What is this electronic component for my custom flashlight design?

Hi Folks,

I've read this forum for years (and very impressed), first time posting (hopefully in the correct area), looking for some EE guidance. I'm searching for a component, and any input would be highly appreciated. In effect, I'm looking for the equivalent of a multi-channel MOSFET.

With your standard LOGIC N-channel transistor, say FQP50N06L, simply pop the gate with 20mA, and 700mA will flow between the source and sink to light up LEDs. The logic level 'type' is handy for high efficiency and utilizing various PWM, which I've tested successfully at some respectable frequencies.

Like most of the kind, this fet is disconnected (off) till hit with a control signal, then switches active (on) when triggered, allowing the current to pass. For my design, I need the equivalent. However, I'd like channel A "on" all the time. When the control signal arrives, it switches channel A "off," and routes the power through channel B (turns channel B "on").

In hopes of making myself understandable, think of a railroad switcher. The trains can cruise down the main avenue unimpeded, but bump the switching post, and the trains travel down another rail.

It would make sense for this magical component to exist, I just don't know what it is, and have come up empty in my searches. Roughly, it needs to be as cheap, same size, quick, and readily available in a similar capacity to what I mentioned above. Heck, add another pin to the FQP50N06L with this functionality, and life is groovy.

Any advice? Thanks for reading.

you want something A on, all the time... until a "control signal" arrives, then A turns off and B turns on?

sounds like you are describing a "flip flop".

when i was younger and much more into digital logic, a "flip flop" was a IC package... it consumes very little power itself, and is always putting out juice on A or B output... the control signal just switches it back and forth.

i dont know how much into digital switching logic you are, so bear with me... in electronics, you are designing a "black box" typically... doesnt matter what is IN the "box" (project) it just has to work... we typically worked with signals that were either ON or OFF (1 or 0)... for input AND output both... these input lines went to the pins on the chip (IC)... based on the logic of which input pins were high or low, our circuit would light up the appropriate output monitor lines...

while this does not seem inherently useful by ITSELF, remember that any output line (led lighting up...) is easily replaced by a RELAY, which can turn a large device on or off... input lines that are large can be "monitored" to lower their level to the input pins in a similar fashion...

just look up how a FLIP FLOP works, you'll get the idea.

TTL was the "old school" chips... they operted on 12v... then CMOS dropped in price and they would operate on like 3.3 volts...

its all as simple s it sounds, there's just practical circuit details to watch out for... for instance, any unused leg (pin on the IC...) had to be tied to ground, etc etc...

these IC chips are also available in ever-smaller packages with SMT technology taking off, you just need a lighted magnifier (microscope? lol) and the soldering IRON looke like a heated sewing needle, lol...

Depending on the precise requirements you might be able to get away with just 2 FETs to get the functionality you want, and because what you want is easy to make from discrete elements I'm not sure there's likely to be a composite component to do the same job.

In the simplest case, you might be able to just have a normally-driven FET for channel B, with a FET for channel A having its gate connected to the channel B FET's drain (a FET plus a load may effectively act as an inverter with respect to the FET's gate voltage).

Depending on supply voltages, gate thresholds, maximum gate voltages and load characteristics it might need 2 or 3 more extra resistors, but those circuit-dependent things are another thing possibly making it less worthwhile for someone to try and make a single device to do the job, since different versions of device might be needed in different circuits.

If I am interpreting what you are asking for, this will do what you want. As uk_caver stated, just watch the max voltages on the gate, etc.

Semiman

kansaswater said:

. . . . With your standard LOGIC N-channel transistor, say FQP50N06L, simply pop the gate with 20mA, and 700mA will flow between the source and sink to light up LEDs. . . . . . .

Click to expand...

No current flows when a FET or MOSFET gate is in the ON state - it's controlled by the voltage at the Gate. The only current flows to charge or discharge the gate capacitance when input voltage changes.