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I built a full prototype per the plans available. Yes it seems power is getting to the low side. I wired on ammeter to the low side. I'm running my special power supply on the high side so that i can keep the current down to a level readable by my 250ma ammeter. Pictures I am attaching:

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What I am finding out right now is that when I plug in my 6V battery to the low side my 5A short stopper fuse is blown pretty much immediately. I'm doing this while the driver_test.ino is connected and running on Arduino. So at this point I can see that if I were to plug in my battery to the low side without a shortstop I think what will happen is that mosfet will melt down (6V @ 6A = mosfets max power dissipation).

So at this point I ask is this happening because its in the design or am I doing something that is causing this?

By the way I added to this design a 470KOhm resistor on M3 between gate and source. I knew this was going to happen and I tried to prevent it with that big resistor. It didn't work.

Thanks in advance for any more information. I really liked the design especially the current sensing IC.

For reference the schematic: enter image description here

Eae
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1 Answers1

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Where to begin?

The most obvious problem you have is layout. Switching supplies require that the power and ground paths be as short and as thick as possible. That specifically includes the connection to IC2. Try to emulate the layout of the commercial PC board.

What is your "special supply"? It apparently is able to source more than 5 amps, if that's where your fuse current is coming from, but I doubt that it is.

Where, exactly, is your "shortstopper fuse"?

Assuming your fuse is on the battery output, the most likely problem is that your output voltage is too low, and the battery is back-driving the circuit. Put a high-current (5 amps or more) diode between the output and the battery, allowing only charge current to enter the battery. Before you connect the battery, put a 10 ohm resistor on the output, and verify that the load voltage is more than the battery no-load voltage.

The MOSFETs are rated for 20 to 30 amps continuous, with pulse rating over 100 amps, so as long as they are being properly driven you should have no worries there.

Why do you think a gate/source resistor on M3 will help? That's just idle curiosity on my part, but the fact that you think it will suggests that you need to learn more about how the circuit works. Although, to be fair, I'd really like to see the rationale for M3 being there in the first place.

WhatRoughBeast
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  • My short stopper fuse is affixed to the positive line of my 6v lantern battery. I bought it at home depot. My special supply yes can output more than 5 amps however for the purposes of the demonstration on this post it's putting out about 150 milli amps onto the high side. – Eae Feb 01 '15 at 15:05
  • To answer your question about the gate source resistor I think I understand that with that resistor in place current leakage to the gate can be prevented. I've seen it happen in sim. I think what you might be saying is that when Mos 3 is open it doesn't matter that there is a gate source resistor. – Eae Feb 01 '15 at 15:13
  • Thank you for posting this answer. I found your post very informative. – Eae Feb 01 '15 at 15:16
  • @user2209542 - You don't need a gate resistor on M3 as long as it is connected to IC2. IC2 is a special-purpose gate driver, and it never leaves the gate floating. – WhatRoughBeast Feb 01 '15 at 19:44