I have created a boost converter which boost 12v to 60v. I want to be able to pulse this voltage under water. I would like to have only the positive lead (Vout from boost) to come off the boost controller where the negative lead can just connect directly to the batter. I was wandering if a relay is what I need and if yes would this one work. lh1501ba


Ok, after reading all your helpful comments and answers I decided that the relay I chose might not be the right choice if I ever decide increase the frequency. The delay will just be to much. I made a amateurish attempt to include a PMOS to do the switching for me. The voltage will be variable controlled, and because of the nature of the Vgs on the PFET, I needed to also include a NMOS along with a voltage divider to help me provide the the correct gate voltage. I have it working correctly in LTspice but not sure how it will work in real life.

Here is the current schematic:

enter image description here

M2 is the PMOS and M3 is the NMOS. Also the signals are coming from the microcontroller and I have included a driver to drive the FETs.

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    \$\begingroup\$ What is the frequency (Hz) you want your pulses to be and what is the load you are driving (Ohms)? \$\endgroup\$ – Tom L. Aug 8 '13 at 4:05
  • \$\begingroup\$ 30 Hz and 1.2K Ohms \$\endgroup\$ – Wallace Aug 8 '13 at 4:14

Yes, that should work. Food for thought: SSRs (solid-state relays) are great because they "just work", but if you're building large quantities of this device, you'll probably want to use a high-side switch; they're way more economical, and can switch at much higher frequencies (since they're electrically, and not optically, coupled). You have to think a little harder when you go to hook one up, though.

  • \$\begingroup\$ How would I connect the output portion of the relay. Would 60v connect to pin 6 and when switch is closed would it come out of pin 5 or 4? I'm not sure what the datasheet means by s, dc, s'. \$\endgroup\$ – Wallace Aug 8 '13 at 5:53

Here's how you would connect it: -

enter image description here

Take note of the poor turn on and turn off times of this device. Using the maximum numbers your 30Hz square wave (33ms period) will have 3ms turning on and turning off eating into the quality of the square wave shape.

I'd use a p channel MOSFET if this was important.

  • \$\begingroup\$ Hey Andy, Thanks for the explanation on how to connect the relay. The delay is not a big factor but I'm curious on how to implement a PMOS so that it works the same way. What would be an example of using it in a circuit and what voltages would I need for gate. \$\endgroup\$ – Wallace Aug 8 '13 at 7:45
  • \$\begingroup\$ I have it running in Ltspice using a pmos, but I need a higher gate voltage than source voltage to switch it off. I know I didn't mention in my question but the boost voltage will be variable so i'm not sure if or how to use the pmos in this instance. But if you have any ideas it will be greatly appreciated. \$\endgroup\$ – Wallace Aug 8 '13 at 8:37
  • \$\begingroup\$ @Wallace the P channel MOSFET will need source connecting to 60V and load connected to drain. Gate will need to be pulled down to about 10V less than the source typically to turn on the device properly. Don't pull gate down to 0V though because the MOSFET will be damaged by excessive gate voltages. \$\endgroup\$ – Andy aka Aug 8 '13 at 9:39

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