Solid State Amplifier design...Need some help.

Discussion in 'Amateur Radio Amplifiers' started by WG3U, Jan 3, 2011.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    How'd you figure that? Normally if you full wave rectify the AC mains (not a good idea), you'd have 170Vdc (120 * sqrt2). From a safety perspective this is a really bad idea. If you intend to use 100V devices, you'd want a 100V power source, so you'd want a transformer that steps down 120V to about 70Vrms.
     
  2. WG3U

    WG3U Ham Member QRZ Page

    Also, I thought there was voltage drop across the rectifier, but then the voltage increases above the input once the smoothing cap is put into place?
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Voltage drop across each rectifier is typically 1V or less per junction: In a full-wave bridge, you have two diode drops effectively in series, so that's 2V at most. Except for low voltage applications you can pretty much ignore it.

    An effective filter capacitor will charge up to the Vpk value. For 15A you need a very big capacitor!
     
  4. WG3U

    WG3U Ham Member QRZ Page

    heres my math, 120v AC RMS into a full wave rectifier should be 169 v pk minus 4v for the rectifier your at 165vpk. so the DC potential output would be but only 106v DC.

    Then with the smoothing cap in place it would be near 160vdc.
    am I looking at this right?
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Without the filter cap, you don't have DC. You have pulsating DC with pulse peaks about 168V. Can't use that to power anything. When you filter it, it becomes DC at ~168V.
     
  6. W8JI

    W8JI Ham Member QRZ Page

    The average voltage with a full wave rectifier and no filter cap is about 106 volts.

    This would also be the filtered dc voltage from a choke input supply with a properly sized choke and capacitor.

    But like you say, either the 106 volts from a choke input or the 168 volts from capacitor input is almost useless, especially when the negative rail would have to be at least 58 or 84 volts above ground with a full wave rectifier.

    The most simple supply would be a 35V RMS transformer, rectifier, and capacitor but a better supply would be a choke input like Ameritron uses or a $witching $upply like they use.
     
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