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Power Supply Topology for Use with Multifrequency Monitors

IP.com Disclosure Number: IPCOM000112589D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 97K

Publishing Venue

IBM

Related People

Coyne, D: AUTHOR [+2]

Abstract

Disclosed is an economic power supply (PS) topology suitable for multifrequency monitors that offers greater efficiency than conventional monitor PS designs plus simple power management. Typically, this topology will benefit any application where the range of frequencies supported requires a variation in the B+ supply of more than 20%.

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Power Supply Topology for Use with Multifrequency Monitors

      Disclosed is an economic power supply (PS) topology suitable
for multifrequency monitors that offers greater efficiency than
conventional monitor PS designs plus simple power management.
Typically, this topology will benefit any application where the range
of frequencies supported requires a variation in the B+ supply of
more than 20%.

      An inherent problem with multifrequency monitors is the
requirement to change the supply level to the deflection circuitry
and high voltage transformer as the frequency of operation changes.
The usual topology in monitor designs is a single transformer to
convert the rectified mains into the multiple secondary voltages.
These secondaries are scaled together by the transformer.  So to
obtain a variable output all outputs will be varied by the same
ratio.  If this method was used in a multifrequency monitor when
changing from the lowest to the highest frequency, the variation
would be such as to cause excessive dissipation in the other
secondaries which, ideally, require to remain at a fixed voltage
regardless of operating frequency.

      Conventionally, the method of overcoming this is to use a
secondary DC/DC converter which will take a fixed voltage from the
initial SMPS transformer and transform it into a secondary DC level
which can be independently varied with frequency.  This second
converter is usually a buck or a boost topology.  The B+ supply is
the major power source of the supply and will typically deliver
between 35 and 40 watts to the High Voltage Transformer and the
Deflection circuitry.  With this cascaded topology the efficiency of
the system is inherently poor, as shown below.

  E(f) = Efficiency of flyback converter, typically of the order of
80%

  E(b) = Efficiency of boost converter, typically of the order of 85%

  E(s) = Efficiency of total system

  E(s) = E(f)*E(b) = 0.8 * O.85 = 0.68.

      With an efficiency for the primary power source of only 68% the
input power required to deliver typically 35 to 40W is between 51.5
and 58.8W.

      An advantage of using this approach is to offer power
management by allowing the second DC/DC converter to be switched off
by a device running from the initial transformer.  Any alternative
approach must satisfy three basic criteria.

1)  It should avoid the compound inefficienc...