74LS47 substitution

On 06/16/2016 10:38 AM, Peter Heitzer wrote:
> rickman <gnuarm@gmail.com> wrote:
>> On 6/15/2016 1:34 PM, bitrex wrote:
>>> Is there a CMOS-type substitute for the 74LS47 with "open collector"
>>> type outputs suitable for sinking around 20mA?
>
>> There are about a million I2C/SPI LED drivers out there that have built
>> in PWM dimming.  Have you looked at any?
> I think the OP is looking for a part costing less than a dollar. The
> drivers I found are rather costly.
>
>

Yup. Definitely looks like the cheapest way is to drive the segments of 
the common anode display directly to ground right from a uC, if it can 
take the punishment.

If there were more displays to drive instead of instead of just one, it 
might be worth looking at using a dedicated driver chip for each 
display. Or who knows, it might still be cheaper to use a uC for each 
display, slaved together on a serial bus.

On 6/16/2016 10:48 AM, bitrex wrote:
> On 06/16/2016 10:38 AM, Peter Heitzer wrote:
>> rickman <gnuarm@gmail.com> wrote:
>>> On 6/15/2016 1:34 PM, bitrex wrote:
>>>> Is there a CMOS-type substitute for the 74LS47 with "open collector"
>>>> type outputs suitable for sinking around 20mA?
>>
>>> There are about a million I2C/SPI LED drivers out there that have built
>>> in PWM dimming.  Have you looked at any?
>> I think the OP is looking for a part costing less than a dollar. The
>> drivers I found are rather costly.
>>
>>
>
> Yup. Definitely looks like the cheapest way is to drive the segments of
> the common anode display directly to ground right from a uC, if it can
> take the punishment.
>
> If there were more displays to drive instead of instead of just one, it
> might be worth looking at using a dedicated driver chip for each
> display. Or who knows, it might still be cheaper to use a uC for each
> display, slaved together on a serial bus.

MCUs often have a total sink rating which can limit how many loads you 
drive at the same time.

Not sure what you've found before, but a quick search turned up some TI 
parts, TLC6C598 - 8 bits, $0.34 and TLC6C5912 - 12 bits, $0.50 at 1k 
quantity.  These are basic shift registers with a clear and buffer 
register (open drain output) with a blanking control which can be used 
for PWM.  30 mA per output up to 40 volts.  Supply current in uA.

-- 

Rick C

In article <%kg8z.2$e94.1@fx01.iad>, bitrex@de.lete.earthlink.net 
says...
> 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.
> 
I had to update a product that used two of them recently.
What I opted to use was an AS1109.  It uses an SPI style interface 
instead of a parallel BCD input and you will need to use a look up table 
for the decoding, but that's all pretty trivial.
It has a single input for dimming and you can daisy chain them together 
so you don't need multiple /CS lines.  It also has the advantage of a 
built in CC driver, so you don't need to put down individual resistors 
for each output and a dimming input that handles all the output 
channels.  
Don't know if that will work for you, but it's worth a look.

http://www.digikey.com/product-search/en?mpart=AS1109-BSOT&v=961

rickman <gnuarm@gmail.com> Wrote in message:
> On 6/16/2016 10:48 AM, bitrex wrote:
>> On 06/16/2016 10:38 AM, Peter Heitzer wrote:
>>> rickman <gnuarm@gmail.com> wrote:
>>>> On 6/15/2016 1:34 PM, bitrex wrote:
>>>>> Is there a CMOS-type substitute for the 74LS47 with "open collector"
>>>>> type outputs suitable for sinking around 20mA?
>>>
>>>> There are about a million I2C/SPI LED drivers out there that have built
>>>> in PWM dimming.  Have you looked at any?
>>> I think the OP is looking for a part costing less than a dollar. The
>>> drivers I found are rather costly.
>>>
>>>
>>
>> Yup. Definitely looks like the cheapest way is to drive the segments of
>> the common anode display directly to ground right from a uC, if it can
>> take the punishment.
>>
>> If there were more displays to drive instead of instead of just one, it
>> might be worth looking at using a dedicated driver chip for each
>> display. Or who knows, it might still be cheaper to use a uC for each
>> display, slaved together on a serial bus.
> 
> MCUs often have a total sink rating which can limit how many loads you 
> drive at the same time.
> 
> Not sure what you've found before, but a quick search turned up some TI 
> parts, TLC6C598 - 8 bits, $0.34 and TLC6C5912 - 12 bits, $0.50 at 1k 
> quantity.  These are basic shift registers with a clear and buffer 
> register (open drain output) with a blanking control which can be used 
> for PWM.  30 mA per output up to 40 volts.  Supply current in uA.
> 
> -- 
> 
> Rick C
> 

The TLC6C598 is a cool part...if at some point I have to control
 more than one display it would make sense to use that for each
 and drive them from a single uC,

I was surprised though that most AVR uCs in SOIC can sink a total
 of 200 mA to ground, at usually 20 mA or over per pin. The
 packages have a total dissipation rating of 500 mW at 30C, so if
 the output low voltages are only a few hundred mV I think I
 should come in under that, even with 7 segments.

-- 


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