DC DC PSU input filtering

[andersendr]

Not sure of the best description for the subject as I do not have a lot of experience with power supply's.  Not even sure if this would be called a PSU.  I have 24VDC supplied from lead acid batteries with the need to apply filtering or isolation to better clamp over voltages.  This will be regulated down later to power a MCU but this post is mainly on the over voltage protection.  Also connected to these batteries are the DC PM motors which are connected through a controller that will allow for regenerative breaking.  I am trying to determine a solution to reduce the high voltage transients during regen braking.  My current thinking is to use TVS diodes but thought I should ask the community what they think.  If you need more info let me know. 

[Kremmen]

The battery will absorb a not insignificant amount of braking current. If you supply the MCU from a psu circuit with high enough max input voltage, then it is quite possible that's all you need. You cannot easily use overvoltage clamping diodes or TVSes since you don't have a low impedance reference handy where to shunt the overvoltage. The battery won't do because that will always exhibit the voltage of your regeneration...
Depending on the size of your motors you might need braking resistors to keep the voltage in check. But then you also need a way to activate the resistors which creates more complications... Easiest solution: design the MCU psu with high enough max input voltage that you won't hit it in normal operation. Possibly you will want to look into some kind of emergency crowbar if there is a real risk of significant surges.

[andersendr]

All right that makes sense. I never really thought about that I had no where to dump the over voltage when using a TVS.  Good point about just using a voltage reg with a high enough input.
Would it be acceptable to maybe use two regulators?  Have the first one that will convert a range of 24V to spike down to 24V and then another one that will regulate that 24V max down to the MCU voltage.

[Kremmen]

Sure you can use 2 regulators in series. Commonly that arrangement is used so that you have a rougher (switching) pre-regulator that drops the voltage nearer to the final voltage and then an accurate one (linear) to produce the final output. The is no physical law that says how you must do it but that way you minimize power losses and maximize accuracy and dynamics of the solution. Most commonly you see these in lab power supplies where transformer secondaries may additionally be switched as needed.