RU21097U1 - WIDTH-PULSE MODULATOR - Google Patents

Abstract

A pulse-width modulator containing a power source, a control element, the first output of which is connected to the first output of the power source, and the second output to the first output of the limiting resistor, the current source of the controlled circuit, the first and second conclusions of which are connected respectively to the first and second terminals of the resistor current sensor, CMOS chip containing more than two inverters, the first power output of which is connected to the first output of the power source, and the second output of the power to the second output of the power source , the output of the first inverter is connected to the input of the second inverter, the output of which is the output of a pulse-width modulator, a frequency-setting capacitor connected between the input of the first inverter and the output of the second inverter, a frequency-setting resistor connected between the input and output of the first inverter, characterized in that, for the purpose increasing the temperature stability of the output parameters, the maximum operating frequency, expanding the area of operation stability and increasing the functionality of the pulse-width module a torus, a third inverter is introduced into it, a diode whose anode is connected to the input of the first inverter, and a cathode is connected to the output of the third inverter, the input of which is connected to the first output of the resistor current sensor, the second output of which is connected to the first output of the limiting resistor, the second output of which is connected to the second output of the power source.

Description

Pulse Width Modulator.

The utility model relates to electrical engineering and can be used in the construction of control devices for switching power supplies.

A pulse-width modulator (PWM) is known, comprising a linearly varying voltage generator, a feedback signal amplifier, a current protection comparator, and a pulse-width modulated signal comparator 1, 2. PWM is used in the construction of control devices for switching power supplies to generate power switch control signals.

The disadvantages of this technical solution include its implementation on analog functional units (amplifiers, comparators), which, regardless of the operating mode, continuously consume current. As a result, the entire PWM node consumes relatively high current (tens of milliamps). This reduces the overall efficiency of the power supply using the specified PWM, complicates it, forcing to introduce an additional low-voltage channel specifically for powering the PWM. If, in addition, the modulator operates at a high frequency (hundreds of kilohertz), the above-mentioned functional units are executed on bipolar, 1x transistors, which increases energy consumption even more. With a decrease in the load at the output of the power source or at idle, the voltage of the power channel of such a PWM decreases to values that impede the normal operation of the power source as a whole. These shortcomings narrow the functionality and the area of applicability of the considered technical solutions. power supply, given in 3. Its functional diagram is shown.

in FIG. 1. The pulse-width modulator contains a power source, a control element, the first output of which is connected to the first output of the power source, and the second output to the first output of the limiting resistor, the second output of which is connected to the first output of the summing resistor, the second output of which is connected to the first outputs the current source of the controlled circuit and a resistor current sensor, the second terminals of which are connected to the second terminal of the power source. A CMOS chip containing more than two inverters, the first power of which is connected to the first output of the power source, and the second power output to the second output of the power source, the output of the first inverter is connected to the input of the second inverter, the output of which is the PWM output, a frequency setting capacitor connected between the input of the first inverter and the output of the second inverter, a frequency resistor connected between the input and output of the first inverter and a transistor, the first electrode of which is connected to the input of the first inverter, second electrode - to the second terminal of the power source and the control electrode - to the first output of the summing resistor.

In the PWM functional diagram shown in 3, the regulating element is made on a phototransistor VT2 optocoupler with resistor R8. the limiting resistor is resistor R5, the transistor is transistor VT1, the summing resistor is resistor R6, the current source of the controlled circuit is made on current transformer TA1 and diode VD3, and the resistor current sensor is resistor R7. The role of the frequency-setting capacitor and resistor is performed by the SZ and R4 elements, respectively. and the first and second inverters - inverters D1 and D2, respectively. It is powered by PWM energy accumulated in capacitor C1, which, in turn, is charged from an external energy source through resistor R2. Moryi microcircuit inverters that are not involved in the work of the PWM circuit are connected in parallel to the second inverter to power the output

the entire block (not shown in FIG. 1).

Common features of the proposed technical solution and prototype are a power source, a control element, the first output of which is connected to the first output of the power source, and the second output to the first output of the limiting resistor, the current source of the controlled circuit, the first and second conclusions of which are connected respectively to the first and second the findings of the resistor current sensor. A CMOS chip containing more than two inverters, the first power input of which is connected to the first output of the power source, and the second power output to the second output of the power source, the output of the first inverter is connected to the input of the second inverter, the output of which is the output of a pulse-width modulator, frequency setting a capacitor connected between the input of the first inverter and the output of the second inverter, a frequency-setting resistor connected between the input and output of the first inverter.

At the first and second inverters, a square-wave driving oscillator was made, the initial pulse duration and pause of which is determined by the values of the frequency-setting resistor and capacitor. The timing diagram of the voltage at the output of the master oscillator, the output of which is the PWM output, is shown in FIG. 2a. The current source of the monitored circuit measures the instantaneous current value in the power switch circuit. The instantaneous voltage value across the resistor current sensor is proportional to the value of the indicated current and is shown in FIG. 26. During a single state at the PWM output, the power switch is turned off, the current in the monitored circuit increases, during the zero state at the PWM output, the power switch is closed, and there is no current in the monitored cegn1. The maximum current value in the controlled circuit K.k corresponds to a voltage on the resistor current sensor, equal to the voltage "base-emitter of an open transistor UOSOTKP 0.7 Volts.

Ucm

3 Regulation is as follows. When turned on

first, the PWM generates pulses of maximum duration, and the voltage on the resistor current sensor increases, remaining less than the opening voltage of the transistor UajoTKp (pigv). There is no feedback signal. The resistance of the control element is extremely high. If during the next working cycle the above value Uo, 01 kr 0.7 Volt is reached, the transistor will open, and at the PWM output 6} det, the zero state is forced. The power switch will close, which will protect it from overcurrent. When the adjustable parameter is PWM. for example, the output voltage of a switching power supply will reach its nominal value, a feedback signal will appear, the resistance of the control element will decrease, and the current flowing through it will create a constant bias based on the transistor. Since the limit value of the voltage based on the Ube open transistor could not exceed 0.7 Volts, the amplitude of the pulse component of the voltage — the voltage drop across the resistor current sensor — should decrease. And this, in turn, can be achieved only by reducing the pulse duration at the PWM output. Thus, by varying the degree of conductivity of the regulating element, it is possible, within wide limits, to change the duration of the PWM output pulse.

The disadvantages of the technical solution under consideration include the temperature dependence of the maximum current in the controlled circuit K ,,,,,, .. It is due to the fact that the ibe voltage drifts when the temperature changes at a speed of about -2.2 mV / ° C. When the temperature of the PWM is changed from -60 ° С to +100 ° С, this change will be approximately 50%. The value of the maximum current in the controlled penny will change as many times.

Another important drawback of this technical solution is that to reduce the current consumed by the PWM from the power source, the transistor must operate in low current mode. However, at the same time

UOW (

4 increases the time of its closing, because the absorption of excess charge in

areas of the base and collector occurs precisely by current. This feature does not allow reducing the minimum duration of the PWM output pulse to less than a certain value (for the device in question, it is about 2 microseconds). This limits the maximum frequency of PWM operation, worsens its dynamic characteristics at short output pulse durations, i.e., narrows its functional capabilities.

Another drawback of this PWM is the following. The pulse component of the voltage based on the transistor Uc ,, m, coming from a resistor current sensor, is determined from the expression:

Uo. imp Up. ,, (Rorp + Rpcr) / (Rv + RO, -P + Rpcr), where

Up; ,, - voltage on the resistor current sensor;

Rv is the resistance of the summing resistor;

Ro, p is the resistance of the limiting resistor;

Rpe, is the resistance of the regulating element;

With an increase in the feedback signal, the degree of opening of the regulatory element increases, i.e., its resistance decreases. In this case, the constant bias at the base of the transistor increases and the amplitude of the pulse component allocated to the resistor current sensor decreases. However, as follows from the above expression, the amplitude and steepness of the linearly increasing part of the pulse component based on the transistor decrease even more. This, in turn, reduces the stability during operation in the short output pulse mode and the maximum frequency of operation, increases the likelihood of excitation of the entire unit as a whole.

The technical task of the proposed utility model is to increase the temperature stability of the output parameters, the maximum operating frequency, expanding the area of stable operation and increasing the functionality of PWM.

5

The stated technical problem is solved by the fact that a PWM is proposed that contains a power source, a control element, the first terminal of which is connected to the first terminal of the power source, and the second terminal is connected to the first terminal of the limiting resistor, the current source of the controlled circuit, the first and second terminals of which are connected respectively to the first and second terminals of the resistor current sensor, a CMOS chip containing more than two inverters, the first power output of which is connected to the first output of the power source, and the second power output - with the second output of the power source, the output of the first inverter is connected to the input of the second inverter, the output of which is the output of a pulse-width modulator, a frequency-setting capacitor connected between the input of the first inverter and the output of the second inverter, a frequency-setting resistor connected between the input and output of the first inverter, a third inverter and a diode are introduced into it, moreover, its anode is connected to the input of the first inverter, and the cathode is connected to the output of the third inverter, the input of which is connected to the first output of the resistor yes snip current, a second terminal of which is connected to a first terminal limiting resistor, a second terminal of which is connected to the second terminal of the power source.

The introduction of additional elements and new non-obvious connections into the devices made it possible to eliminate the temperature 3aBHCHNmcTb of the output parameters and expand the area of stable PWM operation. increase the maximum operating frequency, which extends its functionality.

The applicant did not find technical solutions having similar features with features that distinguish the claimed solution from the prototype, and, therefore, the proposed technical solution has significant differences. 6

typical installation operations using standard equipment and does not require adjustment, which is especially important for serial production. Therefore, the proposed device meets the criterion of industrial applicability.

In FIG. 3 shows a functional diagram of the proposed PWM.

The proposed pulse-width modulator contains a power supply 1, a regulating element 2, a limiting resistor 3, a current source of a controlled circuit 4, a resistor current sensor 5, a frequency-setting capacitor 6 and a resistor 7, a diode 8, and a CMOS chip 9 containing more than two inverters I1 - Ip.

In the proposed PWM, the first power output of the microcircuit 9 is connected to the first terminals of the regulating element 2 and the power source 1. The second power output of the microcircuit 9 is connected to the second BbiBOzia ui of the limiting resistor 3 and the power source 1. The second input of the regulating element 2 is connected to the first output of the limiting resistor 3 and the second conclusions of the current source of the controlled circuit 4 and the resistor current sensor 5, the first conclusions of which are connected to the input of the third inverter FROM. The output of the third inverter FROM is connected to the cathode of the diode 8, the anode of which is connected to the input of the first inverter And K the output of which is connected to the input of the second inverter And2, the output of which is the PWM output. Frequency-setting capacitor 6 is connected between the input of the first inverter I1 and the output of the second inverter I2. Frequency control resistor 7 is connected between the input and output of the first inverter I1.

As a regulatory element 2, as in the prototype, some element can be used that changes its resistance, for example, a phototransistor or optocoupler photodiode, magnetodod, etc. The current source of the controlled circuit 4 can be, for example, a current transformer, primary whose winding is included in the protected power circuit.

when turned on, there is no feedback signal, the regulating element 2 is closed, the voltage at the limiting resistor 3 is almost 0. At the PWM output, rectangular pulses of maximum duration are generated, as in the prototype (Fig. 2a). A timing diagram of the current of the monitored circuit (or voltage across the resistor current sensor 5) is shown in FIG. The difference is that the maximum current value corresponds to the voltage on the resistor current sensor not Ube open J Volt, as in the prototype, but the threshold voltage of the microcircuit. When the instantaneous value of the indicated voltage reaches the threshold value (for CMOS chips this value is 0.4 ... 0.5 of their supply voltage), the inverter output FROM, and after it the PWM output, the state is set to logical O, thereby limiting the increase current in a controlled circuit. However, since the threshold of CMOS microcircuits is practically independent of temperature 4, the proposed PWM retained the value of the maximum current in the controlled circuit over the entire range of operating temperatures, which distinguishes it from the prototype.

Since the input resistance of the CMOS inverter is extremely large (1 ° ... 1 ° Ohm), the instantaneous voltage value at the input of the inverter FROM is equal to the sum of the voltage drop across the limiting resistor 3 and the resistor current sensor 5:

When the resistance of the regulating element 2 changes during the operation of the PWM at the input of the third inverter, the constant bias and ,,, p. However, the amplitude and steepness of the linearly increasing portion of the pulse component Upai, as follows from the expression, does not depend on the values or resistance of the regulating element 2. This means that the proposed PWM has stable stability, independent of the duration of the output pulse, which extends its functionality .

UBX from Warp + Upj.,.

significantly less than that of a bipolar transistor in microcurrent mode, the minimum duration of the output pulse of the proposed PWM is much shorter than that of the prototype. The tested PWM sample has a minimum output pulse duration of approximately 0.5 microseconds. which is 4 times less than that of the prototype. This allows you to significantly increase the maximum operating frequency, or with the same value of the frequency to obtain four times shorter duration of the output pulse, which extends the functionality of the device. Moreover, the consumed 1 PWM current remains at the same level as that of the prototype.

In addition, since the KMO 1 microcircuit that has been produced since now always contains more than three inverters (up to six), the electrical circuit of the proposed PWM is still implemented on a single microcircuit, but compared to the prototype, the transistor and summing resistor Rv are excluded, which reduces the overall the number of elements and simplifies the proposed device.

Sources used when writing an application.

1. Integrated microcircuits: Microcircuits for switching power supplies and their application. - M. DODEKA, 1997, 224 p. - 1SSN-587835-0010-6. from. 38.

2. Integrated circuits: Integrated circuits for switching power supplies and their application. - M. DODEKA, 1997, 224 p. - ISSN-587835-0010-6. from. 87.

3.A. A. Mironov. Experience in developing a control circuit for DC power modules. Scientific and Technical Collection “Power Supply. Vol. 3, p. 76-79.- M., 2001

4. Zeldin E. A. Digital integrated circuits in information-measuring equipment. - L .: Energoatomizdat. Leningrad Department, 1986.- p. 77.

Claims (1)

A pulse-width modulator containing a power source, a control element, the first output of which is connected to the first output of the power source, and the second output to the first output of the limiting resistor, the current source of the controlled circuit, the first and second conclusions of which are connected respectively to the first and second terminals of the resistor current sensor, CMOS chip containing more than two inverters, the first power output of which is connected to the first output of the power source, and the second output of the power to the second output of the power source , the output of the first inverter is connected to the input of the second inverter, the output of which is the output of a pulse-width modulator, a frequency-setting capacitor connected between the input of the first inverter and the output of the second inverter, a frequency-setting resistor connected between the input and output of the first inverter, characterized in that, for the purpose increasing the temperature stability of the output parameters, the maximum operating frequency, expanding the area of operation stability and increasing the functionality of the pulse-width module a torus, a third inverter is introduced into it, a diode whose anode is connected to the input of the first inverter, and a cathode - to the output of the third inverter, the input of which is connected to the first output of the resistor current sensor, the second output of which is connected to the first output of the limiting resistor, the second output of which is connected to the second output of the power source.