RU2519246C2 - Control device for flyback converter - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device contains a transformer for the insulated voltage flyback converter, a diode, a secondary circuit with load and a switching element, at that one output of the switching element is connected to anode of the first diode while its cathode is connected to the summator input and to one input of the primary transformer winding, by the other input this winding is connected to the power supply bus; the second output of the switching element is coupled to the common bus at the side of the transformer primary winding; the third output of the switching element is coupled to the control device output; secondary winding though the secondary circuit is connected to the load; the summator is connected to the power supply bus by its one input and to the output of the controlled signal source by its other input, while its output is connected to the input of a measuring instrument; the measuring instrument has two input coupled to the tripping pulse generator; he tripping pulse generator is connected to the control device input.

EFFECT: universality of device, potential use of any voltage flyback converter with control device during operation with insignificant capacity of the load or operation with high-intensive loads leading to significant excess of output current without use of specialised control devices.

3 cl, 5 dwg

Description

The invention relates to the field of electrical engineering, and more specifically to devices for monitoring the status of the outputs of isolated flyback voltage converters (OXP) connected to a load with a large capacitive resistance.

Currently, one of the most common schemes for constructing network and DC-DC voltage converters is a flyback voltage converter (OXP). The relatively small number of components, the flexibility of application in a wide range of input voltages and output currents, and the ability to easily increase the number of output channels make this topology attractive for execution.

In industrial power supplies, the flyback voltage converter is typically controlled based on pulse-width modulation (PWM),

To control voltage converters, specialized microcircuits are used, PWM controllers, which usually include a clock generator, a reference voltage source, an error amplifier, a comparator with an RS latch and an output driver.

When choosing a controller suitable for use, special attention should be paid to the logic of the state machine, especially to the logic of emergency operation. The transition to emergency mode when critical situations are detected may include both forced current limitation and complete blocking of the converter operation. When locked, the PWM oscillator stops and the active signal for the power transistor is prohibited. Two blocking scenarios are possible depending on the type or modification of the microcircuit.

In the first case, after the interlock is triggered, the converter “snaps” in this state and does not change it, even if the condition that caused this state has already disappeared. Restoring the operation of the converter is possible only after turning the power off and on again.

In the second case, attempts are made to automatically restore the normal operation of the converter. To do this, a timer for a certain time is started in the controller structure. After this time expires, the controller again checks for critical situations, and if they persist, the lock remains.

A known system and method for monitoring a voltage converter ("Control system for a voltage converter and method", patent US 7738265, H02M 3/335, priority from 08/28/2006).

In this device, the control circuit ensures operability when charging output capacitive loads by analyzing the output voltage voltage on the primary winding of the transformer 11. The voltage is evaluated at each cycle. The output signal from the comparator 61 reduces the duration of the control pulse ST, which leads to a limitation in output power in the initial charge mode of the capacitance. The output signal from the comparator 71 turns off the control pulse ST at the beginning of each cycle when a short circuit mode is detected at the output. T.O. Due to the control action of the comparators 61 and 71, a specialized PWM controller is required, corresponding to a similar control scheme.

A device is known, patent US 5841643 "Method and apparatus for isolated flyback regulator control and load compensation" with priority from 10/01/1997, H02M 3/24, H02M 3/335.

This device monitors the output condition of the flyback converter according to the results of the voltage analysis on the primary winding. The voltage is estimated at each cycle, due to this either the PWM control signals of the power transistor occur, or it turns off when the output current exceeds or the output voltage decreases and a specialized PWM controller is required that corresponds to a similar control circuit.

A device for charging an output capacity is known, patent US 7787262 "Capacitor charging methods and apparatus" with a priority of 12/19/2006, H02M 3/335 for charging a flash.

In this device, the control of the output condition of the flyback converter is carried out according to the results of the voltage analysis on the primary winding, where the voltage is estimated at each cycle and when the value decreases below a certain threshold, additional PWM pulses of the power transistor control signals begin to form to ensure the charge of the output capacitor, which leads to an increase in the frequency conversion and requires a specialized PWM controller that matches a similar control scheme.

Known devices and methods for charging capacities ("Capacitor charging methods and apparatus", patent US 7646616, H02M 3/335, priority dated May 09, 2005) for charging the flash.

Methods and devices are shown that make it possible to analyze the load in each PWM conversion cycle and, when the value is lower than a certain threshold, additional PWM pulses of the power transistor control signals begin to form to ensure the charge of the output capacitor, which leads to an increase in the conversion frequency and requires a specialized PWM controller corresponding to such management scheme.

Common disadvantages of all the above devices are:

- the converter in the short-circuit mode at the output can be unlimited time and inefficiently uses electricity;

- for the converter to operate at a large output capacity, a specialized PWM controller is required, corresponding to the above control schemes;

- the open circuit voltage feedback is not analyzed.

Such solutions cannot be applied to previously developed microcircuits.

The aim of this invention is to provide protection for non-specialized OCP with a PWM controller when operating at significant capacitance in a load or working for energy-intensive loads (DC motors), leading to a significant excess of the output current or output voltage

Using information on the output voltage obtained on the side of the primary winding of the transformer to ensure protection of the OCP:

- when a short circuit occurs at the output;

- with increasing output voltage above a given maximum.

The technical result is achieved due to the fact that the OCP control device (Fig. 1), including: the source of the monitored signal 1, including: an isolated OCP transformer 13, diode 11, the load in the secondary circuit 15 and the key element 14, moreover: one output of the key element 14 is connected to the anode of the first diode 11, the cathode of which is connected to the input of the adder 21, and one terminal of the primary winding of the transformer 13, which is connected to the power bus Vin by the other terminal; the second output of the key element 14 is connected to a common bus from the side of the primary winding of the transformer 13; the third output of the key element 14 is connected to the output of the control device 12; the secondary winding of the transformer 13 is connected through a secondary circuit to a load 15; an adder 21 of the input voltage signals Vin and the voltage on the primary winding of the output transformer Vsn; a meter 22 connected to the output of the adder 21, and a switching pulse generator 23 having two inputs from the meter 22 with signals ON1 and ON2 and an output with an ON / OFF signal connected to the input of the control device 12.

To describe the operation of the device, we use a typical OCP scheme with the control circuit included in it (Fig. 2).

In a preferred embodiment, a typical OCP circuit includes a source of a monitored signal 1, comprising: an isolation transformer 13, a key element 14 connected by one output to the primary winding of the transformer 13, and the other by an output to a common bus, a control device 12 connected by the output to the third output of the key element 14 and the input with the output of the control device 2, one diode 11 connected by the anode to a common connection point of the transformer 13 and one output of the key element 14, and the cathode with one input of the control circuit 2, the secondary a transformer 13 connected to the anode of the second diode 17, the cathode of which is connected to one terminal of the capacitor 16, the other terminal of which is connected to a common bus, and one terminal of the load 15, which is, for example, a DC motor or a large capacitor, the other terminal of which connected to a common bus.

In a preferred embodiment of the invention, the control device 2 comprises: an adder 21, which includes: a first resistor 24, to one terminal of which are connected: one terminal of a second resistor 25 connected by the other terminal to the positive input voltage bus Vin; one terminal of the first capacitor 26 connected by another terminal to the positive input voltage bus Vin; the anode of the first diode 27, to the cathode of which are connected: one terminal of the second capacitor 28 connected by the second terminal to the positive input voltage bus Vin; one terminal of the resistor 34, the second terminal connected to the emitter of the transistor 33; the anode of the second diode 32, to the cathode of which the anode of the diode 31 is connected, the cathode of which is connected to one terminal of the resistor 30, the second terminal of which is connected: one terminal of the resistor 29, the second terminal of which is connected to the positive input voltage bus Vin; the base of the transistor 33, the collector of which is connected to the input of the meter circuit 22; a meter 22, including: a voltage divider made of three series-connected resistors 35, 36, 37 located between the output of the adder 21 and the common bus of the voltage converter on the side of the primary winding of the transformer 13; one voltage comparator 38, wherein its direct input is connected to a common point of the first 35 and second 36 resistors, the inverse input is connected to a reference voltage source 40, and the output is connected to one input of the switching pulse generator 23; another voltage comparator 39, wherein its inverse input is connected to a common point of the second 36 and third 37 resistors, the direct input is connected to a reference voltage source 40, and the output is connected to another input of the switching pulse generator 23; connected by the output to the input of the control device 12.

Despite the fact that this circuit implementation of the adder is known from the prior art, and it is also known to use a positive supply voltage level as a “zero” bus, the combination of all these signs for the current prior art is unknown and allows you to:

- process signals of large magnitude without non-linear distortion;

- to increase the speed of the control device;

- refuse to use non-linear elements, for example, comparators, which slow down the signal processing, require an additional power source and take up space on the board in the circuit for isolating the measured signal.

An OCP monitoring device, with a key element in the form of a field effect transistor, in a preferred embodiment of the invention operates as follows.

During the return of the OCP on the drain of the transistor 14, a controlled voltage is formed

Vin is the input voltage of the converter;

Vout - output voltage of the converter (voltage on the secondary winding of the transformer);

Nps is the transformation ratio of the transformer 13.

The magnitude of this voltage is determined relative to the common bus side of the primary winding of the transformer 13 OHP.

The voltage Vsn from the drain of the transistor 14 is fed to the input of the adder 21, where it is integrated, detected and converted into a current measuring signal Vs.

A voltage is formed at the input resistor divider (24, 25)

This voltage scales to the differential voltage Vs, which is directly proportional to the voltage difference

where k is the division coefficient of the resistors 24, 25.

Since Vin is used as a voltage reference bus, a signal proportional to Vout / Nps is scaled on the divider

To reduce the error due to an ejection at the moment of closing the transistor, an integrating circuit is used (resistor 24, capacitor 26). The differential voltage Vs smoothed in this way is supplied to the peak detector (diode 27, capacitor 28), the output voltage from which is supplied to the current generator (diodes 31, 32, resistors 29, 30, 34, transistor 33). Further, the current measuring signal Vs is supplied to the input of the meter circuit 22.

The circuit of the meter 22 is made in the form of a ternary comparator without feedback and includes: a voltage divider Vs proportional to the output voltage of the OHP voltage divider (resistors 35, 36, 37), from which two comparison voltages Vmin and Vmax are removed; two binary comparators 38, 39 having a common reference level Vref c of the generator 40.

If the input signal Vs has a value lying in a predetermined voltage range between the maximum and minimum possible voltage values Vs_max and Vs_min (Vs_max≥Vs≥Vs_min), then the OCP operates in normal mode and its operation is controlled by any known method. The shape of the voltage pulse at the drain of the transistor 14 has the following form (figure 3). In this case, the condition Vmin> Vref> Vmax is met and at the outputs of the comparators 38 and 39 there is no turn-on signal of the turning-off pulse generator 23. And in this case, the output signal of the generator 23 is ON, allowing the operation of the control device 12.

If the Vs value is less than the minimum voltage value Vs_min (Vs <Vs_min), then the inverter operates in emergency short circuit mode. In this case, the shape of the voltage pulse at the drain of the transistor 14 corresponds to the following form (figure 4). In this case, the input signal Vmin at the non-inverse input of the comparator 38 becomes less than Vref (Vmin <Vref) and the ON1 signal appears at the output of the comparator 38. This signal will start the generator 23, which after a predetermined period of time t1, necessary for charging the capacitive load, will give a signal OFF, which prohibits the operation of the control device 12, and the converter will be turned off for a predetermined time interval t2 necessary to restore the OCP. At the end of the time interval t2, the generator 23 again provides the enable signal of the control device 12 - ON, turns on the converter and again evaluates the voltage Vmin. If the condition Vmin <Vref is still met (i.e., Vs <Vs_min), then the cyclogram is repeated until the short circuit disappears, i.e. until the condition for normal operation of the converter is met.

If the value of Vs is greater than the predetermined maximum permissible value of the output voltage, then an emergency overvoltage mode occurs in the converter, which can be caused, as a rule, by a break in the voltage feedback. In this case, the shape of the voltage pulse at the drain of the transistor 14 is as follows (figure 5). In this case, Vout becomes greater than a predetermined upper threshold value of the output voltage. In this case, the input signal Vmax supplied to the inverse input of the comparator 39 will be greater than Vref (Vref <Vmax). In this case, the comparator 39 will signal ON2 to start the generator of the shutdown pulse 23, which will give a signal inhibiting the operation of the control device 12-OFF, and turn off the converter immediately after this signal, without a delay for the time t1. After a pre-calculated time t2, the voltage Vmax is again evaluated. If the condition Vmax greater than Vref is satisfied (Vref <Vmax), then the cyclogram is repeated until the overvoltage disappears, i.e. until the condition for normal operation of the converter is met.

One of the advantages of this invention is its versatility, i.e. it can be used in any OCP with a control device (for example, in the form of a PWM controller) during its operation for significant capacitances in the load or for energy-intensive loads (DC motors), leading to a significant excess of the output current without the use of specialized control devices.

Claims (3)

1. A control device for a flyback voltage converter, including: a source of a controlled signal, including a transformer of an isolated flyback voltage converter, a secondary circuit with a load and a key element, moreover: one terminal of the key element is connected to the anode of the first diode, the cathode of which is connected to the input of the adder, and one the output of the primary winding of the transformer, which is connected to the power bus by another output; the second terminal of the key element is connected to a common bus from the side of the primary winding of the transformer; the third terminal of the key element is connected to the output of the control device; a secondary winding is connected through a secondary circuit to a load; an adder connected by one input to the power bus, the other with the output of the source of the controlled signal, and the output with the input of the meter; a meter having two outputs connected to an off-pulse generator; a shutdown pulse generator connected to the input of the control device. 2. The device according to claim 1, characterized in that the circuit for isolating the measured signal includes: a first diode connected by an anode between the first terminal of the first transistor and the other terminal of the primary winding of the transformer, and one terminal of the first resistor is connected to its cathode, the other terminal of which is connected : one terminal of a second resistor connected by another terminal to a positive input voltage bus; one terminal of the first capacitor connected by another terminal to the positive input voltage bus; the anode of the second diode, to the cathode of which are connected: one terminal of the second capacitor connected by the second terminal to the positive input voltage bus; one terminal of the third resistor, to the other terminal of which the first terminal of the second transistor is connected; the anode of the third diode, to the cathode of which the anode of the fourth diode is connected, to the cathode of which one terminal of the fourth resistor is connected, the other terminal of which is connected: to the first terminal of the fifth resistor, the second terminal of the input voltage connected to the positive bus; with the second (control) terminal of the second transistor, the third terminal of which is connected to the input of the control and monitoring circuit. 3. The device according to claim 1, characterized in that the control and monitoring circuit includes: a monitored signal detector, comprising: a voltage divider made of sixth, seventh and eighth resistors connected in series between the output of the measuring signal shaper and the common bus of the flyback voltage converter on transformer primary side; a circuit for determining the minimum value of the measuring signal, made in the form of a first voltage comparator, and its non-inverse input is connected to a common point between the sixth and seventh resistors, the inverse input is connected to a reference voltage source, and the output is connected to one input of the control signal generator; a circuit for determining the maximum value of the measuring signal, made in the form of a second voltage comparator, and its inverse input is connected to a common point of the seventh and eighth resistors, the direct input is connected to a reference voltage source, and the output is connected to another input of the control signal generator.

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