Is there a CMOS-type substitute for the 74LS47 with "open collector" type outputs suitable for sinking around 20mA? That uses less quiescent power than the 47's ~10mA. Supply voltage either 5 or 3.3 volts, depending. It doesn't really matter if the chip itself does a conversion from BCD to the appropriate outputs, as that mapping can be done in software, but the chip would need to have at least a 3 bit address space. The '47 has an input that's suitable for dynamic dimming of the loads by applying PWM, it would be cool if the replacement had something like that. I think JL posted something along these lines in response to another question of mine, but I can't find the thread.
74LS47 substitution
Started by ●June 15, 2016
Reply by ●June 15, 20162016-06-15
On Wed, 15 Jun 2016 13:34:50 -0400, bitrex <bitrex@de.lete.earthlink.net> wrote:>Is there a CMOS-type substitute for the 74LS47 with "open collector" >type outputs suitable for sinking around 20mA? > >That uses less quiescent power than the 47's ~10mA. Supply voltage >either 5 or 3.3 volts, depending. It doesn't really matter if the chip >itself does a conversion from BCD to the appropriate outputs, as that >mapping can be done in software, but the chip would need to have at >least a 3 bit address space. > >The '47 has an input that's suitable for dynamic dimming of the loads by >applying PWM, it would be cool if the replacement had something like that. > >I think JL posted something along these lines in response to another >question of mine, but I can't find the thread.A TPIC6595 might work. The data sheet says it needs 5 volts, but there is an appnote that says it's OK at 3.3. We use them at 3.3. The input is SPI serial, and the /G pin can do dimming. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●June 15, 20162016-06-15
John Larkin <jjlarkin@highlandtechnology.com> Wrote in message:> On Wed, 15 Jun 2016 13:34:50 -0400, bitrex > <bitrex@de.lete.earthlink.net> wrote: > >>Is there a CMOS-type substitute for the 74LS47 with "open collector" >>type outputs suitable for sinking around 20mA? >> >>That uses less quiescent power than the 47's ~10mA. Supply voltage >>either 5 or 3.3 volts, depending. It doesn't really matter if the chip >>itself does a conversion from BCD to the appropriate outputs, as that >>mapping can be done in software, but the chip would need to have at >>least a 3 bit address space. >> >>The '47 has an input that's suitable for dynamic dimming of the loads by >>applying PWM, it would be cool if the replacement had something like that. >> >>I think JL posted something along these lines in response to another >>question of mine, but I can't find the thread. > > A TPIC6595 might work. The data sheet says it needs 5 volts, but there > is an appnote that says it's OK at 3.3. We use them at 3.3. > > The input is SPI serial, and the /G pin can do dimming. >Thanks! Will look into it... -- ----Android NewsGroup Reader---- http://usenet.sinaapp.com/
Reply by ●June 15, 20162016-06-15
John Larkin <jjlarkin@highlandtechnology.com> Wrote in message:> On Wed, 15 Jun 2016 13:34:50 -0400, bitrex > <bitrex@de.lete.earthlink.net> wrote: > >>Is there a CMOS-type substitute for the 74LS47 with "open collector" >>type outputs suitable for sinking around 20mA? >> >>That uses less quiescent power than the 47's ~10mA. Supply voltage >>either 5 or 3.3 volts, depending. It doesn't really matter if the chip >>itself does a conversion from BCD to the appropriate outputs, as that >>mapping can be done in software, but the chip would need to have at >>least a 3 bit address space. >> >>The '47 has an input that's suitable for dynamic dimming of the loads by >>applying PWM, it would be cool if the replacement had something like that. >> >>I think JL posted something along these lines in response to another >>question of mine, but I can't find the thread. > > A TPIC6595 might work. The data sheet says it needs 5 volts, but there > is an appnote that says it's OK at 3.3. We use them at 3.3. > > The input is SPI serial, and the /G pin can do dimming.The CD74AC238 appears to be rated for 50 mA through a pin, 200 mA continuous to ground, at 1.5 to 5.5 volts supply, so that might also be a possibility. The edge case would be the "8"... -- ----Android NewsGroup Reader---- http://usenet.sinaapp.com/
Reply by ●June 15, 20162016-06-15
On Wed, 15 Jun 2016 16:02:30 -0400 (EDT), bitrex <bitrex@de.lete.earthlink.net> wrote:>John Larkin <jjlarkin@highlandtechnology.com> Wrote in message: >> On Wed, 15 Jun 2016 13:34:50 -0400, bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>>Is there a CMOS-type substitute for the 74LS47 with "open collector" >>>type outputs suitable for sinking around 20mA? >>> >>>That uses less quiescent power than the 47's ~10mA. Supply voltage >>>either 5 or 3.3 volts, depending. It doesn't really matter if the chip >>>itself does a conversion from BCD to the appropriate outputs, as that >>>mapping can be done in software, but the chip would need to have at >>>least a 3 bit address space. >>> >>>The '47 has an input that's suitable for dynamic dimming of the loads by >>>applying PWM, it would be cool if the replacement had something like that. >>> >>>I think JL posted something along these lines in response to another >>>question of mine, but I can't find the thread. >> >> A TPIC6595 might work. The data sheet says it needs 5 volts, but there >> is an appnote that says it's OK at 3.3. We use them at 3.3. >> >> The input is SPI serial, and the /G pin can do dimming. > >The CD74AC238 appears to be rated for 50 mA through a pin, 200 mA > continuous to ground, at 1.5 to 5.5 volts supply, so that might > also be a possibility. > >The edge case would be the "8"...Do you need open drain? HC or AC logic will sink 20 mA, probably better with Vcc=5. The 6595 is a beast, designed for a lot of current. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●June 15, 20162016-06-15
On 06/15/2016 04:39 PM, John Larkin wrote:> On Wed, 15 Jun 2016 16:02:30 -0400 (EDT), bitrex > <bitrex@de.lete.earthlink.net> wrote: > >> John Larkin <jjlarkin@highlandtechnology.com> Wrote in message: >>> On Wed, 15 Jun 2016 13:34:50 -0400, bitrex >>> <bitrex@de.lete.earthlink.net> wrote: >>> >>>> Is there a CMOS-type substitute for the 74LS47 with "open collector" >>>> type outputs suitable for sinking around 20mA? >>>> >>>> That uses less quiescent power than the 47's ~10mA. Supply voltage >>>> either 5 or 3.3 volts, depending. It doesn't really matter if the chip >>>> itself does a conversion from BCD to the appropriate outputs, as that >>>> mapping can be done in software, but the chip would need to have at >>>> least a 3 bit address space. >>>> >>>> The '47 has an input that's suitable for dynamic dimming of the loads by >>>> applying PWM, it would be cool if the replacement had something like that. >>>> >>>> I think JL posted something along these lines in response to anotherh >>>> question of mine, but I can't find the thread. >>> >>> A TPIC6595 might work. The data sheet says it needs 5 volts, but there >>> is an appnote that says it's OK at 3.3. We use them at 3.3. >>> >>> The input is SPI serial, and the /G pin can do dimming. >> >> The CD74AC238 appears to be rated for 50 mA through a pin, 200 mA >> continuous to ground, at 1.5 to 5.5 volts supply, so that might >> also be a possibility. >> >> The edge case would be the "8"... > > Do you need open drain? HC or AC logic will sink 20 mA, probably > better with Vcc=5. > > The 6595 is a beast, designed for a lot of current.I don't think so. The 74LS47 outputs don't pull down much lower than 0.3 volts. While it looks like most HC logic can sink 20 mA, the problem is it seems most are rated for only 50mA continuous through GND, and the SOIC-16 packages are rated for only 500mW continuous dissipation. The CD74AC238 can sink 200mA to ground, and is rated for 1.1 watts dissipation at 30 degrees, so even if I have to derate it a bit for 140mA passing through the device when all segments are lit, it seems it should be okay.
Reply by ●June 16, 20162016-06-16
On 16.6.16 00:39, bitrex wrote:> On 06/15/2016 04:39 PM, John Larkin wrote: >> On Wed, 15 Jun 2016 16:02:30 -0400 (EDT), bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>> John Larkin <jjlarkin@highlandtechnology.com> Wrote in message: >>>> On Wed, 15 Jun 2016 13:34:50 -0400, bitrex >>>> <bitrex@de.lete.earthlink.net> wrote: >>>> >>>>> Is there a CMOS-type substitute for the 74LS47 with "open collector" >>>>> type outputs suitable for sinking around 20mA? >>>>> >>>>> That uses less quiescent power than the 47's ~10mA. Supply voltage >>>>> either 5 or 3.3 volts, depending. It doesn't really matter if the chip >>>>> itself does a conversion from BCD to the appropriate outputs, as that >>>>> mapping can be done in software, but the chip would need to have at >>>>> least a 3 bit address space. >>>>> >>>>> The '47 has an input that's suitable for dynamic dimming of the >>>>> loads by >>>>> applying PWM, it would be cool if the replacement had something >>>>> like that. >>>>> >>>>> I think JL posted something along these lines in response to anotherh >>>>> question of mine, but I can't find the thread. >>>> >>>> A TPIC6595 might work. The data sheet says it needs 5 volts, but there >>>> is an appnote that says it's OK at 3.3. We use them at 3.3. >>>> >>>> The input is SPI serial, and the /G pin can do dimming. >>> >>> The CD74AC238 appears to be rated for 50 mA through a pin, 200 mA >>> continuous to ground, at 1.5 to 5.5 volts supply, so that might >>> also be a possibility. >>> >>> The edge case would be the "8"... >> >> Do you need open drain? HC or AC logic will sink 20 mA, probably >> better with Vcc=5. >> >> The 6595 is a beast, designed for a lot of current. > > I don't think so. The 74LS47 outputs don't pull down much lower than 0.3 > volts. > > While it looks like most HC logic can sink 20 mA, the problem is it > seems most are rated for only 50mA continuous through GND, and the > SOIC-16 packages are rated for only 500mW continuous dissipation. > > The CD74AC238 can sink 200mA to ground, and is rated for 1.1 watts > dissipation at 30 degrees, so even if I have to derate it a bit for > 140mA passing through the device when all segments are lit, it seems it > should be okay.How about the ULN2001 family, 500 mA / pin? -- -TV
Reply by ●June 16, 20162016-06-16
bitrex <bitrex@de.lete.earthlink.net> wrote:>Is there a CMOS-type substitute for the 74LS47 with "open collector" >type outputs suitable for sinking around 20mA?Although kind of overkill. Perhaps a small µC. The AVRs for example can sink about 20 mA/pin with a total of 200 mA for VCC and GND. Of course the outputs are not open collector. If you need OC and more than one digit to drive a combination of µC and one OC driver can be the solution with the least components. The µC could also do PWM and multiplexing. -- Dipl.-Inform(FH) Peter Heitzer, peter.heitzer@rz.uni-regensburg.de
Reply by ●June 16, 20162016-06-16
On 06/16/2016 04:31 AM, Peter Heitzer wrote:> bitrex <bitrex@de.lete.earthlink.net> wrote: >> Is there a CMOS-type substitute for the 74LS47 with "open collector" >> type outputs suitable for sinking around 20mA? > Although kind of overkill. Perhaps a small µC. The AVRs for example > can sink about 20 mA/pin with a total of 200 mA for VCC and GND. > Of course the outputs are not open collector. If you need OC and more > than one digit to drive a combination of µC and one OC driver can be > the solution with the least components. The µC could also do PWM and > multiplexing. >Yeah, there's going to be a uC involved one way or the other...I'm trying to figure if it would be better to just use an AVR with more pins vs an 8 pin AVR and an external switch IC. An ATTiny85 that costs under a dollar in quantity plus an external switch that costs 25 cents in quantity is a better value than something like a Mega168 that costs $1.65 in quantity, as the board size would be pretty much fixed by larger components either way. There are other weird AVR devices that seem to use a "Tiny" core but have more pins, but I'm taking advantage of the Arduino toolchain and AFAIK they're not supported, and I don't really want to take the time to write an implementation.
Reply by ●June 16, 20162016-06-16
On 06/16/2016 04:07 AM, Tauno Voipio wrote:> On 16.6.16 00:39, bitrex wrote: >> On 06/15/2016 04:39 PM, John Larkin wrote: >>> On Wed, 15 Jun 2016 16:02:30 -0400 (EDT), bitrex >>> <bitrex@de.lete.earthlink.net> wrote: >>> >>>> John Larkin <jjlarkin@highlandtechnology.com> Wrote in message: >>>>> On Wed, 15 Jun 2016 13:34:50 -0400, bitrex >>>>> <bitrex@de.lete.earthlink.net> wrote: >>>>> >>>>>> Is there a CMOS-type substitute for the 74LS47 with "open collector" >>>>>> type outputs suitable for sinking around 20mA? >>>>>> >>>>>> That uses less quiescent power than the 47's ~10mA. Supply voltage >>>>>> either 5 or 3.3 volts, depending. It doesn't really matter if the >>>>>> chip >>>>>> itself does a conversion from BCD to the appropriate outputs, as that >>>>>> mapping can be done in software, but the chip would need to have at >>>>>> least a 3 bit address space. >>>>>> >>>>>> The '47 has an input that's suitable for dynamic dimming of the >>>>>> loads by >>>>>> applying PWM, it would be cool if the replacement had something >>>>>> like that. >>>>>> >>>>>> I think JL posted something along these lines in response to anotherh >>>>>> question of mine, but I can't find the thread. >>>>> >>>>> A TPIC6595 might work. The data sheet says it needs 5 volts, but there >>>>> is an appnote that says it's OK at 3.3. We use them at 3.3. >>>>> >>>>> The input is SPI serial, and the /G pin can do dimming. >>>> >>>> The CD74AC238 appears to be rated for 50 mA through a pin, 200 mA >>>> continuous to ground, at 1.5 to 5.5 volts supply, so that might >>>> also be a possibility. >>>> >>>> The edge case would be the "8"... >>> >>> Do you need open drain? HC or AC logic will sink 20 mA, probably >>> better with Vcc=5. >>> >>> The 6595 is a beast, designed for a lot of current. >> >> I don't think so. The 74LS47 outputs don't pull down much lower than 0.3 >> volts. >> >> While it looks like most HC logic can sink 20 mA, the problem is it >> seems most are rated for only 50mA continuous through GND, and the >> SOIC-16 packages are rated for only 500mW continuous dissipation. >> >> The CD74AC238 can sink 200mA to ground, and is rated for 1.1 watts >> dissipation at 30 degrees, so even if I have to derate it a bit for >> 140mA passing through the device when all segments are lit, it seems it >> should be okay. > > How about the ULN2001 family, 500 mA / pin? >It's a good chip, it doesn't look like it draws any current whatsoever unless the Darlington outputs are switched on...only 25 cents in quantities of 100 surface mount. But it needs one address line for each output, and I was hoping to cut costs by using an el cheapo 8 pin AVR and an el cheapo driver, instead of shelling out for an AVR with more pins but also more features and code space which I don't need for this. If I wanted to use 7 pins it would make more sense to just use a uC with more pins, as a poster mentions below I think even the AVRs in SMT can handle 20mA per pin and 200mA to ground (though driving the outputs of the display directly from the processor close to the limits makes me feel a little uncomfortable.)
