CS223982B2 - Low-frequency capacity amplifier - Google Patents

Abstract

1. Low-frequency power amplifier having a pulse modulator (10) which converts a low-frequency input signal into at least two phase-shifted pulse sequences (E1 , E2 ) with identical frequency and containing width-modulated pulses, and at least two switching stages (11, 13) which are controlled by the pulse sequences and the supply-voltage inputs (38, 39) of which are connected in parallel, and a low-pass filter (17) which follows the switching stages in the circuit and at the output of which the power-amplified low-frequency signal appears, characterised in that the phase shift between the pulse sequences (E1 , E2 ) is 180 degrees, and the outputs (44, 45) of the switching stages (11, 13) are electrically isolated from the supply-voltage inputs (38, 39) and are connected in series for the purpose of summing the output voltage.

Description

BACKGROUND OF THE INVENTION The present invention relates to a low frequency power amplifier, in particular as a modulator for a radio frequency high power stage, comprising a single input pulse modulator for an amplified analog low frequency input signal and at least two output lines for two 180 ° phase shifted pulse train of equal frequency and width modulated pulses. having at least two switching stages, the signal input of which is connected to one or the other of the pulse modulator output lines and whose output lines are galvanically isolated from the signal input and supply voltage lines and are connected to the input of at least one low-pass filter; the output is an amplified low frequency signal.

The high power low power amplifiers hitherto used are virtually all based on the same basic wiring. They contain a double-acting class V amplifier with at least two amplifier tubes and an output transformer. The amplified low-frequency signal is applied to the grids of the two tubes whose anodes are coupled They are connected with the terminals of the primary winding of the output transformer. One terminal of the secondary winding of the output transformer is grounded through the capacitor and the other terminal is connected to the load. The supply voltage for both low-frequency amplifier tubes is taken from the intermediate tap of the primary winding of the output transformer.

Low-frequency power amplifiers of this kind can be adapted to a wide variety of applications and can be sized for a wide range of output power, for example for driving large loudspeakers, inductive heating devices, control amplifiers and modulating amplifiers for radio transmitters. All designs have several major drawbacks for high performance. The double-acting amplifier of class V must be fitted with power tubes, which are expensive and have a relatively short life. These tubes have to be supplied with high voltage in amplifiers with high output power, which complicates the whole connection. The output transformer is a large and heavy building element whose weight can be about 6 t for a 300 kW modulator amplifier. Finally, the efficiency of a sine-wave modulated double-acting class V amplifier and subsequent load is modulation dependent and is at best 70%.

The principle of pulse width modulation, which has long been known, has advantages in terms of efficiency, but is associated with considerable design difficulties. *

One known solution described in German Pat. No. 1,218,557 is characterized in that a switching tube connected to the high potential between the high voltage rectifier and the load is driven into the control grid by pulse width modulated signals.

Also known is the radio transmitter solution described in Punktechnik, Volume 32, No. 13/1977, wherein the output stage high frequency vacuum tube is connected in series with a pulse width modulated switching tube, wherein the radio frequency terminal tube cathode is grounded for high frequency, however, it oscillates in the rhythm of the modulation frequency. Both of these solutions require complicated wiring and, moreover, have limited operational reliability because they contain tubes.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a simple and inexpensive low-frequency power amplifier which overcomes both the efficiency and cost disadvantages while eliminating the complexity of the pulse width modulation difficulties. The low frequency power amplifier is to be supplied with medium voltage, to have an overall high efficiency, independent of the degree of modulation, and to be implemented with power semiconductors instead of tubes.

This object is achieved according to the invention in that the inputs of the supply voltage of the switching stages are connected in parallel and connected to the same DC voltage source and the output lines of the switching stages are connected in series via a connecting line. in one output line of each switching stage and between the output line connections of adjacent switching stages, a rectifier.

Conversion of the low-frequency signal into pulses makes it possible to use suitable electronic switches with very short switching times instead of amplifier tubes, which improve the efficiency of the amplifier at the same output power. The cascading of the switching element outputs allows the power amplifier to be supplied with a low supply voltage, which simplifies and reduces the cost of the construction. In addition, the use of a plurality of switching stages connected in series or in series can provide a useful redundancy of the entire low frequency power amplifier so that its functional capability is not appreciably affected by failure of one of the stages.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a schematic diagram of a preferred embodiment of a low frequency power amplifier according to the invention; FIG. 2 shows a block diagram of a pulse modulator suitable for the amplifier of FIG. 1; FIG. for the power amplifier of FIG. 1, FIG. 4 is a schematic representation of the integrated low pass filter; FIG. 5 is a schematic representation of the output pulse train modulation by superposing two mutually offset input pulse train; pairs of input pulses.

In the drawings, corresponding elements are provided with the same reference numerals.

The low frequency power amplifier of FIG. 1 serves to power an amplitude modulated radio transmitter. Such power amplifiers are subject to particularly high demands in terms of frequency response and gain, so that the amplifier is particularly suitable for explaining the design and operation of the new amplifier.

The low frequency power amplifier comprises a pulse moodlator 40, several groups of switching stages paral connected in parallel. 12, 13, 14 and connecting conduit 15 which connects the outputs of the switch ^with EC ^H s'tu ^Pn of 11 and ^a Ц. ^are converted to lower vs.tu propuusi 12 * Switching stu ^p Ц them to H are supplied by voltage U. The output of the bottom 17 is connected with the load on the 13th

In the illustrated example, it is assumed that the load 18 is a high frequency output stage of an amplitude modulated transmitter.

Giant. 2 shows a block diagram of a suitable pulse modifier 10. The pulse modifier 10 comprises a pulse generator 20, the output of which is coupled to one input of the modulator 21 and to the input of at least one phase shifter 62. The output of the phase shifter 22 is connected to the input of another modulator 23. The second input of this modulator is connected to the input terminal 24 for the low-frequency signal. To the outputs of both models 21. 23, the signal line 26 is connected.

As will be described _podroObeti> may be advantageous pouuít pulse. ^ 0, which transmits more than two output signals. In this case, further phase shifters 22 are connected to the pulse generator 20 with the following meters 23 as indicated in broken lines in FIG.

Giant. 3 shows a block diagram of a switching stage, e.g. switching stage 11 suitable níztoí ^P ro ^ e ^ ENCN above ^the ones Amplifier ^{No. P} ccording to the invention. The switches S ^ u ^{t p Step 11} comprises ДО signal input 21 that is connected to one of the signal lines .26. 27 from pulse 10 and which is connected to a primary winding 32 of a control unit, for example a control transformer 21. The self-winding windings 11, 35 of the control transformer 33 are connected to the control electrode of at least one switching element 36. 37. Electrodes The switching elements 33 are connected to the positive busbar 38 and the negative busbar 39 of the power supply and to the primary winding 41 of the power transformer 42. The winding 43 of the power transformer 42 is connected to the output lines 44. 45.

^The pull-off degree ^of Ц ^Z 14 and further comprising two diodes 46. .47. are exercised as ^to the ^p Ojen ^y between the negative lead of the primary winding of the power transformer 42 and between the positive. the positive supply voltage busbar and the negative supply voltage busbar 39, and protect the switching elements 36 against surge voltages when power is interrupted.

According to a preferred embodiment, the step 11 to 14 comprises two control units, one of which transmits the switching pulses for the switching elements 36, 37 and the other transmits the switching pulse. Furthermore, instead of the two switching elements 33, 37 shown, two groups of parallel switching switches can be used. ^What elements allows increasing CONTRARY TO Prou ^{br d} prostheses jícího primary winding 41 of power transformer 42. As the switching elements are preferably used in a suitable power semiconductors elekronky or combinations thereof.

One output line 44 of each switching stage 11 to 11, FIG. 1 is connected directly and the other output line 45 via the rectifier 50 to the connection line 12. In addition, the connection line 15 between the connections of each pair of output lines 44 includes a further rectifier 51. rectifiers 22 »21 with power pulses of individual. The output lines 44, 45 on the connecting line 15 add up and are fed to the inlet 53 of the low pass filter 73.

The connection of the low pass filter 17 need not necessarily be formed according to FIG. 1. Another possible solution consists in that the lowpass filter 17 is entirely or partially integrated into the outlet conduit 44. 45 degrees with ^p inac ^{ORLEANS 11} and ^a £ 4, ^p with ^p řípadně to ojovacích ^d in measurement Ц. Possible measurement ^{of width} e 'shown in Fig. 4.

In operation of the described low frequency power amplifier, the applied low frequency output signal is converted into at least two pulse sequences consisting of 2 pulse width modulated pulses of the same repetition rate, which are phase shifted halfway between two successive pulses, which will be described in more detail below. These pulse sequences are amplified separately in the respective switching stages 11 to 14 and then fed to a common connection line 12, which is galvanically separated from the supply voltage. The output pulse train formed from the two superimposed input pulse train is then converted in the low pass 17 into a power amplified low frequency signal that corresponds to the original low frequency signal.

When constructing a new low-frequency power amplifier, it should be assumed that the switching frequency of conventional switching elements is limited and that the pulse alternating current is about 1: 1 or a 50 percent moovusac due to the over-agglomeration of the power transformer.

To improve the pulse train duty cycle, resp. modulation of the output pulse train is used two herring vstupníc ^h of phase shifted pulse ^of about ¹⁸ 0 ^o, j and ^k utozuje schemaaicky FIG. 5. The two sequences of input pulses E and EG ®ají suntan same frequency and are phase shifted by ^{about 18} 0. ^SIR ka solid pulse znázortoná ^No Arami ^d of ^d tells á mmáduaci ^12, 5 percent toika dashed lines mod ^ ation 50 percent sequence of input pulses. As shown in FIG. 5, a supeepozzcí these two sequences of input sequence of output pulses A, G, which are practicing promodulovány to ¹⁰⁰ percent, where a and ^b SLE ^dy ^ i IMPP vstupntoh modulated to 50 percent. ,

To generate the disclosed sequences of input pulses serving pulsed odue ^ m ^ 1, or 10 depicted in FIG. 2. The pulse 20 produced genneátor triangular pulse train whose frequency is a thread, not ^of the highest ^Yss the switching Toit ^ t switching stu ^p n ^{s 11} and ^ž Ь4. ^{They also} MPulse ^y in mooduátoru 21 superponuuí nízkofeekvenčním the signal at input terminal 24th CD-OHT arise width modulated pulses which are fed to a signal line 26. Triangular pulses produced by the pulse generator 20 is also fed into eoinuvače stage 22, which pulse ^y ^ inches by ¹⁸ ° ⁰ not oH ^ o ^ loviční temporal distance between two impulses. Fézov ^of shifted, the sequence of pulses in a subsequent m ^ o ^ ^ tror DUT 23 also mo01užujz nízкnfeeкvenčuía signal, thereby providing width modulated pulses fed to a signal line 27th

It is said that different types of pulse modifiers can be used and that the pulse moohulator 10 need not be formed in the embodiment shown in FIG. 2. the generation of which senses a low-frequency signal. The following log-Kem circuit is then ^{characterized} tvářeZí width modulated pulses. The amplitude of the low frequency signal. Such techniques and devices are known to those skilled in the art, so there is no need to describe them in detail.

As already stated, the frequency of the input pulse sequence to each signal management especially limited maai 26 and ²⁷ ^ the switching frequency of the switching ^P-hundred Nu 11 and ^a Ц. ^{As a} foregone ^dk in this vznitoe with SLE ^Importan toožKí two input pulses, ^{the phage} ZOV ^e ^ sunutých 180 ° sk ^ output pulses at twice the frequency opakovaaí. In order to generate higher pulse train sequences, for example twice the frequency, two of the two above described pulse train sequences can be used, which are phase-shifted inuaarally, as shown in FIG. 6.

The upper Cass FIG. 6 shows the described sequence of input pulses E, Eg and phase-shifted by ^{about 18} 0, as stiředí Cass daltons dojtoe íípu1s sequence ^of E ^ and Ед. Ba rallies ° pulse E ^ E ^ ^p are vzéijemto osunuty also ^{Ez 18} 0 ^o ^ and ^ are the i th Pushing ojpooí sequences of pulses ^ ve úvojice ⁹ 0 ^{o tolyl-u} E ^j s1z against SLE ^d u E ^j. and col.e ^d E ^ to the sequence Eg. Superposition Tocht ^Four high input pulse sequences gives the sequence of output pulse A; _{24, with a} four-byte frequency of a single input sequence ^, optionally at 50% aonds, of an output pulse train consisting of two superimposed pulse train patterns, which are modulated. almost 100 percent.

To generate such pulse train sequences, the pulse generator 10 of FIG. 2 includes two additional phase shifters 22 with a subsequent modulator 23 as indicated by the dotted line.

It is understood that the repetition frequency sequence of output pulses can be further increased if produced nappíklad four straight ^ <3e ^^ r ^ é sequences of input pulses "which are described oprooi ga sequences of IC ^ ⁰ im ^p ULS-shot ^{in the fa p} osunut ^Y 45 ° and d ^ ·

OF ' .

Each sequence im ^p ulsů is assigned at least one switching stage 11 to 14 incoming pulses actuate the switching elements 36, 37 a'případně other ,, so that the primary winding 41 of power transformer 42 is excited by a pulse width and · outlet conduit 44, 2 and possibly others, power amplified pulses appear which are galvanically separated from the supply voltage. As already mentioned, a plurality of switching elements 36, 37 can be connected in parallel to increase the power gain in each switching stage 11 to 14, and a plurality of switching stages 11 to 14 can also be connected in parallel. which power amplified pulses

Low-frequency power amplifier according to the invention allows using · described modulation sequence of input pulses, which are aligned along UvopicícO and phase-shifted by? O ⁰ mo ^ Lovat SLE ^d výsW ^ ic ⁰ pulse ^u ^ akticty ¹ 00 ^ ocent and ^ Uzzi vešito ^p vinegars such Uvooíc sequence of input pulses to increase the frequency of tanning sequence of output pulses at several times the repetition rate of each sequence of input pulses,

In a practically tried and tested embodiment, the low frequency power amplifier of the present invention serves to power an anpitude modulated low frequency radio transmitter in the conventional range of audio frequencies with a peak power of more than 1 MW. In order to obtain sufficient transmission quality, the low-frequency signal is in this case polished, as shown in FIG. 6, into two pairs of mutually offset input pulse sequences,

Claims (6)

1, a low frequency power amplifier, in particular as a pulse generator for the radio frequency power stage of a radio transmitter, comprising a single pulse signal board with a single input for an amplified analog low frequency input signal and at least two output lines for two 180 ° phase shifted pulse train of equal frequency and width modulated pulses , with at least two switching stages, the signal input of which is connected to one or the other of the pulse generator output line and whose output lines are galvanically separated from the signal input lines and the supply voltage input lines and are connected to the input of at least one lower irp. j ^ ejj ^ MŽ output the amplified low frequency ^ gnál, characterized ^ bore formed with a tip ^that ga ^py (38, 39) supply overvoltages ^ spínacíc ^h growth ^ s (Π to 14) are connected in parallel and are connected to steným direct current napěěí (U) and output line ^(44, 45), switching-growth ^ s ⁽¹¹ and ^{Z 14)} are connected in series irρst ^of e ^u nictvíp connecting line (15), wherein for seůčtání α ^ ί · ^ output signals along the connecting line (15) they are connected in one output line (44 to 45) of each switching stage (11 to 14) between the terminals of the output lines of adjacent switching stages, · rectifiers (50 and 51, respectively), 2. The low-frequency power amplifier according to item 1, characterized by: characterized in that each switching stage (11 to 14) comprises a transformer (42), the primary winding (41) of which is connected via at least one switching element (36) to the supply voltage line (38, 39) and the secondary winding (43) with an output line (44, 45) and a control unit consisting of a control terminal (33), the primary part of which is connected to the respective output (26) of the pulse generator (10) and for which at least one output (22) 34) is connected to the control electrics of at least one switching element (36, 37), 3. The low-frequency power amplifier according to claim 2, wherein the primary winding (41) of the power transformer (42) is connected from both sides via a switching element (36, 37) to the supply voltage inputs (38, 39) and a control unit formed. the control transformer (33) has two seloindrical windings (34, 35), each of which is connected to a control electrode of one of the two switching elements (36, 37). 4. The low-frequency power amplifier according to claim 3, characterized in that the switching elements (36, 37) are formed by power semi-rotors. or their co-ordinations. 5. The low-frequency power amplifier according to claim 1, characterized in that the connection line (15) is connected to the input of the lower propussion (17). Sixth audio power amplifier according to claim 1 · ^ i ^ significance in that each switching stage (11 and ^{1 4)} with its output connected to the low-pass down outpu ^Py · ^^ pass! they are connected together to form the sum of the output voltages.