Re: Voltage regulator with alternate voltage source...

nd Off-Topic Posts' Subject: RE: Voltage regulator with alternate voltage source... Dwight wrote: > How many pixels will the camera have? 1024. The (at the time) secret sauce image sensor is a Mostek MK4008-9. 32x32 pixel image. Bill S.

Re: Voltage regulator with alternate voltage source...

On Monday (04/11/2016 at 11:21AM -0400), Bill Sudbrink wrote: > Dwight wrote: > > How many pixels will the camera have? > > 1024. The (at the time) secret sauce image sensor > is a Mostek MK4008-9. 32x32 pixel image. Which was a topless DRAM right? Not often a guy gets to use the word

RE: Voltage regulator with alternate voltage source...

Dwight wrote: > How many pixels will the camera have? 1024. The (at the time) secret sauce image sensor is a Mostek MK4008-9. 32x32 pixel image. Bill S.

Re: Voltage regulator with alternate voltage source...

The data sheets all spec stability when the output has a fraction of one uF on the output, but for a variety of (bad) reasons some designers insist on putting, sometimes, tens thousands of often very low ESR uF at the output. That's extremely hard on the protection diode and it'll have to be

Re: Voltage regulator with alternate voltage source...

To protect a regulator against a back volt, you can put a diode, in reversed polarity. How many pixels will the camera have? Dwight

RE: Voltage regulator with alternate voltage source...

Brent Hilpert wrote: > Well that's neat. Thanks. > I assembled the Cromemco kit version of the Cyclops > (The kit version presented an interface for a computer > rather than the scope drive of the magazine article. I was recently able to acquire the S-100 interface cards for the Cyclops. I'm

Re: Voltage regulator with alternate voltage source...

Bill, surely you have a pile of 1N400x diodes someplace. Put 6 in series, forward, between the input and supply. That should ensure it is safe. If the voltage is higher than 8 volts, it would mean there isn't enough current to worry about. Dwight

Re: Voltage regulator with alternate voltage source...

On 2016-Apr-08, at 11:58 AM, Bill Sudbrink wrote: > I don't know why I bothering to be coy about it... > > My unit here: > > http://wsudbrink.dyndns.org:8080/images/cyclops-latest/P4060005.JPG > http://wsudbrink.dyndns.org:8080/images/cyclops-latest/P4060006.JPG > > Actually, I'm further

Re: Voltage regulator with alternate voltage source...

On 2016-Apr-08, at 11:27 AM, Mouse wrote: >> I archive all data sheets I run across and I found this information >> on both TI and Fairchild data sheets for the 78H05, LM340 and LM78XX >> devices - it is usually under a heading called Application Hints and >> for some reason Fairchild have

RE: Voltage regulator with alternate voltage source...

> > > 1) I have a 12 volt DC supply. 12 volts seems to be > > >within the VIN range for the 7805s whose data > > >sheets I've now read. Can I simply apply 12 volts? > > > > Yes, but that regulator might get mighty hot! I would > > not do this for fear of cooking the poor thing. > >

RE: Voltage regulator with alternate voltage source...

> > First, a few quick "whys": > > 1) The 7805 is actually a Motorola MC7805CP, date >code 7308 with gold leads. Very hard to exactly >replace. Any reason why it would have to be an exact replacement? In any case, the behaviour of the 7805 if you apply a voltage to the output with

RE: Voltage regulator with alternate voltage source...

I don't know why I bothering to be coy about it... My unit here: http://wsudbrink.dyndns.org:8080/images/cyclops-latest/P4060005.JPG http://wsudbrink.dyndns.org:8080/images/cyclops-latest/P4060006.JPG Actually, I'm further along than that, but I don't have more recent photos. Original unit

RE: Voltage regulator with alternate voltage source...

William Donzelli wrote: > > 1) The 7805 is actually a Motorola MC7805CP, date > >code 7308 with gold leads. Very hard to exactly > >replace. > > Is that the big flat plastic package with the wide > flat leads? Nope, purple ceramic. The heat transfer plate is gold plated too. > > 1) I

Re: Voltage regulator with alternate voltage source...

Silly question, but then I'm feeling silly today: Why not just connect the output and input of the 7805 together and power from the normal +8 line with your +5 supply? --Chuck

Re: Voltage regulator with alternate voltage source...

> 1) The 7805 is actually a Motorola MC7805CP, date >code 7308 with gold leads. Very hard to exactly >replace. Is that the big flat plastic package with the wide flat leads? I might have a few of those around, but I agree, not an easy variant to find. > 1) I have a 12 volt DC supply.

Re: Voltage regulator with alternate voltage source...

> I archive all data sheets I run across and I found this information > on both TI and Fairchild data sheets for the 78H05, LM340 and LM78XX > devices - it is usually under a heading called Application Hints and > for some reason Fairchild have removed these Hints from the sheets > you quote. >

RE: Voltage regulator with alternate voltage source...

First, a few quick "whys": 1) The 7805 is actually a Motorola MC7805CP, date code 7308 with gold leads. Very hard to exactly replace. 2) As per the design of the unit, the 7805 is soldered to the foil side of a single sided, copper clad circuit board with no through hole plating.

Re: Voltage regulator with alternate voltage source...

Keep in mind that "not powered" and "open" are very different things. What do the data sheets say? I will admit that this is all careening towards the academic at this point... -- Will On Fri, Apr 8, 2016 at 1:31 PM, John Robertson wrote: > On 04/08/2016 8:54 AM, wulfman

Re: Voltage regulator with alternate voltage source...

On 04/08/2016 8:54 AM, wulfman wrote: https://www.fairchildsemi.com/datasheets/LM/LM7805.pdf http://www.ti.com/lit/ds/symlink/lm78l05.pdf ( page 8 gives you the internals for a low power version ) Nothing in the data sheet saying you cant apply voltage to the output. As per the low power

Re: Voltage regulator with alternate voltage source...

https://www.fairchildsemi.com/datasheets/LM/LM7805.pdf http://www.ti.com/lit/ds/symlink/lm78l05.pdf ( page 8 gives you the internals for a low power version ) Nothing in the data sheet saying you cant apply voltage to the output. As per the low power version circuit diagram i cant see how you

Re: Voltage regulator with alternate voltage source...

On 04/07/2016 4:41 PM, William Donzelli wrote: Does this warning assume that there is something on Vin, and not open? With a quick look at the internal schematic of an old-school 7805, it seems like what Bill suggests (leaving Vin open) will not actually do much. -- Will This warning is for

Re: Voltage regulator with alternate voltage source...

"...if you leave the unregulated rail _unattached_ and put +5 switcher straight onto the regulated +5 rail..." My error, I read that as "attached". In any event, just lift both the 7805 IN and OUT pins, and then supply known-solid +5DC between the OUT and GND pads on the board. No, you can't

Re: Voltage regulator with alternate voltage source...

Does this warning assume that there is something on Vin, and not open? With a quick look at the internal schematic of an old-school 7805, it seems like what Bill suggests (leaving Vin open) will not actually do much. -- Will On Thu, Apr 7, 2016 at 7:23 PM, John Robertson

Re: Voltage regulator with alternate voltage source...

On 04/07/2016 2:18 PM, Bill Sudbrink wrote: drlegendre wrote: Not saying it's going to smoke-out, but it does seem like a wonky thing to do. I disagree about "wonky" let me try with more diagram and less English: (+8) | VIN|ceramic cap |-][- ___| | |

Re: Voltage regulator with alternate voltage source...

On 04/07/2016 2:25 PM, geneb wrote: On Thu, 7 Apr 2016, Bill Sudbrink wrote: Maybe I'm overthinking this. If I just put regulated +5 on the 7805 VIN will it work? Isn't the minimum input voltage for a 7805, 6vdc? g. More like 7VDC input minimum (dropout voltage) for 7805 - there are data

RE: Voltage regulator with alternate voltage source...

On Thu, 7 Apr 2016, Bill Sudbrink wrote: Maybe I'm overthinking this. If I just put regulated +5 on the 7805 VIN will it work? Isn't the minimum input voltage for a 7805, 6vdc? g. -- Proud owner of F-15C 80-0007 http://www.f15sim.com - The only one of its kind.

RE: Voltage regulator with alternate voltage source...

drlegendre wrote: > Not saying it's going to smoke-out, but it does > seem like a wonky thing to do. I disagree about "wonky" let me try with more diagram and less English: (+8) | VIN|ceramic cap |-][- ___| | | 7805 |--GROUND | |

Re: Voltage regulator with alternate voltage source...

On 04/07/2016 2:03 PM, William Donzelli wrote: Per his description, the 7805's input will be open. It will not try to source any current, as it will have none to give. I suppose there might be a little leakage. -- Will If his intention is to bypass the 7805 then it should have both input

Re: Voltage regulator with alternate voltage source...

-Oorspronkelijk bericht- From: Bill Sudbrink Sent: Thursday, April 07, 2016 10:38 PM To: 'General Discussion: On-Topic and Off-Topic Posts' Subject: Voltage regulator with alternate voltage source... If you have a circuit which is normally designed to operate with an unregulated supply

Re: Voltage regulator with alternate voltage source...

Per his description, the 7805's input will be open. It will not try to source any current, as it will have none to give. I suppose there might be a little leakage. -- Will On Thu, Apr 7, 2016 at 4:58 PM, drlegendre . wrote: > Err.. unless the voltage of the switcher is

Re: Voltage regulator with alternate voltage source...

Err.. unless the voltage of the switcher is identical to that of the 7805, then one device will source current, and the other will sink it. Like putting two 6V batteries in parallel, where one is fresh and the other weak. Current will flow until the potentials are equalized. But with two

Re: Voltage regulator with alternate voltage source...

You should be just fine. On 4/7/2016 1:38 PM, Bill Sudbrink wrote: > If you have a circuit which is normally designed to > operate with an unregulated supply, through a regulator... > say unregulated +8 through a 7805 to a regulated +5 and > you want to test it independent of the +8 supply, if >

Voltage regulator with alternate voltage source...

If you have a circuit which is normally designed to operate with an unregulated supply, through a regulator... say unregulated +8 through a 7805 to a regulated +5 and you want to test it independent of the +8 supply, if you leave the unregulated rail unattached and put +5 switcher straight onto