error amplifier design for SMPS (buck converter)

Discussion in 'General Electronics Chat' started by arunkps, Apr 3, 2014.

  1. arunkps

    Thread Starter New Member

    Jan 28, 2014
    16
    0
    Hi,

    I am designing a synchronous buck converter & the specs are as follows:
    Vin = 1.8V
    Vo = 0.5V
    Io = 1mA
    Fsw = 1Mhz
    Vripple(p-p) = 500 micro volts

    For this I need to design error amplifier. My understanding is that I need to design a two stage op-amp with input differential amplifier followed by a common source amplifier. I read multiple sources for designing a two stage opamp but I did not get the grip. I am confused how to choose the specifications like input swing, Bandwidth, gain, required output voltage from error amplifier. Please help me to design a error amplifier and a suitable compensation for my project.
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,542
    1,251
    Why in the world do you want to use a switching power supply for an output power of 0.0005 W? There is no switcher topology that will do this. You could do it with a linear regulator, but again - why? I guess you could use a 470 ohm resistor and two shottkey diodes stacked up to form a low-voltage zener, but there's no adjustability there. You don't have to worry about power dissipation in a shunt regulator because the total circuit power (regulator + load) would be only 5 mW. AND - no ripple.

    ak
     
    arunkps likes this.
  3. arunkps

    Thread Starter New Member

    Jan 28, 2014
    16
    0
    Hi,

    Basically I am doing my project on buck converter. The specifications are chosen by myself with no specific technical considerations. May be that is the reason I did not notice the very low output power requirement. Thanks for mentioning that. My objective is to design a synchronous buck converter. Now as you said I will change my specification & increase my output current.

    Can you help me to design an error amplifier?, I hope the output current will not affect the opamp specs much. My concern is I am wondering how to chose the specification for the error amp like the gainbandwidth, input swing,output swing, slew rate etc...,
     
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