Electronics > Beginners
Small switching amplifier up in smoke. Twice.
John0922:
Fortunately I’ve avoided the grounding mistake thus far! Thanks for the heads up, though.
T3sl4co1l:
Yikes, they actually suggest powering it up without decoupling?!
I wonder what their bench supply and lead lengths were. Possibly that can be done with short leads and a stable supply. At some point I doubt it's going to survive. It may be that you've found that point...
Tim
rstofer:
We never discussed the power supply. So, I'll make some unwarranted assumptions...
If your supply has current limit, look at page 4 of the datasheet. The quiescent current (no input, with 8 Ohm output) is just 9 mA. So, set the supply for 10 mA if you can. This way there is probably no chance of the magic scope escaping. See how it goes before you apply a signal. Feel around for heat - you won't find any at this current level but it won't hurt to look (feel).
What you don't want is a power supply with no current limit and capable of 3A or 5A. What should happen is, if the current exceeds the 10 mA settiing, the output voltage starts to roll back. On a flat out short circuit, the voltage should drop to zero.
The other thing you might do is put your DMM, in current mode, in series with the power supply. Assuming you don't have a low level ammeter in the PS itself. This is a place where an analog meter is handy. If I see the needle start to swing wildly, I can shut off the PS. The slow update rate of many DMMs means I won't know there is a problem nearly as soon.
My Simpson 260 VOM (analog) has a 10 mA and 100 mA scale. I might select the 100 mA scale and if the needle swings much past 10 mA it's time to hit the switch. Later on, I can verify the quiescent current on the 10 mA scale.
One of the modern bench supplies from Rigol or Siglent would be highly recommended. I bought the Rigol DP832 a couple of years ago and it has been terrific. I have actually saved some chips by setting the current limit fairly low. The chips drew too much current (address conflict) and the PS rolled the output voltage back to about 2V. All chips survived!
There are many other options for power but something with current limit would be very handy for this project.
Just some random thoughts...
John0922:
Hi Tim-
Thanks for your comments. I’m using a Dr. Meter power supply— not particularly stable I would imagine, and lead lengths are fairly long. So maybe that’s my problem. Next time through I will start with the decoupling capacitors on, and then maybe give a listen with them off, knowing that might blow the amp.
It will be a few more weeks until I can try this again. I have to order these amps from a special place in Canada because they are tiny surface mount parts— this place sells them mounted to a breakout board.
John0922:
Rstofer-
Thanks for your suggestions. I am able to set a current limit on my Dr Meter power supply, so that’s something I will definitely do. I don’t have an analog ammeter like you (actually I have Dave’s EEVblog Ucurrent Gold ammeter) but monitoring the current is a great idea.
Thanks again.
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