What is the best heat transfer method

[Inquisitive]

This way 6 months or 2 years from now people can learn and follow the logic of how it was resolved and not guess what was going on. A picture or schematics can say a thousand of words

 

[kinarfi]

Thank you for input, I'm sure my project has benefited from the changes I have made because of the help I have received here.
Lots of thanks and appreciation!!
Some of the screen shots and show the difference the transistorized FET drive makes over just a 1K pull up, also is the schematic updated to what I plan to use.
If you down load and run the .asc file, look at TR,TL,BR,BL and in a separate plot IR13, & if you jumper around theLEMHX50, the wave forms look better. I'll take a few more photos to post when I get done with changes.
Thanks again
Jeff

 

[chemelec]

Kinarfi, Well the Mosfet is a Voltage controlled device, but it also has a consideable amount of Gate to source Capacitance.
The More the Capacitance and the Higher the Frequency, than it does require More Drive Current to Offset Delays in Charging that Capacitance and turning on the Mosfet.

In the Last circuit you Posted, you should also have a Gate to Source Resistor. (about 5 to 10K)

Putting Circuits and Pictures Directly on this site is Better.
It will always be there for people with Simular problems.

 

[kinarfi]

In the Last circuit you Posted, you should also have a Gate to Source Resistor. (about 5 to 10K)

Actually I do, they are attached to the FETs, I usually use .125w resistor wrapped under the leads.

Thanks, Jeff

 

[chemelec]

Hi Jeff, OK

 

[MrAl]

Hi,

I am in favor of putting the picture right on this site too. Too often i see broken links on the web. It also makes it much easier to correct the schematic if needed.

 

[tcmtech]

I am curious as to why you are not driving your power fets with a common fet or IGBT driver IC set like the IR2113 or such that have built in totem pole architecture specifically designed for high side gate driving at multi 10's of KHz frequencies?

 

[kinarfi]

Because I don't know of them and don't have them on hand and at $4.55 a pop, it's a luxury I can't afford, wanna send me a few?
and now that you brought the subject up, is the 2N2222 going to be a good driver or is it too weak? I already popped one and fried one on the high side, my hand wound inductor shorted out, popped the quad opamp and the inductor drive FET got hot and I burnt my little finger.
It's a good thing I screw up a lot, other wise, I'd get every thing done and wouldn't have anything to do and be bored.
Jeff AKA Kinarfi
EDIT- Also, Spice is saying that there are 250 ma spike to drive the FET on. I found that interesting.

 

[tcmtech]

Because I don't know of them and don't have them on hand and at $4.55 a pop, it's a luxury I can't afford, wanna send me a few?

Then how are you affording to build, operate, break and redesign this whatever it is you are making?

My point is if you can afford to do it wrong twice or more you can afford to do it right once.

 

[kinarfi]

Then how are you affording to build, operate, break and redesign this whatever it is you are making?

My point is if you can afford to do it wrong twice or more you can afford to do it right once.

What I am making is a motor driver for a steering power assist that uses a much more powerful motor than stock and the controlling sensor is a Hall effect device that senses the movement of a magnet that moves maybe 3/16 of an inch, similar in design to the hand throttle on a motorcycle, but much less travel.
If I were a multi national company worth billions or had years of university education or years of engineering under my belt, I probably would have gotten it right the first time.
But, I am just a retired person with an 1970s Associated Degree in Electronic Technologies from a trade school that has lots more time to spend than money and I try to learn from my mistakes and improve as I go.
Why must you always be so critical and condescending, that's not helpful!!

 

[MrAl]

Because I don't know of them and don't have them on hand and at $4.55 a pop, it's a luxury I can't afford, wanna send me a few?
and now that you brought the subject up, is the 2N2222 going to be a good driver or is it too weak? I already popped one and fried one on the high side, my hand wound inductor shorted out, popped the quad opamp and the inductor drive FET got hot and I burnt my little finger.
It's a good thing I screw up a lot, other wise, I'd get every thing done and wouldn't have anything to do and be bored.
Jeff AKA Kinarfi
EDIT- Also, Spice is saying that there are 250 ma spike to drive the FET on. I found that interesting.

Hi again,

If you dont have any MOSFET driver chips then use two transistors, one PNP and one NPN with the emitters and bases tied together. That makes a much better driver than a resistor.

The 'spike' would be the current when the MOSFET internal capacitance is being charged up. That's part of the issue regarding the correct drive for MOSFET's. If we dont have the spike then we get very slow turn on and/or slow turn off. That spike turns it on (or off) and then we dont need that high current anymore, just the correct voltage level.

 

[tcmtech]

Why must you always be so critical and condescending, that's not helpful!!

Because I am a terrible uncaring person. Just ask my wife.

More to the point sometimes it's necessary to be less polite in order to make people step back and re evaluate their views of how or why they are doing something. I make people think even though I am very aware many do not like it when I make them do it.

Hey at least you know what a totem pole gate driver IC is now and what they are good for!

 

[kinarfi]

IMHO, and in my mind, this is as good a totem, it has the npn of a totem but the pnp is replace by the schottky. If I had a less than 0 potential, then the use of the pnp would be better. As soon as I get my circuit repaired and functioning, I will post some screen shots from my scope.
Being that I am using the 2N2222N, and have had one of the burn up and then in same one (circuit wise) blow up & I can't see any physical causes, (solder traces that short & the likes), so I'm concerned about it electrically.
Chemelec, while I was having problems with LM555 in the past, I made a tester to see if they were functional, well I had several of them laying around and decided to make another on and in the process, I could see their value as a FET driver. I had a red and a blue LED and used them as the indicators and it makes for an interesting visual que.

 

[ChrisP58]

Kinarfi,
I can give you a couple FAN7842 parts to play with if you'd like. They're in SO-8 SMT packages though.

 

[kinarfi]

That would be nice, thank you, PM sent, I have some adapters go I can use them, with recent developments, I have been thinking I need to rebuild the circuit board on a bigger board and may/probably move the power FETs outside the control box and on a larger heat sink or sinks.

One problem I'm still working on is how to sense and limit the stall current which happens when it reaches the end of travel mechanically, this has to be done electrically as I see no way to do it with a limit switch or position sensor.

 

[MrAl]

Hi,

Sensing current isnt that easy but it is done quite often. If you can get away with a current limiting resistor that might work but that also limits torque.

If using a limit switch or position sensor that detects the end of travel, it would have to switch just before the end of travel.

 

[kinarfi]

In the circuit I do have a .1 ohm resistor as an attempt to limit current and the Lem HX50 is a Hall effect current transducers that outputs .0125 volts per amp with a 2.50v center and can measure up to 150 amps in either direction.

 

[MrAl]

Hi,

Well 0.1 ohm probably is not enough resistance, but it depends on your source voltage. If your motor can draw lots of current at 12v then at 12v a 1 ohm resistor for example would only limit current to about 12 amps, and then it would have to be high power rated. So it may not work as good as you want it to depending on the source voltage and the typical current draw.

If you already have a current sensor and it is fast enough then you can use that as feedback to shut down for a given amount of time like 10 seconds or something like that.

 

[kinarfi]

MrAl, Your not thinking large enough, Motor specs, Operating v: 6v - 12v, Nominal v: 12v, Stall Torque: 343.27 oz-in, Stall Current: 133A, Kt: 2.58 oz-in/A, Kv: 443 rpm/V
.1 ohm may be a bit shy, .2 may be a bit heavy, IMHO. The LEM transducer is instantaneous and is being used as a feed back, with .2 ohms and LEM feed back, I was limiting out near 30 amps, then I blew another FET and got on the forum and asked for advice about heat sinking,

 

[MrAl]

Hi,

I am not sure what you are asking then. Current limiting with a resistor only works in certain situations, and if you have the current already being measured then there is a way to use that measurement to feed back to a circuit (perhaps another circuit altogether) to either shut down or just lower the current.

A typical method is to measure the current through the transistor itself and shut down if the current goes too high.