Modularization is the development trend of switching power supplies. Parallel operation is an effective solution for large-capacity power supply products. The N+l redundant power supply system can be designed to achieve capacity expansion. This system is a high-frequency switching power supply (1000A/15V) intelligent module in parallel, the power supply unit and the monitoring unit are based on the AT89C51 microcontroller, the power unit's current sharing is coordinated by the monitoring unit, and the monitoring unit can communicate with each power unit. , can also communicate with the PC to achieve remote monitoring.
1 PWM control circuit TL494 is a kind of excellent pulse width modulation controller, TL494 consists of 5V reference voltage, oscillator, error amplifier, comparator, flip-flop, output control circuit, output transistor, dead time circuit. Its main pin function is:
Pins 1 and 2 are the non-inverting and inverting inputs of the error comparison amplifier, respectively;
Pin 15 and Pin 16 are the inverting input and the non-inverting input of the control amplifier, respectively;
Pin 3 is a common output for controlling the comparison amplifier and the error comparison amplifier, and it exhibits output control characteristics when output, that is, in both amplifiers, the output amplitude is large; when the level of pin 3 becomes high, The drive pulse width sent by the TL494 becomes narrow, and when the pin 3 level goes low, the drive pulse width becomes wider;
Pin 4 is a dead-band level control terminal, and adding a dead-zone control voltage from pin 4 can control the maximum width of the drive pulse so that it does not exceed 180°, which can protect the triode in the switching power supply circuit.
The sawtooth wave generated by the oscillator is sent to the inverting input of the PWM comparator, and the pulse width modulated voltage is sent to the non-inverting input of the PWM comparator. The PWM comparator compares and outputs a pulse wave of a certain width. When the widening voltage changes, the pulse width of the output of the TL494 also changes, thereby changing the on-time of the switching tube to achieve the purpose of adjusting and stabilizing the output voltage. The pulse width adjustable voltage can be controlled by the voltage directly input by the pin 3, and can also be respectively input from the input ends of the two error amplifiers, through the comparison, amplification, and output to the non-inverting input terminal of the PWM comparator via the isolation diode. The two amplifiers can be used independently, such as for feedback regulation and overcurrent protection, respectively. At this time, pin 3 should be connected to the RC network to improve the stability of the entire circuit.
As shown in Figure 1, the duty cycle of the PWM pulse is modulated by the internal error amplifier EA1, and the internal error amplifier EA2 is used to turn the TL494 on and off for protection control. Pin 2 is connected to pin 15 and communicates with pin 3 of the common output pin. Because pin 3 has a fixed potential, the TL494 drive pulse width is mainly controlled by pin 1 (PWM adjustment control pin); pin 16 is the system protection input pin. The over-current, over-voltage, under-voltage, and over-temperature faults of the system, as well as the turn-off signal when the regulator or steady-state current is switched, are controlled via the pin 16. Sawtooth generator timing capacitor CT = 0.01μF, timing resistor RT = 3kΩ, the crystal frequency fosc = = 36.6kHz. The two internal output transistor collectors (pin 8 and pin 11) are connected to a +12V high level, and their emitters (pins 9 and 10) drive V1 and V2, respectively, to control the S1 and S2, S3 and S4 tubes to turn on and shut down.
2 Software introduction 2.1 Power supply unit and monitoring unit The software high-frequency switching power supply unit mainly includes data acquisition, voltage and current output given, keyboard and LED display, fault processing and subroutines such as RS485 communication with the monitoring unit. The monitoring unit consists of a keyboard, a liquid crystal display, EEPROM, and subroutines such as RS485 communication with the power supply unit and the PC. EEPROM is used to store operating parameters and Other information that cannot be lost. It uses the X5045 chip, the X5045 has 512 bytes, the connotation watchdog circuit, and the power supply VCC detection and reset circuit.
If there is a failure, the power supply unit immediately responds accordingly, and actively requests an interruption from the monitoring unit. The failure data is transmitted to the monitoring unit. The monitoring unit immediately calls the troubleshooting program. If the failure is severe, the failed power supply is cut off and the backup power supply is started. Send the fault condition to the PC.
2.2 Current Sharing Processing Procedure The high-frequency switching power supply unit sends its own voltage and current to the monitoring unit. The monitoring unit immediately enters the current sharing determination processing program after receiving the voltage and current information of each power supply unit. Based on the requirements of the current sharing accuracy, this procedure calculates how to adjust which power supply unit to achieve the current sharing requirement. The program mainly includes the following two modules: The first module mainly completes the voltage inspection work, and finds that the voltage offset of the power supply unit exceeds the requirement, and immediately adjusts accordingly to ensure that the voltage is the required value; the second module is used to perform the current sharing. For calculation, the module will find out the power supply unit whose average current deviation exceeds the specified requirement, and make corresponding adjustments. The flow-sharing flow chart is shown in Figure 2.
Since in practical use, the voltage values ​​of the power supply units are not exactly the same, this system has two requirements for the voltages of the parallel connection of the multiple power supply units.
1) When multiple power supply units are connected in parallel, if the maximum voltage deviation between each power supply unit is > 0.5%, then the output voltage after parallel connection is required between the voltages of each power supply unit; if the voltage deviation between each power supply unit is less than 0.5 %, then the output voltage after paralleling should add 0.25% error to the middle value of each power supply unit voltage. This requirement at the same time takes into account the requirements to maximize voltage regulation accuracy and to prevent excessive voltage regulation.
2) The difference between the parallel output voltage and the voltage of any power supply unit is ≤ 1% (this power supply requires a regulation accuracy of <1%).
If no voltage point that meets the requirement is found, the program considers that the voltage deviation of the power supplies connected in parallel with each other is too large, stops the current sharing adjustment, and provides a warning as required.
The second module is used to calculate the current of each module. In this system, the average current accuracy of the software is set at 5%. The program finds a module that is larger or smaller than the average current. If the accuracy range is exceeded, the program will set the corresponding flag and then start the communication program and notify the corresponding power module to start the adjustment program.
3 Conclusion The field operation shows that the above RS485 communication program and the current sharing processing program fully meet the requirements, and the PWM control circuit has flexible control and convenient debugging. When the power supply unit fails, the power supply unit interrupts the active application and monitoring unit, which greatly improves the real-time performance. The power supply unit can have an independent function, and can also be managed by the monitoring unit. Multiple power supply units work in parallel.
Source: Power Technology Applications When the pin 3 level goes high, the drive pulse width sent by the TL494 becomes narrower, and when the pin 3 level goes low, the drive pulse width becomes wider;
Pin 4 is a dead-band level control terminal, and adding a dead-zone control voltage from pin 4 can control the maximum width of the drive pulse so that it does not exceed 180°, which can protect the triode in the switching power supply circuit.
The sawtooth wave generated by the oscillator is sent to the inverting input of the PWM comparator, and the pulse width modulated voltage is sent to the non-inverting input of the PWM comparator. The PWM comparator compares and outputs a pulse wave of a certain width. When the widening voltage changes, the pulse width of the output of the TL494 also changes, thereby changing the on-time of the switching tube to achieve the purpose of adjusting and stabilizing the output voltage. The pulse width adjustable voltage can be controlled by the voltage directly input by the pin 3, and can also be respectively input from the input ends of the two error amplifiers, through the comparison, amplification, and output to the non-inverting input terminal of the PWM comparator via the isolation diode. The two amplifiers can be used independently, such as for feedback regulation and overcurrent protection, respectively. At this time, pin 3 should be connected to the RC network to improve the stability of the entire circuit.
As shown in Figure 1, the duty cycle of the PWM pulse is modulated by the internal error amplifier EA1, and the internal error amplifier EA2 is used to turn the TL494 on and off for protection control. Pin 2 is connected to pin 15 and communicates with pin 3 of the common output pin. Because pin 3 has a fixed potential, the TL494 drive pulse width is mainly controlled by pin 1 (PWM adjustment control pin); pin 16 is the system protection input pin. The over-current, over-voltage, under-voltage, and over-temperature faults of the system, as well as the turn-off signal when the regulator or steady-state current is switched, are controlled via the pin 16. Sawtooth generator timing capacitor CT = 0.01μF, timing resistor RT = 3kΩ, the crystal frequency fosc = = 36.6kHz. The two internal output transistor collectors (pin 8 and pin 11) are connected to a +12V high level, and their emitters (pins 9 and 10) drive V1 and V2, respectively, to control the S1 and S2, S3 and S4 tubes to turn on and shut down.
2 Software introduction 2.1 Power supply unit and monitoring unit The software high-frequency switching power supply unit mainly includes data acquisition, voltage and current output given, keyboard and LED display, fault processing and subroutines such as RS485 communication with the monitoring unit. The monitoring unit consists of a keyboard, a liquid crystal display, EEPROM, and subroutines such as RS485 communication with the power supply unit and the PC. EEPROM is used to store operating parameters and other information that cannot be lost. It uses the X5045 chip, the X5045 has 512 bytes, the connotation watchdog circuit, and the power supply VCC detection and reset circuit.
If there is a failure, the power supply unit immediately responds accordingly, and actively requests an interruption from the monitoring unit. The failure data is transmitted to the monitoring unit. The monitoring unit immediately calls the troubleshooting program. If the failure is severe, the failed power supply is cut off and the backup power supply is started. Send the fault condition to the PC.
2.2 Current Sharing Processing Procedure The high-frequency switching power supply unit sends its own voltage and current to the monitoring unit. The monitoring unit immediately enters the current sharing determination processing program after receiving the voltage and current information of each power supply unit. Based on the requirements of the current sharing accuracy, this procedure calculates how to adjust which power supply unit to achieve the current sharing requirement. The program mainly includes the following two modules: The first module mainly completes the voltage inspection work, and finds that the voltage offset of the power supply unit exceeds the requirement, and immediately adjusts accordingly to ensure that the voltage is the required value; the second module is used to perform the current sharing. For calculation, the module will find out the power supply unit whose average current deviation exceeds the specified requirement, and make corresponding adjustments. The flow-sharing flow chart is shown in Figure 2.
Since in practical use, the voltage values ​​of the power supply units are not exactly the same, this system has two requirements for the voltages of the parallel connection of the multiple power supply units.
1) When multiple power supply units are connected in parallel, if the maximum voltage deviation between each power supply unit is > 0.5%, then the output voltage after parallel connection is required between the voltages of each power supply unit; if the voltage deviation between each power supply unit is less than 0.5 %, then the output voltage in parallel should be the voltage of each power supply unit
1 PWM control circuit TL494 is a kind of excellent pulse width modulation controller, TL494 consists of 5V reference voltage, oscillator, error amplifier, comparator, flip-flop, output control circuit, output transistor, dead time circuit. Its main pin function is:
Pins 1 and 2 are the non-inverting and inverting inputs of the error comparison amplifier, respectively;
Pin 15 and Pin 16 are the inverting input and the non-inverting input of the control amplifier, respectively;
Pin 3 is a common output for controlling the comparison amplifier and the error comparison amplifier, and it exhibits output control characteristics when output, that is, in both amplifiers, the output amplitude is large; when the level of pin 3 becomes high, The drive pulse width sent by the TL494 becomes narrow, and when the pin 3 level goes low, the drive pulse width becomes wider;
Pin 4 is a dead-band level control terminal, and adding a dead-zone control voltage from pin 4 can control the maximum width of the drive pulse so that it does not exceed 180°, which can protect the triode in the switching power supply circuit.
The sawtooth wave generated by the oscillator is sent to the inverting input of the PWM comparator, and the pulse width modulated voltage is sent to the non-inverting input of the PWM comparator. The PWM comparator compares and outputs a pulse wave of a certain width. When the widening voltage changes, the pulse width of the output of the TL494 also changes, thereby changing the on-time of the switching tube to achieve the purpose of adjusting and stabilizing the output voltage. The pulse width adjustable voltage can be controlled by the voltage directly input by the pin 3, and can also be respectively input from the input ends of the two error amplifiers, through the comparison, amplification, and output to the non-inverting input terminal of the PWM comparator via the isolation diode. The two amplifiers can be used independently, such as for feedback regulation and overcurrent protection, respectively. At this time, pin 3 should be connected to the RC network to improve the stability of the entire circuit.
As shown in Figure 1, the duty cycle of the PWM pulse is modulated by the internal error amplifier EA1, and the internal error amplifier EA2 is used to turn the TL494 on and off for protection control. Pin 2 is connected to pin 15 and communicates with pin 3 of the common output pin. Because pin 3 has a fixed potential, the TL494 drive pulse width is mainly controlled by pin 1 (PWM adjustment control pin); pin 16 is the system protection input pin. The over-current, over-voltage, under-voltage, and over-temperature faults of the system, as well as the turn-off signal when the regulator or steady-state current is switched, are controlled via the pin 16. Sawtooth generator timing capacitor CT = 0.01μF, timing resistor RT = 3kΩ, the crystal frequency fosc = = 36.6kHz. The two internal output transistor collectors (pin 8 and pin 11) are connected to a +12V high level, and their emitters (pins 9 and 10) drive V1 and V2, respectively, to control the S1 and S2, S3 and S4 tubes to turn on and shut down.
2 Software introduction 2.1 Power supply unit and monitoring unit The software high-frequency switching power supply unit mainly includes data acquisition, voltage and current output given, keyboard and LED display, fault processing and subroutines such as RS485 communication with the monitoring unit. The monitoring unit consists of a keyboard, a liquid crystal display, EEPROM, and subroutines such as RS485 communication with the power supply unit and the PC. EEPROM is used to store operating parameters and Other information that cannot be lost. It uses the X5045 chip, the X5045 has 512 bytes, the connotation watchdog circuit, and the power supply VCC detection and reset circuit.
If there is a failure, the power supply unit immediately responds accordingly, and actively requests an interruption from the monitoring unit. The failure data is transmitted to the monitoring unit. The monitoring unit immediately calls the troubleshooting program. If the failure is severe, the failed power supply is cut off and the backup power supply is started. Send the fault condition to the PC.
2.2 Current Sharing Processing Procedure The high-frequency switching power supply unit sends its own voltage and current to the monitoring unit. The monitoring unit immediately enters the current sharing determination processing program after receiving the voltage and current information of each power supply unit. Based on the requirements of the current sharing accuracy, this procedure calculates how to adjust which power supply unit to achieve the current sharing requirement. The program mainly includes the following two modules: The first module mainly completes the voltage inspection work, and finds that the voltage offset of the power supply unit exceeds the requirement, and immediately adjusts accordingly to ensure that the voltage is the required value; the second module is used to perform the current sharing. For calculation, the module will find out the power supply unit whose average current deviation exceeds the specified requirement, and make corresponding adjustments. The flow-sharing flow chart is shown in Figure 2.
Since in practical use, the voltage values ​​of the power supply units are not exactly the same, this system has two requirements for the voltages of the parallel connection of the multiple power supply units.
1) When multiple power supply units are connected in parallel, if the maximum voltage deviation between each power supply unit is > 0.5%, then the output voltage after parallel connection is required between the voltages of each power supply unit; if the voltage deviation between each power supply unit is less than 0.5 %, then the output voltage after paralleling should add 0.25% error to the middle value of each power supply unit voltage. This requirement at the same time takes into account the requirements to maximize voltage regulation accuracy and to prevent excessive voltage regulation.
2) The difference between the parallel output voltage and the voltage of any power supply unit is ≤ 1% (this power supply requires a regulation accuracy of <1%).
If no voltage point that meets the requirement is found, the program considers that the voltage deviation of the power supplies connected in parallel with each other is too large, stops the current sharing adjustment, and provides a warning as required.
The second module is used to calculate the current of each module. In this system, the average current accuracy of the software is set at 5%. The program finds a module that is larger or smaller than the average current. If the accuracy range is exceeded, the program will set the corresponding flag and then start the communication program and notify the corresponding power module to start the adjustment program.
3 Conclusion The field operation shows that the above RS485 communication program and the current sharing processing program fully meet the requirements, and the PWM control circuit has flexible control and convenient debugging. When the power supply unit fails, the power supply unit interrupts the active application and monitoring unit, which greatly improves the real-time performance. The power supply unit can have an independent function, and can also be managed by the monitoring unit. Multiple power supply units work in parallel.
Source: Power Technology Applications When the pin 3 level goes high, the drive pulse width sent by the TL494 becomes narrower, and when the pin 3 level goes low, the drive pulse width becomes wider;
Pin 4 is a dead-band level control terminal, and adding a dead-zone control voltage from pin 4 can control the maximum width of the drive pulse so that it does not exceed 180°, which can protect the triode in the switching power supply circuit.
The sawtooth wave generated by the oscillator is sent to the inverting input of the PWM comparator, and the pulse width modulated voltage is sent to the non-inverting input of the PWM comparator. The PWM comparator compares and outputs a pulse wave of a certain width. When the widening voltage changes, the pulse width of the output of the TL494 also changes, thereby changing the on-time of the switching tube to achieve the purpose of adjusting and stabilizing the output voltage. The pulse width adjustable voltage can be controlled by the voltage directly input by the pin 3, and can also be respectively input from the input ends of the two error amplifiers, through the comparison, amplification, and output to the non-inverting input terminal of the PWM comparator via the isolation diode. The two amplifiers can be used independently, such as for feedback regulation and overcurrent protection, respectively. At this time, pin 3 should be connected to the RC network to improve the stability of the entire circuit.
As shown in Figure 1, the duty cycle of the PWM pulse is modulated by the internal error amplifier EA1, and the internal error amplifier EA2 is used to turn the TL494 on and off for protection control. Pin 2 is connected to pin 15 and communicates with pin 3 of the common output pin. Because pin 3 has a fixed potential, the TL494 drive pulse width is mainly controlled by pin 1 (PWM adjustment control pin); pin 16 is the system protection input pin. The over-current, over-voltage, under-voltage, and over-temperature faults of the system, as well as the turn-off signal when the regulator or steady-state current is switched, are controlled via the pin 16. Sawtooth generator timing capacitor CT = 0.01μF, timing resistor RT = 3kΩ, the crystal frequency fosc = = 36.6kHz. The two internal output transistor collectors (pin 8 and pin 11) are connected to a +12V high level, and their emitters (pins 9 and 10) drive V1 and V2, respectively, to control the S1 and S2, S3 and S4 tubes to turn on and shut down.
2 Software introduction 2.1 Power supply unit and monitoring unit The software high-frequency switching power supply unit mainly includes data acquisition, voltage and current output given, keyboard and LED display, fault processing and subroutines such as RS485 communication with the monitoring unit. The monitoring unit consists of a keyboard, a liquid crystal display, EEPROM, and subroutines such as RS485 communication with the power supply unit and the PC. EEPROM is used to store operating parameters and other information that cannot be lost. It uses the X5045 chip, the X5045 has 512 bytes, the connotation watchdog circuit, and the power supply VCC detection and reset circuit.
If there is a failure, the power supply unit immediately responds accordingly, and actively requests an interruption from the monitoring unit. The failure data is transmitted to the monitoring unit. The monitoring unit immediately calls the troubleshooting program. If the failure is severe, the failed power supply is cut off and the backup power supply is started. Send the fault condition to the PC.
2.2 Current Sharing Processing Procedure The high-frequency switching power supply unit sends its own voltage and current to the monitoring unit. The monitoring unit immediately enters the current sharing determination processing program after receiving the voltage and current information of each power supply unit. Based on the requirements of the current sharing accuracy, this procedure calculates how to adjust which power supply unit to achieve the current sharing requirement. The program mainly includes the following two modules: The first module mainly completes the voltage inspection work, and finds that the voltage offset of the power supply unit exceeds the requirement, and immediately adjusts accordingly to ensure that the voltage is the required value; the second module is used to perform the current sharing. For calculation, the module will find out the power supply unit whose average current deviation exceeds the specified requirement, and make corresponding adjustments. The flow-sharing flow chart is shown in Figure 2.
Since in practical use, the voltage values ​​of the power supply units are not exactly the same, this system has two requirements for the voltages of the parallel connection of the multiple power supply units.
1) When multiple power supply units are connected in parallel, if the maximum voltage deviation between each power supply unit is > 0.5%, then the output voltage after parallel connection is required between the voltages of each power supply unit; if the voltage deviation between each power supply unit is less than 0.5 %, then the output voltage in parallel should be the voltage of each power supply unit
ATX Power Supply,Laptop Adapter Co., Ltd. , http://www.chpowersupply.com