0
\$\begingroup\$

I need a voltage controlled switch that is able to turn on and off using voltage in the range 0 to +10VDC. When it's on it should be able to handle the flow of +24VDC across it. I had a look on the internet and asked on others forms as well, but not quite sure about this. MOSFET was one I though about it, but it requires its gate voltage (Vgs) to be higher than the source. But I cannot get the gate voltage to higher unless I OP-amp, which is making this a bit more complicated.

For MOSFET I have a diagram done, maybe it's not right but I tried. enter image description here

Adam-4024

This is ideally what I'm looking for. The Adam module (ADAM-4024) is only capable of applying 0 to +10VDC max. Not use if it's possible.

Is there any simple circuit/component that is capable of doing this.

Thank You

* Thank you for the diode suggestion. I have found a 2N7000 N-Channel Enhancement Mode Field Effect Transistor would this would be prefect, I added the datasheet link hereMOSFET 2N7000 datasheet. Also I'm not particularly sure about the Rd(on) value.

Also another thing to mention, Peter Smith suggested a diagram below, when you were talking about in the comments you said "a 0-volt control input may destroy the MOSFET" is that applying to the diagram below and not the diagram I drew? Yes? I asked this as I will be supplying 0V to turn off the MOSFET.

Furthermore, I'm not sure if I'm correct to say this but, if I use MOSFET to active the SY3220 by switch and when I want to switch off the SY-3220 still active because the MOSFET self lock it. Is this correct or I'm wrong and I can perfectly turn off the SY3220-5L device.

Thank you for the help

\$\endgroup\$
  • \$\begingroup\$ Sorry - made the changes \$\endgroup\$ – Satvir Singh Sep 22 '15 at 14:08
  • \$\begingroup\$ With a correctly chosen MOSFET, your circuit should have no problem turning on with 10 V control voltage. The source is connected to ground, so every voltage in the circuit is positive relative to the source. \$\endgroup\$ – The Photon Sep 22 '15 at 15:41
0
\$\begingroup\$

Your circuit will, in principle, work fine. There is no need for the gate voltage to be higher than Vdd, although it does have to be higher than the MOSFET source pin.

In general, you should add a flyback diode across the load, oriented with the anode to Vdd. The diode should be rated for a voltage more than Vdd, and a current greater than the load current, although this last is not really necessary but it's good practice. This will prevent possible damage to the MOSFET when it turns off, particularly if the load has any inductance, such as a motor or coil. And since this is a solenoid valve it does have a coil and it definitely needs a diode.

The MOSFET should have a voltage rating greater than Vdd (which shouldn't be hard at 24 volts, but pay attention anyways) and a current rating of, say, twice the load current or greater. Having a little margin is always a good thing. The catalog is hard to use for the coil resistance, but it does say the maximum power draw is 0.4 watts with an indicator LED. This suggests a current of about 17 mA, and you should be able to use just about anything.

| improve this answer | |
\$\endgroup\$
  • \$\begingroup\$ Thank you for the explanation just what I was looking for. I read your comment and made modifications to the diagram could you please have a look and just confirm that it's all fine ? Thank you \$\endgroup\$ – Satvir Singh Sep 23 '15 at 9:11
  • \$\begingroup\$ Could anyone please confirm that my diagram is fine? \$\endgroup\$ – Satvir Singh Sep 24 '15 at 8:57
  • \$\begingroup\$ @ArranRai - Well, it ought to work. But why on earth have you specified an 8 amp power supply for a circuit that will only (nominally) draw 0.017 amps? \$\endgroup\$ – WhatRoughBeast Sep 24 '15 at 12:33
  • \$\begingroup\$ well that's the only power supply I have been able to get hold off. So the rating is 8A. It's not the adjustable one, so I have no option. \$\endgroup\$ – Satvir Singh Sep 24 '15 at 14:08
  • \$\begingroup\$ @ArranRai - Also, your diode is waaaay bigger than necessary. Something like a 1N4148 will be much cheaper and will work fine. \$\endgroup\$ – WhatRoughBeast Sep 24 '15 at 18:34
0
\$\begingroup\$

A P channel MOSFET will do the job. Pull the gate low relative to the source to turn on.

Here is a typical setup

PMOS as a switch

HTH Edit. Drive the p channel gate with a n channel device. Make sure both devices have a Vds rating of at least 30V.

That will let you drive a 24V load.

| improve this answer | |
\$\endgroup\$
  • \$\begingroup\$ Thank you. The issue I'm having is that the device has to have 24VDC to turn on, otherwise it doesn't. My project involves using of Adam-4024 module. which gives out 0 - 10VDC max. I had a look into other modules, but than I would just another module for only controlling one device, which is not ideal. That's why I'm restricted to 10Vdc to turn on. \$\endgroup\$ – Satvir Singh Sep 22 '15 at 14:25
  • \$\begingroup\$ This cannot work in the poster's system. With a 24 volt supply, and 0-10 volts in, the MOSFET will always be turned on. In addition, most MOSFETs have a Vgs limit of +/- 20 volts, so a 0-volt control input may destroy the MOSFET. \$\endgroup\$ – WhatRoughBeast Sep 22 '15 at 15:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.