propstick usb onboard vreg very hot, no worky now.
TonyZ
Posts: 13
Hi,
I guess it was the nokia lcd i had·using the onboard·3vout that did it, but the voltage regulator now gets really hot (even with no load, just the 5v power supply·hooked up to the prop)
I figure it was the lcd load that did it because i have had the same 5v power supply powering prop for months, and decided to use the 3v out (lazyness) to power the lcd's 3vin . It was running fine for a week or so then suddenly not working. no smoke when it went out, but the vreg was/gets very hot.
The vdd now has·something like·.11 mv out at the vdd now. So I took the onboard smd vreg off and supplied 3v to the vdd but the prop tool still doesn't recognize the prop. what else could be toasted that i could replace on the prop stick? any hope of recovery? or is it curtains for this popstick?
thx
kids, don't be lazy, play it safe, use a separate 3v source for your components!
<edit>This definitely·qualifies as a stupid thing done to a·propeller.·**kicks self..again**
Post Edited (TonyZ) : 4/21/2007 1:21:50 AM GMT
I guess it was the nokia lcd i had·using the onboard·3vout that did it, but the voltage regulator now gets really hot (even with no load, just the 5v power supply·hooked up to the prop)
I figure it was the lcd load that did it because i have had the same 5v power supply powering prop for months, and decided to use the 3v out (lazyness) to power the lcd's 3vin . It was running fine for a week or so then suddenly not working. no smoke when it went out, but the vreg was/gets very hot.
The vdd now has·something like·.11 mv out at the vdd now. So I took the onboard smd vreg off and supplied 3v to the vdd but the prop tool still doesn't recognize the prop. what else could be toasted that i could replace on the prop stick? any hope of recovery? or is it curtains for this popstick?
thx
kids, don't be lazy, play it safe, use a separate 3v source for your components!
<edit>This definitely·qualifies as a stupid thing done to a·propeller.·**kicks self..again**
Post Edited (TonyZ) : 4/21/2007 1:21:50 AM GMT
Comments
-Phil
Thanks, knowing that it would be ok to power the lcd with the 3vdd of the prop, I dont feel quite as stupid.
The only short that could have happened is where wire·I had going the vin on the prop·broke off of the plug it was soldered to·and i didn't have a soldering iron handy so i wrapped it around where it once was soldered. Maybe one of the threads in the wire shorted Vin to Resn or Vin to P8. Might that be bad enough for the vreg to cook and the now dead prop?
Pic attached.
thx
thanks Mike
just a idea
dan
oops.. .disregard... i see you dont have the dip version
sorry
Great thought. yep not possible. I wish.
Mike, you really think they might give me a discount even though it was my own brainless move that killed it?
thx
On Monday contact Jim Carey, our Sales Manager (jcarey@parallax.com) - yes, that's his real name.
He doesn't tease our customers, so if you blew it up you can just tell him the facts.
I think he will replace it for free anyway.
Ken Gracey
Parallax, Inc.
but its better now, replaced the chip
dan
I have a Parallax 4-Line LCD (Parallax P/N 27979) on a proto-board Propeller design almost identical to the Parallax designs (series LDO 5V & 3V regulators, fed by 7VDC). When the back-light of the LCD is on (no additional load other than the Propeller and EEPROM), my regulators get pretty warm. I'm using two TO-220 regulator packages standing vertically plugged into the protoboard. When I turn the LCD backlight off the regulators run as cool as cucumbers.
I swapped the LCD with another brand-new one of the same P/N - same result. Otherwise the LCD's work just fine.
Looking at the LCD, it sems Parallax took an OEM parallel LCD module and plopped an SX-based controller on it via a piggy-back board.
This leads me to wonder if in the SX LCD controller, Parallax is multiplexing the backlight LED's or not - a common practice to avoid this back-light LED power drain. Seems not... Even if the SX couldn't handle the multiplexing along with it's other tasks - multiplexing the backlight LEDs would be a simple matter with a few cents worth of external components.
Anyone else have experience with these Parallax LCD's drawing a lot of backlight current?
Dave
http://forums.parallax.com/showthread.php?p=621507
Graham
I don't know if Graham means current limit from +5V or from a higher voltage. If it's from +5V then it will reduce the current but that also means the backlight brightness. If it's from higher voltage then the “current limiter” (resistor) will have the same problem as the regulator and get very hot.
Although it is possible to use a switching regulator to +5V or even a +5V switching power-pack the easier way to do it is with PWM. The trouble with doing this PWM under software is that it is possible to cook the backlight if you are running from a higher voltage. One solution that I used on the same type of LCD was a simple 555 timer driving an NPN into the backlight via a small peak current limiting resistor. I even got away with using little SOT-23 pack transistors to drive the backlight while the input supply was +13.8V.
Of course you can switch the backlight on and off from +5V to achieve a lower average current and cut heat dissipation in the regulator but the PWM drive from the higher voltage is a better approach I feel and allows for full brightness.
*Peter*
Drone, to help clarifiy, my LCD (color w/backlight) was ripped from a Nokia and is controlled by Sparkfun's breakout board.
cheers
Tony, I suspect your screen will be more power efficient, you could always measure the current anyway, I think Dave was just making the general point that a backlit LCD can draw quite a bit of current.
graham