Home > power > 12V or 24V switch circuit

# 12V or 24V switch circuit

February 15Hits:2

I need circuit to choice between two voltages. So, circuit has two input terminals 12V,24V and one output terminal. If there is no 12V on input (floating) - output is connected to 24V, and if there is 12V - output connected to 12V. Is it possible to design such circuit without comparators? I think there should be P- channel mosfet on 24V.

For an electronic switch you can use the circuit below :

– Schematic created using CircuitLab

R5/R6 create a voltage divider that keeps M2 gate at about 9.5-10v (if the 24v can be much lower you can use a zener instead of the divider).
R4 is a pull down resistor keeping the source grounded when there is no 12v supply, that results to Vgs=10v which turns on the mosfet, that pulls the lowr side of R2 down and R1/R2 works as a voltage divider that feeds about 12v to the gate of M1 turning it on.

When the 12v supply is applied then the source of M2 becomes 12v and Vgs becomes almost 0 (slightly negative actually) which turns the mosfet off. That leaves the lower side of R2 floating (high impedance to ground) so R1 works as a pull up with Vgs=0 and M1 turns off.

The two Schottky diodes are used to prevent the current flowing from 12v to 24v and from 24v to the M2 gate (or the 12v during the M1 transition).

Use a SPDT Relay. Attach the coil to the incoming 12volts. Coil rating needs to be 12v of course. NC contact connects to 24v. NO contact to 12v. Contact pole (aka common) output to your load.

Tags:power

## Related Articles

• ### 12V or 24V switch circuitFebruary 15

I need circuit to choice between two voltages. So, circuit has two input terminals 12V,24V and one output terminal. If there is no 12V on input (floating) - output is connected to 24V, and if there is 12V - output connected to 12V. Is it possible to

• ### How can I build a switching circuit that scales several 12v signals down to 5v?October 15

Let me start off by saying that I know just enough about electronics to be dangerous (how to solder, follow a simple schematic, and check for connectivity problems and usually figure out what each wire is for). I've installed a cruise control kit in

• ### 12V to 24V 3A boost converter using LM2587October 29

I'm trying to build a 12v to 24v boost converter. I have an output current requirement of 3A. I'm thinking of using two LM2587 5A Flyback Regulators in parallel like this: http://www.ti.com/lit/an/snva552/snva552.pdf Will this circuit work for me? (k

• ### Running a 220v dust collector with 24v switchesNovember 9

I have a 5hp 220V 30A dust collector that I want to turn on and off with 24v switches attached to my blast gates. Can I simply use a 220v to 24v transformer? --------------Solutions------------- I suggest you go to Lumberjocks (http://www.lumberjocks

• ### Using a 12V lighted toggle switch with an ArduinoMay 25

I would like to connect a 12V lighted toggle switch to an Arduino and be able to read its state (replacing the momentary button in this tutorial with this switch). But the Arduino has only 5V power supply. Can I connect the 12V switch to the 5V power

• ### What is the difference between a 12V and 24V DC motor?February 6

I was buying DC motors for making robots. I wanted to ask whether the voltage written on the motor, e.g. 12V or 24V, matters. Whether a 100 RPM 5kg/cm torque 12V DC motor is any different from a 100 RPM 5kg/cm torque 24V DC motor. If I give 24V to a

• ### Simple SPST Switch Circuit - Pull-down Resistor VS. Current Limiting ResistorFebruary 22

Super Noob EE question: Here is my quick draw-up of my SPST switch circuit schematic. I know I probably did not do this right, but if it gets the idea across, then thats good enough for me atm. – Schematic created using CircuitLab The right boxed sec

• ### Is it possible to design a switch circuit with XNOR's truth table value?September 25

We all know XNOR's truth table right? Is it possible to design a switch circuit (not a gate circuit) using XNOR's truth table value. I had tried for 40 mins and it seems impossible. Switch Circuit Example: image --------------Solutions------------- I

• ### why and how do I use a capacitor in a switch circuit?June 2

I have seen many designs of switch circuit: I know that a capacitor will help anti-shake but I realy do not know how i can anti-shake. Does it work like a decoupling capacitor or a low-pass RC filter? and then I want design another switch circuit but

• ### How to design a power switching circuit using a photo-interrupterAugust 22

Okay. I'm completely at a loss here. I was trying to design a switching circuit for a 3A load (Solenoid) using a photo-interrupter. I got to about here: But I have no idea what to look for in my parts. I plan to use these as the current limiters, and

• ### Deciding base resistor for transistor switch circuitSeptember 10

I'm building a transistor switch circuit and below is the schematic. – Schematic created using CircuitLab I calculated R2 resistor (base resistor) value from this formula: $$R_{R2}=\frac{V_{BAT2}-V_{be}}{(V_{BAT1}-V_{ce})/R_{R1}/h_{fe}*2}.$$ Is this

• ### Impedance Matching a switching CircuitMay 14

I'm trying to mathematically model a Class E amplifier in the hopes of deriving a relationship between the input and output (Transfer Function). One particular difficulty i'm facing is impedance matching the load to the rest of the circuit. The regul

• ### 12v on/off switch to toggle state of two circuitsJanuary 18

I have an existing latching button switch that controls a low power LED (no more than 1W) from a 12V power supply. I'd like to add an extra circuit to the same power source that is controlled by the same switch, the other circuit will consume more po

• ### Solar Panels Series / Parallel Switching CircuitOctober 11

I am an electronics know-not-much :) I do understand the basics of current/voltage/amps etc. I have an array of 10 x 15watt x 12v (max 17.5v) amorphous solar panels here in the UK. I want to arrange them in 5 banks of two (5 pairs) and when light lev

• ### Choosing the right transistor for a switching circuitMarch 31

I want to control a siren speaker (has a built-in driver) with an Arduino. The siren needs 12V and consumes about 480mA. The Arduino output pin is 5V and can source 40mA maximum. I would like to use a transistor to switch the siren on and off. Is thi

• ### Understanding a Momentary Switch Circuit to Power Up MainsDecember 28

Source: http://www.amb.org/audio/epsilon24/ I have been trying to understand the operation of the above circuit. To simplify, I am ignoring K1, Q1, R4 and D2. I also assume there is a jumper across T1 and T2. Since I assume there is no K1, I assume t

• ### Low power timer switch circuitJune 29

Our car sharing club is working to implement a smart system in our vehicles which will allow access via RFID-cards, and which will record milage for the booking and billing system. We are using a tracker unit (http://flextrack.dk/en/products/tracking

• ### Materials required to convert NiMH rechargeable 24V/6Ah circuit (20 C-cell) to Li-Ion rechargeable circuitJuly 8

Below is a picture of a battery shell for a NiMH circuit for a power assist wheelchair battery. I'm taking a guess that each of the 20 batteries is 1.2V because the entire circuit is 24V. These are rechargeable. I'd like to convert this circuit to th

• ### 12v driver 24v h-bridgeAugust 30

Hi, I want to run a 24v motor with a 12v h-bridge mosfet driver (HIP4081A). I haven't try it in real life but I made the schematic. I want to know before testing it if you can find any error or bad idea in my schematic. I was successful to run the mo

• ### Connecting a 12v relay to microcontroller circuitDecember 9

I am trying to build an automatic plant watering system using ATmega16. We are using moisture sensor for our project. The circuit diagram is as follows: We are using the following 12V relay: I have no experience of using relay. How I will connect the