GB2241621A

GB2241621A - Amplifier with linear power output to reactive load

Info

Publication number: GB2241621A
Application number: GB9004087A
Authority: GB
Inventors: Alan Geoffrey Pateman; Peter John Farkas
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-02-23
Filing date: 1990-02-23
Publication date: 1991-09-04
Anticipated expiration: 2010-02-23
Also published as: GB2241621B; GB9004087D0

Abstract

An amplifier which drives reactive loads and in particular loudspeakers in a more efficient and effectively linear manner than previous amplifiers. An amplifier which does not clip the voltage output under conditions of normal drive or over drive from the input signal. (see fig. 9). From this amplifier an output current proportional to the input signal is produced across the load and the output voltage is seen as a result of the load's impedance and emf. This voltage being available for feedback against the incoming signal; thus scaling the output current with respect to the impedance and emf of the load. This enables linear power driving of electrically and electromechanically reactive and or linear loads. (see fig.7). An amplifier where the damping current flowing through both the devices is inversely proportional to the output current drive and that maximum damping is provided in the static position where the output impedance equals the load impedance for maximum power transfer from this position. (see fig. 8). <IMAGE>

Description

A NEW METHOD OF AMPLIFICATION This Invention is a new method of Amplification.

The following graphs and circuit drawings are used to show the reason and operation of this invention and the example circuit described: Figure 1 shows a block diagram of the amplifier when used as compressor or limiter.

Figure 2 shows the method of operation for the example amplifier.

Figure 3 is the circuit for the example amplifier.

Figure 4 is a graph showing the relationship of voltage current and power output with respect to changing load impedance of a class B amplifier.

Figure 5 is a graph showing the relationship of voltage current and power output with respect to changing load impedance of a class A amplifier at full drive.

Figure 6 is a graph showing the relationship of voltage current and power output with respect to changing load impedance of the new method of amplification without feedback.

Figure 7 is a graph showing the relationship of voltage current and power output with respect to changing load impedance of the new method of amplification with feedback.

Figure 8 is a graph showing the damping,driving and resultant output of this method of amplification.

Figure 9 shows the input signal and the resultant output waveform for this method of amplification under conditions of over drive.

This amplifier is designed to drive reactive loads and in particular loudspeakers in a more efficient and effectivly linear manner than previous amplifiers.It is an amplifier which does not clip the voltage output under conditions of normal drive or over drive from the input signal.(See fig.9).

Whereas in previous amplifiers an output voltage which is proportional to the input signal is produced across the load and current is provided to the load by a variety of means.Thus the voltage gain is normally fixed or preset.The power transfer characteristics of these amplifiers are not stable with a change cf load impedance or emf.Fig.4 and Fig.5 show class B and class A amplifier's transfer characteristics respectively.

From this amplifier an output current proportional to the input signal is produced across the load and the output voltage is seen as a result of the loads impedance and emf.This voltage being available for feedback against the incoming signal;thus scaling the output current with respect to the load impedance and emf from the load.This enables linear power driving of electrically and mechanically reactive and or linear loads. (see fig.7).

In this amplifier the ratio or gain of the output current to the input signal is fixed or preset at the nominal load impedance by setting the static device current and the feedback ratio if used.

Below you will find an example Amplifier which works by the method described: Fig.2 shows the method of operation for the example amplifier.The two devices shown are P and N mosfets.The input signal is applied to the gates of the devices.The output is formed by the drains of the devices.DC potentials are applied to the sources of the devices.VB+ and VB- are bias voltages to the gates of the devices which set the static current flowing through the devices.Negative feedback is supplied from the output to the gates of the devices.The amount of negative feedback being adjusted by RX.Thereby setting the slope of the output power relative to the change of impedance of the load. Fig.6 and fig.7 show the transfer characteristics without and with feedback repectively.

For a 30W Amplifer with a 7.5 ohn nominal load.

z=7.5 ohms.

Voltage supply for each device equals ( 2 Mult Z )Mult square root( W Div Z ).=15V Static current setting for each device equals ( square root( W Mult Z ) Div ( 2 Mult Z ).=1A Because amplifier output impedance=nominal load impedance for most efficient power transfer from the static position.

Fig 3 shows the circuit for the example amplifier.The resistors R1.R2.R3 and R4 bias the gates of Mosfets to enable their source to drain current to be set at 1A.

Resistor R7 controls the amount of feedback required.Resistors R5 and R6 couple the incoming signal voltage and enable correct operation of the feedback.The input sensitivity was found to be in the region of 3 volts peak to peak for full output drive.The input impedance was approximately 10000 ohms.

The mathematics above worked for the example circuit shown.

Terms: Z=load impedance. R=resistor.

I=A=current. V=voltage.

W=watts=power. emf=electro motive force.

Mult=multiply. Div=divide.

Load=Both resistive and reactive components connected to the output.

Transformerless Amplifier=An amplifier not requiring a transformer on the output or in the signal path to enable correct operation.

Damping current=Current flowing across the end cf but not through the load.

Loudspeakers=Transducers which convert electrical energy into air vibration or vibration of other gases liquids or solids and in particular electromagnetic transducers.

Diaphram=Part of loudspeaker which causes air vibration Previcus Amplifiers=Class A, class B or any other amplifier where the output voltage is proportional to the input signal.

Device=Electrical components which drive the current directly to the load.

Static=Amplifier with no input signal present.

Claims

Claims:

1) A transformerless output amplifier which by supplying an outsut current to the load which is proportional to an input signal but where the reflected voltage from irpeilance and emf developed across the load are floating.:thus current and voltage developed in the load are in phase.

2) By feeding back a proportion of the resultant voltage and emf develcped across the load,in antiphase with respect to the input signal:output current scaling proportional to the load impedance is realised:thus causing power drive to the load when: Where Z=Z Mult 2 I=I Div square root 2 and V=V Mult square root 2 (See fig.7).

3) A transformerless output amplifier where the static position output impedance equals the nominal load impedance for the most efficient power transfer from the static position.

4) A transformerless output amplifier where the damping current flowing through both the devices is inversely proportional to the resultant current output (see fig.8) and that maximum damping is provided in the static position and that minimum damping is provided at maximum positive and negative peak drive levels.

5) An Amplifier which when connected to loudspeakers causes the loudspeakers to reproduce a more accurate and efficient air vibration mcdel cf the input signal with less diaphram movement than was achieved using previous amplifiers.In the practice it has been found that when using a ccmposite musical signal through this amplifier the diaphrams of the driven loudspeakers vibrate in the audio range without moving backwards and forwards outside this range.Study of loudspeakers connected to previous amplifiers under similar conditions show large subsonic diaphram movements for the same apparant scund level thereby loosing sound efficiency and creating distortion as a result of higher powers being required for the same average sound level.

6) An amplifier which by driving the load with power exhibits no voltage clipping on the output under conditions of normal drive or over drive from the input signal.Under conditions of overdrive this forms the basis of a realtime compressor or limiter.Fig.l is the block diagram and fig.9 shows the input signal and resultant output waveform under conditions of over drive.

Cle@m@ 7@ A transformerless amplifier where the @olta@e gain is proportional to the impedance of the load connected to the output.

8) The Me@hod of amplification and its embodiment in the example shown.