{"id":4105,"date":"2014-10-11T12:58:30","date_gmt":"2014-10-11T01:58:30","guid":{"rendered":"http:\/\/new.radio-active.net.au\/web3\/?page_id=4105"},"modified":"2014-10-11T12:58:47","modified_gmt":"2014-10-11T01:58:47","slug":"switch-mode-power-supply","status":"publish","type":"page","link":"http:\/\/www.radio-active.net.au\/web3\/Articles\/SMPS","title":{"rendered":"Switch Mode Power Supply"},"content":{"rendered":"

Switching Power Supplies By Darryl Smith, VK2TDS<\/h2>\n

By Darryl Smith, VK2TDS<\/b><\/p>\n

These are notes of an impromptu lecture
\ngiven to the Fisher?s Ghost Amateur Radio Club on 18 March 1997. They are not
\nmeant to be an introduction into switching power supplies only. One note of
\nwarning. Switching or switch-mode power supplies often operate with high
\nvoltage DC, with large capacitors. These capacitors may take weeks to discharge
\nif their discharge resistor has blown, and will kill you easily.<\/p>\n\n\n
<\/p>\n

<\/span><\/p>\n<\/td>\n

\n

\tConventional power supplies have the
\n\tfollowing components.<\/p>\n

\n\t<\/p>\n

  • Transformer\n
  • Diode(s)\n
  • Capacitor
    \n\t<\/tul>\n\t<\/td>\n<\/tr>\n<\/table>\n\n\n
    <\/p>\n

    <\/p>\n<\/td>\n

    		\nSwitching Power Supplies have some things
    \nbackward. They have<\/p>\n

    \t<\/p>\n

  • Diode\n
  • Capacitor\n
  • switch\n
  • Transformer
    \n\t<\/tul>\n\t<\/td>\n<\/tr>\n<\/table>\n

    The Diode and the capacitor rectify the
    \nincoming mains voltage generating high voltage direct current. This is done
    \nwithout using a transformer, so a device is added to reduce the turn on current
    \nto the capacitor.<\/p>\n

    Once DC has been generated the transformer
    \nis powered by rapidly turning on and off the DC supply to the transformer. The
    \neffect of this is to create a very high frequency AC signal from the DC signal
    \nin a similar way to an audio amplifier. <\/p>\n\n\n

    \n <\/p>\n<\/td>\n<\/tr>\n<\/table>\n<\/div>\n

    \nBut by turning the switch on and off very
    \nfast the transformer does not need to be as large. Think of a transformer as a
    \ncouple of inductors as shown in this circuit diagram. As the frequency
    \nincreases more signal can get through the inductors. In effect if you ignore
    \nthe voltage change a transformer is not much more than a high pass filter. And
    \nonce the inductive losses are reduced as frequency increases, the transformer
    \ncan get smaller.<\/p>\n

    The capacitor and the diode at the end act
    \nlike a normal power supply. However as the capacitor is being charged more
    \noften, a smaller capacitor may be used.<\/p>\n

    \n\n\n

    \n <\/p>\n<\/td>\n<\/tr>\n<\/table>\n

    Voltage regulation is performed by changing
    \nthe duty cycle of the switch, such that the voltage goes up or down. By turning
    \non the switch longer we have a higher voltage at the output.<\/p>\n

    Turning a switch on and off fast creates
    \nharmonics which cause problems to other equipment nearby. To remove this
    \ninterference, inductors are added on the input and the output.<\/p>\n

     <\/p>\n

    Since Switching power supplies have no
    \nnormal voltage regulator they become up to 90% efficient. Normal linear power
    \nsupplies are about 60% efficient. That means 40% of the power going into your<\/p>\n

    power supply is being lost as heat.<\/p>\n

     <\/p>\n

    In summary Switching power supplies are
    \ncheaper because<\/p>\n

    <\/p>\n

  • Transformers are smaller containing less copper<\/p>\n
  • They have no series voltage regulators as in
    \nnormal power supplies (Such as a 3 pin voltage regulator)<\/p>\n
  • Output capacitors are much smaller<\/p>\n
  • They are more efficient<\/p>\n
  • They are physically smaller<\/p>\n

    <\/tul><\/p>\n

    Of course these power supplies are more
    \ncomplex, but with mass production they become much cheaper.<\/p>\n","protected":false},"excerpt":{"rendered":"

    Switching Power Supplies By Darryl Smith, VK2TDS By Darryl Smith, VK2TDS These are notes of an impromptu lecture given to the Fisher?s Ghost Amateur Radio Club on 18 March 1997. They are not meant to be an introduction into switching …<\/p>\n

    Switch Mode Power Supply<\/span> Read More »<\/a><\/p>\n","protected":false},"author":3,"featured_media":0,"parent":4099,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"jetpack_post_was_ever_published":false,"footnotes":""},"jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/P5cfmK-14d","_links":{"self":[{"href":"http:\/\/www.radio-active.net.au\/web3\/wp-json\/wp\/v2\/pages\/4105"}],"collection":[{"href":"http:\/\/www.radio-active.net.au\/web3\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"http:\/\/www.radio-active.net.au\/web3\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"http:\/\/www.radio-active.net.au\/web3\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"http:\/\/www.radio-active.net.au\/web3\/wp-json\/wp\/v2\/comments?post=4105"}],"version-history":[{"count":1,"href":"http:\/\/www.radio-active.net.au\/web3\/wp-json\/wp\/v2\/pages\/4105\/revisions"}],"predecessor-version":[{"id":4106,"href":"http:\/\/www.radio-active.net.au\/web3\/wp-json\/wp\/v2\/pages\/4105\/revisions\/4106"}],"up":[{"embeddable":true,"href":"http:\/\/www.radio-active.net.au\/web3\/wp-json\/wp\/v2\/pages\/4099"}],"wp:attachment":[{"href":"http:\/\/www.radio-active.net.au\/web3\/wp-json\/wp\/v2\/media?parent=4105"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}