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High Current Transistor Circuit — Parallax Forums

High Current Transistor Circuit

codysprakercodyspraker Posts: 46
edited 2012-04-29 04:01 in Robotics
I am trying to build an autonomous helicopter using a basic stamp homework board to control to the motors in flight along with a ping sensor to manage height. The problem I am having is trying to find a transistor that can handle the current needed to drive that 3 Amp motors. What I am looking for specifically is a transistor that can handle 3 Amps at most more like 1 or 2 amps most of the time at 7.4V. Does someone know of a transistor that can handle this type of thing? I have been looking for days. Thanks for any help!

Comments

  • jvrproductionsjvrproductions Posts: 61
    edited 2012-04-17 19:50
    Hey cody sorry for my english but I think will be easer to conect the bs to the reciever. On that way you wil not need a transistor and you will be available to control.the heli with the bs and the remote too
  • xanaduxanadu Posts: 3,347
    edited 2012-04-17 20:09
    Are the 3 amp motors brushless? Can you post a pic of the motors and receiver electronics?
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-04-17 20:15
    The thing to do is use the original speed controller of the helicopter and control the speed controller with the BS2.

    A lot of RC speed controllers are controlled the same way one would control a servo.
  • jvrproductionsjvrproductions Posts: 61
    edited 2012-04-17 20:58
    Duane Degn wrote: »
    The thing to do is use the original speed controller of the helicopter and control the speed controller with the BS2.

    A lot of RC speed controllers are controlled the same way one would control a servo.
    Thats exactly.what I try to explain... But.with horrible english :) .. Be aware.that some helis have the speed control integrate on the reciver and others separate. The ones that are separate can be controlled with the same codes to control servos
  • codysprakercodyspraker Posts: 46
    edited 2012-04-18 15:49
    With regards to the idea of using to controller on the helicopter and connect the basic stamp to the controller to send commands this thread link was my past attempt at doing this and was unable to get the finished product:

    http://forums.parallax.com/showthread.php?139311-Autonomous-Helicopter-With-Basic-Stamp

    In the end, after numerous trials and attempts the signal was never sent to the helicopters speed control board from the controller and we weren't quite able to figure out why. I had used a PWM signal from the BS2 with a capacitor and an op-am and the voltmeter was showing the right voltage range however when connected to the signal pin on the controller the helicopter never responded. I decided that I would pursue direct motor control using a single transistor and still incorporate the transistor concept for a more direct and less problematic approach. I understand that there is going to be added difficulty in getting the helicopter to fly but as it stood with the last thread, I was out of ideas and didn't want to get burned out with the project after so much work. Anyway, after all that story telling, I am going to give an update with the circuit design that I have chosen for this helicopter.
    photo.JPG

    This is a first draft of the concept that I will be using to control the two main drive motors on the helicopter. The motors are about 7.4ish Volts and the battery is 7.4V. The current of direct battery to motor is about 1 amp with no torque but goes up to about 3 amps under heavy load. The transistors in the photo are
    SANYO TRANSISTOR TP 3-PIN 50V 8A 15W BCEC
    and the square wave signal represents a PWM (Disregard the slow Hertz it was built in a simulation program)
    photo.JPG
    527 x 372 - 25K
  • xanaduxanadu Posts: 3,347
    edited 2012-04-18 18:43
    To build an autonomous helicopter on a Stamp is going to rely heavily on external electronics. The Basic Stamp is a great development environment to expand your knowledge of building and understanding the individual circuits you would need. If you want to control a large inductive load using PWM from the Basic Stamp, and want to build the circuit yourself you should start out smaller.

    There are circuit considerations for driving high current motors and you are stating up to 22 Watts of considerations. You should experiment with a smaller circuit and use the PDFs mentioned in the earlier threads to get a good understanding of the circuits and components. When you reach that point you can apply it to anything and build anything you want.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-04-18 18:50
    Isn't there something about a Basic Stamp's PWM not being normal? I don't think one can control the frequency of the BS2's PWM which limits its usefulness.

    I'd think the best way to control motors like these would be with speed controllers made for this purpose.
  • codysprakercodyspraker Posts: 46
    edited 2012-04-18 19:14
    What kind of controllers would be better suited for this? I am assuming some kind of multithreading/multicore platform capable of more than one simulataneous PWM out but I don't know of any off hand
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-04-18 19:38
    codyspraker wrote: »
    What kind of controllers would be better suited for this? I am assuming some kind of multithreading/multicore platform capable of more than one simulataneous PWM out but I don't know of any off hand

    You really don't know about the Parallax Propeller?

    It has eight cores. It's a perfect match for this project.

    To control the motors, I'd think a speed controller like this one would be easier to use than trying to use a transistor.

    http://www.hobbyking.com/hobbyking/store/__9090__Turnigy_20A_BRUSHED_ESC.html

    Another option would be to use a motor control chip like a L298N. One L298N can control two motors. If you use a L298N, make sure and get some diodes (you'll need 8).
  • codysprakercodyspraker Posts: 46
    edited 2012-04-18 19:43
    I am familiar with it but wasn't really sure if it was what I needed, now that I think about it I don't know why I didn't look into it farther, I will be looking at it for the next day or so and seeing what people have done with it. Especially since the shipping time for the transistors will take a few days so I can't even work on the project if I wanted to. Thanks for the recommendation

    P.S. Are you recommending the QuickStart Propeller board? I did a quick look and a can't tell if there is more than one out there, thanks
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-04-18 20:28
    There is presently just one kind of Propeller chip (though in several different packages). There are lots of different Propeller boards.

    The QuickStart is really easy to use since it gets its power from the same USB cable used to program it.

    The Propeller Protoboards (USB and normal) have beefier voltage regulators that make them a better match for some robotic projects.

    Post #2 of my index (see my signature for a link) lists some of the projects I've done with the Propeller. Make sure and check out the "Mecanum Wheeled Robot with Machine Vision" project since one version used signals from a RC receiver to control four motors with PWM.

    Posts 8 & 9 in my index have links to a bunch of different Propeller boards.
  • codysprakercodyspraker Posts: 46
    edited 2012-04-20 14:18
    My transistors have come in the mail and I am looking to put them through a test in a few hours with on the of motors and the battery that came with the helicopter. I wanted to do one last check though before this and just have someone's opinion on the transistors that I got. This is the datasheet:

    http://bit.ly/HYfRUo

    The motor runs at 7.4V and the battery is 7.4V

    Thanks for any help!
  • Beau SchwabeBeau Schwabe Posts: 6,566
    edited 2012-04-20 21:52
    It's important to know how your going to drive that transistor. What transistor are you using? PNP or NPN:? If the transistor is a PNP and presumably your going to drive it with a lower voltage (5V?) than the supply voltage (7.4V?) ... it needs adequate base current for proper saturation, otherwise it could get very hot. If you drive it directly from a 5V I/O, then a HIGH will not turn it off. The B-E junction will still be forward biased by 2.4V... since the B-E junction only needs about 0.6V, the transistor will remain "on".

    Please show us your exact schematic so that it may be reviewed.
  • codysprakercodyspraker Posts: 46
    edited 2012-04-22 14:59
    Beau Schwabe (Parallax) wrote: »
    It's important to know how your going to drive that transistor.
    Please show us your exact schematic so that it may be reviewed.

    I am new to the idea of drawing schematics which I am working on however there is a video that was a guide I used to my design that shows the schematic and demos the design using similar components. The different components are the transisto, the diode, and the power source. Here are the details for those parts and a link the to the video guide:

    Video Guide:
    http://www.youtube.com/watch?v=cEz1i5xzGEE&feature=fvsr

    Diode:
    http://www.next.gr/components-datasheets/1N5400.pdf

    Transistor:
    http://www.mcmelectronics.com/product/SANYO-2SC5707-/2SC5707

    Power Source:
    7.4V Rechargeable R/C Battery

    I am sorry I could not provide a schematic specifically for my project but I hope this is enough to answer some questions.

    I did attempt this setup using my components and there was no current to the motor. Out of curiosity, I flipped the transistor 180 degrees and then the current to the motor was constant. However the gate was being pulsed HIGH and LOW with a PAUSE 50 in between each change and that was not apparent in the motor's actions. There was no break in the constant flow of current from the battery which was what the HIGH/LOW was supposed to do. I just thought I would put that out if it helps enlighten someone to a possible solution. Also keep in mind that I don't have 100% confidence the circuit was properly assembled on my end so don't take these observations as fact immediately. Thanks!
  • Beau SchwabeBeau Schwabe Posts: 6,566
    edited 2012-04-22 16:56
    "...I flipped the transistor 180 degrees and then the current to the motor was constant...." - pay attention to the pinout of that transistor. i.e. the Base is NOT the center pin. Look at the datasheet to get the proper pinout for the Base, Collector, and Emitter.
  • codysprakercodyspraker Posts: 46
    edited 2012-04-22 17:55
    Beau Schwabe (Parallax) wrote: »
    "...I flipped the transistor 180 degrees and then the current to the motor was constant...." - pay attention to the pinout of that transistor. i.e. the Base is NOT the center pin. Look at the datasheet to get the proper pinout for the Base, Collector, and Emitter.

    OH! That was a great observation I should pay more attention I was assuming it was more or less standard for that configuration. Sadly, the result remains the same the transistor is behaving as if the pin was always turned on to 5V while the pin is actually turning on and off also when the pin is no longer connected the behavior is again the same.
  • xanaduxanadu Posts: 3,347
    edited 2012-04-22 18:20
    What's your PWM code as of now?
  • codysprakercodyspraker Posts: 46
    edited 2012-04-22 18:39
    I have not made any adjustments to my PWM code it would be the same code used at the end of the previous thread since I have yet to make a design that responded to the PWM signal successfully. I am using a basic HIGH LOW PAUSE LOOP style test program so I can clearly see the gate action of the transistor.
  • xanaduxanadu Posts: 3,347
    edited 2012-04-23 10:24
    I forgot to ask about the transistor, is it NPN or PNP? That datasheet goes to both. Can you read the numbers right of the transistor please?
  • codysprakercodyspraker Posts: 46
    edited 2012-04-24 17:45
    The entire chip reads, "C5707
    0G"

    I was going through my parts and found another chip. A IRF510 Power MOSFET Transistor N-Channel and its specs seem like they would also be tolerable for this project. What do you think?
  • xanaduxanadu Posts: 3,347
    edited 2012-04-24 19:03
    I looked at the C5707 datasheet and see that at room temps the max dissipation is 1 watt. So this would work with a smaller motor than what you're using. I don't think any single transistor is going to make a good motor controller. You've got a high current application that is very noisy that needs at least one diode and two caps (if not built into motors) and to boot it's driven by a very small signal.

    The IRF510 is better suited for power dissipation, I'm still not sure if it's cut out for your motor though. Maybe with a big heat sink it would be okay but it's hard to say. If you use that, you'll want to add another one to drive its base to allow it to turn on and off.

    Before you do all of that, are you sure you don't want to start out with a small transistor and an LED? You really don't even need a microcontroller to experiment with transistors. I see too many variables in your project to help you other than saying that. I commend your effort to build this thing, and I want to make sure you get somewhere with it.

    http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv6.pdf It's instant gratification and you will get a huge understanding of what is involved. If you see a rating on a datasheet you don't know just look it up in a search engine, there's a ton of info out there. Those fundamentals can be skipped, and you can just hook things up (I'm guilty too) but there's more than frying expensive parts at risk, the worst thing would be if you didn't learn how it works and move on to bigger and better things!
  • codysprakercodyspraker Posts: 46
    edited 2012-04-25 16:22
    Thanks for the information, it is frustrating that these might not work and I definitely appreciate the tips on progression through complex topics. I will definitely do some looking into the basics of the individual parts and see if I can get a base for the individual parts that seem to be giving me trouble. From what it sounds like though there is not a single transistor solution to the problem that I have.
    Aside from pre bought drivers meant to solve this kind of problem, do you think it will be realistic to try and built the circuit myself?
  • Mark_TMark_T Posts: 1,981
    edited 2012-04-26 06:11
    codyspraker wrote: »
    OH! That was a great observation I should pay more attention I was assuming it was more or less standard for that configuration. Sadly, the result remains the same the transistor is behaving as if the pin was always turned on to 5V while the pin is actually turning on and off also when the pin is no longer connected the behavior is again the same.

    There is no "standard" bipolar transistor pin out - even the same part number can have different pinouts from different manufacturers!! (this is rare though). MOSFET pinouts are much more consistent, but the best rule is always to check the pinout from the datasheet every time. After all you need to consult the datasheet for the specs, you might as well check the pinout at the same time.
  • Mark_TMark_T Posts: 1,981
    edited 2012-04-26 06:15
    codyspraker wrote: »
    I am trying to build an autonomous helicopter using a basic stamp homework board to control to the motors in flight along with a ping sensor to manage height. The problem I am having is trying to find a transistor that can handle the current needed to drive that 3 Amp motors. What I am looking for specifically is a transistor that can handle 3 Amps at most more like 1 or 2 amps most of the time at 7.4V. Does someone know of a transistor that can handle this type of thing? I have been looking for days. Thanks for any help!

    If you want compact, then my favorite candidate is the awesome ZTX851, which can handle 5A continuous, 20A peak and has Vsat of <150mV at 2A. Its in a tiny e-line package (slightly smaller than TO92).
  • xanaduxanadu Posts: 3,347
    edited 2012-04-26 10:21
    @Cody, yes I think you should build your own motor controller because it's a great learning experience. You may find that it costs more to do so and you will not get some of the great features in a pre-built solution. Some of those features such as thermal cut-off and over amp protection are very useful although may be expensive and hard to do on your own. Duane mentioned an ESC earlier, something like that will get you up and running fast and have built in protection. That still doesn't mean you shouldn't work on something smaller scale to learn how it all works though, so I guess my answer is do a little of both.

    @Mark, unless I'm reading that datasheet wrong that transistor is only good for 1 watt Ptot and based on its package would get very hot driving a motor. The voltage drop is as much as 7.3v and up to 3 amps for the motor. So at half throttle you be close to 5-6 watts. Please correct me if I'm wrong, I'm no transistor expert.
  • Mark_TMark_T Posts: 1,981
    edited 2012-04-29 04:01
    xanadu wrote: »
    @Cody, yes I think you should build your own motor controller because it's a great learning experience. You may find that it costs more to do so and you will not get some of the great features in a pre-built solution. Some of those features such as thermal cut-off and over amp protection are very useful although may be expensive and hard to do on your own. Duane mentioned an ESC earlier, something like that will get you up and running fast and have built in protection. That still doesn't mean you shouldn't work on something smaller scale to learn how it all works though, so I guess my answer is do a little of both.

    @Mark, unless I'm reading that datasheet wrong that transistor is only good for 1 watt Ptot and based on its package would get very hot driving a motor. The voltage drop is as much as 7.3v and up to 3 amps for the motor. So at half throttle you be close to 5-6 watts. Please correct me if I'm wrong, I'm no transistor expert.

    You will be using the transistor as a switch with PWM, not running it in linear mode, so the max power dissipation is Vsat x current. With a Vsat of 0.2V 3A gives 0.6W.
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