Hi everybody,

I'm trying to design a darlington pushpull circuit,

here is my beginning :

View attachment darlingtonPshPll base.zip

Can somebody tell me if all these resistances will be usefull for me to design an amplifier which
=> has a voltage gain of 1 ( VS = VE)
=> has in input 40 mA, and I want 1,6 A at output of this amplifier, that means I want 800 mA at XMM12 and XMM13.
=> it should work at the frequency of 13,56 Mhz.

I know how it works for one 2N2222, but for darlington pushpull I have no idea, I looked in the web but there was none for my application...

I don't know how design it, because it's very difficult, maybe somebody can teach me the "beginning" ?

Thanks a lot, your help is welcome

 

Is it 1356 MHz or 13.56 MHz ?

 

Hello,

You have the emittor and collector of Q3 and Q4 switched.
See the picture how they should be:

Bertus

 

Hello,

You have the emittor and collector of Q3 and Q4 switched.
See the picture how they should be:

Bertus

What software is that? ??

 

That's NI MultiSim

 

Hello,

I only changed the transistors using a kind of paint program KolourPaint on my linux machine to show how they should be.
I can not change the parameters or meter values.

Bertus

 

And V2 is wired wrong.
It says -15V but instead you have wired it as +15V

 

why is Re2 & Re3 values different.

 

Thanks a lot for your answers, what a wonderful community... i'm very happy..
I didn't find the section where I could introduce myself..

It's 13,56 Mhz (RFID^^)

@Dr.killjoy : Yeah i'ts multisim 13.00 pro edition, pro edition because there are so much components that other versions. the compiler is SPICE (same as in Altium and LTSpice)

@ bertus : thanks , I will look into your modification and will report how it changes the results.

@ R!f@@ : Thanks ! I just saw the -15V failures, I tought it was possible to plug like that but I will change it and reports too.

I will repost in one/2 hours, when I will back home to use my laptop for multisim.
xoxo

 

Hey forumers !

I did a new simulation with your modifications, here is the schematics and my results :
View attachment Darlington push pull.zip



Can you help me for these questions please ?

- My norton circuit (at the bottom) should simulate a card which supply 0,2 Watts, and a 0 to 10 V voltage. The voltage is correct but why the current is only 0,0069 A (6,9 mA) ? it should give 0,040 A (40 mA)... (ammeter XMM5 at the input of the darlington circuit)

- What can I do, please, in order to get Voltage input of darlington circuit = Voltage output of darlington ? ie : a voltage gain of 1, because in this simulation he is a little below 1.

- Is my circuit safe ? There are not a lot of resistances or capacities... I think it's very strange and unsafe, can you tell me a way in order to make it safer please ?

- Why the ammeter XMM12 doesn't supply the same intensity as XMM13 ? according to the symetry it should be the same, Am i wrong?

- can somebody tell me the formula in order to get my current gain in this schematic ?

- What do you think, please, about values of R1 and R2 & RE1 and RC2 ?


Of course all others advices are welcome !!

Sof,
xoxo

 

I didn't find the section where I could introduce myself..

Off Topic Forum. First thread on the page.

 

@#12 Thanks

 

Hello,

Measure the voltage between D1 and D2 and ground, with no input signal.
Idealy the DC voltage should be 0 Volts.
With no input signal, the output voltage to ground should also be 0 Volts.

To avoid a DC offset from the input signal, you could put a capacitor between the D1, D2 connection and the - connection of XMM5.

Bertus

 

@ Berthus : Thanks for your answer, How do you choose your capacitor ? I think it's related with the frequency ..

I did what you say, but maybe my "Vgnd" is wrong, I let you see it :

without capacitor :


with capacitor :




It's strange because the signal is worse with capacitor

Thanks a lot

 

Hello,

I think you have misunderstood me about the capacitor placement.
I have drawn the measurement points and capacitor in the drawing:

You can also have a look at the following PDF's:
http://educypedia.karadimov.info/library/PushPullAmp.pdf
http://educypedia.karadimov.info/library/lecture12.pdf

Bertus

 

@Berthus : Thanks Bertus for your help,

In multisim I can't mesure a DC variable if it is plugged directly to the ground,
the one thing I can do is on this screen :


Here is the result with capa which is the same so I think my measure are wrong.. :

What is strange is that with capacitor my signal is worse :


Sorry if I ask stupid questions

BTW : Can I know why you chose this value of capa ? Or maybe was it just an example ?

Thanks, you are very helpful for me and I hope i could help you too one day
xoxo

 

Hello,

I see that you have changed the values of R1 and R3 from 1K5 to 3K3.
Is there a reason for this?

I have chosen the 10 nF as given in table III of the following PDF:
rf_proto-1.pdf

In there 10 nF is used for DC block and decoupling in HF circuits.

Bertus

 

@Bertus : Thanks for your explanations..

You know usually in a circuit with one transistor, R1 and R3 are usefull to place the bias point. But here I have 4 transistorss and no ideas how bias their point... and because of the symetry of my schematic, it was very strange that R1 was different of R3..

I just know that the sum of R1 + R3 should be high, near K Ohms, because if R1 + R2 is low, there will be high power loss in my circuit.

Do you know the right way to choose them ? ^^

If I understood, the capacitor was only here in order to calculate DC values. Now that I calculated these values, can I remove this capacitor ?

You know in multisim you have a function "DC Bias point analysis" which allows you to calculate it without modify it

Your pdf is absolutely fantastic for me !!! thanks so much !!!

Do you think my circuit can work in "real" ? The goal is to create it

I Input/ I Output is near 58 when I input is 5 - 20 mA !

If I understood the gain is regulated by RE1 and RC2 in my schematic ? Thanks

xoxo

 

Hello,

Have a look at the attached PDF on calculating the resistors for the amplifier.
It gives an example for an audio amplifier.

Bertus

 

@Bertus : Thanks Bertus you are sooo helpful !!
I did all their procedure and I found 1,4 KOhms for the sum of RB1 + RB2.

So I took RB1 = RB2 = 750 Ohms .

Do you think I should let the capacitor just after the input, please ?

Can somebody tell me if my circuit is safe / realistic or not, please ?
I will make the PCB and test it in real

have a good day !