Short handbook of current sensing in power DC supply lines - Part three

June 12, 2014 // By Petre Petrov
Short handbook of current sensing in power DC supply lines - Part three
Petre Petrov in this third article of the series considers circuits for sensing currents in paralleled rectifiers.

Introduction
 
We may need to connect in parallel simple diodes or bridge rectifiers. In the simplest case the paralleled devices should be from the same type. This approach has several advantages, e.g.:

  • we can use smaller and cheaper rectifiers
  • the individual switching currents of the rectifiers is smaller, the electromagnetic emissions can be smaller and the filtering of these emissions can be a simpler task.
  • the total circuit can be made more reliable. In the case that one rectifier is damaged, the other may take the load for some time and the system will continue to operate.
  • the cooling of the rectifiers/bridges may become simpler.

But the paralleling of rectifiers or bridges has several drawbacks, e.g.:

  • it requires the usage of equalization resistors.
  • if we wish to monitor the operation of each rectifier, we should use special interface circuits capturing the signal from the equalization resistors and sending that signal to the ADC.
  • the pcb design can be more complicated
  • the larger number of the rectifiers or bridges can take more real estate on the pcb
  • we have some voltage drop over the equalization resistors

If need be, we can connect in parallel filtering capacitors for the rectifiers in the mains power supply. We may use smaller capacitors. This approach has several advantages as discussed in the following comment.

The capacitors with smaller capacity usually are:

  • with higher working voltages
  • with smaller leakage currents
  • smaller size, better quality (lower parasitic components), 
  • widely available, lower price, etc.

But the paralleling of filtering capacitors may require equalization resistors in order to make the charge and the discarded currents equal for all paralleled capacitors.
 
Here we will examine several solutions for monitoring the currents in the paralleled rectifiers and paralleled capacitors. That monitoring task is important because ideally the current load should be divided equally between all paralleled rectifiers. Also that is important because we can monitor the operations of the

Design category: 

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