SU752778A1 - Digital pulse-width modulator - Google Patents

Description

The invention relates to a pulse technique and can be used in frequency-pulse control systems, in particular in fuel metering systems of gas turbine engines. Known digital pulse-width modulator with a frequency-pulse input signal, with 6 holding the reference frequency generator / frequency dividers, reversible counter, digital parametrs, synchronization blocks, keys, trigger l. The specified pulse width modulator has insufficient conversion accuracy. Also known is a digital pulse-width modulator containing a reference frequency generator, a counter (frequency divider), a reversing counter connected to the reference frequency generator, a digital synchronizer connected to the code outputs of a frequency divider and a reversible counter, an output trigger connected to the outputs of the frequency divider and digital comparator, the first and second elements And connected to the code output of the reversible counter, cxeNuJ prohibition, connected to the elements And and the inputs of the reversible counter and block and synchronization are connected to the inputs of the modulator, and reference frequency generator 2. This circuitry prohibition modulator, as well as the previous one, has insufficient accuracy of conversion signal. The reason for causing a reduction in the accuracy of the signal conversion is the lack of an anti-intrusion protection device at the input of a reversible counter of alternating pulses. The alternating pulses, arriving at the inputs of the reversible counter, cause an oscillatory process at the most low bits of the counter. Switching interference from the lower bits of the counter penetrates through a digital comparator at the modulator output and reduces the accuracy of the pulse-width conversion. In addition, in connection with the inertia of actuators controlled by the modulator, the real range of operation of the modulator is reduced. The purpose of the invention is to improve the accuracy and the clearing of the range of operation of the auditor.

The goal is achieved in that a digital pulse-width modulator containing a reference frequency generator, a frequency divider connected by a counting input to the output of the reference frequency generator, a reversible counter, the first and second elements I, whose inputs are connected to the corresponding code outputs of the reversible counter digital a comparator, the corresponding inputs of which are connected to the outputs of the reversible counter and frequency divider, and the output trigger, the corresponding inputs of which are connected to the outputs of the time divider The digital frequency comparator and the memory block are entered, the frequency subtractor inputs are connected to the input terminals of the modulator, and the outputs are connected to the reversible counter inputs, the memory block inputs are connected to the corresponding outputs of the first and second elements and the reversible counter installation inputs.

The drawing shows a block diagram of the modulator.

The modulator contains a frequency subtractor 1, And 2, 3 multi-input elements, a memory block made on trigger 4, a reversible counter 5, a digital comparator b, a frequency divider 7, a frequency generator 8, an output trigger 9.

The modulator operates as follows.

 In the initial state, the reversible counter 5 is preliminarily set to the first smallest value exceeding the trigger threshold of the element 2, trigger 4 to the zero position and trigger 9 to the single position. The frequency divider 7. filled with pulses of the reference frequency of the generator 8 generates a time code scan. When equality of the codes of the reversible counter 5 and frequency divider 7 is reached, a pulse is generated at the output of the digital comparator 6, which sets the trigger 9 to zero position. The trigger generates a pulse of a certain duty ratio. At the completion of the sweep of the code at the output of the frequency divider 7, a pulse is formed that sets the trigger 9 to one state, thus completing the cycle of operation of the frequency divider.

The pulse shaping pulse with the minimum duty ratio is violated with the arrival at the input of a reverse pulse counter of the difference frequency. The accumulation of pulses on the counter changes the code at its output, and with it the duty cycle of the PWM signal at the output of the trigger 9,

When the reversible counter code reaches the value corresponding to the maximum permissible width of the ShIM signal, the And 3 element is triggered. An impulse formed by the And 3 element sets the reversible counter 5 back to the initial minimum value and the trigger 4 to the single value.

A trigger 4 connected to the actuator changes the adjustable parameter in a jump-like manner and stores this change so as to compensate for its change caused by a change in the meter setting. When regulating, for example, fuel consumption, the trigger 4 includes an additional metering valve, the flow rate through which corresponds to the fuel consumption at the maximum duty cycle of the PWM signal generated by the trigger 9 o

As a result of such switching of the counter 5 and trigger 4, the overall signal duty cycle does not change, and the range of its possible change is significantly expanded.

The appearance at the input of a reverse pulse counter of a difference frequency of another sign is accompanied by a decrease in the signal's duty cycle. When the counter reaches the code value equal to the lower limit, at the output of the element 2, an impulse is formed that sets the counter 5 to the maximum position, less than the threshold of the element IZ, and the trigger 4 to the zero position. As a result of this to the ommutation of the counter 5 and the trigger 4, the SRM-signal is generated only at the output of the trigger 9.

Thus, by introducing the frequency subtractor and the trigger and connecting the outputs of the elements to the trigger and the installation inputs of the reversible counter, the conversion accuracy is increased and the working range of variation of the duty cycle is expanded.

Claims (2)

1. Author's certificate of the USSR 549886, H 03 K 7/08, 22.15,75. 2. USSR author's certificate  544124, H 03 K 7/08, 01/26/76 (type).