CN203243226U - Switch power source - Google Patents

Abstract

The utility model relates to a switching power supply. The purpose of the utility model is to provide a switching power supply with strong high voltage bearing capacity and not easy to burn out. The technical scheme of the utility model is: a switching power supply, including a rectifier bridge stack, the output end of the rectifier bridge stack is connected with an EMI filter module, an input rectification filter module and a DC-DC conversion circuit in sequence, and it is characterized in that: the EMI filter module A clamping protection module is arranged between the input rectification and filtering module. The utility model is suitable for power supply of an intelligent electric energy meter.

Description

switching power supply

technical field

The utility model relates to a switching power supply, which is mainly used for power supply of an intelligent electric energy meter.

Background technique

At present, the power supply of electronic energy meter is mainly divided into transformer power supply, RC step-down power supply and switching power supply. Transformer power supply has been widely used in smart energy meters due to its advantages of strong anti-interference ability, small ripple voltage, low cost, simple manufacture, stability and reliability, but it also has disadvantages such as narrow voltage working range, low power density, and low efficiency. The limitations caused by the use of transformer power supply. The resistance-capacitance step-down power supply has the advantages of small size and simple circuit, so it is more and more used by electronic energy meter manufacturers, but because it is not isolated, it is not suitable for high-power, capacitive, inductive, and dynamic loads. Device selection requires high disadvantages, so it can only be used in ordinary electronic energy meters. Switching power supplies have been widely used in various fields of the electronics industry due to their high efficiency, small size, wide voltage operating range, multiple technical options, easy isolation of input and output, and high power density. Today's electronic energy meters are developing in the direction of high intelligence, high precision, high reliability and fully automatic billing. The efficiency, load capacity, volume, working voltage range and output voltage accuracy of the power supply are getting higher and higher. requirements. In the past, the switching power supply of the three-phase electric energy meter basically adopted the Flyback topology or the pure Flyback topology based on the Stackfet of the switching power supply chip of PI Company. In these two structures, the power of the former is limited, and the peak current Ipeak generated on the primary winding and the peak voltage Vdspeak generated by the leakage inductance will pass through the upper MOS tube, resulting in increased switching losses of the upper MOS tube, and high voltage enters the power supply input. It is easy to burn the machine; because the latter is a single MOS, the VDSS voltage of the MOS tube is limited, so the high voltage withstand capacity of the power supply is limited.

Contents of the invention

The technical problem to be solved by the utility model is: to provide a switching power supply with strong high-voltage withstand capability and not easy to burn out in view of the above existing problems.

The technical scheme adopted in the utility model is: a switching power supply, including a rectifier bridge stack, the output end of the rectifier bridge stack is connected with an EMI filter module, an input rectifier filter module and a DC-DC conversion circuit in sequence, and it is characterized in that: the EMI A clamp protection module is arranged between the filter module and the input rectification filter module.

The DC-DC conversion circuit includes a transformer connected to the output end of the input rectification and filtering module, and an output rectification and filtering module connected to the output end of the transformer; wherein the primary side coil of the transformer is connected with a switch module for controlling the working state of the transformer, the switch module The control input terminal of the control circuit is connected with a PWM control chip for controlling its on-off; the output terminal of the output rectification filter module is connected with a secondary feedback module, and the output terminal of the feedback module is connected with the PWM control chip to form a feedback loop.

A current sampling resistor is connected in series on the switch module, one end of the current sampling resistor is grounded, and the other end is connected to the PWM control chip through a wire.

The switch module is a power MOS tube, the drain of which is connected to the primary coil of the transformer, the source is grounded after passing through the current sampling resistor, and the gate is connected to the control signal output terminal of the PWM control chip.

The model of the power MOS tube is 5N90 or 6N90.

The model of the PWM control chip is FAN6755W.

The input terminal or output terminal of the clamp protection module is connected to the overvoltage detection port of the PWM control chip through a 0-ohm resistor.

The secondary feedback module includes a three-terminal adjustable shunt regulator, and an optocoupler connected to the output end of the three-terminal adjustable shunt regulator, wherein the input end of the three-terminal adjustable shunt regulator is connected to the output of the output rectification filter module The output terminal of the optocoupler is connected with the PWM control chip.

The model of the three-terminal adjustable shunt regulator is TL431, and the model of the optocoupler is PC817.

The beneficial effects of the utility model are: 1. A clamping protection module is set between the EMI filter module and the input rectification filter module, which can limit the output voltage value to a fixed value, thereby improving the high voltage bearing capacity of the power supply, and simultaneously clamping The bit protection module can limit the current, thereby protecting the subsequent circuit. 2. The PWM control chip of the switching power supply adopts Fairchild's FAN6755W, combined with the clamp protection module, the switching power supply of the utility model not only has the excellent performance of the flyback topology switching power supply, but also has the ability of the Stackfet technology structure of PI company to resist high voltage, and at the same time It can also overcome the power limitation of the Stackfet structure, the upper MOS tube will be affected by the peak current Ipeak of the primary winding of the high-frequency transformer and the peak voltage Vdspeak generated by the leakage inductance, and it is easy to get hot, and the over-voltage range causes the power supply to burn out. Therefore, the design difficulty of the switching power supply in the ultra-wide voltage working range (65~550VAC), small and medium power, and harsh input grid environment is reduced, and it is an electronic smart energy meter (especially a three-phase energy meter) with high intelligence and high reliability. Provides power assurance with high-performance features. 3. FAN6755W has built-in overvoltage protection, overcurrent protection and short circuit protection, thus ensuring the reliability of the power supply. 4. The utility model can work in a wide voltage range of 65~550VAC, the highest input withstand voltage is 1.6KVDC, the single and multiple outputs are isolated from each other, and meet the relevant standards of IEC.

Description of drawings

Fig. 1 is a structural block diagram of the utility model.

Fig. 2 is a schematic circuit diagram of the utility model.

Detailed ways

As shown in Figure 1 and Figure 2, this embodiment is a switching power supply based on the flyback topology and capable of operating in a wide voltage range (65~550VAC). It adds a clamp protection module to the traditional flyback topology switching power supply Specifically, it includes a rectifier bridge stack 1, an EMI filter module 2, a clamp protection module 4, an input rectifier filter module 3 and a DC-DC conversion circuit connected in sequence.

The rectifier bridge stack 1 is composed of four groups of diodes, the input terminals of which are connected to AC IN for rectifying AC into DC.

The EMI filter module 2 mainly includes a common-mode inductor LP1, a capacitor CXP4 (X capacitor), and a capacitor CXP5 (X capacitor), and its input terminal is connected to the output terminal of the rectifier bridge stack 1; the power supply satisfies electromagnetic compatibility characteristics and suppresses common The impact of the mode and differential mode signals on the power grid, as well as the electromagnetic interference of the power supply to other electronic equipment, make it comply with the IEC standard.

The clamp protection module 4 is mainly composed of a clamp protection device (UP5, model HB10071) and corresponding peripheral circuits, and its input terminal is connected to the output terminal of the EMI filter module 2 . When the input voltage is lower than the set clamping voltage value (different values can be set according to the actual situation), the clamping protection module 4 does not work, and the DC voltage is directly sent to the input rectifying and filtering module 3 through this module; When the input voltage is higher than the set clamping voltage value, the clamping protection module 4 will play a clamping role and limit the output voltage value to a certain value. For example, if the set clamping voltage is 700VDC, if the value entering UP5 pin 1 (Vin) after rectification and filtering is >700VDC, which is 1000VDC, then the output voltage of UP5 pin 2 (Vout) is 700VDC (that is, the clamp protection module output The voltage value is 700VDC), and the difference is 300V, which is borne by UP5 to ensure that the DC voltage value entering the input rectification and filtering module 3 will not exceed 700VDC. And when the (Vin) value entering UP5 pin 1 is lower than 700VDC, such as Vin=500VDC, the clamp protection module 4 will not work, and the 500V DC voltage will directly pass through UP5 and be sent to the input rectifier filter module 3. In addition, the clamp protection module 4 also plays the role of current limiting, the current limit value is 1A, when the value passing through UP5 is greater than 1A, the clamp protection module 4 will be turned off, and the Vout output value is 0V, which protects the subsequent circuit role.

The input rectification and filtering module 3 mainly includes two capacitors (ECP1, ECP2, connected in series between pin 2 and PGND of the clamp protection module 4) in series, and four equalizing resistors (RP15, RP16, RP17 , RP18, used to prevent capacitor breakdown and damage caused by the unbalanced voltage of the two capacitors); used to filter out the AC component and make the rectified DC smoother.

The DC-DC conversion circuit includes a high-frequency transformer 5, an output rectification and filtering module 6, a switch module 7 (QP1, using a power MOS tube of model 5N90 or 6N90), a PWM control chip 8 (UP2, using a FAN6755W chip of Fairchild Company ), the secondary feedback module 9 and the current sampling resistor 10; wherein the input end of the transformer 5 is connected to the output end of the input rectification filter module 3, and the output end is connected to the output rectification filter module 6; the switch module 7 is simultaneously connected to the transformer 5 and the PWM control chip 8 connection, use the PWM control chip 8 to control the on-off of the switch module 7, thereby realizing the control of the working state of the transformer 5; the switch module 7 is connected in series with the current sampling resistor 10 to sample the current flowing through the switch module 7; the output rectification filter module 6 The output end of the output terminal is connected to the PWM control chip 8 through the secondary feedback module 9 to form a feedback loop, so as to adjust the duty cycle of the output pulse signal of the PWM control chip 8 according to the output voltage.

In this example, one end of the primary coil of the transformer 5 is connected to the output end of the input rectification filter module 3, and the other end is connected to the drain of the power MOS transistor (QP1). The source of the power MOS transistor (QP1) is passed through the current sampling resistor 10 After grounding, a circuit loop is formed; the gate of the power MOS tube (QP1) is connected to the pin 5 (Gate) of the PWM control chip 8, and the power MOS tube (QP1) is controlled by the output signal of the PWM control chip 8. , so as to control the on-off of the aforementioned loop (the loop where the switch module and the current sampling resistor are located), and then achieve the purpose of controlling the working state of the transformer 5 . One end of the current sampling resistor 10 connected to the power MOS transistor (QP1) is connected to the pin 3 (SENSE) of the PWM control chip 8 through a wire for voltage sampling of the current sampling resistor 10 . The pin 8 (HV) of the PWM control chip 8 is connected to the connection point of two capacitors (ECP1, ECP2) via a resistor RP20 and a resistor RP21.

The secondary feedback module 9 is mainly composed of a three-terminal adjustable shunt regulator TL431 (UP7), an optocoupler PC817 (UP3) and peripheral resistors and capacitors, in which RP48, RP50, and RP51 are voltage divider circuits, and RP49 and CP16 are differential circuits , RP52, and CP17 are integral circuits, and the differential and integral circuits together form the loop compensation circuit of the three-terminal adjustable shunt regulator TL431. The output end of optocoupler PC817 is connected to pin 2 (FB) of PWM control chip 8 .

In order to make full use of the overvoltage detection function of the PWM control chip 8 and improve the reliability of the power supply, the DC voltage rectified by the rectifier bridge stack 1 and passed through the EMI filter module 2 can be detected, and the clamped voltage of the clamp protection module 4 can also be detected. The specific detection point can be selected according to actual needs; for the former, a 0-ohm resistor (RP56) can be connected to the input terminal of the clamp protection module 4 (pin 1 of UP5), and the other terminal of the resistor can be connected to the PWM control Pin 1 (Vin) of chip 8; for the latter, a 0-ohm resistor (RP57) can be connected to the output terminal of clamp protection module 4 (pin 2 of UP5), and the other end of the resistor is connected to pin 8 of PWM control chip 1 (Vin); two resistors (only one of RP56 and RP57 can be soldered in the circuit).

The working principle of this embodiment is as follows: when the switching power supply is turned on, the alternating current is rectified by the rectifier bridge stack 1 and then output direct current to the EMI filter module 2, and then output to the primary side of the transformer 5 through the clamp protection module 4 and the input rectifier filter module 3 in turn Coil; at the same time, the current flows through the external capacitor (ECP3, 100uF/35V electrolytic capacitor) from pin 8 (HV) to pin 6 (Vcc) of PWM control chip 8, when the voltage on the capacitor reaches the start of PWM control chip 8 When the voltage is VDD-on, the PWM control chip 8 starts to work; at this time, the PWM control chip 8 performs overvoltage detection on the input voltage, and when it detects that the input voltage exceeds the voltage value set by the circuit, the PWM control chip 8 will turn off the power The MOS tube (QP1) stops power output, and the PWM control chip 8 enters the Auto-Restart working mode (in this mode, it will automatically resume normal operation after the fault is eliminated); during the period of turning off the power MOS tube (QP1), the aforementioned circuit ( The circuit where the switch module and the current sampling resistor are located) is disconnected, the primary coil of the high-frequency transformer 5 has no current flowing through it, the primary inductor has no energy storage, and the secondary has no magnetic energy converted into electrical energy, so the transformer secondary, That is, there will be no output voltage at the OUT terminal.

When it is detected that the input voltage is lower than the voltage value set by the circuit, the PWM control chip 8 sends a pulse signal to the gate of the power MOS transistor (QP1) through pin 5 (Gate) to control the on-off of the power MOS transistor (QP1); When the power MOS tube (QP1) is turned on, the aforementioned loop (where the switch module and the current sampling resistor are located) is turned on, the primary coil of the transformer 5 flows current, and the primary inductor stores energy; when the power MOS tube (QP1) is turned off , the energy stored in the primary side coil inductance is transferred to the secondary side through the magnetic core, and then through the output rectification and filtering module 6 of the secondary side, the energy is transferred to the output end to realize energy transfer (different from the energy transfer method of the traditional flyback topology consistent).

During the entire energy transfer process, the voltage on the current sampling resistor 10 is sampled (since the current sampling resistor is in series with the power MOS tube, the current flowing through both is the same), and the sampled voltage is sent to the PWM control chip 8 The pin 3 (SENSE) of pin 3 (SENSE) is compared with VLimit through the internal current comparator. If it is greater than VLimit, the comparator outputs a high level, and through the RS flip-flop, the duty cycle of the output pulse signal of the PWM control chip 8 is reduced, thereby reducing small output. On the contrary, increase the duty cycle and increase the output to ensure the stability of the output voltage of the power supply. The principle is as follows: the VLimit value is the reference value set internally by the PWM control chip 8 (FAN6755W), which has nothing to do with the external circuit, and the specific voltage value is between 0.6 and 0.85V; the sampling resistor 10 The current signal (that is, the current flowing through the power MOS tube) is converted into a voltage signal through the V=I*R relationship, and then enters the internal comparator of the PWM control chip 8 to compare with the set reference voltage value VLimit, and then control the chip The size of the duty cycle of the output to stabilize the output secondary voltage.

At the same time, for the secondary feedback module 9, when V=RP51/(RP48+RP50+RP51)*VO>2.5V, that is, VO>12V (the output voltage value of the output rectification and filtering module 6 is required to be controlled at 12V), the three-terminal The pin 1 of the adjustable shunt regulator TL431 outputs a low level, the optocoupler PC817 (UP3) light-emitting diode flows through the current, drives the optocoupler transistor, and pulls down the voltage of the PWM control chip 8 (FAN6755W) pin 2 (FB). When the PWM control chip 8 reduces the duty cycle D of the output pulse signal through the internal control circuit, the energy storage time of the primary side inductance of the transformer 5 is reduced, and then the output voltage of the transformer 5 is reduced; otherwise, when V=RP51/(RP48+RP50+RP51) *When VO<2.5V, that is, VO<12V, the pin 1 of the three-terminal adjustable shunt regulator TL431 outputs a high level, the optocoupler does not work, and the PWM control chip 8 increases the duty cycle D of the output pulse signal to increase The energy storage time of the primary inductor of the transformer 5 increases the output voltage of the transformer 5 . The secondary feedback module 9 urges the PWM control chip 8 to increase or decrease the duty cycle of the pulse signal through repeated feedback, so as to control the output voltage of the output rectification and filtering module 6 to be constant at 12V. the

Claims (9)

1. Switching Power Supply; comprise rectifier bridge stack (1); the output of this rectifier bridge stack is connected with EMI filtration module (2), input rectifying filtration module (3) and DC-DC translation circuit in turn, it is characterized in that: be provided with clamper protection module (4) between described EMI filtration module (2) and the input rectifying filtration module (3).

2. Switching Power Supply according to claim 1, it is characterized in that: described DC-DC translation circuit comprises the transformer (5) that is connected with input rectifying filtration module (3) output, the output rectification filter module (6) that is connected with the transformer output; Wherein be connected with the switch module (7) for control transformer (5) operating state on transformer (5) primary coil, the control input end of this switch module is connected with the pwm chip (8) for its break-make of control; The output of output rectification filter module (6) is connected with secondary feedback module (9), and the output of this feedback module and pwm chip (8) are connected to form feedback loop.

3. Switching Power Supply according to claim 2 is characterized in that: be in series with current sampling resistor (10) on the described switch module (7), and this current sampling resistor one end ground connection, the other end is connected with pwm chip (8) by wire.

4. Switching Power Supply according to claim 3, it is characterized in that: described switch module (7) is power MOS pipe, its drain electrode is connected with transformer (5) primary coil, and source electrode is ground connection behind current sampling resistor (10), and grid is connected with the control signal output of pwm chip (8).

5. Switching Power Supply according to claim 4, it is characterized in that: the model of described power MOS pipe is 5N90 or 6N90.

6. according to claim 2 or 3 or 4 or 5 described Switching Power Supplies, it is characterized in that: the model of described pwm chip (8) is FAN6755W.

7. according to claim 2 or 3 or 4 or 5 described Switching Power Supplies, it is characterized in that: described clamper protection module (4) input or output are connected to the overvoltage detection port of pwm chip (8) by 0 ohm resistance.

8. according to claim 2 or 3 or 4 or 5 described Switching Power Supplies, it is characterized in that: described secondary feedback module (9) comprises three end adjustable shunt pressurizers, and the optocoupler that is connected in this three ends adjustable shunt output end of voltage stabilizer, wherein three end adjustable shunt pressurizer inputs are connected with output rectification filter module (6) output, and the optocoupler output is connected with pwm chip (8).

9. Switching Power Supply according to claim 8, it is characterized in that: the model of described three end adjustable shunt pressurizers is TL431, the model of optocoupler is PC817.

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