Electronics > Beginners
Hiland Power Supply Kit Voltage Spike
<< < (5/6) > >>
Doctorandus_P:
It seems likely / plausible that you damaged more than the single diode at power up.
Measuring such a high frequency oscillation during a voltage step does seem to indicate that there is a serious flaw in your circuit. But I can not tell if it is by design, or because of faulty components.

How does this circuit perform under load? How fast does it regulate?
A common way to torture power supplies is to have a constant load (few 100mA) and a switchable load ( > 1A) and turn that on/off with a beefy MOSfet or transistor.

It does seem to be an "improved" version of the tuxgraphics power supply.
I bought a few of those long ago, but never bothered to build more than one.
The quality was not good enough, and I found the buttons to set voltage / current pretty annoying.
The rotaries of this Hiland Kit seems to be a much better user interface.
Both designs probably would have improved a lot with the addition of a few opamps.

Tuxgraphics uses an R-2R network, but adds a few bits of PWM to the least significant bits.
The idea is quite nice. You get the PWM for free, and the R-2R attenuation makes the ripple caused by the PWM very small and easy to filter.
The_Boots:

--- Quote from: Doctorandus_P on May 25, 2018, 05:00:52 am ---It seems likely / plausible that you damaged more than the single diode at power up.
Measuring such a high frequency oscillation during a voltage step does seem to indicate that there is a serious flaw in your circuit. But I can not tell if it is by design, or because of faulty components.

--- End quote ---

Oh I'd be shocked if I didn't. Because of the breaker on the transformer, I had to run it a few times before I could trace the magic smoke back to its source.


--- Quote from: Doctorandus_P on May 25, 2018, 05:00:52 am ---How does this circuit perform under load? How fast does it regulate?
A common way to torture power supplies is to have a constant load (few 100mA) and a switchable load ( > 1A) and turn that on/off with a beefy MOSfet or transistor.

--- End quote ---
I actually just got a few 10W resistors yesterday to try to set up some kind of dummy load to test it under load. I wasn't willing to risk any more devices I cared about. I don't have a stock of MOSfets, but I have some old electronics lying around. Any suggestions on which to peek into to see if I can salvage something appropriate?


--- Quote from: Doctorandus_P on May 25, 2018, 05:00:52 am ---Tuxgraphics uses an R-2R network, but adds a few bits of PWM to the least significant bits.
The idea is quite nice. You get the PWM for free, and the R-2R attenuation makes the ripple caused by the PWM very small and easy to filter.

--- End quote ---

OH MY GOODNESS. The comment about PWM makes a TON of sense given what I'd been seeing on the first few pins! I just got a $10 Logic analyzer so I could finally watch all 8 pins together and the ways the lines were changing made almost no sense to me. Pins 0 and 1 are definitely prone to going bonkers at certain levels, but it makes sense to swap out "bonkers" for "PWM". On the other hand SOMETHING is making almost all the pins go bonkers in exact unison. Also, when any line is about to change state in the next tick, that's when things (either that specific line, or most of them together) show this behavior. I'll try to read the Tuxgraphics stuff much more carefully. Thanks!

One other think I noted: there are 5 lines connecting the logic/display board to the main power board. +5 and G are obvious. I and V also seem pretty clear (V rises smoothly from 0-2.8ishV in neat 10mV increments. I assume the main board has a 10x amplification somewhere).
But then there's line "K". Lacking any other explanation, this seems like it might be some feedback/monitoring line. When I probe this with a DMM it immediately triggers the spiking, no matter what the set voltage is. It's a 10 MOhm DMM, but whatever is still leaking through is enough to cause the system to spasm. I'm going to do some other tests on this tonight, I think...
Doctorandus_P:

--- Quote from: The_Boots on May 26, 2018, 02:23:58 pm ---When I probe this with a DMM it immediately triggers the spiking, no matter what the set voltage is. It's a 10 MOhm DMM ...

--- End quote ---

This seems to be very close to the cause of your problem.
It could be an intermittent connector/wire, bad solder joint or blown up component that changes properties under mechanical stress.
If the uC gets bad feedback from the output (Voltage / current) then the control algorithm goes haywire and outputs bad data.
(If the software was "smart" it could detect this, but I doubt that so much attention has been given to it.)
toxuin:
I am not sure if my issue is related to this one, but my unit has voltage spikes as well. A little bit different mode though.

Once I connect a load, voltage goes up to 12-17V for a brief moment and then goes back to specified voltage. I was testing with 5V, 0.2A and a 10Ω 5W resistor, attached a DMM across the load on V DC MAX mode and was connecting and disconnecting the power supply. In this setup I was reading 12V, almost every time I was connecting the load DMM would beep indicating a voltage overshoot.

I did not test however if that happens over certain voltages or constantly, as topic starter did, so I am not really sure if I am observing a same or similar error.
mikerj:

--- Quote from: toxuin on June 01, 2018, 03:06:43 pm ---I am not sure if my issue is related to this one, but my unit has voltage spikes as well. A little bit different mode though.

Once I connect a load, voltage goes up to 12-17V for a brief moment and then goes back to specified voltage. I was testing with 5V, 0.2A and a 10Ω 5W resistor, attached a DMM across the load on V DC MAX mode and was connecting and disconnecting the power supply. In this setup I was reading 12V, almost every time I was connecting the load DMM would beep indicating a voltage overshoot.

I did not test however if that happens over certain voltages or constantly, as topic starter did, so I am not really sure if I am observing a same or similar error.

--- End quote ---

The low sample rate and the crude digital control loop (just a simple integrator) means this supply will inevitably have poor transient response.  However I am a little surprised that applying a load makes the voltage go up, I would expect this to happen with the load is removed.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod