JPH0136350Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a power amplifier with a diode limiter using an operational amplifier.

A conventional configuration of this type is shown in FIG. The operational amplifier OA has an input signal applied to its inverting input terminal via an input resistor R1 for gain calculation, and an output terminal of a pair of complementary power transistors Tr ₁ and Tr ₂ connected in a push-pull manner via an output resistor R2 for current limiting. Common base input. The power transistors Tr ₁ and Tr ₂ are a pair of PNP type and NPN type, and each collector has an output current limiting resistor R.
3 and R4 to the positive and negative DC power supplies, and both emitters are connected to each other to serve as the output end of the power amplifier. This output terminal is connected to the inverting input terminal of the operational amplifier OA via a feedback resistor R5 for gain calculation. In addition, variable resistors VR1 and VR2 for setting limiter values are connected between the output terminal and the positive and negative DC power supplies, respectively.
is connected. The output terminals of the variable resistors VR1 and VR2 are connected to the inverting input terminal of the operational amplifier OA via limiter diodes D1 and D2, respectively.
The diode D1 is connected in a direction to limit the negative polarity side of the power amplifier output, and the diode D2 is connected in a direction to limit the positive polarity side of the output.

In this configuration, the power amplifier gain is determined by the resistors R1 and R5, and the positive and negative limiter values are determined by the voltage division ratios of the variable resistors VR1 and VR2, respectively. Here, the minimum value of the positive and negative limiter values is limited by the forward voltage (enlayer voltage) of the diodes D1 and D2, and there is a drawback that it is not possible to set the voltage below this voltage. Further, there is a problem in that the layer voltages of the diodes D1 and D2 vary depending on the temperature, and this variation appears as a variation in the limiter value.

The object of the present invention is to obtain a power amplifier that can control the minimum limiter value down to zero volts and has little temperature fluctuation.

FIG. 2 is a circuit diagram showing an embodiment of the present invention. The difference between this figure and Figure 1 is the variable resistor.
VR1 and VR2 are connected between the output terminal of operational amplifier OA and the positive and negative DC power supplies.

In this embodiment, the cap layer voltages of the diodes D1 and D2 are compensated as the base-emitter voltages of the transistors Tr ₁ and Tr ₂ , respectively, and the limiter value of the power amplifier output can be set up to zero volts. Also, the variation in the en-layer voltage due to the temperature of the diodes D1 and D2 is caused by the transistors Tr ₁ ,
The diodes D1 and D2 and the transistors Tr ₁ and Tr _{2 are arranged so that they are at almost the same temperature, which is compensated for as a temperature-related variation in the base-emitter voltage of Tr 2 .}
For example, by placing the diodes D1 and D2 in contact with the transistors, it is possible to reduce fluctuations in the limiter value due to temperature fluctuations.

As described above, according to the present invention, the minimum limiter value can be set to zero volts, and an output with little temperature fluctuation can be obtained.

[Brief explanation of the drawing]

Figure 1 is a conventional power amplifier circuit configuration diagram, Figure 2
The figure is a circuit configuration diagram showing an embodiment of the present invention. OA...Operation amplifier, VR1, VR2...Variable resistor, D1, D2...Diode, Tr ₁ , Tr ₂ ...
...transistor.

Claims (1)

[Scope of utility model registration request] An operational amplifier to which an input signal is applied via an input resistor, a variable resistor for setting a limiter value connected between the output terminal of this operational amplifier and a DC power supply, and a variable resistor for setting a limiter value connected between the output terminal of this variable resistor and the above calculation a diode connected between the inverting input terminal of the amplifier;
A pair of complementary power transistors connected in a push-pull manner, each of which has an output from the output terminal of the operational amplifier as its base input, and a feedback resistor connected between both emitter output terminals of the transistors and an inverting input terminal of the operational amplifier. A power amplifier with a diode limiter.