small number of elements. For example, if the power amplifier protection circuit of the present invention is used, a power amplifier that handles a load such as a motor has the advantage of being able to increase the capacity against overload at the time of startup. When the input I _{i of} the amplifier is negative, the direction of the output current I _d of the amplifier 6 is inverted from that shown in the figure, and instead of the MOS-FET 61 which operates when the input signal I _i is positive. , MO
S-FET62 operates. Therefore, the drain of MOS-FET62
Similarly to the case described above, the source-to-source voltage is detected by a detection amplifier (not shown), and if the detection output is calculated by a divider (not shown), the negative result of the calculation by the divider 12 shown in Equation (1) is obtained. An output showing the calculation result of can be obtained. The result of this operation is added to the other input terminal B'of the clipper circuit 4.
The clipper circuit 4 replaces when the input signal I _i is positive,
If the input signal I _i is negative and | A | <| B ′ |
Is output to the output C, and when | A |> | B '|, C = B'
By limiting the input of the power amplifier 6 so that the input signal I _i is positive, the amplification element 62 of the constant current amplifier 6 is protected even when the input signal I _i is negative. Can be done. Next, FIG. 3 shows an embodiment of the clipper circuit 4 in the protection circuit of the power amplifier shown in FIG. The clipper circuit 4 is provided with three input terminals 4A, 4B and 4B ', and the respective inputs A, B and B'to the respective input terminals 4A, 4B and 4B' are respectively the respective inputs A, B and B '. Buffer amplifiers 402, 404, and 406 each having a gain of 1 are installed corresponding to the above. A protection resistor 408 is connected in series as a protection circuit to the input part of the buffer amplifier 404, and a diode 410 whose ground side is an anode is connected to the input part of the buffer amplifier 404. 412 are connected in series, and a diode 414 whose cathode is on the ground side is connected. Each output side of each buffer amplifier 402, 404, 406 has a diode 416 whose cathode is the output side of the buffer amplifier 404,
The output side of the buffer amplifier 404 is coupled through a protection resistor 418 and a diode 420 which is an anode of the output side of the buffer amplifier 406, and an output buffer amplifier 424 having a gain of 1 is installed as an output means for extracting the output of the coupling point 422. There is. An output terminal 4C for taking out the output of the clipper circuit 4 is provided on the output side of the buffer amplifier 424. With this configuration, the input signal I _i is
As an output of 402, it appears at a connection point 422 through a protection resistor 418. When the input signal I _i is positive, the diode 416 is non-conductive as long as the output of the buffer amplifier 404 satisfies A <B, that is, | A | <| B | Is applied to the output buffer amplifier 424, and the input A appears at the output C of the output terminal 4C. However, inputs A and B
When the magnitude relationship of | A |> | B | becomes, the diode 416 conducts, and if the voltage drop of this diode 416 is ignored, the potential of the node 20 becomes equal to that of the input B. On the other hand, when the input signal I _i is negative, the magnitude relationship between the inputs A and B, that is, the condition of | A | <| B | is equal to A> B. As long as this condition holds, the diode 420 is non-conductive.
Also, when | A |> | B |, A <B, so the diode 42
0 becomes conductive, and the potential of the connection point 422 is set to the potential of the input B '. The protection resistor 408 and the diode 410 prevent the diode 416 from accidentally conducting when the potential of the input terminal 4B becomes negative. The protective resistor 412 and the diode 414 on the input terminal 4B 'side also have the same function. In the embodiment, the MOS-FET is used as the amplification element to be protected.
However, the present invention can also be applied to the case where a bipolar transistor is used. Further, although the case where the amplifying element to be protected is configured by the push-pull circuit has been described, it can be applied to a single circuit. Further, the protection circuit of the power amplifier of the present invention may be used in combination with the conventional protection system, and by doing so, the drawbacks of the conventional system can be greatly improved and the protection function of the amplification element can be further enhanced. .

【The invention's effect】

As described above, according to the present invention, it is possible to perform the amplifying operation by matching the operating region of the amplifying element of the power amplifier with the safe operating region limit, so that it is possible to eliminate a waste area and to amplify the amplifying element. Can be reliably protected from destruction, and moreover, it is possible to realize the efficient operation by maximizing the ability of the amplifying element.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a power amplifier protection circuit according to the present invention, FIG. 2 is a diagram showing operating characteristics of the power amplifier protection circuit shown in FIG. 1, and FIG. 3 is shown in FIG. FIG. 4 is a circuit diagram showing an embodiment of a clipper circuit in the protection circuit of the power amplifier shown in FIG. 4, and FIGS. 4 and 5 are diagrams showing a conventional method in the protection circuit of the power amplifier. 4 ... Clipper circuit (output limiting means) 6 ... Constant current amplifier (power amplifier) 7 ... Constant voltage amplifier (power amplifier) 10 ... Detection amplifier (voltage detection means) 11 ... Detection amplifier (current detection means) 12 …… Divider (calculation means) 13 …… Multiplier (calculation means) 14 …… Comparison amplifier 61, 62, 71, 72 …… MOS-FET (amplification element) V _ds …… Element voltage (terminal voltage )

Front page continuation (72) Inventor Bungo Abe 6-3-20 Tsunashima-East, Kohoku-ku, Yokohama-shi, Kanagawa Yokofuhama factory, NUF Co., Ltd. (56) Reference JP-A-57-37912 (JP, A) ) JP-A-57-109409 (JP, A) JP-A-60-112303 (JP, A) JP-A-57-129008 (JP, A) Actually-laid-open Sho-56-39715 (JP, U)

Claims (1)

[Claims] 1. A constant current power amplifier, wherein a voltage detecting means for detecting a voltage between terminals of an amplifying element installed at an output stage of the constant current power amplifier and an output signal of the voltage detecting means are input, and the output signal is used as a denominator. Arithmetic means for generating an output representing a division result; and an input signal for the constant current power amplifier, which is installed in the preceding stage of the constant current power amplifier, as a first input, and an arithmetic result of the arithmetic means as a second input. , The amplitude of the first input is the second
The first input is input to the constant current power amplifier at that amplitude when it is smaller than the amplitude of the input of the input, and the first input is input when the amplitude of the first input is larger than the amplitude of the second input. A power amplifier protection circuit, comprising: output limiting means for suppressing the amplitude of the second input and then inputting it to the constant current power amplifier to limit the output of the constant current power amplifier.