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Old Feb 28, 2013, 05:20 AM
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help choice FET , design for ESC

hello GUY

I'm wondering, choose type FET which for control motor

I see the two FET have Ampere high IRF 7843 and IRF 3205

IRF 7843 SMD 252 160A (very good)

IRF 3205 DIP 110A (good)

7843 is small, but larger amps 3205. What is the difference between them?

thanks
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Old Feb 28, 2013, 01:45 PM
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The main difference is that the IRF3205 exists, whereas the IRF7843 doesn't.

Assuming you meant IRLR7843, it is rated for lower voltage (30V vs 55V) but has much lower on resistance (0.0033 Ohms vs 0.008 Ohms), requires less gate voltage to turn on, and has much lower gate charge (34nC at 4.5V vs 146nC at 10V).

So unless you need to switch more than 26V and/or require a TO-220 package, the IRLR7843 is probably a better choice.

Quote:
IRF 7843 SMD 252 160A (very good)

IRF 3205 DIP 110A (good)
Be aware that these ratings are not realistic. The package limitation is 30A for the IRLR7843, and 75A for the IRF3205. In practice, even these lower values will not be achievable without a large heatsink.
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Old Feb 28, 2013, 05:06 PM
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Originally Posted by Bruce Abbott View Post
The main difference is that the IRF3205 exists, whereas the IRF7843 doesn't.

Assuming you meant IRLR7843, it is rated for lower voltage (30V vs 55V) but has much lower on resistance (0.0033 Ohms vs 0.008 Ohms), requires less gate voltage to turn on, and has much lower gate charge (34nC at 4.5V vs 146nC at 10V).

So unless you need to switch more than 26V and/or require a TO-220 package, the IRLR7843 is probably a better choice.
I see 7843 often use for esc for plane , I use the battery 2s lipo, motor brushed 540 ,but I want to compact, 7843 or 3205 is a reasonable choice?
34nC at 4.5V vs 146nC, 0.0033 Ohms vs 0.008 Ohms?
I do not understand it, small resistance, good electrical conductivity ?





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Originally Posted by Bruce Abbott View Post
Be aware that these ratings are not realistic. The package limitation is 30A for the IRLR7843, and 75A for the IRF3205. In practice, even these lower values will not be achievable without a large heatsink.
Thanks for giving me the information (75a of 3205 ) , why datasheet is 110a but in fact is 75a ? what is current 110a of FET ?

this is esc 320a with 14 fet 252 smd (very small ) and esc 320a which 6 fet 220 !!!!
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Old Feb 28, 2013, 05:25 PM
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If you pick the IRF3205, you'll need a mosfet driver to supply it with 10V gate voltage to full turn it on. If you supply it with 4.5V, it will have a high on resistance.

The IRLR7843 is designed for a 4.5V gate drive.

The datasheet 161A is a calculated value based on the Rdson (on resistance) and the thermal resistance. The 30A is the current limit of the physical package.

That's why the 3205 has a higher rating (75A) than the 7843 (30A) even though the 7843 has a higher theoretical current (161A vs 110A). The 3205 is in a bigger TO-220 package.
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Old Feb 28, 2013, 09:40 PM
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The package current rating is given in the small print in the footnotes. Sometimes the package rating is shown in the large print but don't count on it. In any case the current rating shown in the bold print is never the real rating. Most datasheets have a chart for drain current vs case temperature which shows the package limits.

The other very important rating is the current rating of the body diodes and the diode voltage drop. At ½ throttle the body diodes carry the same current as the Fet. The forward voltage drop for the IRF3205 is 1.3 volts and 1.0 volts for the IRLR7843 at current ratings far beyond the package limits. Within the package limit the voltage drop is the normal .7 volts. Either can handle currents within the package limits.
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Old Mar 01, 2013, 06:47 AM
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thank all for giving me the information
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Old Mar 01, 2013, 08:26 PM
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Originally Posted by viperidae View Post
If you pick the IRF3205, you'll need a mosfet driver to supply it with 10V gate voltage to full turn it on. If you supply it with 4.5V, it will have a high on resistance.

The IRLR7843 is designed for a 4.5V gate drive.

The datasheet 161A is a calculated value based on the Rdson (on resistance) and the thermal resistance. The 30A is the current limit of the physical package.

That's why the 3205 has a higher rating (75A) than the 7843 (30A) even though the 7843 has a higher theoretical current (161A vs 110A). The 3205 is in a bigger TO-220 package.
why in ESC brushed ,I donot see they use IC driver ir2101 to gate drive 10v ?

I just see ESC brushless have IR2101

someone help me schematic drive for FET ( ESC brushed )use IR21xxx .
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Old Mar 01, 2013, 08:42 PM
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Originally Posted by Jame David View Post
why in ESC brushed ,I donot see they use IC driver ir2101 to gate drive 10v ?

I just see ESC brushless have IR2101

someone help me schematic drive for FET ( ESC brushed )use IR21xxx .
The IR2101 works well with a brushless ESC.
It does not work very well with a brushed ESC. Unless you are a clever circuit designer do not even attempt to use the ir2101 in a brushed ESC.

Look here for schematics:

http://www.rcgroups.com/forums/showthread.php?t=157193
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Old Mar 01, 2013, 09:05 PM
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Originally Posted by mjsas View Post
The IR2101 works well with a brushless ESC.
It does not work very well with a brushed ESC. Unless you are a clever circuit designer do not even attempt to use the ir2101 in a brushed ESC.

Look here for schematics:

http://www.rcgroups.com/forums/showthread.php?t=157193
hello mjsas

I have seen many electrical circuit diagram on the website that you provide,most of the use PWM 4.5V to drive the FET,
 but it is difficult for me, I use a 24v 500w motor. so very hot FET although I used large heasink

design ESC brushed with high power battery not easy .

help me
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Old Mar 02, 2013, 03:27 AM
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Quote:
Originally Posted by Jame David View Post
design ESC brushed with high power battery not easy
Which design(s) did you try, and what FETs were you using?
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Old Mar 02, 2013, 04:13 AM
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hello Bruce abbott


I use esc brushed design with 12f675 that I find on the internet
http://www.bhabbott.net.nz/ICS100Li.html

I use it to make electric car for my child

with a strong engine 24 v 300 W. and batteries 24v

I bought ten fet ir 3205

circuit operation but FET is very hot, even when running slowly or quickly., I think , caused by driving gate bad (4,5v pwm )

I can not solve this problem, can you help me ?
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Old Mar 03, 2013, 01:25 AM
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Originally Posted by Jame David View Post
I use esc brushed design with 12f675 that I find on the internet
http://www.bhabbott.net.nz/ICS100Li.html
That's my website.

Quote:
I bought ten fet ir 3205

circuit operation but FET is very hot, even when running slowly or quickly., I think , caused by driving gate bad (4,5v pwm )
You need a gate driver that produces ~10V and can drive a high capacitance load. If you are using 2S Lipo then you only have ~7.4V available from the battery, so you will need a voltage booster.

Below is a circuit I sketched up which should do the job. Note that it is untested (hopefully there aren't any errors!). The TC4427 has two outputs, each of which may be able to drive multiple FETs. I would start by using just two FETs (one on each output) as with this driver circuit they should be able to switch 12A without breaking a sweat.

You must also make sure that the Schottky diode across the motor is able to handle the recirculating current. The ICS-100Li gets away with a low current diode because it is only rated for 2A output, but yours needs to handle >12A peak so it should be rated for at least 3A average (eg. 1N5822).
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Old Mar 03, 2013, 08:33 PM
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hey Bruce abbot
great when see the owner of that website here

with your schematic, I understand how to create a high-voltage power

great, I'll do it now
thanks a lot
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Old Nov 04, 2013, 11:40 AM
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First of all, very very sorry for the thread hijack.

I'm a little stuck and I was hoping Mr. Bruce Abbott could help as I have found his posts and his website very useful.

My name is Birger de la Peña and I came across your name while doing searches for power circuits for brushed ESCs. Since you have provided a lot of information in this area I was hoping maybe you could help me with a little design challenge I have. I have some experience in micro-controller based control system design but when it comes to analog and/or power circuits I'm pretty hopeless.

I'm currently working on an Afterburner LED driver for a friend I met here on RCG. The design can be seen here:

Two-stage LED Afterburner Prototype Test (2 min 41 sec)


and the project thread (for the airplane it will go in) can be seen here:

http://www.rcgroups.com/forums/showthread.php?t=1799004

I am using the following parts:

Controller: https://www.sparkfun.com/products/11113
ESC: http://www3.towerhobbies.com/cgi-bin...&I=LXKBF2&P=ML
LED: http://www.hobbypartz.com/79p-10219.html

For now this design is complete and I set off for PCB prototyping but it is pretty large (not a problem for his plane) and also expensive (since I'm using expensive brushed ESCs).

What I'm looking to do is to replace the ESCs with a simple PWM based solution. I would drive a transistor from a digital pin on the Arduino board and feed power to the LEDs that way. This will eliminate the need for the ESCs and the large PCB I'm using to hold the ESCs. Since you have a fair amount of experience with this (or at least similar concepts) I was wondering if you could help me with a driver component design that would take the output from an Arduino pin and turn on/off the LED strip including the ability to take PWM for LED dimming. I am planning to drive two channels (as shown in the video) at max 1M length which should requie about 400mA per LED strip.

In addition, if it is not too much imposition, a second circuit with the ability to drive longer LED strips (for lighting up entire planes for night flying) would also be highly appreciated, let's say 5A - 7A.

Thanks so much for you help with this I really appreciate it and if you don't have time to help I completely understand and still appreciate you taking the time to read my message.

Regards,

- Birger
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Old Nov 05, 2013, 02:32 PM
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Originally Posted by bdelapen View Post
I would drive a transistor from a digital pin on the Arduino board and feed power to the LEDs that way... I am planning to drive two channels (as shown in the video) at max 1M length which should require about 400mA per LED strip.
Use a logic-level N Channel MOSFET rated for at least 5A. To limit capacitive loading on the Arduino and prevent ringing, put a 220 Ohm resistor in series with the gate of each FET. That's it!

Quote:
In addition, if it is not too much imposition, a second circuit with the ability to drive longer LED strips (for lighting up entire planes for night flying) would also be highly appreciated, let's say 5A - 7A.
For that you need the same circuit, but with a higher current FET, eg. IRL3103. You can also use these FETs for the 400mA strips.

If you are applying PWM to long wires drawing 5~7A then it might be worth adding a small schottky diode to soak up back-emf. The circuit would look something like this...
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