RU2572815C2 - Pulse voltage converter with regulation at ac-side based on optical coupler for security equipment - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to electric engineering and may be used for power supply of consumers supplied with inlet voltage in wide range, specifically for security equipment in security alarm systems. Pulse voltage converter consists of power supply filter, mains rectifier, pulse transformer, voltage rectifier, filter, power component, optical coupler. Technical result is attained due to usage of optical coupler by ensuring accurate value of output voltage at any load current.

EFFECT: improved operational reliability due to simplified control circuit.

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Description

The invention relates to the field of electrical engineering, can be used to power consumers receiving an input voltage in a wide range, can be used for security equipment in alarm systems and allows to obtain a technical result - to improve reliability due to a simplified control circuit. The specified technical result is achieved through the use of an optocoupler, ensuring the accuracy of the output voltage value at any value of the load current.

Known stabilized voltage Converter (Patent No. 2474948 C1, 2011). The technical result of the invention is to increase reliability by simplifying the control circuit of transistor switches.

Known step-down Converter AC to DC (Patent No. 2470450, C1, 02/02/2011). The technical result consists in increasing the power factor and simplifying the design of the claimed device.

A device is known (Patent No. 2467460 C1, 05/31/2011), selected for the prototype. The output circuit of a pulse voltage converter, a method for galvanically isolating it, a pulse voltage converter and a switching power supply. EFFECT: creation of technical solutions for galvanic isolation of the output circuit of a switching power supply and / or a pulse voltage converter, including payload circuits. The pulse converter contains a constant voltage source (not shown conventionally), a key stage and an output circuit including a galvanic isolation device with a rectifier and a smoothing filter, while the rectifier is connected to the key stage through two or more isolation capacitors, which are an element of galvanic isolation, and the payload connected to the rectifier through two or more isolation inductances, which are also an element of galvanic isolation and at the same time elements of a smoothing filter. The payload can be connected to isolation inductances and using an additional smoothing filter. The pulse converter may include at least one additional output circuit, similar to the circuit.

The disadvantage of this pulsed voltage converter is the low value of ideal galvanic isolation between the power circuit and the control circuit.

The aim of the present invention is to increase work efficiency, that is, the ability to provide ideal (galvanic) isolation between the power circuit and the control circuit; unidirectional control over the optical channel, the lack of feedback from the receiver to the emitter; a wide frequency bandwidth of the optocoupler, the absence of restrictions from the low frequencies (which is typical of pulse transformers); the immunity of optical communication channels to the effects of electromagnetic fields, determines their immunity to interference and eliminates mutual interference.

This problem is solved by the fact that an optocoupler pair is additionally introduced into the block diagram.

The invention is illustrated in the drawing,

where figure 1 shows the structural diagram in accordance with paragraph 1 of the formula.

The pulse voltage converter has a line filter 1, a line rectifier 2, a pulse transformer 3, a voltage rectifier 4, an output filter 5, a control element 6, an optocoupler 7.

Mains filter 1. The supply voltage of the mains 85-265 V at a frequency of 50 Hz is supplied to a noise suppression filter, consisting of a reactor L1 and capacitors C1, C2, C3. The RK1 thermistor limits the inrush current through the rectifier diodes.

Network rectifier 2. The rectifier is assembled according to the bridge circuit on diodes VD3-VD6. Capacitors C4-C7 are designed to equalize reverse voltages during transients on diodes VD3-VD6 and to protect against interference. The mains voltage through the thermistor RK1 is supplied to the bridge circuit and, after rectification, charges the capacitor C8.

Control node It implements the pulse-width principle of stabilizing the output voltage. The elements DD1.1, DD1.2 made a master oscillator operating at a frequency of about 100 kHz with a duty cycle close to two. Pulses with a duration of about 5 μs are supplied through the capacitor C11 to the input of the element DD1.3, and then are amplified by the current elements DD1.4 - DD1.6 connected in parallel.

In order to stabilize the output voltage of the pulse voltage converter, the pulse duration during regulation is reduced. To this end, the transistor VT1, opening every period of the generator, forcibly sets the input level of the element DD1.3 low. This state is maintained until the end of the next period by a discharged capacitor C1.

A powerful current amplifier is made on transistors VT2, VT3, which provides forced switching of the switching transistor VT4.

When transistor VT4 is open, the current flowing through it and the winding I of transformer T1 increases linearly. The pulse voltage from the current sensor R11 through the resistor R7 is supplied to the base of the transistor VT1. To eliminate the false opening of the transistor, current surges smoothes the capacitor C12.

Voltage rectifier 4. The voltage rectifier is made on a VD9 diode, a Schottky diode, which allows switching functions to be performed at a significantly higher speed than conventional diodes. Due to the small voltage drop across the VD9 diode, the power loss is minimal.

The first after the start of several periods, the instantaneous voltage based on the transistor VT1 remains less than the opening voltage. As soon as the instantaneous voltage during the next period reaches the threshold of 0.7 V, the transistor VT1 opens, which, in turn, will close the switching transistor VT4. Thus, the current in the winding I, and therefore in the load, cannot exceed a certain value predetermined by the resistance of the resistor R11. This ensures protection of the overvoltage protector against overcurrent.

Pulse transformer 3. The phasing of the windings of the transformer T1 is set such that during the open state of the transistor VT4, the diodes VD7 and VD9 are closed by reverse voltage. When the switching transistor closes, the voltage across all windings changes sign and increases until these diodes open. Then the energy accumulated during the pulse in the magnetic field of the transformer T1 is directed to charging the capacitors of the output filter C15 and the capacitors C9. Phasing windings II and III will match. Therefore, the voltage on the capacitor C9 in the stabilization mode of the output voltage is also stabilized regardless of the value of the input voltage of the PID.

Regulating element 6. The regulating element of the IPN is the DA2 chip with a fixed output voltage of the КР142 series - integrated voltage stabilizers produced by the domestic industry. When the voltage at the control input of the microcircuit reaches 2.5 V, a current begins to flow through it and through the emitting diode of the optocoupler U1.2 (7), increasing with increasing output voltage. The phototransistor of the optocoupler U1.2 opens, and the current flowing through the resistors R5, R7 and R11, creates a voltage drop on them, also increasing with increasing output voltage.

The instantaneous voltage based on the transistor VT1, equal to the sum of the voltage drop across the resistor R7 and the current sensor R11, can not exceed 0.7 V. Therefore, with an increase in the current of the optocoupler phototransistor, the DC voltage across the resistor R7 increases and the amplitude of the pulse component on the resistor R11 decreases, which, in turn, it occurs only due to a decrease in the duration of the open state of the switching transistor VT4. If the pulse duration decreases, then the “portion” of energy that is pumped each period by the transformer T1 to the load is also reduced.

Thus, if the output voltage of the PID is less than the nominal value, for example, during its start-up, the pulse duration and the energy transmitted to the output are maximum. When the output voltage reaches the nominal level, a feedback signal will appear, as a result of which the pulse duration will decrease to the value at which the output voltage stabilizes.

If for some reason the output voltage increases, for example, with a sharp decrease in the load current:

- the feedback signal will also increase;

- the pulse duration will decrease, down to zero;

- the output voltage of the IPN returns to the nominal value.

On the DA1 chip, a conversion start node is made. Its purpose is to block the operation of the control unit if the supply voltage is less than 7.3 V. This is due to the fact that the switch - the IRFBE20 field-effect transistor - does not fully open when the gate voltage is less than 7 V.

The start node operates as follows. When you turn on the IDI, capacitor C9 starts charging through resistor R8. As long as the voltage across the capacitor is a few volts, the output of the DA1 chip is kept low and the operation of the control unit is blocked. At this moment, the DA1 chip draws a current of 0.2 mA, and the voltage drop across the resistor R1 is about 3 V. After about 0.15-0.25 s, the voltage across the capacitor reaches 10 V, at which the voltage across the DA1 chips is equal to the threshold value ( 7.3 V). At its output, a high level appears, allowing the operation of the master oscillator and the control unit. The converter starts to start. At this time, the control unit is powered by the energy stored in capacitor C9. The voltage at the output of the converter will begin to increase, which means it will increase at the winding II during a pause. When it becomes more than the voltage across the capacitor C9, the diode VD7 will open, and the capacitor will subsequently be recharged every period from the auxiliary winding II. Here, however, attention should be paid to an important feature of IIT.

The charging current of the capacitor through the resistor R8, depending on the input voltage of the IPN, is 1-1.5 mA, and the consumption of the control unit during operation is 10-12 mA. This means that during the up to the threshold level of the DA1 microcircuit, the control unit will turn off, and since in the off state it consumes no more than 0.3 mA, the voltage across the capacitor C9 will increase until it is turned back on.

This occurs either during reboot, or with a large capacitive load, when the output voltage does not have time to increase to the nominal value during the starting time of 20-30 ms. In this case, it is necessary to increase the capacitance of capacitor C9. The specified feature of the operation of the control unit allows the IDU to be in overload mode for an unlimited time, since in this case it operates in a pulsating mode, and the operating time (start-up) is 8-10 times less than the idle state. The switching elements do not heat up.

Another feature of the SPD is the protection of the load from overvoltage, which occurs, for example, in the event of a failure of any element in the feedback circuit. In operating mode, the voltage across capacitor C9 is approximately 10 V, and the Zener diode VD1 is closed.

In the event of a break in the feedback circuit, the output voltage rises above the nominal value. But along with it, the voltage across the capacitor C9 increases, and at a value of about 13 V the Zener diode VD1 opens. The process lasts 50-500 ms, during which the current through the zener diode gradually increases, many times exceeding its maximum value. In this case, the element's crystal heats up and melts - the zener diode practically turns into a jumper with a resistance from units to several tens of ohms.

The voltage across capacitor C9 is reduced to values insufficient to turn on the control unit. The output voltage, having received, depending on the load current, an increment of 1.3-1.8 times, decreases to zero. An additional filter is made on the elements L2, C19 (5), which reduces the amplitude of the output voltage ripples. To reduce the penetration of high-frequency interference into the network, an output filter C1-C3, C4-C7 is installed, which, moreover, smoothes out the pulse current consumed during operation at a frequency of 100 Hz. The RK1 thermistor has a relatively high resistance in the cold state, which limits the starting current of the converter when turned on and protects the diodes of the mains rectifier. During operation, the thermistor heats up, its resistance decreases several times and practically does not affect the efficiency of the IPN. When the transistor VT4 is closed, a voltage pulse appears on the winding of the transformer T1, the amplitude of which is determined by the leakage inductance. To reduce it, a VD8, R9, C14 circuit is installed in the converter. It eliminates the risk of breakdown of the switching transistor and reduces the requirements for the maximum voltage at its drain, which increases the reliability of the IDI as a whole.

The heat sink of the transistor is connected to a common point of the capacitor C1 and C2. In this case, it is better to connect the IPN to a three-pin socket with grounding. This will significantly reduce the noise emitted by the converter.

Thus, the IPN made using an optocoupler compares favorably with the known IPN, since its reliability is enhanced due to the simplified control scheme.

The proposed IPN is implemented on a modern elemental base, according to its technical characteristics it fully meets the requirements for power supply for modern technical security equipment.

Literature

1. Polushkin I.S., Alekhine M.Yu. Switching power supplies for technical security equipment // Scientific journal "Special equipment" 2011. - No. 6. - S. 30-35.

2. Shmakov S.B. How to create DIY power supplies. - St. Petersburg: Science and Technology, 2013 .-- 288 p.

Claims (1)

A pulse voltage converter with regulation on the alternating current side, consisting of a mains filter made of capacitors C1, C2, C3 and an inductor L1, to which the mains voltage is supplied, a network rectifier assembled according to the bridge circuit on VD3-VD6 diodes and C4-C7 capacitors, switching transistor VT4, pulse transformer T1 with three windings, through the first of which flows a linearly increasing current of the open transistor VT4, a circuit of diode VD8, resistor R9 and capacitor C14, which reduces the amplitude of the pulse voltage I the first winding of the pulse transformer when closing the transistor VT4, voltage rectifier 4, the capacitor of the output filter C15, charged by the magnetic field energy of the transformer T1 after closing the transistor VT4, a control unit that implements the stabilization principle, characterized in that it contains a trigger unit, an optocoupler U1.2 and control element 6, made on a chip with a fixed output voltage, through which the emitting diode of the optocoupler U1.2 also flows, increasing with increasing output voltage, after reaching voltage at the control input of the regulatory element of the threshold value, which leads to an increase in the current of the phototransistor optocoupler U1.2 and to a decrease in the duration of the open state of the transistor VT1.

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