Benjolin/Zeitgeist questions

macumbista · Posted: Fri Aug 31, 2012 6:07 am Post subject:

I'm having a bit of a situation here... I've got a beautiful-sounding Benjolin PCB made, problem is it runs really hot! I've got an 18V AC adapter running to a Vellman regulator board (LM337 and LM317 pair), Giving out 15V DC. At first I noticed that the Vellman regulators were hot because I had them choked down to 12V, so I took them up to 15V. Then I noticed that the on board regulators on the Benjolin are getting hot... I checked over the whole PCB and didn't find any shorts. Weird because it sounds fine.... Positive and negative rails each appear to be drawing 50 mA (got reading of 0.05 on the 10A setting, am I reading this correctly?). Any things to look for in particular?

[EDIT: decimal places are not my friend today. Been up all night working on this thing...]

prgdeltablues · Posted: Fri Aug 31, 2012 9:04 am Post subject:

Well, I'm not familiar with the details, but regulating 15V down to 9V at 50mA is quite a tall order in terms of the energy = heat that the regulators have to shed. That's 6*50 = 300mW power, and if you're using the 100mA LM317 their thermal resistance to air is about 160 degC/W so expect a surface temperature of about 85 degC. That's hot, but within spec. You'd be better off adding heatsinks. Or using a lower voltage AC adapter. (As you've found out, you can reduce the demand on the on-board regulators by applying a lower voltage to them, but that simply transfers the problem to your AC/DC converter - the energy has to be lost as heat somewhere!)

Peter

macumbista · Posted: Fri Aug 31, 2012 9:46 am Post subject:

Thanks for the reply. First thing I did was put some heatsinks in last night. The instrument will be away from me for a while, it was kind of a last minute thing, but in a couple weeks I'll reevaluate the power supply. It's interesting that Rob says the Benjolin can be powered from up to 18V DC, that's why I didn't think about the heat of the regulators... Live and learn, unfortunately in that order. Just don't want to see the instrument go into thermal shutdown in the middle of a performance!