Hi everyone :D
I would like the help of the more knowledgeable in electronics to design or show me a design of a circuit that uses 2 transistors to do the same work as a SPDT switch does. I have the components to build but can't find a basic circuit that does this. I have some IRF840's and a signal generator that has +20v -20v pulse peak to peak that I can use as gate triggers. I also have a built working 555 if that can work to flip flop (back and forth) the 2 mosfet's since I think it only goes on off, so it may not work with that circuit.
All I will be doing with the circuit is charging a cap from a bridge then disconnecting from bridge and discharging the cap to a coil. I need isolation between bridge and coil.
Thank you for your help. This will help me to further study my spark effect in a solid state way.
Luc
Luc,
Look here: http://home.no/ufoufoufoufo/bedini/bicp.htm
The bottom part of the circuit can be driven from a 555. You can also use just one fet transistor instead of two.
Groundloop.
Quote from: Groundloop on August 21, 2008, 06:05:50 PM
Luc,
Look here: http://home.no/ufoufoufoufo/bedini/bicp.htm
The bottom part of the circuit can be driven from a 555. You can also use just one fet transistor instead of two.
Groundloop.
Thanks for the relpy and link Groundloop :D This looks more complicated than I thought :-\.
Luc
Luc,
Not really complicated. Look at the switch itself and forget the microcontroller circuit. Then take away the extra fet transistors
and you get the attached switch. It will be controlled by a +5 volt for ON and 0 volt for off. This will charge the capacitor and
then discharge the cap into a load.
Groundloop.
http://www.doctronics.co.uk/4016.htm
c0mster,
The 4016 are a great ICs, but they are not suitable for high voltage and current. The 4016 can handle +/- 7,5 Volt at maximum.
Since the internal ON resistance of each switch is typical in the 200-300 Ohm range, the current through each swicth will be very limited.
Groundloop.
Thought it might be good to drive the fets.
c0mster,
Ah, sorry, did not think of that. :-)
Another way to control my circuit is by using a 555 as a oscillator with one inverted, and one non-inverted output.
Groundloop.
Luc,
I have added a 555 oscillator circuit for controlling the switch. The 1uF capacitor may be bigger to get the correct switch frequency.
Groundloop.
@gotoluc
Very good question. Just what the doctor ordered. I have been puzzling about thin one myself.
@c0mster
Good to read you again and thanks for that link.
@Groundloop
You too. Thanks.
So I could connect my FG to the 4016 to drive my 9540's on the positive side and my 840s on the negative side of a given coil scheme.
Wattsup,
If you set your voltage output to less than 15 volt peak to peak on the function generator and wire
the 4016 switches to do the job, then yes, you could probably control a P-channel and N-channel FET.
(I assume that 9540 is a P-Fet (IRF5Y9540CM) and that 840 is a N-Fet (IRF840), correct?)
Groundloop.
It looks complcated but it isn't when you start to breadboard the circuit....
http://www.4qdtec.com/h.html
This is the only true SS function of a DPDT switch. Same can be done with FETs. Expand the idea to be driven by another signal source like a 555 circuit. The common mistake is to do something that will allow the 'on' time of the top and bottom switch to overlap. This would be a short.
Cheers!
>>Edit
As usual. I'm in a hurry....
You said 'SPDT' not DPDT. Only one half of this circuit is needed then and the posts by others are more correct for your question.
However, if you need to consider actually reversing applied voltage instead of flipping it between two loads consider the above.
I've never thought turning things on in a sequence was of any value. So I use something similar to the above to sequencially move or reverse a charge. This way all parts of the circuit are always doing something.
@Groundloop,
thanks for the extra time you put in to make the circuit simple enough for even me :P to understand. I will give this a try since I already have the 555 built. By the way I did chose a 1uf at ct but I got to get a 500k pot since my 100k does not give me enough Frequency range.
@c0mster,
thanks for the link to the 4016 device. Looks simple enough for me to understand. I think I'll get one of these for future tests as the logic is simple to understand and one could quickly put something together.
@wattsup,
thanks for looking and sharing that you also have a need for this. I like the simple idea of using a P-Fet and N-Fet like Groundloop is confirming below
If you set your voltage output to less than 15 volt peak to peak on the function generator and wire
the 4016 switches to do the job, then yes, you could probably control a P-channel and N-channel FET.
(I assume that 9540 is a P-Fet (IRF5Y9540CM) and that 840 is a N-Fet (IRF840), correct?)
Groundloop.
@BEP,
thank you also for sharing that circuit. Since I may also need reversing of applied voltage in future work.
Luc