SU760434A1 - Pulse-width modulator - Google Patents

Description

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The proposed pulse-width modulator is intended for use in automation systems for various purposes, for example, in electric drive control systems.

Known pulse width modulation trimmer ⁵ comprising forming a cascade circuit and negative feedback retarded [ΐ].

The disadvantages of this modulator are from -. inaccuracy of measurements near the zero level is carried, · the presence of a dead zone and the ability to measure only signals of positive polarity. - ¹ < ₅

Of the known pulse-width modulators, the closest to the invention in its technical essence is a modulator comprising a shaping stage made on a differential operational amplifier with positive feedback, a lagging negative feedback circuit consisting of resistors, a capacitor, and 2

go parallel to the diode capacitor, whose cathode is connected to the output of the operational amplifier, and the anode to the common bus.

However, the known device has several disadvantages. First, when the input signal is less than or equal to zero, a negative voltage is observed at the output of the modulator, which is determined by the voltage drop across the open diode, equal to ~ 1 V, which is a false signal for the rest of the automation system path. the input signal is positive polarity, less voltage release the driver, the modulation stops. This input signal determines the value of неч deadband, the presence of 'which reduces the sensitivity of the device. Thirdly, the operation of the circuit only from the input signals of positive polarity limits the range of application of this pulse-width modulator, in particular

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. It doesn’t allow it to be used in electric drive control systems.

The aim of the present invention is to increase the sensitivity and broaden the range of input signals of the latitude-but-pulse modulator.

This goal is achieved by the fact that in the pulse-width modulator containing the driver and the delayed negative feedback circuit, the connecting output and the first input of the driver, the second driver, the delaying negative feedback connection connecting the output and the first input of the second driver , inverter 15 And a summing node. ' The output of the first driver is connected through a communication circuit to the second input of the second driver, the output of the second driver is connected to the second input of the first driver through a communication circuit, the third input of the first driver is connected to the input terminal and through the inverter to the third input of the second driver, and exits

Shapes - with the inputs of the summing node, the output of which is connected to the output terminal.

FIG. 1 shows a block diagram of a modulator; in fig. 2, a, b, c - pulse sequences at the output of the first and second drivers and at the output of the modulator, respectively.

The pulse-width modulator is made according to a two-arm circuit containing identical shapers 1 and 2, each 35 of. which are made on a differential amplifier operating in a two-position symmetrical relay by hysteresis, identical negative feedback links 3 and 4, for example, on resistors, capacitors and two stabistors, identical cross-circuits 5 and 6 that serve to synchronize pulses the outputs of the formers, the inverter 7 on the operational amplifier, and the summing 45 ¹ node 8 on the differential operational amplifier. The output of the summing node 'I & l ^ ё'ts output modulator.

The modulator works as follows: ₅₀ ZOM. '

When power is applied to the circuit at the outputs of the formers 1 and 2, a pulsed signal arises, having the form of bipolar .synphase pulses of equal duration. In this case, the signal at the output of the device is zero. 'If there is a' signal • at the device input, the pulse duration at the outputs of the formers changes | The change in the pulse duration is proportional to the size of the input signal (Fig. 2a, b). At the output of the device, there is a sequence of width-modulated unipolar pulses, the duration of which is proportional to the magnitude of the input signal, and the polarity corresponds to the polarity of the input signal.

The implementation of the pulse-width modulator suggestedly eliminated the deadband, since the modulation does not stop when the input signal is equal to zero, and also get rid of the false signal at zero and expand the input signal range to the signal area of negative polarity. This increases the scope of application of the pulse-width modulator, in particular, makes it possible to use it in electric drive control systems.

Claims (1)

Claim· A pulse width modulator containing a driver and a lagging negative feedback circuit connecting the output and the first driver circuit, characterized in that, in order to increase the sensitivity and expansion of the input signal range, a second driver, a lagging negative feedback circuit, is inserted in it · the output and the first input of the second driver, the inverter and the summing node, the output of the first driver ', through the communication circuit connected to the second input of the second driver, the output of the second Through the communication circuit, the former driver is connected to the second input of the first driver, the third input of the first driver is connected to the input terminal nd via the inverter with the third input of the second driver, and the driver outputs are connected to the inputs of the summing node whose output is connected to the output terminal.