Re: power supply regulation
- From: MooseFET <kensmith@xxxxxxxxx>
- Date: Mon, 15 Dec 2008 16:57:29 -0800 (PST)
On Dec 15, 9:23 am, Phil Hobbs
<pcdhSpamMeSensel...@xxxxxxxxxxxxxxxxxx> wrote:
MooseFET wrote:
On Dec 15, 12:40 am, Jamie Morken <jmor...@xxxxxxx> wrote:
Hi,
I am using the voltage error * gain to set dutycycle for regulating the
voltage output of a power supply, under load we are getting a couple
volts lower output voltage than the desired output voltage, but other
than that overall the regulation seems to be working well. What is a
good way to regulate up to the last couple of volts? I was thinking
adding an intergral term to the dutycycle calculation (summed voltage
error over time * gain) to make it a PI loop, but is there other
techniques that work well or better than the standard PID loop technique
for power supply regulation?
A PI control is fairly simple to do and works very well for this sort
of situation. You may want to do something like this:
+-!<--+
! !
+-->!-+
! !
---/\/\-------+----/\/\-+-!!--+-
! !
---!-\ !
! >----------+----
GND-----!+/
The diodes restrict the range over which the "I" part of things can
swing.
Those diodes for anti-windup are a good idea, but you have to design the
loop carefully. The wave-a-dead-chicken school of anti-windup design
will often cause nonlinear oscillations during transients, and so make
things worse rather than better. Back around 1981 I was building PLLs
for satcom frequency references, and when I put in anti-windup diodes I
had some pretty amusing looking settling transients until I figured out
what was going on.
As with many thing, if you do it wrong the results aren't very good.
The advantage of the diodes over other simple methods of doing the
antiwindup is that you don't cause large difference voltages to appear
on the input of the op-amp.
You never want to do just an integrator and then let it clip at the
rails unless the op-amp has nose to tail diodes on its input. Hitting
the rail builds up a large difference voltage on that op-amp that can
lead to all manner of strangeness and long recovery times.
.
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