Hi all, sorry for the bad English..
I have some transistor switch design question that I would like to consult with.
basically the project is to design electric circle for the transistor based switch in the wireless charger transmitter.
the circle have two power source:
the first is a PWM signal with 1/2 duty cycle, 10 [v] tops.
the second is is constant 12 [v] supply.
it also has a inductance 100mic [H] and a capacitator in parallel to the inductance.
the circle should change the duty cycle of the PWM signal in case of higher current.
I didnt really had any experience in such a design and i wonder if someone could help me, by just drawing the block diagram that I need to use.
im adding to the post the translated project, in case of missing details.
Thanks for the help!

 

Welcome to AAC!
I take 'circle' to mean 'circuit'.
This is a Homework Help forum, not a Homework-done-for-you forum, so please post your best effort so far at a design. We can then guide you if there's a particular point of difficulty. Your studies should have given you enough knowledge to get started on the project.

 

Hi Alec,
thanks for the answer.
Im Mechanical Engineer student, and I never been design circuit before.
In the specific course we learned about all the electric components but we didn't had any type of project like this.
My problem right now is that I dont really know how to start model the problem.
I know the circuit has two power sources, and that it should have inductance and capacitator that are connected in parallel.
from my understanding, I cannot just place a transistor in the switch because the switch has other things it should do like cut the duty cycle to half when the current is too high.
so I need to design some circuit that acts like the transistor switch but also plays with the PWM signal.

 

A search of "wireless charger transmitter schematic" should get you started.

 

after short search I draw this circuit, will it work? also, I didnt understand how do I consider the PWM signal.
*I forget to attach the inductance

 

Post #1 says you have one capacitor and one inductor. Why does your design show 8 capacitors and 3 inductors?
Why 2 FETs?
What are the diodes for?

 

I dont really know what to do, I saw some scheme on google that may fit what im looking for.
the mission is to design the transistor switch but the only things I found is the whole transmitter and I tried to copy it.

 

You didn't answer the questions in post #6. Each component in a circuit should be there for a good reason, not added at random.
I suggest you look for some more wireless energy transmission circuits and compare them to see what they have in common, then pick a simple one as a possible start point for your project. The circuit should contain at least a transistor (field effect or bipolar type) driving an inductor in parallel with a capacitor.

 

Thanks for the help Alec,
the circuit need to function as a switch , and this switch connected to inductor in parallel to capacitor ,
in the switch design you can use whatever you want, as long its do whats it need to do that define in the project pdf that I added in post #1.
ill continue search the web, although I did it for the last 3 days

 

Here's a related thread that you might find helpful.

 

Hi,
after I met my professor I manage to built the following circuit:
the values of the resistors and the capacitor are not relevant right now.
the main power source (V1) , can be 12[v] or 18 [v], according the the main power source voltage, i need to change the PWM duty cycle from T/2 to T/4 .
I need to connect the Vref of the LM324 to the LPF, but I dont know how to do it while changing the PWM duty cycle according and not alter the frequency.
maybe using a diode after the LPF and then connect it to other thing?
* PWM controller is not allowed.

 

That's a more promising start .
Check the battery polarity.
I see no oscillator to establish the driving frequency, and no PWM source. Are you expected to design those also?

 

I may misunderstood the question entirely.
there is no pwm signal, just the bipolar voltage source, and we need to control its duty cycle just like pwm.
the oscillations comes from the bipolar voltage source I think?
is there a smart way to control the duty cycle, like a series of flip-flops, or I should convert the bipolar signal to triangle signal and then control the duty cycle with the ref and the LM324?

 

there is no pwm signal, just the bipolar voltage source

So now we have a bipolar power supply? It is difficult to help you when you don't, at the outset, tell us all the details .
How are you expected to make use of the two polarities?
Use of a triangle wave, an adjustable reference voltage and a comparator is a conventional way of generating a PWM signal.

 

Sorry for the mess.
I have two power sources :
#1 is the 12 [V] DC , that can be alter to 18[V] according to the battery internal resistant ( on the receiver side, witch we dont care)
#2 is the bipolar voltage source, that oscillate between 10 [V] to 0 [V].
I decided to work with the triangle wave, and then connect it to the LM324 with Vref that comes from the LPF.
I have one big problem right now:
how to get the right Vref- basically when the DC source set on 12 [V] the Vref need's to be at value that we will get the original duty cycle (T/2) and when we change the DC source to 18[V] the Vref will make the duty cycle T/4 after the LM324.
I thought to add another LM324 right between the resistor and the capacitor in the right LPF but I haven't figure it all out yet, any recommendation?

 

Your 10V oscillator frequency is 1MHz. Read the datasheet for the LM324 and you will see that its unity-gain bandwidth is 1MHz. Do you understand the significance of that?
The power supply for an op-amp should be a fixed DC voltage, not a varying signal.

 

Thank for the help!
can I take the power supply from the 12[V] DC?
I tried to switch to different op-amp , LM7171, but when I ran the simulation it was impossable to get somthing because of the time scale, do you think on different op-amp that may fit?

 

An opamp can use a 12V supply.
Your 10V oscillator is a single polarity. As I previously asked, how are you expected to make use of two polarities?

when I ran the simulation it was impossable to get somthing because of the time scale

Are you saying the opamp bandwidth was insufficient to handle 1MHz from the oscillator?