Input voltage detection and protection circuit

Abstract

The utility model is suitable for the field of power electronic technology improvement, and provides an input voltage detection and protection circuit, which comprises an input voltage detection signal transmitted to a post-stage circuit, and the post-stage circuit comprises a sampling comparison unit, a frequency signal forming unit and an isolation unit, the output end of the sampling comparison unit is connected with the input end of the frequency signal forming unit, and the output end of the frequency signal forming unit is connected with the input end of the isolation unit. According to the power conversion circuit, the functions of input overvoltage protection, input undervoltage protection and linear load reduction of output along with input voltage are realized, rapid alarm and protection of a front-stage circuit and a rear-stage circuit can be realized when instantaneous overvoltage is input, and the reliability of the power conversion circuit is also improved.

Description

Technical Field

[0001] The utility model belongs to the field of power electronic technology improvement, and in particular relates to an input voltage detection and protection circuit. Background Art

[0002] At present, the industry has various mature technologies for AC input voltage detection. For the common two-stage ACDC power conversion technology, the two-stage power conversion is divided into a front stage and a rear stage. The front stage is generally a pre-voltage regulation technology, such as the power factor correction (PFC) circuit in the ACDC power conversion. For the common two-stage DCDC power conversion technology, the two-stage power conversion is divided into a front stage and a rear stage. The front stage is generally also a pre-voltage regulation technology, such as the BOOST circuit in the DCDC power conversion; the rear-stage DCDC conversion of the two-stage ACDC or DCDC power conversion technology realizes electrical isolation, safety isolation and high-frequency rectification output between the input and output sides. If the front-stage circuit adopts analog control, the input voltage also uses analog sampling and protection. If the front-stage circuit adopts digital control, the input voltage can be detected by analog sampling or digital detection. At present, for the front stage using analog detection and control, the back stage using digital control ACDC forklift charger or ACDC power supply or DCDC isolated output vehicle power supply, usually only the output load reduction can be carried out in a graded manner, that is, by selecting 1 to 2 specific input voltage points to reduce the output power of different powers; generally, the real-time value of the input voltage sampled by analog method is compared with the set graded load reduction point voltage to output a high-level signal or a low-level signal, and then the high-low level signal is transmitted to the back stage through the isolation optocoupler for outputting the load reduction signal. Each load reduction voltage point requires a corresponding comparison circuit and an isolation optocoupler for signal transmission in the front stage, and the back stage also needs to have matching detection resources. Therefore, this method cannot meet the demand for linear load reduction of the output as the input voltage decreases, mainly because the input voltage sampling signal is inconvenient to be transmitted to the back stage control unit in real time. To solve this problem, the back stage control unit circuit can use a linear optocoupler or isolation op amp that meets safety isolation to detect the input voltage in real time, but the cost of this analog isolation sampling method is relatively high, and the industry currently rarely adopts this solution just to solve the real-time detection of input voltage. Utility Model Content

[0003] In view of the above problems, the utility model proposes an optimal technical solution, which quickly samples the single-phase AC input voltage. This voltage sampling signal is filtered into a DC signal, and then converted into a frequency signal. The frequency value is linearly related to the effective value of the input voltage. This frequency signal is transmitted to the subsequent control unit circuit through an optical coupler. The subsequent control unit circuit detects and calculates the effective value of the input voltage corresponding to this frequency signal. The subsequent stage can flexibly realize the output linear load reduction function, input undervoltage protection function and input overvoltage protection function according to this input voltage effective value; because the effective value sampling delay is relatively long, in order to ensure that the previous stage circuit and the subsequent stage circuit can be quickly protected in the case of abnormal input overvoltage, this voltage sampling signal is quickly processed by an operational amplifier or a comparator to generate a quick alarm signal of the previous stage. This alarm signal is used as a quick protection shutdown signal of the previous stage. At the same time, the alarm signal of the previous stage is transmitted to the subsequent control unit circuit through an optical coupler as a quick alarm protection signal of the subsequent stage. The input voltage effective value overvoltage protection can be used as input overvoltage and undervoltage shutdown protection under normal input, while the fast protection is used as fast protection under abnormal input with superimposed instantaneous peak overvoltage. Therefore, under the premise that the stress derating of the front-stage power tube is allowed, the overvoltage protection point of the fast protection can be deliberately set to be slightly higher than the peak value corresponding to the effective value overvoltage protection point, mainly to improve the adaptability to the abnormal input voltage distortion scene under the premise of ensuring reliability. This preferred solution can easily transmit the real-time value of the input voltage to the rear-stage control unit circuit, realize the rear-stage input overvoltage protection, input undervoltage protection, and the output can be linearly reduced as the input voltage decreases. It can also quickly alarm and protect the front and rear stage circuits when the input is instantaneous overvoltage, and also improve the reliability of the power conversion circuit. For sampling of DC input, the rectifier diode of AC input can be omitted compared with sampling of single-phase AC input. At the same time, the sampling and filtering parameters of DC voltage sampling are adjusted according to the specific transient characteristics of DC input voltage. Other principles are basically the same. In addition, the single-phase AC input sampling method itself can also be used in DC input scenarios. The two-stage ACDC conversion circuit that needs to be compatible with single-phase AC input and DC input adopts the single-phase AC input sampling method. Therefore, DC input sampling is not explained separately.

[0004] The utility model is implemented as follows: an input voltage detection and protection circuit includes an input voltage detection signal transmitted to a subsequent circuit, wherein the input voltage detection signal is transmitted to the subsequent circuit including a sampling comparison unit, a frequency signal forming unit and an isolation unit, wherein the output end of the sampling comparison unit is connected to the input end of the frequency signal forming unit, and the output end of the frequency signal forming unit is connected to the input end of the isolation unit.

[0005] The input voltage detection and protection circuit also includes a diode VD1, a diode VD2, an input voltage sampling circuit, an input overvoltage fast protection alarm circuit and an input overvoltage fast protection transmission to a subsequent stage alarm circuit. The anode of the diode VD1 is connected to the input Vin_L, the anode of the diode VD2 is connected to the input Vin_N, the cathode of the diode VD1 and the cathode of the diode VD2 are respectively connected to the input end of the input voltage sampling circuit, the output end of the input voltage sampling circuit is respectively connected to the input end of the input overvoltage fast protection alarm circuit and the input end of the input voltage detection signal transmitted to the subsequent stage circuit, and the output end of the input overvoltage fast protection alarm circuit is connected to the input end of the input overvoltage fast protection transmission to the subsequent stage alarm circuit.

[0006] A further technical solution of the utility model is: the cathode of diodes VD1 and VD2 are connected to one end of the input voltage sampling circuit.

[0007] A further technical solution of the utility model is: the input voltage sampling circuit requires fast sampling of the input voltage, so the sampling circuit cannot have a large filter circuit, and no capacitor is needed for sampling and filtering, so as to quickly sample the instantaneous value of the input voltage.

[0008] A further technical solution of the utility model is: the fast sampling signal formed by the input sampling circuit is sent to the input voltage detection signal and transmitted to the subsequent circuit. The input voltage detection signal is transmitted to the subsequent circuit to perform effective value sampling on the input sampling signal, and then a frequency signal that is linearly related to the effective value of the input voltage is formed. The frequency signal is transmitted to the subsequent control unit circuit through electrical isolation and safety isolation, so that the subsequent circuit can perform input overvoltage protection, input undervoltage protection and output linear power reduction functions as the input voltage decreases based on the frequency signal.

[0009] A further technical solution of the utility model is: the fast sampling signal formed by the input sampling circuit is sent all the way to the input overvoltage fast protection alarm circuit, and this input overvoltage fast protection alarm circuit quickly compares the input sampling signal. When the input instantaneous value exceeds the preset overvoltage protection value, this input overvoltage fast protection alarm circuit outputs a previous stage input overvoltage fast alarm signal, which is a high level or low level signal and is used to provide corresponding protection for the previous stage circuit.

[0010] A further technical solution of the utility model is: the front-stage input overvoltage fast alarm signal output by the input overvoltage fast protection alarm circuit is sent to the input overvoltage fast protection and transmitted to the subsequent-stage alarm circuit. After this input overvoltage fast protection is transmitted to the subsequent-stage alarm circuit, the signal is transmitted to the subsequent-stage circuit in an electrical isolation and safety isolation manner as the subsequent-stage input overvoltage fast alarm signal. This signal is a high-level or low-level signal, and this signal is used as a subsequent-stage fast alarm protection signal.

[0011] A further technical solution of the utility model is: the input voltage sampling circuit includes resistors R4, R8, R10 and R13, one end of the resistor R4 is connected to the cathode of the diode VD1 and the cathode of the diode VD2 respectively, the other end of the resistor R4 is connected to one end of the resistor R10 via the resistor R8, and the other end of the resistor R10 is grounded via the resistor R13.

[0012] A further technical solution of the utility model is: the input voltage detection signal is transmitted to the subsequent circuit including resistor R11, resistor R12, capacitor C4, capacitor C5, operational amplifier D3B, resistor R14, capacitor C7, resistor R20, resistor R17, capacitor C6, capacitor C9, resistor R22, capacitor C3, resistor R19, capacitor C10, chip D4, resistor R18, capacitor C8, resistor R21, resistor R15, resistor R16 and optical coupler D5, one end of the resistor R11 is respectively connected to the other end of the resistor R10 and one end of the resistor R13, the other end of the resistor R11 is respectively connected to one end of the resistor R12 and one end of the capacitor C4, the other end of the resistor R12 is respectively connected to one end of the capacitor C5 and the 5th pin of the operational amplifier D3B, the 6th pin and the 7th pin of the operational amplifier D3B are respectively connected to one end of the resistor R14, The other end of the resistor R14 is respectively connected to one end of the capacitor C7, one end of the resistor R20 and one end of the resistor R17, the other end of the resistor R17 is respectively connected to one end of the capacitor C6 and the 7th pin of the chip D4, the 6th pin of the chip D4 is respectively connected to one end of the capacitor C9, one end of the resistor R22 and the 1st pin of the chip D4, the 5th pin of the chip D4 is respectively connected to one end of the resistor R19 and one end of the capacitor C10, the other end of the resistor R19 is respectively connected to one end of the capacitor C3 and one end of the resistor R15, the 2nd pin of the chip D4 is connected to one end of the resistor R21 via the resistor R18, the 3rd pin of the chip D4 is respectively connected to one end of the capacitor C8 and the 2nd pin of the optocoupler D5, the 1st pin of the optocoupler D5 is connected to the other end of the resistor R15, and the 4th pin of the optocoupler D5 is connected to one end of the resistor R16 and the output signal.

[0013] A further technical solution of the utility model is: the input overvoltage fast protection alarm circuit includes a resistor R2, a resistor R9, a capacitor C1, a capacitor C2, a resistor R6, an operational amplifier D1A and a resistor R1, the second pin of the operational amplifier D1A is respectively connected to one end of the resistor R6 and one end of the capacitor C2, the other end of the resistor R6 is respectively connected to one end of the resistor R11, the other end of the resistor R10 and one end of the resistor R13, and the third pin of the operational amplifier D1A is respectively connected to one end of the capacitor C1, one end of the resistor R1, one end of the resistor R2 and one end of the resistor R9.

[0014] A further technical solution of the utility model is: the input overvoltage fast protection is transmitted to the subsequent alarm circuit including resistor R5, resistor R7, resistor R3 and optocoupler D2, one end of the resistor R5 is respectively connected to the bottom 1 pin of the operational amplifier D1A and the other end of the resistor R1, the other end of the resistor R5 is respectively connected to one end of the resistor R7 and the first pin of the optocoupler D2, and the bottom 4 pins of the optocoupler D2 are connected to one end of the resistor R3 and the output signal.

[0015] In addition, if the protection function of specific front-end and rear-end circuits is to be realized, a matching main power circuit, front-end analog control circuit and rear-end digital control circuit are also required, which will not be described in detail here.

[0016] The beneficial effects of the utility model are as follows: the circuit of the application can easily transmit the real-time value of the input voltage to the subsequent control unit circuit, thereby realizing the subsequent input overvoltage protection, input undervoltage protection and the linear load reduction function of the output as the input voltage decreases. It can also quickly alarm and protect the previous and next stage circuits when the input is instantaneously overvoltage, thereby improving the reliability of the power conversion circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The utility model provides an input voltage detection and protection circuit principle block diagram.

[0018] Figure 2 It is an electrical schematic diagram of an input voltage detection and protection circuit provided by an embodiment of the utility model. DETAILED DESCRIPTION

[0019] In order to make the technical means of the present invention clear, the following further describes the preferred embodiments of the present invention in conjunction with the accompanying drawings. Figure 2 The specific implementation methods and related principles of the main power circuit, the front-stage analog control circuit and the back-stage digital control circuit that need to be matched therewith are not further elaborated.

[0020] like Figure 1As shown in FIG. 2 , the input voltage detection and protection circuit provided by the utility model comprises: the circuit as a whole comprises: input voltage detection diodes VD1 and VD2, an input voltage sampling circuit, an input overvoltage fast protection alarm circuit, an input overvoltage fast protection is transmitted to a subsequent alarm circuit, and an input voltage detection signal is transmitted to a subsequent circuit.

[0021] Specifically, refer to Figure 2 , the input voltage Vin_L is connected to the anode of the diode VD1, the input voltage Vin_N is connected to the anode of the diode VD2, the cathode of the diode VD1, the cathode of the diode VD2 and one end of the resistor R4 are connected, the other end of the resistor R4 is connected to one end of the resistor R8, the other end of the resistor R8 is connected to one end of the resistor R10, the other end of the resistor R10 is connected to one end of the resistor R13, one end of the resistor R11 and one end of the resistor R6, and the other end of the resistor R13 is connected to the previous stage working ground GND1;

[0022] Principle description: The voltage on the resistor R13 is sampled by the voltage VIN_SE. There is basically no delay in sampling here. The sampled value is the instantaneous value. Let the effective value of the input voltage be VIN, and the frequency of the AC power grid be f. Then the instantaneous value of the AC input at time t is VIN(t), which can be simplified as: VIN(t) = VIN·1.414·cos(2π·f·t)

[0023] When the input is a DC voltage,

[0024] VIN(t)=VIN

[0025] The instantaneous value of the sampled voltage is VIN_SE(t):

[0026] Further, the other end of the resistor R6 is connected to one end of the capacitor C2 and the inverting input pin 2 of the operational amplifier D1A, the other end of the capacitor C2, the pin 4 of the operational amplifier D1A, one end of the capacitor C1 and one end of the resistor R9 are connected to the front-stage working ground GND1, the other end of the capacitor C1, the other end of the resistor R9, one end of the resistor R2, one end of the resistor R1 and the non-inverting input pin 3 of the operational amplifier D1A are connected, the other end of the resistor R2 and the pin 8 of the operational amplifier D1A are connected to the power supply +12Vpfc, the other end of the resistor R1 is connected to the output pin 1 of the operational amplifier D1A and one end of the resistor R5, and the signal of the output pin 1 of D1A is the front-stage input overvoltage fast protection alarm signal KSGJ_PFC;

[0027] Further, the other end of the resistor R5 is connected to one end of R7 and the first pin of the optocoupler D2, the other end of R7 and the second pin of the optocoupler D2 are connected to the front-stage working ground GND1, the third pin of the optocoupler D2 is connected to the back-stage working ground GNDS, the fourth pin of the optocoupler D2 is connected to one end of the resistor R3 and generates the back-stage input overvoltage fast protection alarm signal KSGJ, and the other end of the resistor R3 is connected to the power supply +3.3V_S of the back-stage control unit circuit;

[0028] Principle description: The instantaneous value of the sampling signal VIN_SE is filtered out by resistor R6 and capacitor C2 to remove interference and then compared with the set overvoltage protection value VREF_OV. When the instantaneous value of the input voltage is not greater than VREF_OV, that is, the input voltage is normal and not over-voltage, KSGJ_PFC is high level, and the KSGJ transmitted to the next stage is low level; when the instantaneous value of the input voltage is higher than VREF_OV, that is, the instantaneous value of the input voltage is overvoltage, KSGJ_PFC is low level, and the KSGJ transmitted to the next stage is high level; when the previous stage detects that KSGJ_PFC is low level, the previous stage is immediately shut down for protection, and the subsequent control unit circuit immediately takes corresponding protection action when it detects that KSGJ is high level.

[0029] When the input voltage drops back to the normal range from an instantaneous overvoltage, a certain hysteresis voltage is set through the positive feedback resistor R1 to prevent abnormal oscillation from being introduced near the overvoltage protection point.

[0030] Further, the other end of the resistor R11 is connected to one end of R12 and one end of the capacitor C4, the other end of the resistor R12 is connected to the non-inverting input pin 5 of the operational amplifier D3B and one end of the capacitor C5, the other end of the capacitor C4 and the other end of the capacitor C5 are connected to the previous stage working ground, the inverting input pin 6 of the operational amplifier D3B is connected to the output pin 7 of the operational amplifier D3B and one end of the resistor R14, the other end of the resistor R14 is connected to one end of the capacitor C7, one end of the resistor R17 and one end of the resistor R20, and the resistor R14 is connected to one end of the capacitor C7, one end of the resistor R17 and one end of the resistor R20. The other end of resistor R17 is connected to one end of capacitor C6 and the 7th pin of voltage-frequency converter D4 (LM331). The other end of capacitor C7, the other end of capacitor C6 and the other end of resistor R20 are connected to the previous stage working ground. The 6th pin of voltage-frequency converter D4 (LM331) is connected to the 1st pin of voltage-frequency converter D4 (LM331), one end of resistor R22 and one end of capacitor C9. The other end of resistor R22, the other end of capacitor C9, one end of capacitor C10, one end of capacitor C3 and capacitor C One end of the resistor R8, one end of the resistor R21 and the 4th pin of the voltage-frequency converter D4 (LM331) are connected to the front-stage working ground GND1, the 5th pin of the voltage-frequency converter D4 (LM331) is connected to one end of the resistor R19 and the other end of the capacitor C10, the other end of the resistor R19, the 8th pin of the voltage-frequency converter D4 (LM331), the other end of the capacitor C3 and one end of the resistor R15 are connected to the power supply +12Vpfc, the other end of the resistor R21 is connected to one end of the resistor R18, and the resistor R The other end of 18 is connected to the second foot of the voltage-frequency converter D4 (LM331), the third foot of the voltage-frequency converter D4 (LM331) is connected to the other end of the capacitor C8 and the second foot of the optocoupler D5, the first foot of the optocoupler D5 is connected to the other end of the resistor R15, the third foot of the optocoupler D5 is connected to the subsequent working ground GNDS, the fourth foot of the optocoupler D5 is connected to one end of the resistor R16 to generate the input voltage real-time sampling frequency signal VIN_F, and the other end of the resistor R16 is connected to the subsequent power supply +3.3V_S.

[0031] Principle description: When single-phase AC input is used, the instantaneous value of the sampling signal VIN_SE is filtered out by two stages of R11 and C4, R12 and C5 with larger time constants to remove the industrial frequency AC component and become an ideal DC value. When only DC input is used, the filtering time constant formed by R11 and C4, R12 and C5 can be adjusted to a smaller value. After being output by the operational amplifier D3B follower, it is sampled and filtered by the resistor divider as the input voltage signal of the voltage-frequency converter. The linear correspondence between the input voltage and the output frequency is set according to the user manual of the voltage-frequency converter D4 (LM331).

[0032] The frequency of the frequency signal VIN_F is fout,

[0033] When the input is DC input: V1 = VIN_SE

[0034] When the input is industrial frequency AC input:

[0035]

[0036] The input voltage sampling signal is transmitted to the subsequent stage in the form of a frequency signal VIN_F through an isolation optocoupler. After the subsequent control unit detects this frequency signal VIN_F, it can know the real-time value of the input voltage, thereby realizing the output linear power reduction function, input undervoltage protection and overvoltage protection functions as the input voltage decreases.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

[0038] V1=0.9VIN_SE

Claims

1. Input voltage detection and protection circuit, characterized in that, The input voltage detection and protection circuit includes an input voltage detection signal transmitted to a subsequent circuit, and the input voltage detection signal is transmitted to the subsequent circuit including a sampling and comparison unit, a frequency signal forming unit and an isolation unit, the output end of the sampling and comparison unit is connected to the input end of the frequency signal forming unit, and the output end of the frequency signal forming unit is connected to the input end of the isolation unit.

2. The input voltage detection and protection circuit according to claim 1, characterized in that: The sampling and comparing unit includes a resistor R11, a resistor R12, a capacitor C4, a capacitor C5, an operational amplifier D3B and a resistor R14, the 5th pin of the operational amplifier D3B is respectively connected to one end of the resistor R12 and one end of the capacitor C5, the other end of the resistor R12 is respectively connected to one end of the resistor R11 and one end of the capacitor C4, the 6th pin and the 7th pin of the operational amplifier D3B are respectively connected to one end of the resistor R14, the other end of the capacitor C4 and the other end of the capacitor C5 are respectively grounded.

3. The input voltage detection and protection circuit according to claim 2, characterized in that: The frequency signal forming unit includes a chip D4, a resistor R19, a capacitor C10, a resistor R22, a capacitor C9, a capacitor C6, a resistor R17, a resistor R20, a capacitor C7, a capacitor C3, a resistor R15, a resistor R18, a resistor R21 and a capacitor C8. The other end of the resistor R14 is respectively connected to one end of the capacitor C7, one end of the resistor R20 and one end of the resistor R17. The other end of the resistor R17 and one end of the capacitor C6 are respectively connected to the seventh pin of the chip D4. The eighth pin of the chip D4 is respectively connected to one end of the capacitor C3, one end of the resistor R15 and one end of the resistor R19. The 6th pin of chip D4 is respectively connected to one end of the resistor R22, one end of the capacitor C9 and the 1st pin of chip D4, the 5th pin of chip D4 is respectively connected to the other end of the resistor R19 and one end of the capacitor C10, the 3rd pin of chip D4 is grounded via the capacitor C8, the 2nd pin of chip D4 is connected to one end of the resistor R21 via the resistor R18, the other end of the resistor R21, the 4th pin of chip D4, the other end of the capacitor C10, the other end of the resistor R22, the other end of the capacitor C9, the other end of the capacitor C6, the other end of the resistor R20, the other end of the capacitor C7 and the other end of the capacitor C3 are respectively grounded.

4. The input voltage detection and protection circuit according to claim 3, characterized in that: The isolation unit includes an optocoupler D5 and a resistor R16, the first pin of the optocoupler D5 is connected to the other end of the resistor R15, the second pin of the optocoupler D5 is respectively connected to the third pin of the chip D4 and one end of the capacitor C8, the fourth pin of the optocoupler D5 is connected to one end of the resistor R16 and outputs a signal, and the third pin of the optocoupler D5 is grounded.

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