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[Original] How to Design a Power Supply with a Wide Output Voltage Range
[Original] How to Design a Power Supply with a Wide Output Voltage Range
[Original] How to Design a Power Supply with a Wide Output Voltage Range
Author: lii semiconductor Updated: 2022-05-19 Hits:
In applications such as multi-cell battery pack/battery charging, USB PD/QC fast charging, etc., it is often necessary to meet the ultra-wide output voltage range, such as 5-20V (USB-C PD2.0 charger), 3.3-21V (USB-C PD3.0/PPS charger), 10-29.4V (7-cell Li-Ion charger), etc., and in these small and medium-power power supplies, they are generally used. In these small and medium power supplies, the general use of flyback converters, and the high-voltage side of the PWM IC relies on the transformer auxiliary winding for power supply, and therefore will also face the problem of large variations in the supply voltage, the traditional PWM IC is limited by the semiconductor process withstand voltage, and its power supply foot
（Traditional PWM IC is limited by the semiconductor process voltage resistance, its power supply leg (VDD) can only reach 40V, in order to drive the MOSFET normally, the minimum voltage is only 8~9V, so the VDD voltage range is allowed to change less than 5 times, so it will not be able to meet the requirements of the system, then we will use a voltage regulator circuit (voltage limiter) for the power supply of the PWM IC circuit to supply power to the voltage higher than the IC to withstand the ability of the switch to the regulator circuit to bear. A typical voltage regulator circuit is shown in the figure below:
After using this circuit, the power supply voltage of the PWM IC is limited to a level not higher than the voltage regulator's regulated value, realizing normal operation over a wide output voltage range, but there are two significant drawbacks to this circuit: 1) the number of components is large, and the circuit assembly occupies a large area of the board; and 2) the bias current into the regulator is significantly increased when the power supply voltage is high, resulting in a significant increase in the component's own power consumption.
In response to the above needs and problems, Liisemi Semiconductor has formed a separate product for the power supply component in its high supply voltage fast charging IC series, realizing the power supply voltage limiter without peripheral devices, and using it as a general-purpose device for all kinds of PWM ICs to be used as a VDD auxiliary power supply device, as well as providing two types of packages, SOT23-3 and SOT89, which are convenient for users to make flexible choices, and SOT23-3 is more suitable for small power consumption systems. SOT23-3 and SOT89 packages are available for users to choose flexibly, SOT23-3 is suitable for small power consumption and small system size, while SOT89 is suitable for large power consumption and high temperature rise.
This series of auxiliary power supply voltage limiter can also provide 85V and 200V two kinds of voltage input grade products to choose, respectively, corresponding to different output voltage application range, up to meet up to 10 times the variation range.
Typical circuit connections for this voltage limiter are shown in the figure below:
C1 is the VDD capacitor of the PWM IC, and no additional capacitor is required for this limiter.
This solution is simple and easy to use as it can fully support resistor-start PWM ICs or high-voltage-start ICs that are commonly used in the market.
Relying on the dynamic bias circuit inside the chip, the quiescent current of the chip itself increases only slightly even when the input voltage is higher, the typical quiescent current of LN3210 is less than 100uA, and the typical quiescent current of LN3220 is less than 10uA, and the differences of the electrical parameters are as follows.
The differences in electrical parameters are as follows:
Model Package Maximum Input Voltage Output Clamp Voltage Output Current Capability
LN3210 SOT23-3 / SOT89-3 85V 15V 10mA
LN3220 SOT23-3 / SOT89-3 200V 18V 10mA
Tips: By adding independent taps in the auxiliary winding, rectifying and connecting to the PWM IC VDD, and reasonably configuring the tap parameters to reach the clamping voltage point of the voltage limiter when the output voltage is high enough to reach the specified level, thus forcing the voltage limiter to stop outputting, the power consumption of the voltage limiter can be further reduced when the system operates at high output voltages, thus improving the efficiency of the system.
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