SU1256188A1 - Pulse-width modulator - Google Patents

Abstract

The invention can be used in low frequency key amplifiers and switching power supplies. The purpose of the invention is to improve the accuracy of the pulse-width modulator conversion. The device contains a relay element 1, a key amplifier 2 and a low-pass filter 3. The introduction of the comparator 4, the integrator 5 and the amplitude limiter 6 eliminates the effect on the switching period of the modulator of changes in the parameters of the low pass filter 3 and the load. 2 Il. sl ts9 sl O5 00 cx

Description

The invention relates to a pulse technique and can be used in low frequency key amplifiers and pulsed power sources.

The aim of the invention is to improve the accuracy of the conversion of the pulse-width modulator by eliminating the effect on the switching period of the modulator of changes in the parameters of the low-pass filter and the load.

FIG. 1 is a functional diagram of a pulse width modulator; in fig. 2 - an example of the implementation of its elements.

The pulse width modulator contains a relay element 1, a key amplifier 2, a low-pass filter 3, comparator 4, an integrator 5, an amplitude limiter 6, and a comparator 4 is connected in series, an integrator 5, an amplitude limiter 6, a relay element 1, a key amplifier 2 and a low-pass filter 3, the output of which is connected to the output volume and the first input of the comparator 4, the second input of which is connected to the input bus.

Comparator 4 is designed to compare the input signal U and the feedback signal received at its input from the output of the low-pass filter 3, to form a pulse signal by comparison, and can be performed on a differential operational amplifier without feedback.

The integrat ()) 5 and the amplitude limiter b are used to convert the output pulses of the comparator 4 into trapezoidal voltages, the amplitude V of which, determined by the response threshold of the amplitude limiter 6, is somewhat greater than the half width A of the hysteresis loop of the relay element 1. Integra. 5 and the amplitude limiter 6 can be performed respectively on the RC circuit and opposite zener diodes.

Pulse width modulator operates as follows.

The input signal Um is fed to the input of the comparator 4, where it is compared with the feedback signal U ,,,, coming from the output of the low-pass filter 3. With respect to the times of the HCiiCTBa zero of the difference signal Up Uo, - UM, the comparator 2 switches, forming a sequence of rectangular pulses at the input of the integrator 5. The pulses are integrated by the integrator 5 and through the amplitude limiter b in the form of trapezoidal voltage are fed to the input of the relay element 1, at the output of which a sequence of pulses is formed, the fronts of which are delayed relative to the output pulses of the comparator

4 to a constant value TO. The magnitude of the delay TO is determined by the amplitude Eo of the output pulses of the comparator 4, the integration time constant r „of the RC circuit, and

also the value of D thresholds of operation of the relay element 1 and the amplitude limiter 6

(Y + A) t. Yo (1)

The output impulses of the relay element 1 are amplified in power by the key amplifier 2 and are fed to the input of the low-pass filter 3, which extracts useful low-frequency components of the pulse sequence at the load.

Since the formation of a pulse sequence in a pulse-width modulator is based on the condition that the difference between the input and output signals is equal to zero, the low-frequency components of the output signal generated by the low-pass filter almost completely reproduce the input signal of the device.

The duration of the impulse processes in the pulse-width modulator can be determined as follows.

Taking into account 80 that the low-frequency components of the output filter 3 of the lower frequencies and, accordingly, the feedback signal are equal to the input signal UM, the magnitude of the difference signal at the instants of switching the key amplifier IK and tl are determined by the relations

Up (tK) 4- (E + im); Up (tK) f- (E-UM),

Lcp

(2)

where TF is the time constant of filtering their frequencies.

At the same time, the switching period is as follows:

t o, u (b) tF, u (1k) tf I 2to + ((E + u.)

Where, taking into account (2), we obtain

4G T

; i-v «) (i + VM)

where is viak e

 The normalized value of the input signal. Thus, in a pulse-width modulator, the switching period remains constant when the parameters of the low-pass filter and the load change within wide limits. The introduction of additional blocks and links into the pulse-modulator modulator allows it to have a constant switching period when the low-pass filter and load parameters change over wide limits, which improves the conversion accuracy. This allows the use of a pulse-width modulator in low-frequency key amplifiers, since a change in the constant time of the low-pass filter does not lead to additional distortion of the output signal, as well as in pulsed power sources to stabilize their load characteristics.

Claims (1)

Invention Formula A pulse width modulator comprising a relay element connected in series, a key amplifier and a low-pass filter whose output is connected to the output bus, characterized by that, in order to improve the accuracy of the conversion, a comparator connected in series, an integrator and an amplitude limiter, the output of which is connected to the input of the relay element, are inserted into it, while the inputs of the comparator are connected to the input and output buses of the device. FIG. 2