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74HCT259 and prma1a05 combination help

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neazoi

neazoi

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Hello, I would like to combine 74HCT259 and prma1a05 miniature relay, to make multi switch in order to switch different filters in an HF receiver.

I think that each prma1a05 coil draws 10mA, is that right?
The 74HCT259 can drive the coils of the prma1a05 directly without the need for a driver?
I think it can provide 25mA max, can you verify this from the datasheet?
Is that current for each output separately or for all togeter?
 

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The prma1a05 has a coil resistance of typ. 140 ohm and the HCT259 output is specified for a 4mA LOW level output. At 5V supply that will create an overload(short current) situation for the HCT259, which is not specified. The prma1a05 has also a minimum coil voltage of 3.75V. Thus you need an additional driver to ensure at worst case situation a proper operation. Driver iCs like the ULN2001/3 or discrete transistor.

Enjoy your design work!
 
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    neazoi

    neazoi

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HTA said:
The prma1a05 has a coil resistance of typ. 140 ohm and the HCT259 output is specified for a 4mA LOW level output. At 5V supply that will create an overload(short current) situation for the HCT259, which is not specified. The prma1a05 has also a minimum coil voltage of 3.75V. Thus you need an additional driver to ensure at worst case situation a proper operation. Driver iCs like the ULN2001/3 or discrete transistor.

Enjoy your design work!
Click to expand...

Hello,
I have some uln2803a chips to use as the PRMA1A05 drivers.
Will these be compatible for 5V output to drive the relays?

Also there are clamp diodes for driving relay loads connected to pin 10. How should I connect these diodes to the relays? Is it enoigh to connect pin10 to 5v (the input of the relay coil)?

Finally what if I need to drive double amount of chips (16). Imagine that each set of relays will be energised at the same time, so for each enable, two relays will be switched to on. Can I use one clamp diode for two relays in parallel, or I need to use another uln2803a, and connect it's inputs in parallel with the first one?
 
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