Hi am using a power supply (SMPS) that has output of 5V. even the variation of 20mV is affecting my relay operation.the feedback what am using is TL431. still there is some 20 mV variation. can any one tel me how to improve the regulation?

 

Typically ripple voltage is a function of two variables: capacitance value and ESR. You should be able to calculate the needed value of capacitance based upon analytical equations for your switching topology. You should use a standard value above the calculated, then solely use tantalum capacitors (in parallel if needed) to ensure low ESR.

Steve

 

thank you Steve. by increasing the value of post filter capacitor, required regulation is achieved.

 

yeah, that's right ,but there are other factors that can be at play.. input ripple from high supply impedance / not enough input capacitance. Low switching period, etc.

Steve