Need hardware advice: ULN2003A

[Christopher4187]

I use PIC's for EVERYTHNING!!

Anyhow, can anyone confirm my thinking for the use of a ULN2003A with more outputs to spread the flyback voltage?

[mister_e]

in theory... it's suppose to work. In real-world... maybe yes maybe no.

Personnally i would use 2 mosfet or transistor for about the same price and board space... but it's my own opinion

[sayzer]

I quote myself "go for it"

[Christopher4187]

So, it looks like the general consensus is that I can "gang" together some outputs and the potential issue of the flyback voltage should be mitigated. Are there any objections?

[Luciano]

Hi,

When you use only one output of the ULN2003A you can drive a relay with
a coil current up to 500mA. (450 mA with 100% duty cycle, N package).
The internal protection diode will suppress the self-induction current when
you deenergise the relay. Do not forget to connect PIN9.
All unused inputs must be tied to GND.

If you use two outputs simultaneously, then the current of each
output is limited to 280 mA. (100% duty cycle, N package).
See the picture below if you use more than two outputs simultaneously.
(The picture is from the datasheet of the ULN2003A).


(Click to enlarge the picture)


(Click to enlarge the picture)

Best regards,

Luciano

[sayzer]

Nice explanations Luciano. But I am confused.

You are saying, actually, 500mA is only valid when we use one output at a time. Interesting! because if we make a parallel connection as the data sheet says, then this statement can not be correct.

In a parallel connection, we will be using two outputs at the same time.
In that case, we multiply the current capacity so we get 2x500=1000mA, but according your information, "If you use two outputs simultaneously, then the current of each output is limited to 280 mA". So we get back to where we started.
No change!

Isn't this interesting?




Also, what about the protection diodes? I checked the datasheet but very poor information there.

[Luciano]

Hi,

The IC package can only dissipate a certain amount of heat.
If you use only one output the max current for the package is 480mA.
If you use two outputs, the current is 280 mA per output so the total
current for the package is 560 mA. This small difference is because
some of the heat is dissipated by the metal of the pin connected to
the PCB.

There is no need for a parallel connection.
Do not use a parallel connections with this IC.

Best regards,

Luciano