JPH066598Y2 - Negative feedback amplifier circuit - Google Patents

Description

TECHNICAL FIELD The present invention relates to a negative feedback amplifier circuit for driving a capacitive load such as a horizontal deflection plate of a cathode ray tube for an oscilloscope.

(Prior Art and Its Problems) FIG. 2 shows a circuit of a negative feedback amplifier for driving a capacitive load such as a horizontal deflection plate of a cathode ray tube for an oscilloscope. 1 is an input terminal, 2, 5, 6, 8 are resistors, 3, 10, 11 are transistors,
4, 9 are capacitors, 7 is a constant voltage source, 12 is an output terminal, and 13 is a capacitive load of the cathode ray tube.

In order to faithfully apply a wide range of high speed deflection signals such as those of an oscilloscope to the deflection plate of the cathode ray tube, it is necessary to supply a sufficient displacement current to charge the capacitor 13 of the deflection plate.
It should be noted that the capacitor 4 is for switching the charging / discharging of the capacitive load 13, that is, for correcting the current of the high frequency component at the change point of the signal. The bias component that is

A current, which is determined by the difference between the resistance value and the voltage applied across the resistance 8, flows in the resistance 8.

A constant power supply voltage Vc is applied to one end of the resistor 8, and the emitter voltage of the transistor 10 is applied to the other end.
Is a constant voltage determined according to the voltage divided by the resistors 5 and 6. Therefore, a constant DC current flows through the resistor 8. The power loss of the transistor 10 is determined by the product of the current (almost emitter current) flowing between the collector and the emitter of the transistor 10 and the voltage between the collector and the emitter.

Therefore, the PNP transistor 10 in the output stage must have a large current capacity so that a large current can flow, and it has the drawback of being expensive, large, and paying attention to heat dissipation.

FIG. 3 shows a conventional embodiment in which these drawbacks are eliminated.

The feature of this circuit is that the power loss of the PNP output transistor 10 is reduced by distributing a part of the supply current to the resistor 14. However, in the circuit of Fig. 3 as well, the capacity of the resistor 14 for shunting became large, and a new thermal problem remained.

(Object) An object of the present invention is to provide a negative feedback amplifier that reduces the power loss of the PNP transistor in the output stage.

(Embodiment) FIG. 1 shows an embodiment of the present invention.

In this circuit, when the collector current of the NPN type output transistor 11 decreases, the output current of the PNP type output transistor 10 charges the capacitor of the capacitive load 13 to generate a positive voltage and discharges it in the opposite case.

The current to be supplied through the resistor 8 is necessary only when charging the capacitor of the capacitive load 13 to generate a positive voltage, not during the discharging period. That is, unlike the conventional method, it is not necessary to constantly supply a constant current to the PNP type output transistor 10.

In consideration of this, the present invention applies a voltage source 16 ( ₀ ) having a polarity opposite to that of the output terminal 12 to the base voltage of the PNP type output transistor 10 which controls the current, as described above. Is used to control the current and reduce the power loss of the PNP type output transistor 10.

(Effects) As described above, according to the present invention, the PNP type output transistor may have a smaller current capacity than conventional ones, which is inexpensive and compact.

In addition, the voltage of the opposite polarity to the above-mentioned output, in the differential output type amplifier such as the horizontal axis output stage of the oscilloscope,
The outputs of each polarity can be crossed and used.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIGS. 2 and 3 are conventional circuit diagrams. 1: Input terminal, 2,5,6,8,14,15: Resistor, 3,10,11: Transistor, 4,9: Capacitor, 7: Constant voltage source, 12: Output terminal, 13: Deflection plate Capacitor, 16: indicates a signal source ( ₀ ) having a polarity opposite to the output voltage E ₀ of the output terminal 12.

Claims (1)

[Scope of utility model registration request] 1. An output stage having an input end supplied with an input signal and an output end connected to a capacitive load, the output stage driving the capacitive load in response to an output signal of the input stage, and the output. A negative feedback circuit connected between the output terminal of the stage and the input terminal of the input stage, the output stage being an NPN transistor driven by the output signal of the input stage, and the collector being the collector of the NPN transistor. Connected to P
A first predetermined voltage is supplied to the NP transistor, a capacitor connected between the base of the PNP transistor and the base of the NPN transistor, and the emitter of the PNP transistor via a first resistor. At the same time, the negative feedback amplifier circuit is characterized in that the output signal of the input stage is applied to the base through the capacitor together with a signal having a polarity opposite to that of the output signal of the output stage.