1-5VDC step up for 12VDC relay

[albersondh]

Just a simple project I’m working on and my limited knowledge has run out. I need to step up the out-put current/voltage from a 0-5VDC variable transducer. I need the current/voltage increase to come on linearly along with the transducer out-put (0-5VDC) current/voltage. On either the pre or post step up side I need a potentiometer that will allow me to control the point at which the 0-5VDC signal actually is stepped up to 12VDC.

So if I could get signal 1VDC = step up 12VDC, and a subsequent rising rate of 1VDC : 1VDC thereafter, that would be great. Is this doable with just transistors?

Or is there a SPDT 1VDC (very low amp) switched/on relay that can switch 12VDC at less than 1 amp??? I couldnt find anything....

 

[kchriste]

Are you saying that you want to turn on a relay with a 1Vdc signal? If so, a simple transistor circuit will work. If you want an accurate and adjustable trigger point, then a comparator will be the way to go. What exactly are you trying to build?

 

[albersondh]

Are you saying that you want to turn on a relay with a 1Vdc signal? If so, a simple transistor circuit will work. If you want an accurate and adjustable trigger point, then a comparator will be the way to go. What exactly are you trying to build?

Thank you. Any links and or product advice would be greatly appreciated.

I want to make an on/off switch that will activate a SPDT 12vdc relay, using an automotive MAP sensor's 0-5vdc variable out put signal. I need the on/off point to be adjustable. Adjustable overboost warning device.

 

[Leftyretro]

Thank you. Any links and or product advice would be greatly appreciated.

I want to make an on/off switch that will activate a SPDT 12vdc relay, using an automotive MAP sensor's 0-5vdc variable out put signal. I need the on/off point to be adjustable. Adjustable overboost warning device.

Conceptually you need a op-amp type voltage comparator circuit. Input one would be your MAP 0-5vdc signal, input 2 would be an adjustable 0-5vdc from a pot to set your adjustable trip point. Output of the comparator would drive the 12vdc relay coil.


Here is a link explain comparator circuits:

**broken link removed**

Lefty

 

[kchriste]

I want to make an on/off switch that will activate a SPDT 12vdc relay, using an automotive MAP sensor's 0-5vdc variable out put signal. I need the on/off point to be adjustable. Adjustable overboost warning device.

Lefty's link will get you started. You may want to consider having different ON and OFF voltage trigger points. ie: Have the relay turn ON at say 1.2V but turn OFF at 1.0V. This will prevent the relay from chattering on and off when the voltage is near the trip point. This is called hysteresis and is discussed on the page Lefty linked. You could also have the relay timed so it switches ON for a minimum amount of time if the signal is jittering around the trip point.

 

[Leftyretro]

And you will probably need a driver transistor from the comparator output to the relay coil depending on the coil current needed by the relay you select.

Lefty

 

[albersondh]

Conceptually you need a op-amp type voltage comparator circuit. Input one would be your MAP 0-5vdc signal, input 2 would be an adjustable 0-5vdc from a pot to set your adjustable trip point. Output of the comparator would drive the 12vdc relay coil.


Here is a link explain comparator circuits:

**broken link removed**

Lefty

Thanks for the link. So let me explain this back, and please correct me if I’m wrong, because I think I have an understand of this now. The comparator (in basic form) has two inputs, one is a steady voltage and the other is a variable signal voltage. It has one out put that is a stepped up version of the variable signal voltage. Does this sound right???

My steady reference voltage will be 12vdc and my variable signal voltage will be 0-5vdc.

Questions- Do all comparators output a variable voltage based on the constant reference voltage and the variable signal voltage?

- How do I determine the amount of voltage increase based on the input signal rise?

- I need to go from less than 1vdc to 12vdc (using a 12vdc reference voltage). These are specs for the relay I would like to use:

• Operating Voltage: 12vdc
• Current Draw: 30Ma
• Relay Contacts: Form "C" 30vdc @ 10A
• Min. Pull-in Voltage: 9vdc


How do I determine what comparator will meet my requirement???