Need hardware advice: ULN2003A

[Christopher4187]

But why would TI say you could gang together outputs. I mean, it's in the data sheet.....should we believe everything we read? :-)

[Luciano]

@Luciano,

If your field is large, I guess it could. The problem is that the clamp diodes within the ULN2003A are most likely not matched and you are forcing that large field into one diode for a very short time. Maybe one way to mitigate that problem would be to put discrite resistors on each output to ensure the current does not go above an acceptable level. I don't have formal education to confirm this but it sounds like it may work.

The diode is not a problem because when the outputs are paralleled you will
have from two up to seven protection diodes in the circuit.

The datasheet says that: (Sorry I did not see that).

The collector-current rating of a single Darlington pair is 500 mA.
The Darlington pairs can be paralleled for higher current capability.

The datasheet says that, go head and connect the buffers in parallel
following the rules of figure 14 and figure 15 of the TI datasheet.

To put resistors on each output to ensure the current does not go above
an acceptable level is a good idea. (For the buffers and for the diodes
if they are not matched).

Best regards,

Luciano

[rwskinner]

I've been using ULN2803's on about 200 systems for 3 years now driving 24 volt relays which mine require 80 ma, using only the ULN2803's onboard freewheeling diodes and had absolutley no problems.

But I most likely have been lucky according to what you folks are saying.

The only problem I had was when they drive filliment type lamps, the element burns out, shorts, and causes 24 volts to directly sink via the 2803 and fry it.

We're going to fix that by limiting the current going to the 2803 for protection.

[mvs_sarma]

I've been using ULN2803's on about 200 systems for 3 years now driving 24 volt relays which mine require 80 ma, using only the ULN2803's onboard freewheeling diodes and had absolutley no problems.

But I most likely have been lucky according to what you folks are saying.

The only problem I had was when they drive filliment type lamps, the element burns out, shorts, and causes 24 volts to directly sink via the 2803 and fry it.

We're going to fix that by limiting the current going to the 2803 for protection.

Hi
what is the wattage of the filament lamps you are trying to drive with ULN2003--
the issue is with cold resistance of filament lamp and the surge currewnt that flows before the filament becomes HOT-- the driver device should haVE DOUBLE THE CAPACITY OF THE INRUSH CURRENT II believe.

[rwskinner]

Hi
what is the wattage of the filament lamps you are trying to drive with ULN2003--
the issue is with cold resistance of filament lamp and the surge currewnt that flows before the filament becomes HOT-- the driver device should haVE DOUBLE THE CAPACITY OF THE INRUSH CURRENT II believe.

It's not an overload issue, well, it is, but not caused by normal operation. It's when a lamp burns out and we get unlucky enough that the element rolls around or puddles and causes a direct short. We have done two things to stop this.

1) Changing all the Lamps with LED replacements
2) Active current limiting circuit

When I was researching 2803's "after" the fact, I found that lots of arcade games used them to control light arrays, and they too had many problems with lamps shorting and burning up the 2803. There were some pretty neat ideas on the net on how to avoid it.

[mvs_sarma]

Hi Rwskinner

If the failure rate is not high and things are running-- i feel no need to change ULN2003 unless it gives you an advantage-- like cost reduction-- etc,

perhaps you need not change for technology upgradation - as far as failure is occasional and tolerable without letting reputation down-- please continue

even the diode matrix inside need be used only when load is inductive like a relay coil.