Transistors-Please help

Discussion in 'General Electronics Chat' started by mohiuddin1111, May 3, 2013.

  1. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    Guys, i am new here.
    i have a toy r/c car.
    it works on 6v. i am feeding it 7.2v. what the problem is it stopped forward-back button working. changed transistor (that switches on the motor ) and it worked . but, now the spinning force of the motor is a alot less. the pair of transistors it uses are ml8550 and ml8050 (with base at side).
    Now what i want, a transistor set with more voltage capacity (around 7-8v) with less internal resistance.
    What i have to have in mind to get that thing working properly, like base voltage or any frequency ( idont know if it has any) ?.
    Please give a little idea of what these model number of transistor represent.
    and a wide range of transistors that may replace this transistor set effectively. i am a noob here please help. will go to buy tommorow. Oh, the radio frequency is 49mhz.
     
  2. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    anyone guys?? i need answer quickly. please please please.
     
  3. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
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    You would need to provide more information like pictures. We could see the transistors and identify their case type.

    The part numbers of those transistors are not familiar to me. If you have a datasheet for them, you should provide a link. If you don't have a datasheet then you should search for one. I can't tell you what the model numbers represent, and don't have enough information to properly find out.

    When you say the base is at the side I am not clear on how you have determined that.

    Transistors with less than 10Volts rating are very rare. What we would need to know is a current rating.

    It sounds like you have replaced the battery, perhaps it took 4 C Cells and you are plugging in a 6 N Cell NiMH battery.

    That could reduce your current capacity and increase your source resistance drastically, either of which would cause reduced motor torque.
     
  4. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    here it is in a zip file, as i took the picture with a mobile and those pics are large and i dont know how to reduce size. please kindly see that .
    1st picture has a,b,c,d markings all of them are transistor saying ml c8550 38 or ml c8050 38 and 2nd pic is zoomed to see the model by yourself. please i need a quick answer.
     
  5. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    2N2222A (NPN) or 2N2907A (PNP )... would these help?
     
  6. absf

    Senior Member

    Dec 29, 2010
    1,493
    372
    8550 & 8050 are common transistors used in toys and output stages of audio amp.

    They are quite easy to get depending on which part of the world you live. Please see the datasheets attached. If you must use 2n2222A then 2n2219A is a better choice for your application.

    Allen
     
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  7. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    hey man, i am literally noob compared to you guyz.
    can u please tell me the npn and pnp model name of that 2n2219a?
    and why that is better than 2n222a? please note that those would be used as a push-
    pull setup so total 4 ( 2 npn & 2pnp ) is needed . you guys know better though. and is there any frequency thing for a transistor ? if yes , then is it important in this case?

    and what is a c8550? is it an indian version of ss8550/s8550 ?
     
  8. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
    92
    There are frequency limits for transistors, but that is unlikely to be a problem.

    I would like to know more about the change in voltage that you mentioned in your original post.

    If you replaced alkaline batteries with rechargeables, I expect the batteries will be a source of most of your problems.
     
  9. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    i used alkaline nonrechargable batteries before. but i wanted more power. :p. so used a 7.2 v 6cell rechargable battery.
    ( yea i am nooby noob ). somehow it worked. but, the motor became faulty and the one c8550 transistor burnt due to over current flow ( i think :p )..
    but thats not the point, i want a transistor that would bear the 7.2v effectively with enough motor torque. as in my area electronic parts are not that available, give more than one model that are suitable. plz.
     
  10. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    any one?? please. if i am misssing some information please yell me. will try to help u to help me. :p
     
  11. studiot

    AAC Fanatic!

    Nov 9, 2007
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    How do you know these are the only damaged components?

    Overdriving often causes resistor damage as well. Check the resistor by Q7.

    As regards transistor substitutions, try the BC 337 (NPN) / 327 (PNP) pair, which are readily available in the far east and Europe.
    They are more than man enough for your job and have the same pinouts as your originals.
     
    Last edited: May 7, 2013
  12. absf

    Senior Member

    Dec 29, 2010
    1,493
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    I strongly agree with the above substitutes. The 8050 and 8550 are most probably made in China now.

    If you are from Asia, you'll probably use the European or Japanese transistors for subs. But if you are from US, you would use the 2Nxxxx series for subs.

    The BC337 is very low priced and I've bought 200 pcs from farnell and still have <100 pcs in my drawer .

    http://my.element14.com/on-semiconductor/bc337-40zl1g/transistor-npn-45v-to-92/dp/9558675

    Allen
     
  13. KrisBlueNZ

    Member

    Oct 17, 2012
    111
    14
    I agree with the BC337/327 recommendation. You might also want to consider the low-VCE high-current transistors made by Zetex (now Diodes Inc) such as the ZTX689 (NPN) and ZTX789 (PNP) if you want to minimise voltage drop in the transistors. Look on www.diodes.com in the <25V bipolar transistors section.
     
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  14. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    Guyz sorry for late reply. I am abit busy now so did not get any chance to goto shops. don't know what type of transistors available in local stores.
    But, i learned a bit about datasheet.
    What should i look for in datasheet to find compatible transistors of c8550?
    and also what should i look for , to find transistors which meet my expectations?
    maximum collector current?

    Can i use FET/MOSFET?

    thanks. i will check it out.


    thanks. but Ic(max) is low for bc337. i am very new at reading datasheet, so i could be verrry wrong.:p
     
    Last edited: May 12, 2013
  15. KrisBlueNZ

    Member

    Oct 17, 2012
    111
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    According to the Wing Shing data sheets, the S8050 and S8550 are rated for 500 mA collector current. (I assume the ML8050 and ML8550 are equivalents from a different manufacturer.)

    They are general purpose bipolar NPN and PNP transistors. A collector current rating higher than 500 mA would be a good idea, as well as a low Vce(sat) voltage. That's why I suggested those two Zetex/Diodes Inc devices. But I just checked and Digikey don't have them in stock. They do have ZTX618 and ZTX718 which look suitable.

    If you're looking locally you might be able to get BC337/327. I can't be more specific because you haven't filled in your location in your profile so I don't know where you are.

    You can't usually just substitute MOSFETs for BJTs. If you can trace out the schematic diagram of the output stage, including the circuitry that drives the bases of the transistors, someone here will be able to tell you whether you can use MOSFETs, or what circuit changes would be needed.
     
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  16. KrisBlueNZ

    Member

    Oct 17, 2012
    111
    14
    I just noticed... the Fairchild SS8050 and SS8550 are rated at 1.5A collector current. If your original transistors are rated for 1.5A then the BC337/327 aren't suitable.

    The ZTX618/718 are rated for 3.5A and 2.5A respectively. You won't find them locally. You'll have to order them from Digikey or Mouser or a similar company.

    You might be able to get by with BD135/136 but those old standard power transistors have fairly low gain. That's what's so good about the Zetex devices. They have high current ratings, low VCE(sat) voltages, AND fairly high gain (100 and up).

    If you really want to get the best performance, you need to trace out the circuit diagram of the board and post it.
     
  17. studiot

    AAC Fanatic!

    Nov 9, 2007
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    You are quite right, Kris. Towers has Samsung versions of the SS8050 / 8850 as 1.5 amps and they are in a TO92 case. However in that casing they can only run at 0.6W so must be run bottomed at that current ie in switched mode and this was for an analogue transmitter so I expect the BC transistors would still be OK. Incidentally some of the far eastern BC transistors I have had have also claimed 1 amp+

    The Zetex transistors are good candidates for replacement and are in an X11 case, with the base in the middle, as the other data sheets.

    Care should be taken with the BC transistors as there are many variaions of pinout.
     
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  18. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    hey guys , went to a number of local stores.
    no ztx series transistors or bc337. now, i bought d882 and b772(complementary to d882) of NEC .
    here the datasheet link of d882 -

    http://bbs.dianyuan.com/bbs/u/81/3228701252035536.pdf

    or any of the transistors listed below??

    1. bc640 - bc639
    2. 2sb1007, 2sb1000 , 2sb1001 - 2sd1366, 2sd1378 , 2sd1367
    3. 2sa1534 - 2sc3940 ?

    guys i found s8550, s8050 but sadly all are base in the middle :(
    so i searched those for side base.

    and also please see the link below>>

    http://alltransistors.com/crsearch....5&ueb=5&ic=1&tj=0&ft=200&cc=0&hfe=0&caps=to92
     
  19. KrisBlueNZ

    Member

    Oct 17, 2012
    111
    14
    You should be able to work out which ones are suitable. Look on the data sheets for the following specifications.

    1. Maximum rated continuous collector current. It seems that the 8050 and 8550 are rated for 0.5A or 1.5A depending on the manufacturer. You need something rated better than that.

    2. Gain may or may not be important. I suggest you aim for a device with a minimum gain of 50 at 500 mA or more collector current. Not all devices have their gain specified at this much current, and gain normally drops as current increases, so it's hard to be sure on this specification. The BC639/640 have relatively low gain compared to the Zetex devices, which is why I recommended the Zetex parts. I don't know about the others off-hand but you can check the data sheets for these specifications.

    3. Saturation voltage, Vce(sat). This should also be specified at a certain collector current, and the typical and maximum values are significant and should be as low as possible. This will ensure that most of the battery voltage is available for the motor, and will reduce power dissipation and heating in the transistors. Most transistors are not optimised for low Vce(sat) but the Zetex ones are; that's another reason why I recommended them.

    4. Pinout. You don't need to obsess about having a B-C-E pinout because it's easy enough to cross the wires over if you put a bit of insulation on each one.

    It's very difficult to be more specific because we really don't know enough about the circuit. It may be that high gain is important; it may not be important at all. We don't really know what collector current is needed.

    I understand that you don't feel confident drawing up a schematic diagram of the board, but any other information you can give us, including part numbers, markings on the motor, and photographs of the board (both sides) might help.
     
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  20. mohiuddin1111

    Thread Starter New Member

    Apr 28, 2013
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    thanks for explaining. and yea i am not confident about giving a circuit diagram. i will buy a multimeter soon i guess. then i may give voltage , Amps around the transistor pinouts.
    By the way, here d882 and b772 is very available. so i replaced with these, and they somehow partially fulfill my purpose somehow.
    But, d882 found here are of two qualities . how can i get the original one. both from NEC.
    1. like this>
    http://i00.i.aliimg.com/photo/v1/435764600/D882.jpg

    2. other one>
    http://www.gooddealchina.com/upimage/images/2011033039609581.JPG

    i will find more models here.

    Now, i want to learn a bit about MOSFET only as a motor switch.
    i read two PDF. file but understood very little.
    please give a link to a very easy simple link or pdf of "mosfet as motor switch". and also please tell at least a little about how it act as a switch.
    will i need to connect motor between D-S and controlling voltage to G-S for an N-channel MOSFET?
     
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