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Posts posted by HarryA

  1. I got a package of 3 boards and jumper wires via Amazon.com and they are crap! Very difficult to insert the jumpers into. I also left my review of them and it was not nice. Also I saw a video on youtube.com where the instructor instructed the students to use needle noise pliers to insert the jumpers into the same type of breadboard.

    beware of:




  2. You points are well made; thanks.

    On day one I found two voltage boosters on Ebay that gave more than 100 volts so I ordered both of them from China. The first  one I received was a 12v dc to 200 v dc. After connecting it up and adjusting it for 200 v I put a 100k resistor across the output  and got 2 volts output! It took a one mega-ohm load to keep 200 v.

    The   second one (12v dc to 220 v ac) works well. I connected it to the 220v to 120v step down transformer and into a full wave bridge rectifier with a 100mfd capacitor and got 140 v dc; 9.6 volts input. With a 8.4 v NiMH rechargeable battery I get 128 v dc.
    So I am happy with that  and  very surprised that the 50/60 hertz transformer works at all!

  3. Hello from cold and snowy NE PA,

    In my quest to convert 9 - 12 volts dc into 140 volts dc I purchased a "40W DC-AC 12V To 220V Step-up Transformer Boost Module Inverter" via Ebay. I also purchased a 220 volt to 120 volt 50-60 hertz step down transformer; the type travelers use.

    But the inverter's output is 38.4k hertz!  So my transformer is useless here. I am wondering if one can find a transformer that will handle that frequency and is two to one?

    I am driving a class D pulse amplifier that outputs 100 Volts peak at a current of 0.10 amperes max. The pulse is 0.4 ms duration at and interval  of 2 ms. So I am thinking that I need: 100v * 0.10 * 0.4/2 = 2.0 watts for the amplifier output so I am thinking about 10 watts for the amplifier and the conversion from 120 ac to 140 dc. 



  4. Most likely you have a few screws loose John ;)

    see: http://en.allexperts.com/q/Electrical-Wiring-Home-1734/2009/6/Circuit-reads-60-volts.htm

    also  search on: "electrical problem 60 volts on 120"

    good luck.


    As this a common problem could a poor connection between copper (or better yet corroded copper; copper oxide) and plated steel act as a diode and the the results (at very low current) is a half wave rectifier? That would yield the 60 volts rms.

    ref: http://www.tutorvista.com/physics/half-wave-rectifier-calculation



  5. Thanks for the reply.

    I have a a 400 microsecond pulse every 20 ms that I wish to amplify. I need about 100 volts so I an thinking I need a 150-200v transistor.

    I need to preserve the varying amplitude so I can not just emulate it with a switching transistor.

    Speaking of transformers; I tried amplifying it with a 2n7000 n channel MOSFET using an audio transformer in reverse (input into the 8 ohm windings ) but I could not get a decent output pulse in spite of using various combination of diodes.


    HarryA  \../

    To close this out. I found mouser.com to be helpful as they have a system of filters that makes it easier to find what you want - with some effort.

    I ordered the n-channel ZVNL120 eMOSFETs from then; 200v and 120ma.

    The book "Electronic Devices and Circuits" by "Schaum's easy outlines" has good information on circuit design using bipolar, FETs, and MOSETs tranistors.




  6. Hello from NE PA,

    Where do you all find data on MOSFET transistors?

    I look on ebay  for MOSFETs but most do not have specs so you have to search for
    a data sheet, download it, open it, and find it's not what you want!

    I am looking for an n channel  eMOSFET for a class D amplifier that has 150 to 200 volt
    drain to source. Some 20 to 40 ma for current.

    I find lots of power switching MOSFETs references.

    Are there any good books on using MOSFET transistors?

    thanks in advance,

  7. Hello from NE PA,

    A question for you. How to TENS machines generate 40 to 60 volts

    from say 4.2 volts without using a coil or transformer?

    Pictured is a TENS circuit that is about 1.26 inches by 1 inch.
    The battery is on the reverse side of the board.

    thanks in  advance,

    tens circuit board.png

  8. I picked up some LM317's today (1.5 amperes max.). Set the output to 7.0 volts and
    connected to a brushed motor. The motor drew 0.68 amperes. The output voltage
    dropped to 6.86 volts; the li-po battery output drop to 11.55 from 11.80 volts.

    This is with no load on the motor; I need to get propeller on it. Someday I will
    receive the ESC and can reverse the motor on the fly.  :)


  9. My "bright" idea is to use the mosfet to get more than the 1 ampere that the 8 volt regulator is rated at.  I have a large 11.1v li-po battery for the main motor so I don't want to add another battery to get the 8 volts.

    I wonder if one can put two or three regulators in parallel for more current?

    This current is the power supply for the speed controller; it connects to the
    receiver for the PWM.  It is the brushed type used with rc cars so it can reverse
    the motor for left and right control. 

  10. Hello all,

    I need to connect an 8 volt electronic speed control to an 11.1 battery.
    I have an 8 volt regulator and a power mosfet. I have not worked with
    mosfets before so I am puzzled on how to make the connections and
    what values of resistors are required. Please take a look at my diagram.
    Any advice would be appreciated.

    This motor control is for the stern of a model blimp to control the direction
    much like a helicopter's directional control.


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