Lakeshore Learning Materials 622 - Manual (Page 16)

Lake Shore Model 620/622/623/647 Magnet Power Supply User’s Manual
Introduction 1-6
1.3.3 Highly Efficient, Air Cooled, Compact Unit
Lake Shore MPS: Quiet switched-mode design. The output uses a proprietary pulse width modulated
technique that incorporates power hybrid circuitry. Extremely low conduction loss components minimize
internal power dissipation. The MPS is not a direct off-line switching supply. The output is fully floating and
isolated from ground. Active power factor correction draws a sinusoidal AC current waveform from the utility,
minimizes AC line harmonics, and lowers AC current required. Power factor is the ratio of real power
(measured in watts) to the apparent power (measured in volt-amperes). The combination of quiet switched-
mode design and active power factor correction results in a compact, highly efficient, air-cooled unit.
Conventional MPS: Most use linear regulated outputs. The output transistor pass-bank internally dissipates
power not delivered to the magnet. Some units use an off-line switching supply to provide the bulk power and
add output regulation. There is no input power factor correction. Low overall efficiency means higher input
power and current. Without power factor correction, a non-sinusoidal current with high peaks places
tremendous stress on fuses, circuit breakers, outlets, and wiring. Dedicated lines may be required because of
potential interaction with other equipment. These factors result in low overall efficiency, large size, and
considerable weight.