Author Topic: Rigol DP832 question  (Read 1178 times)

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Offline alank2

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Rigol DP832 question
« on: September 17, 2016, 07:32:58 AM »
If I go from 30V to 5V, I noticed that the current spikes up to a few hundred mA briefly.  It once was enough to trip the overcurrent I had set to 350mA.  Is this normal?  I had it connected to a scope and was testing the output.  You could see it move from 30V to 5V not instantly but with some delay...  Any thoughts?
 

Offline rstofer

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Re: Rigol DP832 question
« Reply #1 on: September 17, 2016, 08:03:58 AM »
Charging and or discharging the output capacitors?
 

Online Kleinstein

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Re: Rigol DP832 question
« Reply #2 on: September 17, 2016, 05:42:37 PM »
Some delay is normal as this is a power supply and not a signal generator for fast signals. It already takes some time to discharge the output capacitor.

Going down that much would cause a change in transformer tap, may be even more than one step. This might be the cause for an upset - should not happen, but a cap at the low end might be all it takes. I would also think the current comes from charging the output cap - so there should also be a dip in the output voltage, so the current spike would be consequence of the voltage dropping too much.
 

Offline alank2

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Re: Rigol DP832 question
« Reply #3 on: September 18, 2016, 12:48:19 AM »
So I put a current meter in between and sure enough, this current is not at the terminals, but internal.
 

Offline rstofer

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Re: Rigol DP832 question
« Reply #4 on: September 18, 2016, 02:06:12 AM »
Sure!  Capacitor current i(t) = C dv/dt.  If C is large, dv is large and dt is small, the current can get up there.
 

Offline saturation

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Re: Rigol DP832 question
« Reply #5 on: September 18, 2016, 02:06:49 AM »
I can only speak theoretically, I do not own this unit.

The output cap has to be discharged down to obtain the new set voltage.  In common designs the bleeder resistor is across the output cap so this is done passively.

If there is no output resistor of any type then the design must switch a bleeder in, and it may appear internally as a current spike until the regulator  stabilizes the output to your setting.  There are many reasons for the spike to happen, such as the regulator circuit seeing too rapid a discharge of the output cap and attempts to pull it up to reach your set voltage.

So long as this current does not appear on the output, your UUT is safe, however, if this is not a bug or a design flaw, its still undesirable since the PSU's meters should always represent the status of its outputs, not what may be happening internally. 
Best Wishes,

 Saturation
 


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