Summary
All portable Electronic devices, such as mobile phones, radios, digital cameras, and laptop computers, need to rely on batteries to maintain power. In order to maintain these electronic devices to continue to work, the depleted batteries must be repeatedly charged through the charger through the mains. . However, the battery charging process that everyone is accustomed to invisibly brings about energy consumption, so innovative technologies are needed to reduce unnecessary energy consumption. Especially when it is in standby, it can meet the requirements of energy-saving regulations, such as the California Energy Commission (CEC) energy-saving regulations, and the Energy Star (Energy Star) labeling program, so this article will discuss a new type of polar Power control IC with low standby power consumption.
Fairchild’s newly launched FAN302HL driver control IC can achieve a standby power consumption of less than 10mW in the application of mobile phone chargers, and combines a number of leading technologies to improve the performance of low-power flyback converters, such as: built-in High-voltage activation circuit, low working voltage and working current during standby, the secondary-side feedback control method is used to adjust the fixed output voltage, and the primary-side feedback control method is used to adjust the fixed output current. FAN302HL will be the best choice for extremely low power consumption power control IC design in standby.
Introduction
Oil prices have skyrocketed, raw material prices have repeatedly hit new highs, and global energy management is on the verge of collapse. “Energy conservation” has once again become the hottest topic. With the continuous strengthening of the concept of environmental protection, modern people’s concept of daily energy saving is becoming more and more sound. However, in order to save energy, in addition to turning off unnecessary electrical appliances or using timed switches to save energy, in fact, these electronic devices themselves are due to the design of the power supply circuit. limits. On weekdays, the power consumption of operating and standby power is increasing, which makes the application of energy inefficient. Effective power management can make the benefits of “energy saving” more immediate. The most important trend in power management is to minimize standby power consumption. It may generally be considered that the power consumed by an electronic device in standby is negligible compared to the power consumption of the power supply during operation. In fact, this is far from the truth, so the California Energy Commission (CEC) energy-saving regulations, as well as the Energy Star (Energy Star) logo program, etc., in the planning of all power supplies, the specification for “standby power consumption” great attention. Therefore, under the promotion and advocacy of the International Energy Agency (IEA), the energy plan of the “1 Watt Plan” was proposed. The goal is to reduce the standby power consumption of most electrical products to 1 watt by 2010. In December, the US Energy Independence and Security Act of 2007 was enacted, establishing the first mandatory federal energy standards for consumer electrical equipment.
What is striking is the standby specification for new mobile phone chargers announced by the world’s major mobile phone suppliers in November 2008, clearly defining different standby power consumption with different star ratings, as shown in Figure 1 for the new mobile phone The standby power consumption standard of chargers, in which the standby power consumption of the highest five stars must be reduced to less than 30mW. Therefore, how to make the power converter achieve lower standby power consumption will be what power design engineers need to meet in the future. challenge.
FAN302HL Standby Power Source Analysis and Low Standby Power Solution
How to reduce the standby power consumption of FAN302HL to less than 30mW, or even lower than 10mW, will be analyzed in detail below. First of all, we can analyze the power architecture of the basic flyback converter, as shown in Figure 2.
Figure 2: Typical flyback converter circuit
Figure 3: Analysis diagram of each part of standby power consumption
The distribution of standby power consumption can be seen from Figure 3. For a flyback converter, the main standby power consumption includes switching power consumption (switching loss) and conduction power consumption (conduction loss) and the PWM control circuit. power consumption. Table 1, Table 2, Table 3, and Table 4 respectively list the estimation formulas and improvement measures for these main power consumptions.
1. Control circuit loss (15%):It can be seen from Table 1 and equation (1) that in order to maintain the normal operation of the PWM IC during standby, it must be confirmed that sufficient voltage supply (VDD) can be provided in the auxiliary circuit design. Due to the minimum operating voltage (VDD_OFF) of FAN302HL It is 5V, so it is usually ideal to be designed around 7V. In terms of working current of PWM IC, FAN302HL has multi-stage current work control, as shown in Figure 4, when working in burst mode, it will reduce the standby power consumption of FAN302HL with extremely low working current.
2. Primary side component loss:It can be seen from Table 2 that the primary-side component loss is mainly the sum of the activation resistance loss, the snubber loss and the power transistor (Power MOSFET) loss.
Activation resistance loss (1%): In order to enable the PWM IC to obtain the power supply voltage before normal operation, an activation circuit is usually set up, as shown in Figure 5, but after the PWM IC obtains the power supply from the auxiliary winding, the activation circuit is lost However, at this time, the cross-voltage on the activation resistor will continue to cause power consumption. As shown in equation (2), the built-in high-voltage activation circuit (HV) of FAN302HL replaces the setting of the traditional activation circuit, which can reduce the power consumption caused by the activation resistor. And can speed up the boot time and high voltage activation ability.
Buffer loss (13%):When the power transistor is turned off, there will be a high voltage spike on the voltage between the drain/source (VDS), as shown in Figure 6, this is due to the leakage inductance on the transformer, so avoid leakage inductance The generation of , and the increase of the peak current can effectively improve the consumption loss, as shown in equation (3)
Power transistor loss (29%):The power transistor losses mainly include switching and conduction losses, as shown in equations (4) and (5), and in the application of mobile phone chargers, switching losses account for the majority, so in addition to selecting a suitable In addition to the power transistors, through the Burst mode technology, the switching times of the power transistors per unit time are reduced to reduce the switching loss and maintain the stability of the output voltage, which can effectively improve the power consumption of this part. Figure 7 shows the relevant parameters of the Power MOSFET. .
3. Transformer core loss (2%):The consumption of the transformer when transmitting electric energy is mainly divided into copper loss and iron loss. The copper loss is the loss caused by the primary side current flowing through the impedance of the transformer coil, but the current flowing through the transformer coil in the case of no-load standby is very small, so in the The effect of copper loss under this condition can be ignored.Table 5 and Equation (6) list the power dissipation formula of iron loss. It can be seen from the formula that reducing the switching frequency and magnetic flux density can improve the iron core loss, while adjusting the magnetic flux density will inevitably increase the turns ratio, while The increase in the number of coil turns will also lead to an increase in copper loss, as shown in equation (7), so it is necessary to reasonably design the magnetic flux density and operating frequency of the magnetic core to achieve the improvement of power consumption
4. Secondary side component loss:It can be seen from Table 4 that the secondary-side component loss is mainly the sum of the output diode, the shunt adjustment resistor and the optocoupler loss.
Output Diode Loss (2%):Figure 8 shows the power dissipation path of the output diode. When the current flows in the forward direction of the diode, it will cause losses due to the forward conduction voltage generated on the PN diode, as shown in equation (8). An output diode with a lower forward voltage is one of the prerequisites.
Shunt adjustment resistor loss (2%): Since the shunt regulator must be turned on through the shunt adjustment resistor and compared with the reference potential to achieve a constant output voltage, but this adjustment resistor will still occupy a small amount of power consumption, such as Formula (9), so increasing the adjustment resistance can effectively improve the power consumption, but it will also affect the feedback stability, so the choice in this part should also be carefully considered. Figure 9 shows the power consumption path.
Optocoupler loss (35%): The optocoupler is used to provide signal transfer from the secondary side to the primary side without noise interference, and also provides a signal path for regulation control, through the current limiting resistor (Rbias) to Provide the normal operating current of the optocoupler to achieve stable operation, but the current limiting resistor flowing through will also cause a certain amount of power consumption to the system, as shown in equation (10), so this part of the trade-off is also It needs careful consideration, and the path diagram is shown in Figure 9.
It can be clearly seen from the above discussion that most of the power consumption is closely related to the switching frequency, whether it is switching loss, conduction loss or the power consumption caused by the PWM control circuit. Therefore, it is necessary to control the power consumption during standby more effectively. FAN302HL adopts the technology of pulse mode (Burst mode) to achieve the effect of power saving. The method used by FAN302HL is to judge the conduction period of the pulse mode according to the voltage change of the FB pin, so as to achieve extremely low standby power consumption when there is no load. It can be seen from Figure 10 that the FB pin is also responsible for the PWM task adjustment. Regulation of pulse mode tasks. When the IC works in the pulse mode, the FB pin will judge the action of the voltage level. When the VFB is lower than VFB_L, the PWM output will be forced to turn off, so that there is no energy supply, and the pulse period will be increased. At this time, the output voltage There will be some decline, so VFB will increase quickly, so when VFB is higher than VFB_H, it will be forced to turn on PWM to supply output energy, and use such an alternate operation to achieve appropriate pulse mode deployment. Figure 11 shows the operating principle in the pulse mode and the related parameters in the pulse mode.
FAN302HL no-load standby power consumption calculation example
Use the energy-saving PWM IC developed by Fairchild semiconductor; FAN302HL, placed on the test board, as shown in Figure 12 (its rated output voltage and current specifications are 5V/1A), the measurement conditions are: input 264V AC voltage and work at No load, and the power consumption value calculated from Table 5, the standby power consumption is about 9.07mW. This result is similar to the actual test result of the system. Figure 13 is a graph of the actual test result of the system.
in conclusion
In the field of power supply, there are more and more demands for products with extremely low standby power consumption. Therefore, this article mainly discusses the method of reducing the overall standby power consumption of the power supply based on the newly launched FAN302HL driver and control IC of Fairchild Semiconductor. The main switching and control circuit losses are calculated mathematically, and a number of Fairchild’s innovative and patented technologies are introduced to achieve lower overall standby power consumption. Finally, when the rated output voltage/current specification is 5V/1A, 264V AC input and no-load output, the standby power consumption can be less than 10mW. In addition, the FAN302HL driver IC can not only achieve excellent energy-saving control, but also achieve high-frequency operation (85KHz) and high-efficiency operation, which can definitely meet the application of mobile phone chargers and achieve the goal of “light, thin, and short”.
Summary
All portable Electronic devices, such as mobile phones, radios, digital cameras, and laptop computers, need to rely on batteries to maintain power. In order to maintain these electronic devices to continue to work, the depleted batteries must be repeatedly charged through the charger through the mains. . However, the battery charging process that everyone is accustomed to invisibly brings about energy consumption, so innovative technologies are needed to reduce unnecessary energy consumption. Especially when it is in standby, it can meet the requirements of energy-saving regulations, such as the California Energy Commission (CEC) energy-saving regulations, and the Energy Star (Energy Star) labeling program, so this article will discuss a new type of polar Power control IC with low standby power consumption.
Fairchild’s newly launched FAN302HL driver control IC can achieve a standby power consumption of less than 10mW in the application of mobile phone chargers, and combines a number of leading technologies to improve the performance of low-power flyback converters, such as: built-in High-voltage activation circuit, low working voltage and working current during standby, the secondary-side feedback control method is used to adjust the fixed output voltage, and the primary-side feedback control method is used to adjust the fixed output current. FAN302HL will be the best choice for extremely low power consumption power control IC design in standby.
Introduction
Oil prices have skyrocketed, raw material prices have repeatedly hit new highs, and global energy management is on the verge of collapse. “Energy conservation” has once again become the hottest topic. With the continuous strengthening of the concept of environmental protection, modern people’s concept of daily energy saving is becoming more and more sound. However, in order to save energy, in addition to turning off unnecessary electrical appliances or using timed switches to save energy, in fact, these electronic devices themselves are due to the design of the power supply circuit. limits. On weekdays, the power consumption of operating and standby power is increasing, which makes the application of energy inefficient. Effective power management can make the benefits of “energy saving” more immediate. The most important trend in power management is to minimize standby power consumption. It may generally be considered that the power consumed by an electronic device in standby is negligible compared to the power consumption of the power supply during operation. In fact, this is far from the truth, so the California Energy Commission (CEC) energy-saving regulations, as well as the Energy Star (Energy Star) logo program, etc., in the planning of all power supplies, the specification for “standby power consumption” great attention. Therefore, under the promotion and advocacy of the International Energy Agency (IEA), the energy plan of the “1 Watt Plan” was proposed. The goal is to reduce the standby power consumption of most electrical products to 1 watt by 2010. In December, the US Energy Independence and Security Act of 2007 was enacted, establishing the first mandatory federal energy standards for consumer electrical equipment.
What is striking is the standby specification for new mobile phone chargers announced by the world’s major mobile phone suppliers in November 2008, clearly defining different standby power consumption with different star ratings, as shown in Figure 1 for the new mobile phone The standby power consumption standard of chargers, in which the standby power consumption of the highest five stars must be reduced to less than 30mW. Therefore, how to make the power converter achieve lower standby power consumption will be what power design engineers need to meet in the future. challenge.
FAN302HL Standby Power Source Analysis and Low Standby Power Solution
How to reduce the standby power consumption of FAN302HL to less than 30mW, or even lower than 10mW, will be analyzed in detail below. First of all, we can analyze the power architecture of the basic flyback converter, as shown in Figure 2.
Figure 2: Typical flyback converter circuit
Figure 3: Analysis diagram of each part of standby power consumption
The distribution of standby power consumption can be seen from Figure 3. For a flyback converter, the main standby power consumption includes switching power consumption (switching loss) and conduction power consumption (conduction loss) and the PWM control circuit. power consumption. Table 1, Table 2, Table 3, and Table 4 respectively list the estimation formulas and improvement measures for these main power consumptions.
1. Control circuit loss (15%):It can be seen from Table 1 and equation (1) that in order to maintain the normal operation of the PWM IC during standby, it must be confirmed that sufficient voltage supply (VDD) can be provided in the auxiliary circuit design. Due to the minimum operating voltage (VDD_OFF) of FAN302HL It is 5V, so it is usually ideal to be designed around 7V. In terms of working current of PWM IC, FAN302HL has multi-stage current work control, as shown in Figure 4, when working in burst mode, it will reduce the standby power consumption of FAN302HL with extremely low working current.
2. Primary side component loss:It can be seen from Table 2 that the primary-side component loss is mainly the sum of the activation resistance loss, the snubber loss and the power transistor (Power MOSFET) loss.
Activation resistance loss (1%): In order to enable the PWM IC to obtain the power supply voltage before normal operation, an activation circuit is usually set up, as shown in Figure 5, but after the PWM IC obtains the power supply from the auxiliary winding, the activation circuit is lost However, at this time, the cross-voltage on the activation resistor will continue to cause power consumption. As shown in equation (2), the built-in high-voltage activation circuit (HV) of FAN302HL replaces the setting of the traditional activation circuit, which can reduce the power consumption caused by the activation resistor. And can speed up the boot time and high voltage activation ability.
Buffer loss (13%):When the power transistor is turned off, there will be a high voltage spike on the voltage between the drain/source (VDS), as shown in Figure 6, this is due to the leakage inductance on the transformer, so avoid leakage inductance The generation of , and the increase of the peak current can effectively improve the consumption loss, as shown in equation (3)
Power transistor loss (29%):The power transistor losses mainly include switching and conduction losses, as shown in equations (4) and (5), and in the application of mobile phone chargers, switching losses account for the majority, so in addition to selecting a suitable In addition to the power transistors, through the Burst mode technology, the switching times of the power transistors per unit time are reduced to reduce the switching loss and maintain the stability of the output voltage, which can effectively improve the power consumption of this part. Figure 7 shows the relevant parameters of the Power MOSFET. .
3. Transformer core loss (2%):The consumption of the transformer when transmitting electric energy is mainly divided into copper loss and iron loss. The copper loss is the loss caused by the primary side current flowing through the impedance of the transformer coil, but the current flowing through the transformer coil in the case of no-load standby is very small, so in the The effect of copper loss under this condition can be ignored.Table 5 and Equation (6) list the power dissipation formula of iron loss. It can be seen from the formula that reducing the switching frequency and magnetic flux density can improve the iron core loss, while adjusting the magnetic flux density will inevitably increase the turns ratio, while The increase in the number of coil turns will also lead to an increase in copper loss, as shown in equation (7), so it is necessary to reasonably design the magnetic flux density and operating frequency of the magnetic core to achieve the improvement of power consumption
4. Secondary side component loss:It can be seen from Table 4 that the secondary-side component loss is mainly the sum of the output diode, the shunt adjustment resistor and the optocoupler loss.
Output Diode Loss (2%):Figure 8 shows the power dissipation path of the output diode. When the current flows in the forward direction of the diode, it will cause losses due to the forward conduction voltage generated on the PN diode, as shown in equation (8). An output diode with a lower forward voltage is one of the prerequisites.
Shunt adjustment resistor loss (2%): Since the shunt regulator must be turned on through the shunt adjustment resistor and compared with the reference potential to achieve a constant output voltage, but this adjustment resistor will still occupy a small amount of power consumption, such as Formula (9), so increasing the adjustment resistance can effectively improve the power consumption, but it will also affect the feedback stability, so the choice in this part should also be carefully considered. Figure 9 shows the power consumption path.
Optocoupler loss (35%): The optocoupler is used to provide signal transfer from the secondary side to the primary side without noise interference, and also provides a signal path for regulation control, through the current limiting resistor (Rbias) to Provide the normal operating current of the optocoupler to achieve stable operation, but the current limiting resistor flowing through will also cause a certain amount of power consumption to the system, as shown in equation (10), so this part of the trade-off is also It needs careful consideration, and the path diagram is shown in Figure 9.
It can be clearly seen from the above discussion that most of the power consumption is closely related to the switching frequency, whether it is switching loss, conduction loss or the power consumption caused by the PWM control circuit. Therefore, it is necessary to control the power consumption during standby more effectively. FAN302HL adopts the technology of pulse mode (Burst mode) to achieve the effect of power saving. The method used by FAN302HL is to judge the conduction period of the pulse mode according to the voltage change of the FB pin, so as to achieve extremely low standby power consumption when there is no load. It can be seen from Figure 10 that the FB pin is also responsible for the PWM task adjustment. Regulation of pulse mode tasks. When the IC works in the pulse mode, the FB pin will judge the action of the voltage level. When the VFB is lower than VFB_L, the PWM output will be forced to turn off, so that there is no energy supply, and the pulse period will be increased. At this time, the output voltage There will be some decline, so VFB will increase quickly, so when VFB is higher than VFB_H, it will be forced to turn on PWM to supply output energy, and use such an alternate operation to achieve appropriate pulse mode deployment. Figure 11 shows the operating principle in the pulse mode and the related parameters in the pulse mode.
FAN302HL no-load standby power consumption calculation example
Use the energy-saving PWM IC developed by Fairchild semiconductor; FAN302HL, placed on the test board, as shown in Figure 12 (its rated output voltage and current specifications are 5V/1A), the measurement conditions are: input 264V AC voltage and work at No load, and the power consumption value calculated from Table 5, the standby power consumption is about 9.07mW. This result is similar to the actual test result of the system. Figure 13 is a graph of the actual test result of the system.
in conclusion
In the field of power supply, there are more and more demands for products with extremely low standby power consumption. Therefore, this article mainly discusses the method of reducing the overall standby power consumption of the power supply based on the newly launched FAN302HL driver and control IC of Fairchild Semiconductor. The main switching and control circuit losses are calculated mathematically, and a number of Fairchild’s innovative and patented technologies are introduced to achieve lower overall standby power consumption. Finally, when the rated output voltage/current specification is 5V/1A, 264V AC input and no-load output, the standby power consumption can be less than 10mW. In addition, the FAN302HL driver IC can not only achieve excellent energy-saving control, but also achieve high-frequency operation (85KHz) and high-efficiency operation, which can definitely meet the application of mobile phone chargers and achieve the goal of “light, thin, and short”.
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