8044 Views 6 Replies Latest reply: Mar 17, 2014 7:35 AM by davecuthbert
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# switching circuit

I need to make a circuit to latch and unlatch a latching relay part # 399-11030-5-nd   using only one wire from a mom. neg. output switch.

• 87 posts since
Feb 18, 2014
Currently Being Moderated
Mar 15, 2014 6:31 AM (in response to jpitman93)
Re: switching circuit

The switch needs to apply at least -9 volts to pin 12 with the return being pin 1. Driving the coil directly from a switch may or may not work well because switch bounce might toggle the relay more than once as it closes and opens. The required coil pulse width is >10 ms and the rise time is described as "fast."

The circuit above will debounce the switch with an attack time of about 2 ms and a debounce time of about 50 ms. The capacitor can be a 33 uF electrolytic, tantalum, or ceramic with a voltage rating of 15 volts or more.

Note that on page 3 of the datasheet the diagrams for the Single coil and the Dual coil are switched (they are in the wrong place).

http://www.kemet.com/kemet/web/homepage/kechome.nsf/vapubfiles/KEM_R7002_EC2_EE2.pdf/\$file/KEM_R7002_EC2_EE2.pdf

• 26 posts since
Mar 14, 2014
Currently Being Moderated
Mar 15, 2014 12:39 AM (in response to davecuthbert)
Re: switching circuit

Don't forget the diode across the coil to absorb switching transients.

• 87 posts since
Feb 18, 2014
Currently Being Moderated
Mar 15, 2014 6:27 AM (in response to NITMOI)
Re: switching circuit

In this circuit the 33 uF capacitor performs the clamp function and a diode is not needed.

• 26 posts since
Mar 14, 2014
Currently Being Moderated
Mar 16, 2014 8:19 PM (in response to davecuthbert)
Re: switching circuit

Unless they fixed the pdf, the diagrams look right to me.  The double latch set coil is between pins 1 and 12 and the reset coil is between pins 5 and 7.  The single latch uses a single coil for both reset and set between pins 1 and 12 thus relying on polarity of the signal/pulse on the pins.  Your circuit will set it, reset is not shown.  On using the capacitor in place of a diode, the diode will impart opposite polarity to a polarized cap - will that matter since it's only briefly?

• 87 posts since
Feb 18, 2014
Currently Being Moderated
Mar 17, 2014 7:35 AM (in response to NITMOI)
Re: switching circuit

You're right! The diagrams are correct, and to operate the single coil latch type a circuit with these characteristics is needed:

• Pin 1 positive and Pin 12 negative to set
• Pin 1 negative and Pin 12 positive to reset
• Coil voltage rise time and fall time < 1ms
• Coil on time >10 ms
• Set by depressing the momentary switch
• Reset by depressing the momentary switch
• Momentary switch supplies -12 volts

Do we want the relay to power-up in the last state it was in or should it have a power-up reset to a specific state?

It will work like so:

• power-up reset to put the relay into a known state or leave it in the state it was in
• Momentary switch signal to
• debouncing circuit to
• flip flop to
• one shot to
• tri-state coil drivers to
• coil

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