I'm going to be using ULN2803APG in a design of mine, and I just noticed on the datasheet [1] that Vce(sat) typ is 1.3 at 350ma. Does that mean that the voltage drop across the Vce will typically be 1.3 at that current? Or does that mean the voltage for Vbe needs to be that high to have saturation? [1] <http://www.semicon.toshiba.co.jp/info/docget.jsp?pid=ULN2803APG&lang=en&type=datasheet>
Meaning of Vce(sat)?
Started by ●March 9, 2014
Reply by ●March 9, 20142014-03-09
On 3/9/2014 3:21 PM, Daniel Pitts wrote:> I'm going to be using ULN2803APG in a design of mine, and I just noticed > on the datasheet [1] that Vce(sat) typ is 1.3 at 350ma. > > Does that mean that the voltage drop across the Vce will typically be > 1.3 at that current?'Fraid so. It's a Darlington, intended for high voltage outputs. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●March 9, 20142014-03-09
On 3/9/14 12:39 PM, Phil Hobbs wrote:> On 3/9/2014 3:21 PM, Daniel Pitts wrote: >> I'm going to be using ULN2803APG in a design of mine, and I just noticed >> on the datasheet [1] that Vce(sat) typ is 1.3 at 350ma. >> >> Does that mean that the voltage drop across the Vce will typically be >> 1.3 at that current? > > 'Fraid so. It's a Darlington, intended for high voltage outputs.That was what I was afraid of. I should still have enough headroom, but that is wasting a bit of power... Any suggestion on a replacement part? I need to enable/disable 8 lines with logic level inputs. It can even be a 1-of-8 decoder I just need it to support up to 1A, and I'd like it to be relatively cheap. My load is going to 24 parallel LEDs (3.3v Vf for 16 of them, 1.8 Vf for 8), each with a constant current sink in line with them. Cheap, for me, is < $1.25 for 8-in-8-out, or < $2.0 for 3-in-8-out (since I'd be able to replace two chips in that case). Thanks, Daniel.
Reply by ●March 9, 20142014-03-09
On 09/03/14 20.21, Daniel Pitts wrote:> I'm going to be using ULN2803APG in a design of mine, and I just noticed > on the datasheet [1] that Vce(sat) typ is 1.3 at 350ma. > > Does that mean that the voltage drop across the Vce will typically be > 1.3 at that current? Or does that mean the voltage for Vbe needs to be > that high to have saturation? > > [1] > <http://www.semicon.toshiba.co.jp/info/docget.jsp?pid=ULN2803APG&lang=en&type=datasheet> >Hello Daniel How about using power MOSFETs?: e.g. DMN6040SSD: 60Vmax, 4.1Amax, 55mOhm max, cheap (normally twice as expensive) (two in each so-8), Logic Level Gate (means fully on while Vgs<5V) Cin=1,3nF: http://www.digikey.com/product-detail/en/DMN6040SSD-13/DMN6040SSD-13DICT-ND/3481122 DMN6040SSD: http://www.diodes.com/datasheets/DMN6040SSD.pdf /Glenn
Reply by ●March 9, 20142014-03-09
On 3/9/14 1:25 PM, Daniel Pitts wrote:> On 3/9/14 12:39 PM, Phil Hobbs wrote: >> On 3/9/2014 3:21 PM, Daniel Pitts wrote: >>> I'm going to be using ULN2803APG in a design of mine, and I just noticed >>> on the datasheet [1] that Vce(sat) typ is 1.3 at 350ma. >>> >>> Does that mean that the voltage drop across the Vce will typically be >>> 1.3 at that current? >> >> 'Fraid so. It's a Darlington, intended for high voltage outputs. > > That was what I was afraid of. I should still have enough headroom, but > that is wasting a bit of power... > > Any suggestion on a replacement part? I need to enable/disable 8 lines > with logic level inputs. > > It can even be a 1-of-8 decoder I just need it to support up to 1A, and > I'd like it to be relatively cheap. My load is going to 24 parallel > LEDs (3.3v Vf for 16 of them, 1.8 Vf for 8), each with a constant > current sink in line with them. > > Cheap, for me, is < $1.25 for 8-in-8-out, or < $2.0 for 3-in-8-out > (since I'd be able to replace two chips in that case).I should add, I'm talking about price for quantities < 20 at the moment, not including shipping.
Reply by ●March 9, 20142014-03-09
On 3/9/2014 4:33 PM, Daniel Pitts wrote:> On 3/9/14 1:25 PM, Daniel Pitts wrote: >> On 3/9/14 12:39 PM, Phil Hobbs wrote: >>> On 3/9/2014 3:21 PM, Daniel Pitts wrote: >>>> I'm going to be using ULN2803APG in a design of mine, and I just >>>> noticed >>>> on the datasheet [1] that Vce(sat) typ is 1.3 at 350ma. >>>> >>>> Does that mean that the voltage drop across the Vce will typically be >>>> 1.3 at that current? >>> >>> 'Fraid so. It's a Darlington, intended for high voltage outputs. >> >> That was what I was afraid of. I should still have enough headroom, but >> that is wasting a bit of power... >> >> Any suggestion on a replacement part? I need to enable/disable 8 lines >> with logic level inputs. >> >> It can even be a 1-of-8 decoder I just need it to support up to 1A, and >> I'd like it to be relatively cheap. My load is going to 24 parallel >> LEDs (3.3v Vf for 16 of them, 1.8 Vf for 8), each with a constant >> current sink in line with them. >> >> Cheap, for me, is < $1.25 for 8-in-8-out, or < $2.0 for 3-in-8-out >> (since I'd be able to replace two chips in that case). > I should add, I'm talking about price for quantities < 20 at the moment, > not including shipping. >You'd think that somebody would make a MOSFET version, but AFAIK they don't. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●March 9, 20142014-03-09
On Sun, 09 Mar 2014 13:33:03 -0700, Daniel Pitts <newsgroup.nospam@virtualinfinity.net> wrote:>On 3/9/14 1:25 PM, Daniel Pitts wrote: >> On 3/9/14 12:39 PM, Phil Hobbs wrote: >>> On 3/9/2014 3:21 PM, Daniel Pitts wrote: >>>> I'm going to be using ULN2803APG in a design of mine, and I just noticed >>>> on the datasheet [1] that Vce(sat) typ is 1.3 at 350ma. >>>> >>>> Does that mean that the voltage drop across the Vce will typically be >>>> 1.3 at that current? >>> >>> 'Fraid so. It's a Darlington, intended for high voltage outputs. >> >> That was what I was afraid of. I should still have enough headroom, but >> that is wasting a bit of power... >> >> Any suggestion on a replacement part? I need to enable/disable 8 lines >> with logic level inputs. >> >> It can even be a 1-of-8 decoder I just need it to support up to 1A, and >> I'd like it to be relatively cheap. My load is going to 24 parallel >> LEDs (3.3v Vf for 16 of them, 1.8 Vf for 8), each with a constant >> current sink in line with them. >> >> Cheap, for me, is < $1.25 for 8-in-8-out, or < $2.0 for 3-in-8-out >> (since I'd be able to replace two chips in that case). >I should add, I'm talking about price for quantities < 20 at the moment, >not including shipping.Somebody, I think TI, makes an LED driver with eight built-in current sinks and a serial interface. It was mentioned here not long ago. We like to use the TPIC6595 for driving relays and LEDs. Serial input and eight open-drain mosfets. -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation
Reply by ●March 9, 20142014-03-09
On Sun, 09 Mar 2014 12:21:50 -0700, Daniel Pitts wrote:> I'm going to be using ULN2803APG in a design of mine, and I just noticed > on the datasheet [1] that Vce(sat) typ is 1.3 at 350ma. > > Does that mean that the voltage drop across the Vce will typically be > 1.3 at that current? Or does that mean the voltage for Vbe needs to be > that high to have saturation?It does not mean that Vce will be 1.3V at that current -- you could have 350mA at 50V, for a little while. It DOES mean that the lowest that the transistor will pull the voltage down when 350mA is going through it is 1.3V. "Saturation" in a BJT means that the Vce is as low as it's going to ever get at that collector current. Basically, the collector isn't acting like a pretty good current source any more -- instead, it's acting like a pretty good short circuit. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
Reply by ●March 9, 20142014-03-09
On Sun, 09 Mar 2014 17:23:35 -0500, Tim Wescott <tim@seemywebsite.please> wrote:>On Sun, 09 Mar 2014 12:21:50 -0700, Daniel Pitts wrote: > >> I'm going to be using ULN2803APG in a design of mine, and I just noticed >> on the datasheet [1] that Vce(sat) typ is 1.3 at 350ma. >> >> Does that mean that the voltage drop across the Vce will typically be >> 1.3 at that current? Or does that mean the voltage for Vbe needs to be >> that high to have saturation? > >It does not mean that Vce will be 1.3V at that current -- you could have >350mA at 50V, for a little while. > >It DOES mean that the lowest that the transistor will pull the voltage >down when 350mA is going through it is 1.3V. > >"Saturation" in a BJT means that the Vce is as low as it's going to ever >get at that collector current. Basically, the collector isn't acting >like a pretty good current source any more -- instead, it's acting like a >pretty good short circuit."Saturation" in a Darlington is equal to a Vbe + Vce-sat of one NPN, thus the odd-looking number. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●March 9, 20142014-03-09
On 3/9/2014 3:26 PM, Jim Thompson wrote:> On Sun, 09 Mar 2014 17:23:35 -0500, Tim Wescott > <tim@seemywebsite.please> wrote: > >> On Sun, 09 Mar 2014 12:21:50 -0700, Daniel Pitts wrote: >> >>> I'm going to be using ULN2803APG in a design of mine, and I just noticed >>> on the datasheet [1] that Vce(sat) typ is 1.3 at 350ma. >>> >>> Does that mean that the voltage drop across the Vce will typically be >>> 1.3 at that current? Or does that mean the voltage for Vbe needs to be >>> that high to have saturation? >> >> It does not mean that Vce will be 1.3V at that current -- you could have >> 350mA at 50V, for a little while. >> >> It DOES mean that the lowest that the transistor will pull the voltage >> down when 350mA is going through it is 1.3V. >> >> "Saturation" in a BJT means that the Vce is as low as it's going to ever >> get at that collector current. Basically, the collector isn't acting >> like a pretty good current source any more -- instead, it's acting like a >> pretty good short circuit. > > "Saturation" in a Darlington is equal to a Vbe + Vce-sat of one NPN, > thus the odd-looking number. > > ...Jim Thompson >There are other chips in the same series that have pregain and a single output stage. I seem to have misplaced the number, but just threw a bunch of them away. Great chips. -- Many thanks, Don Lancaster voice phone: (928)428-4073 Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552 rss: http://www.tinaja.com/whtnu.xml email: don@tinaja.com Please visit my GURU's LAIR web site at http://www.tinaja.com
