RU23006U1 - 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, a logic microcircuit based on complementary MOS transistors (CMOS microcircuit), containing at least two inverters, the first power output of which is connected to the first output of the source and the power supply, 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, 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 the CMOS chip contains at least five inverters and a second capacitor, a second resistor and a diode are also introduced into it, and the input of the third inverter 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 cathode of the diode is connected to the output of the third inverter, and its anode through the second resistor to the second terminals of the power supply and the limiting resistor, the second capacitor is connected between the output of the second inverter and the anode of the diode, which is connected to the input of the fourth an inverter whose output is connected to the input of the fifth inverter, the output of which is the output of a pulse-width modulator.

Description

Pulse Width Modulator.

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

Known pulse-width modulator (PWM), containing 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 a relatively large current (tens of milliamps). This reduces the overall efficiency of the power source 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 transistors, which further increases energy consumption. 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 scope of the considered technical solutions.

MKI7: G 05 F 1/56 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 a current source of the controlled circuit and a resistor current sensor, the second terminals of which are connected to the second output of the power source, a logic chip based on complementary MOS transistors (hereinafter - K OP-microcircuit), containing at least two inverters, the first power output 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, 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 and a transistor whose collector is connected to the input of the first inverter, e Itter - to the second terminal of the power source and the base - to the first output of the summing resistor.

In the SHR1M functional circuit shown in 3, the regulating element is made on a phototransistor VT2 optocoupler with resistor R8, the limiting resistor is resistor R5, transistor transistor VT1, summing resistor is resistor R6, the current source of the controlled circuit is made on current transformer TA1 and diode VD3, and resistor current sensor is a resistor R7. The role of the frequency-setting capacitor and resistor are respectively performed by the SZ and R4 elements, and the first and second inverters are the 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. Unused PWM circuits inverters microcircuits can

2 be connected in parallel to the second inverter to power output

block (not shown in FIG. 1).

Common features of the proposed technical solution and prototype are a power source, an adjustable 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 outputs of the resistor current sensor, a CMOS chip containing at least two inverters, the first power output of which is connected to the first output of the power source, and the second power output - a second power supply terminal, an output of first inverter is connected to the input of a second inverter frequency control capacitor coupled between the input of the first inverter and the output of the second inverter frequency control resistor connected between the input and output of the first inverter.

PWM prototype works as follows. At the first and second inverters, a square-wave driving oscillator was made, the initial pulse duration of “max and pauses” whose max 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 output of SR1M, 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 open, the current in the controlled circuit increases, during the zero state at the PWM output, the power switch is closed and there is no current in the controlled circuit. The maximum current value in the controlled circuit 1max corresponds to the voltage on the resistor current sensor, equal to the voltage "base-emitter of the open transistor Ibe open 0.7 Volt.

3 Regulation is as follows. When turned on

first, the FSB generates pulses of maximum duration, and the voltage on the resistor current sensor increases, remaining less than the opening voltage of the transistor Ugg open (figv). There is no feedback signal. The resistance of the control element is extremely high. If during the next working cycle the above value Ube open 0.7 Volt is reached, the transistor will open and the PWM output will be forced to zero. The power switch will close, which will protect it from overcurrent. When the adjustable PWM parameter, for example, the output voltage of the switching power supply, reaches its nominal value, a feedback signal appears, the resistance of the control element decreases and the current flowing through it creates a constant bias based on the transistor. Since the limit value of the voltage based on the Ibe open transistor cannot be more than 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 to widely vary the duration of the PWM output pulse.

The disadvantages of the considered technical solution include the temperature dependence of the maximum current in the controlled circuit 1maxOne due to the fact that the Ube voltage drifts when the temperature changes at a speed of about -2.2 mV / ° C. If the PWM temperature changes from -60 ° С to +100 ° С, this change will be approximately 50%. The value of the maximum current in the controlled circuit will change as many times.

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

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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 TTTIM 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 functionality.

Another drawback of the PWM under consideration is the following. The pulse component of the voltage based on the Ube imp transistor coming from the resistor current sensor is determined from the expression:

Ibe imp ird, (Rorp + Rper) / (RE + Rorp + Rper), Where

UpjT - voltage on the resistor current sensor;

RS is the resistance of the summing resistor;

Rorp - resistance of the limiting resistor;

Rper is the resistance of the regulatory 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 mode of a short output pulse and the maximum frequency of operation, increases the likelihood of excitation of a pulsed power source in which the described PWM operates.

In addition, the operation features of the PWM under consideration include the regulation of the duty cycle of the output pulses by reducing the duration of the initial pulse “max up to the minimum

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5

its value is “min at a constant pause duration”. In the process of regulation, the frequency of PWM operation changes, which makes it impossible to synchronize it with other equipment nodes and reduces the functionality of the PWM under consideration.

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

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 at least two inverters, the first power output of which is connected to the first output of the power source, and the second output is pi - with the second output of the power source, the output of the first inverter is connected to the input of the second inverter, 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, and a second capacitor, a second resistor are introduced into it and a diode, and the CMOS chip must contain at least five inverters, and the input of the third inverter is connected to the first output of the resistor current sensor, the second output of which is connected to the first by the output of the limiting resistor, the cathode of the diode is connected to the output of the third inverter, and its anode through the second resistor to the second terminals of the power supply and the limiting resistor, the second capacitor is connected between the output of the second inverter and the anode of the diode, which is connected to the input of the fourth inverter, the output of which is connected to fifth inverter input, output

which is the output of a pulse width modulator.

The introduction of additional elements and new non-obvious connections into the devices made it possible to eliminate the temperature dependence of the output parameters, expand the area of stable operation of the SHRTM, increase the maximum operating frequency, and make external synchronization possible, which expands its functionality.

The applicant did not find technical solutions that have similar characteristics with the signs, different; they claimed solution from the prototype, and, therefore, the proposed technical solution has significant differences.

The proposed device is made of standard elements that are commercially available from industry. It is assembled by typical installation operations using standard equipment and does not require adjustment, which is especially important in 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 source 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 CMOS chip 8 containing at least five I1 inverters - Pin, diode 9, a second resistor 10 and a second capacitor 11.

In the proposed PWM, the first output of the microcircuit 8 is connected to the first terminals of the regulating element 2 and the power supply 1, the second output of the microcircuit 8 is connected to the second terminals of the limiting resistor 3 and the power source 1. The second terminal of the regulating element 2 is connected to the first terminal 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

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7 of the third inverter FROM. The output of the third inverter FROM is connected to the cathode

diode 9, the anode of which is connected to the input of the fourth inverter I4, the output of which is connected to the input of the fifth inverter I5, the output of which is the output of ШР1М. Frequency-setting capacitor 6 is connected between the input of the first inverter I1 and the output of the second inverter I2. Frequency-setting resistor 7 is connected between the input and output of the first inverter I1. The second capacitor 11 is connected between the output of the second inverter I2 and the input of the fourth inverter I4, and the second resistor 10 is between the input of the fourth inverter I4 and the second output of the power source 1.

As a regulating element 2, as in the prototype, some element can be used that changes its resistance, for example, a phototrapistor 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.

The operation of the proposed PWM is illustrated using the timing diagrams shown in FIG. 4. When turned on, there is no feedback signal, the regulating element 2 is closed, the voltage at the limiting resistor 3 is practically 0. The master oscillator, made on inverters I1 and I2, generates rectangular pulses with a constant duration of a unit of 1 and zero tn states (the first period of oscillations on Fig. 4a), the duration of which is determined by the values of the frequency-setting capacitor 6 and resistor 7. For the correct operation of the PWM, the ratio must be satisfied:

(tH + tn).

Under this condition, during the pulse and pause time, the second capacitor C2 will not have time to recharge through the second resistor R2, at the input of the fourth inverter, the pulse voltage is almost the same shape as at the output of the master oscillator. This, in turn, means that the voltage at the PWM output has the same shape as that at the output of the master oscillator.

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8 Timing diagram of current controlled price (or voltage on

current sensor 5) is shown in FIG. 46. The difference is that the maximum current value corresponds to the voltage on the resistor current sensor not Ibe open 0.7 Volt, as in the prototype, but the threshold voltage of the microcircuit (for CMOS microcircuits this value is 0.4 ... 0.5 from the voltage of their power). When the instantaneous value of the specified voltage reaches the threshold value, the output of the inverter FROM, and after it the voltage at the input of the fourth inverter, the state of logical O is established, ending the pulse at the PWM output earlier than it ends at the output of the master oscillator. The increase in current in the controlled circuit stops. After that, the output of the inverter FROM is again set to logic 1, however, at the input of the fourth inverter I4, the recharged second capacitor C2 holds the zero state, which continues until a single state is established at the output of the master oscillator. When the adjustable PWM parameter, for example, the output voltage of the switching power supply, reaches its nominal value, a feedback signal appears, the resistance of the control element 2 decreases and the current flowing through it creates a constant bias on the limiting resistor 3 (Fig. 4c). Since the instantaneous voltage value at the input of the inverter FROM cannot be more than the threshold value Unop, the amplitude of the pulse component of the voltage should decrease - the voltage drop across the resistive current sensor Irdt. 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 to widely vary the duration of the PWM output pulse.

During regulation, the pulse width at the PWM output changes, but its frequency remains constant. This makes it possible to synchronize the PWM operation with other equipment nodes, which is not possible with the prototype. The leading edge of the pulse of the proposed modulator coincides in time with the leading edge of the pulse of the master oscillator.

The location of the trailing edge is variable. This means that according to the classification of the theory of automatic control, the proposed modulator belongs to the class of pulse-width modulators of the second kind.

The threshold of CMOS chips is practically independent of temperature 4, therefore, the proposed PWM maintains the maximum current value in the controlled circuit 1max in the entire range of operating temperatures, which compares it favorably with the prototype.

Since the input resistance of the CMOS inverter is extremely high (10 ... 10 ° 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 Uorp changes. However, the amplitude and steepness of the linearly increasing portion of the pulse component Up, as follows from the expression, does not depend on the resistance value of the regulating element 2. This means that the proposed PWM has an unchanged stability level, independent of the duration of the output pulse, which extends its functionality compared to the prototype.

Since the delay when switching elements of the CMOS microcircuit does not depend on the magnitude of the current switched by them and is significantly less than that of a bipolar transistor in microcurrent mode, the minimum duration of the output pulse of the proposed PWM is much less than that of the prototype. The tested PWM sample has a minimum output pulse duration of about 0.5 microseconds, which is 4 times less than that of the prototype. In addition, with a decrease in the pulse width of the proposed PWM, the pause increases, which has a maximum value equal to T - „min T 1i +„., And not tn, as in

UBX from Warp + Upax.

prototype. Thus, the proposed PWM practically provides 7..8 times lower duty cycle of the output pulse than the prototype. This allows you to significantly increase the maximum operating frequency for a given minimum duty cycle of the output PWM pulse, or for the same value of the working frequency to obtain a 7 ... 8 times lower duty cycle, which extends the functionality of the device. Moreover, the consumed PWM current remains at the same level as that of the prototype.

In addition, since CMOS microcircuits currently being manufactured contain up to six inverters, the electrical circuit of the proposed PWM is still implemented on a single chip with the addition of three passive elements.

Sources used when writing an application.

1. Integrated microcircuits: Microcircuits for switching power supplies and their application. - M. DODEKA, 1997, 224 p. - ISSN-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, a logic microcircuit based on complementary MOS transistors (CMOS microcircuit), containing at least two inverters, the first power output of which is connected to the first output of the source and the power supply, 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, 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 the CMOS chip contains at least five inverters and a second capacitor, a second resistor and a diode are also introduced into it, and the input of the third inverter 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 cathode of the diode is connected to the output of the third inverter, and its anode through the second resistor to the second terminals of the power supply and the limiting resistor, the second capacitor is connected between the output of the second inverter and the anode of the diode, which is connected to the input of the fourth an inverter whose output is connected to the input of the fifth inverter, the output of which is the output of a pulse-width modulator.