Power Supplies: Regulated/Unregulated/Switching/Linear

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Power Supplies: Regulated/Unregulated/Switching/Linear

Postby om_tech_support_JT » Fri Mar 23, 2012 5:39 pm

Q: Should I use a regulated power supply as opposed to an unregulated power supply? Switching vs linear? What's the difference?

A: An unregulated linear supply is less expensive and more resilient to current surges, however, voltage decreases with increasing current draw. This can cause issues if the voltage drops below the working range of the motor amplifier/driver. Fluctuations in line voltage is another issue. This can cause an unregulated linear supply to fluctuate.

A regulated supply can maintain a stable output voltage, therefore making it a better choice for high speed performance. Line fluctuations also do not affect it nearly as much as an unregulated power supply. However, because of additional necessary components, they are more expensive. Depending on the current regulation, a regulated supply may lead to a voltage oscillation that can lead to damage. Back EMF can also cause problems for regulated supplies since the current regeneration may be too large for the regulated supply to absorb, and may lead to an over-voltage alarm/condition.

The pass transistor of a switching power supply continuously switches between low-dissipation, full-on and full-off states. It does not spend much time in the high dissipation transitions at all. This minimizes wasted energy. Voltage regulation is accomplished by varying the ratio of on-to-off time. A linear power supply regulates the output voltage by continuously dissipating power in the pass transistor. The higher power conversion efficiency is an major advantage of the switching power supplies. Also known as switched-mode power supplies, they are likely substantially smaller and lighter than a linear supply due to the smaller transformer size and weight. However, their output response time may be slow. Additional components such as low pass filters are usually required to suppress EMI from the high frequency, high amplitude, switching current.

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