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Soft-Start Controller For Switching Power Supplies

From Microchip Technology, Inc.
 

 
This technical brief describes a microcontroller based Soft-Start Controller circuit for a switching power supply. Start-up is a stressful time for the power driver section of a switching power supply. Because the output voltage is initially zero, the feedback error initially jumps to its maximum. The large feedback error then drives the loop filter to its limit, which drives the power switching transistors in the driver section of the power supply at their maximum rating. This condition continues until the output voltage of the power supply approaches its nominal value. If the load being driven by the power supply is capacitive, the problem is exaggerated due to the large transient currents required to charge the capacitive load. In extreme instances, the repeated high stress of start-up can result in catastrophic failures in the driver section, typically, the power MOSFET transistors or the power rectifiers.
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Topics of Interest
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9.2.4 MOSFET Gate Drive Circuits As described above, the gate driver must be able to deliver outward- directed current or be a “source” to drive gates in a positive direction to turn... (Read More)
Chapter 9.2.11 MOSFET Maximum Gate Voltage Specifications Most MOSFET gates have a maximum gate-to-source voltage specification of ±20 V. The gate is easily destroyed if that limit is... (Read More)
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