USB 5V to 1.5V - Page 2 - Electronic Circuits Projects Diagrams Free

Hero999 · 17th September 2007, 03:06 PM

Does it?

An LM317 will go all the way up to 1.5A, although at those sorts of currents a switcher does tend to make more sense.

speakerguy79 · 17th September 2007, 08:54 PM

I think it would. Unless I'm being retarded again

Shouldn't he be able to get 1.5V @ 200ma from a capacitor switcher with an input of 5V @100ma assuming 60% efficiency?

Of course, if the USB port will just allow him to draw whatever current he wants, then I agree a linear would be a better way to go. These capacitive switchers are only good for a few hundred mA I think anyway. Any more and you have to go inductive.

mvs sarma · 18th September 2007, 12:16 PM

Quote:

Originally Posted by iONic

I'm looking for a simple way to use the 5V USB power and step it down to 1.5V in order to power a hand-held Audio player/recorder. I'm not sure PWM is the way to go or not, but would not a simple Zener regulator do??

Don't call it any more Handheld-- it is now PC tied!!

For a 1.5V , why at all bother so much and finally loose its mobility?

Use a duracell which will last for say 20hrs of intermittent use. If forcontinuous listening, transfer them to the PC as wave or MP3 files witha suitable software.

iONic · 21st September 2007, 06:10 PM

I've been reading that the USB power standard, (100mA unless requested by the USB device), is not often followed.

So I connected a Luxeon Star III to the power of the USB port on my laptop and
.....WOW! It lit up well! After hooking up a meter to it it was drawing 1300mA,
with a 1k resistor....maybe 200mA. Either way more than the "allowed" 100mA.

Hero999 · 21st September 2007, 06:17 PM

A 1k resistor in series with the LED gave 200mA? I don't believe you!

What's the LED rated to?

Did you use a series resistor when it drew 1300mA?

mvs sarma · 21st September 2007, 07:12 PM

Quote:

Originally Posted by Hero999

A 1k resistor in series with the LED gave 200mA? I don't believe you!

What's the LED rated to?

Did you use a series resistor when it drew 1300mA?

Hi, As i understand from the post , it is 200mA with !K series resistor or 1300mA dirctly-- and he comments- either way more than the specified 100mA.

Hero999 · 21st September 2007, 08:43 PM

Unless I'm misunderstanding something, ohm's law dictates that only 1.5mA should flow assuming the output from the USB is 5V and the forward LED voltage drop is 3.5V.

mvs sarma · 21st September 2007, 09:37 PM

I agree with you HERO999

iONic · 21st September 2007, 09:59 PM

Digital multimeters are darn accurate. The 1300mA was see when the Luxeon LED was connected without a resistor. The LED got warm within 5 seconds.

vF = 3.9v, Max I = 1000mA

Specs for the LED are here: http://www.luxeonstar.com/item.php?i...rtno=LXHL-LW3C

**Nigel Goodwin** · 21st September 2007, 10:21 PM

Quote:

Originally Posted by iONic

Digital multimeters are darn accurate.

You also said "with a 1K resistor perhaps 200mA", which was complete drivel!!.

iONic · 21st September 2007, 10:41 PM

My apologies, I just remeasured this current and I do believe it's time to put FOOT-IN-MOUTH(yes I fell down and bumped my head), it is 2.25mA.

Hero999 · 21st September 2007, 11:53 PM

May this bee a lesson to you in estimating figures.

2.25mA sounds about right when dealing with values of 5V and 1k, 200mA sounds far to large when dealing with those sorts of values..

**Nigel Goodwin** · 22nd September 2007, 09:29 AM

Quote:

Originally Posted by Hero999

May this bee a lesson to you in estimating figures.

2.25mA sounds about right when dealing with values of 5V and 1k, 200mA sounds far to large when dealing with those sorts of values..

1K is a nice easy value, because it's 1mA/V - so with a 5V supply (and no LED) the absolute maximum possible current is only 5mA.

iONic · 27th September 2007, 01:46 AM

Quote:

Originally Posted by speakerguy79

Just be careful, they are teeny!

Indeed they are! does anyone have any suggestion on how to solder these things? I have some conductive adhesive that supposed to be good or would you have another way. All I have is a 35W soldering iron wit tips that are too big to be accurate.

speakerguy79 · 27th September 2007, 01:51 AM

You need a narrow tip and preferably .015" solder to solder it right. It's the usual put some solder on a pad, tack down one pin to that pad, then solder the other pins. Conductive epoxy can work but getting a correct tip would be better. We've used conductive epoxy to fix some specialized FET's at work where the wire inside the package came off the silicon, but that's about the only place I've used it.

Alternatively, you can use the "horrible but will probably work" method of just flooding all the pins on one side with solder and letting them bridge, then wicking off the excess. Just try not to get the component too hot.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Title	Starter	Forum	Replies	Latest
USB microcontroller programmer	Chris W	Electronic Projects Design/Ideas/Reviews	14	6th August 2008 06:15 PM
USB Power hack with DC/DC Converter - am I crazy?	chconnor	Electronic Projects Design/Ideas/Reviews	14	8th March 2008 10:13 PM
RJ11 to USB convertor vice versa	Jan Bos	Electronic Projects Design/Ideas/Reviews	2	13th September 2007 01:34 AM
usb to RS232 serial port :	simrantogether	Electronic Projects Design/Ideas/Reviews	3	12th September 2007 01:04 PM
How to get 1.5v from 9v?	Axe_Murderer	General Electronics Chat	3	17th November 2003 02:35 PM

17th September 2007, 03:06 PM	(permalink)
Hero999	Does it? An LM317 will go all the way up to 1.5A, although at those sorts of currents a switcher does tend to make more sense. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here.

17th September 2007, 08:54 PM	(permalink)
speakerguy79	I think it would. Unless I'm being retarded again Shouldn't he be able to get 1.5V @ 200ma from a capacitor switcher with an input of 5V @100ma assuming 60% efficiency? Of course, if the USB port will just allow him to draw whatever current he wants, then I agree a linear would be a better way to go. These capacitive switchers are only good for a few hundred mA I think anyway. Any more and you have to go inductive.

21st September 2007, 06:10 PM	(permalink)
iONic	I've been reading that the USB power standard, (100mA unless requested by the USB device), is not often followed. So I connected a Luxeon Star III to the power of the USB port on my laptop and .....WOW! It lit up well! After hooking up a meter to it it was drawing 1300mA, with a 1k resistor....maybe 200mA. Either way more than the "allowed" 100mA.

21st September 2007, 06:17 PM	(permalink)
Hero999	A 1k resistor in series with the LED gave 200mA? I don't believe you! What's the LED rated to? Did you use a series resistor when it drew 1300mA? __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here.

21st September 2007, 08:43 PM	(permalink)
Hero999	Unless I'm misunderstanding something, ohm's law dictates that only 1.5mA should flow assuming the output from the USB is 5V and the forward LED voltage drop is 3.5V. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here.

21st September 2007, 09:37 PM	(permalink)
mvs sarma	I agree with you HERO999 __________________ Regards, Sarma.

21st September 2007, 09:59 PM	(permalink)
iONic	Digital multimeters are darn accurate. The 1300mA was see when the Luxeon LED was connected without a resistor. The LED got warm within 5 seconds. vF = 3.9v, Max I = 1000mA Specs for the LED are here: http://www.luxeonstar.com/item.php?i...rtno=LXHL-LW3C Last edited by iONic; 21st September 2007 at 10:02 PM.

21st September 2007, 10:41 PM	(permalink)
iONic	My apologies, I just remeasured this current and I do believe it's time to put FOOT-IN-MOUTH(yes I fell down and bumped my head), it is 2.25mA. Last edited by iONic; 21st September 2007 at 10:43 PM.

21st September 2007, 11:53 PM	(permalink)
Hero999	May this bee a lesson to you in estimating figures. 2.25mA sounds about right when dealing with values of 5V and 1k, 200mA sounds far to large when dealing with those sorts of values.. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here.

27th September 2007, 01:51 AM	(permalink)
speakerguy79	You need a narrow tip and preferably .015" solder to solder it right. It's the usual put some solder on a pad, tack down one pin to that pad, then solder the other pins. Conductive epoxy can work but getting a correct tip would be better. We've used conductive epoxy to fix some specialized FET's at work where the wire inside the package came off the silicon, but that's about the only place I've used it. Alternatively, you can use the "horrible but will probably work" method of just flooding all the pins on one side with solder and letting them bridge, then wicking off the excess. Just try not to get the component too hot.