Brian Hoskins
New Member
Hi everyone,
I've been assigned with the task of designing a project to suit a particular specification. I won't bother going into the details of the project, but part of the specifications says that the power supply must be regulated and have less than 100mV ripple.
With that in mind I've been looking at the datasheet for a few linear voltage regulators. They quote a Ripple Rejection ratio which is expressed in dB. From the specification I know that a maximum of 100mV ripple is permitted on the output side of the voltage regulator, and I hoped to be able to use information in the datasheet to calculate how much ripple would be permitted on the input side of the regulator such that it's rejection capabilities would leave less than 100mV ripple on the output side. The Ripple Rejection ratio is expressed in dBs and I'm at a loss as to how I use this figure to my advantage to be honest.
If I knew how much ripple I was permitted on the input side of the regulator, I could work out the size of the resevoir capacitors on the output of the bridge rectifier, to make sure the ripple applied to the input of the regulator results in less than 100mV ripple on it's output. Does that make sense?
I've done a bit of googling but I haven't found it too helpful to be honest. I'm not expecting you guys to google for me - if you have some suggestions to mind then I'd be happy if you could put them forward for me, and other than that I'll see if I can find any examples of power supply design where ripple limits are taken into consideration.
Brian
I've been assigned with the task of designing a project to suit a particular specification. I won't bother going into the details of the project, but part of the specifications says that the power supply must be regulated and have less than 100mV ripple.
With that in mind I've been looking at the datasheet for a few linear voltage regulators. They quote a Ripple Rejection ratio which is expressed in dB. From the specification I know that a maximum of 100mV ripple is permitted on the output side of the voltage regulator, and I hoped to be able to use information in the datasheet to calculate how much ripple would be permitted on the input side of the regulator such that it's rejection capabilities would leave less than 100mV ripple on the output side. The Ripple Rejection ratio is expressed in dBs and I'm at a loss as to how I use this figure to my advantage to be honest.
If I knew how much ripple I was permitted on the input side of the regulator, I could work out the size of the resevoir capacitors on the output of the bridge rectifier, to make sure the ripple applied to the input of the regulator results in less than 100mV ripple on it's output. Does that make sense?
I've done a bit of googling but I haven't found it too helpful to be honest. I'm not expecting you guys to google for me - if you have some suggestions to mind then I'd be happy if you could put them forward for me, and other than that I'll see if I can find any examples of power supply design where ripple limits are taken into consideration.
Brian