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Electronics/LED power to latching relay


QUESTION: I have limited electronics knowledge but have managed to drive a latching relay with a solid state relay from an LED's power on a consumer product. The power I am tapping is 1.9VDC at the LED or 3.9VDC before the LED's resistor. The coil of the latching relay Draws 66.7ma @ 3VDC. There is not enough current to drive the latching relay directly. Is there a smaller component I can use in place of the SSR to drive the coil of the latching relay?

ANSWER: Sorry, but I don't understand the question.  Can you send a schematic diagram or at least clarify the question?  What is an SSR?  What properties does it have for current operation, etc.... They are all very different.   

We need to know more about your circuit to know what you want to do....

---------- FOLLOW-UP ----------

QUESTION: Sorry, I was referring to the solid state relay as SSR.
I have a consumer product which lights an LED. I want to use that LED power to close a latching relay. I tried to power the relay coil directly from the LED's power but there is not enough power there. I have tapped into the LED circuit before the limiting resistor and used that to power a solid state relay. This solid state relay then sends power to the coil of the latching relay.
 I am looking for something smaller to replace the solid state relay. I have 1.9VDC and 3.9VDC available to power the device. This new device would need to pass 3V @ 66.7ma to the coil of the latching relay.
I hope this description is better.

ANSWER: What is the consumer product?  It would help to know the source of the circuit supplying the LED.   Most LED lamps have a series resistor that limits the current to the appropriate amount for the specific LED.  Tapping into that circuit will alter the current and voltage drop across the series resistor.  You didn't say if you want the LED to stay illuminated when the relay is switched on or not.  It makes great difference in determining the dynamics of the circuit.

Ohms law is at work here and any increase in current passing through the LED leg of the circuit will change the voltage drops and the current.

You say the device needs to "pass 3v @ 66.7ma" which is a contradiction of terms:  Voltage is 'across' and current passes through. Further I don't know what you mean by "sends power to the coil".  A coil has a resistance and it requires so much current to actuate it.  The voltage across the coil is according to ohms law the current times the resistance of the coil.  Thus the relays or switching devices you are using must be characterized and the circuit calculations for current required and voltage drops accumulated in order to know what is going on.

Probably what you need is a transistor operated switch circuit to actuate the relay.  

But, without a schematic diagram of your circuit I am left guessing what you are trying to do.

Hope this helps.

---------- FOLLOW-UP ----------

QUESTION: Thank you for your help. As you can tell from my terminology, I am not experienced. I have been looking into transistors and it looks like that will solve my problem.
Again, Thank You.

Sorry I was not more help.  If you are pulling power off from a circuit in an unknown product it must be determined how the loading will disturb the functioning of it.  If you use a transistor switch it is likely the small amount of current can be tolerated by the host product.

Hope it works out for you....   Best wishes.  Thanks for using  


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Electronics questions about AC, DC and digital theory.


Graduate electrical engineer with over 40 years in electronic design, manufacturing, project organization and patent review. Experience in fields of industrial and consumer electronics (audio, video, acoustics, etc.)

IEEE (Institute of Electrical and Electronics Engineers); Senior Life member AES (Audio Engineering Society), Fellow Life member

BSEE University of North Dakota

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