npn trigger

Discussion in 'General Electronics Chat' started by Gunz1159, Oct 31, 2010.

  1. Gunz1159

    Thread Starter New Member

    Oct 12, 2010
    Can someone say what kind of npn transistor would i use to trigger a ckt which has 9V power supply. For example with this i have attached a ckt in the right most part around 4 transistors are used what r they. Can u please say me the exact product. ? ? ? ?
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  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    But that would take away from the only 'freedom' a circuit designer has. Most times there is only one Good way to build the circuit, but the choices of components can make it work Okay , or work not so good. Here is where you need the experience.

    Figure out the amperage draw of the motor when stalled. You want a transistor,(or Mosfet) that can handle that amount of current and then some. Most anything that can take more than one amp would probably be good here. Sometimes switching freq is high, if that's the case in your circuit then you will need to consider switching speed of the device.

    Lots of datasheets and little time. The story never changes. :)
  3. Jaguarjoe

    Active Member

    Apr 7, 2010
    This circuit will never work. With 4.5 volts supply for the 324 and 4017, and 9 volts for the H-bridge, T1 and T3 will never turn on.

    Where is the trigger in this circuit?
  4. engineer2010

    New Member

    Oct 31, 2010
    IC2 does not have enough output drive current to turn on most power NPN transistors. Also, Jaguarjoe is right, there is not enough voltage to turn on the top two transistors. For a moment, consider what would happen if there was enough voltage to turn them on: With the limited amount of current from IC2, the transistors would not be saturated (fully-on), so a high amout of voltage would be dropped across the collector-emitter. Combined with the current through the motor, the power dissipation would likely be high enough to destroy them. Not to mention that the transistors do not have base current-limiting resistors; once turned on, enough current could flow through the base to damage the transistor or IC2.

    Not all hope is lost though. There are ICs manufactured to control your H-bridge transistor configuration that you could place between IC2 and the transistors. This IC would have high impedance inputs so IC2 could easily drive it with the same control circuit, and most of these driver ICs have a built in charge-pump that can raise the voltage high enough to drive the top transistors, while only requiring 5V supplies. I believe that there are some for BJTs and MOSFETs, but you might have better luck with a MOSFET.