What factors limit the power supply miniaturization?

- Jun 06, 2018 -

What factors limit the power supply miniaturization?

With the development of power modules, engineers have focused on how to make modules smaller and lighter. In fact, we all understand that we can increase the power density of products by increasing the switching frequency. But why has the module's volume so far not changed so much? What restricts the increase of switching frequency?

With the application of switching power supply products under the market, increasingly smaller, lighter, high-efficiency, low-radiation, low-cost and other characteristics are required to satisfy various electronic terminal equipments. In order to meet the current portable electronic terminal equipment, the switching power supply must be made small in size. Due to its light weight, it has become a matter of increasing concern for designers to increase the operating frequency of switching power supplies. However, what are the factors limiting the frequency of switching power supplies? In fact, it mainly includes three aspects: switch tubes, transformers, and EMI and PCB design.

1, switch and switching frequency

Switching tube as the core device of the switching power supply module, its switching speed and switching loss directly affect the limit of the switching frequency, the following analysis for everyone about

a, switching speed

The loss of the MOS transistor consists of switching loss and drive loss. The turn-on delay time td(on), rise time tr, turn-off delay time td(off), and fall time tf.

For this MOSFET, its limit switching frequency is: fs=1/(td(on)+tr+td(off)+tf) Hz=1/(8ns+91ns+38ns+32ns)=5.9MHz, in practice In the design, since the duty cycle of the control switch achieves voltage regulation, the on and off of the switch tube cannot be instantaneously completed. That is, the actual limit switching frequency of the switch is much less than 5.9 MHz, so the switching speed of the switch tube itself limits the increase of the switching frequency. .

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