madcitysw

Hello, please welcome me to this site as I am a new user here. I seem to find alot of info here than the other sites that I been. However, I still face the problem of my project that I am working on and no on has answer my question about mosfets. This project will be installed in vehicles with 12V - 13.6V. At this time I making a relay board which will have 6 relays (1 power on relay also) and about 12 mosfets. I am using an avr mega128 ic to control everything. When the mosfet is turned on, I want it to output 12V+ - 13.6V+, not ground. I been told so many things, but I think (if I not mistaken) a P-Channel mosfet is what I need in order to output 12V+. I wonder which mosfet I will need because I only drawing 1 amp each mosfet and how to hook it up. I have order the following mosfets and have them in this room right now:

ntp2955g (12a, 60V), a p-channel
mtp2p50eg (2A, -500V) a p-channel
mld1n06clt4g (1 AMP, 62 Volts), think this is a n-channel

Thanks
Shane

Roff

What supply voltage will you be running the mega128 on?
Do your relays really require an amp of coil current?
You will need level translators to drive P-Channels from a mega128. You could drive N-channels directly, but I realize that some loads must be returned to Ground.

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Ron

madcitysw

The mega 128 supply will be run off of a 5V regulator. The relays have to have at least 20 amp output, but that just one of them. The other relays will be 12 amps. I have the following relays for this project:

1 (T9A95D52-12)
5 (t7CS5D-12)

You may be wondering why I did it in relays and not mosfets. I was thinking that would be alot of amps going in the board all at one time and didn't want nothing to go wrong. So in this case, I use relays for the loads and mosfets for changing patterns. The first relay is just to turn on the main power to the warning lights that are connected to the relay board. The other 5 relays are to turn on that device and start flashing. Hell, I don't even know if 20 amps will be ok, I may need more amps?

Can you give me a link to some of the level translators that are design for 5V (AVR) inputs.

Roff

I can't open your relay files.

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Ron

madcitysw

Do you have Adobe Reader Installed?

Oznog

Well, that's an additional problem.
The P-channel will have source to +12v and drain to load. The MOSFET is off when Vgs=0 (or >Vth), so Vgate needs to be +12v. The MOSFET is full on when Vgs=-8V or so (varies a lot per device and how much current you need, generally between -3V and -12v). MOSFETs can only tolerate a limited Vgs- some only +/-10V, some up to +/-20V but higher is extremely uncommon (and that's an absolute max- including voltage spikes seen in an engine-driven 12v system). So you may just pull the gate to gnd with a whole nother transistor (because a microcontroller can only provide +5v, not +12v, so it can't turn the power transistor off), let a resistor pull it back up to +12v when the transistor's off, but still worry about spikes seen in a 12v system. And you'd want one of those +/- 20V Vgs transistors. Or use a zener to limit the gate voltage.

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I thought what I'd do was I'd pretend I was one of those deaf-mutes.

Roff

I finally was able to open the files. The maximum coil current on any of the relays was 83mA with 12V applied to them. Why do you think you need one amp?
From your first post, The circuit below should work. A high output from your mega128 will turn on the relay.

Attached Images

relay dvr.PNG (12.6 KB, 14 views)

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Ron

madcitysw

OK before we all get confuse about something. The relay coils won't be connected to the mosfets. Let me explain a little more about the project.

The purpose of the 5 relays to turn on the loads (Strobe Packs, LED Flashers, Tail Flashers, Etc). The Mosfets are only design to change the patterns to the external devices, this was the reason it needed to be output 12V+, and not the ground. Most of the external devices get the patterns changed when it connected to 12V+. Let me give you the manual to the Whelen Strobe Pack (Strobe Pack). This the Strobe Pack that I would most likely be using. You will see that this strobe pack uses three switches to control the patterns, this was why I need three mosfets for each relay, the relay only controls to turn on the strobe pack (in this case, it the White/Red wire). The patterns are control with Brown, White, Grey wires. Anyway i did pick a more better dual mosfet that is a Low Level P-Channel.

STS4DPF30L

I had talked to someone else on another forums and he helped me out a little about how to connect the mosfets. I will attach the file to show how he had it connected. Oh, I will be driving the relays using a UDN2981 and driving the mofets using ULN2003A.

Attached Images

PCH-Drive_12V.JPG (115.3 KB, 11 views)