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## Solid States Devices => solid state devices => Topic started by: nix85 on March 09, 2021, 11:29:27 AM

Title: Help me understand complementary push pull amp
Post by: nix85 on March 09, 2021, 11:29:27 AM
Here is an article on push pull amps.

https://www.electronics-tutorials.ws/amplifier/amp_6.html

Second diagram shows two NPN transistors back to back and you can see how current flows for each halfcycle as nicely drawn.

But i don't understand NPN PNP combination, first diagram, shown below.

During positive halfcycle TR2 is off, TR1 conducts and current flows through it and through load to ground.

All sweet, but...

During negative halfcycle TR1 is off, TR2 is on and.....? How does the circle close?

TR1 is off, Vcc is disconnected.

Red arrow now shows current flowing in opposite direction.

Something's missing in these diagrams (they are all like this).
Title: Re: Help me understand complementary push pull amp
Post by: lancaIV on March 09, 2021, 12:11:31 PM

Developped in the End80 as low cost renewable energies net-grid infeeder !

Positive half cycle phase + negative half cycle phase = full cycle

Probably therein you will find the right direction of answer

Sincere

OCWL
Title: Re: Help me understand complementary push pull amp
Post by: nix85 on March 09, 2021, 12:25:29 PM
How is the circuit closed during negative halfcycle?
Title: Re: Help me understand complementary push pull amp
Post by: lancaIV on March 09, 2021, 01:14:32 PM
It is combinating the half cycles "automatic",by nature" !

The two transistors ,look for their direction,are only conducting the path !

The dotted lines are the "virtual" path
Title: Re: Help me understand complementary push pull amp
Post by: nix85 on March 09, 2021, 01:23:20 PM
Title: Re: Help me understand complementary push pull amp
Post by: lancaIV on March 09, 2021, 01:29:02 PM

Pardon,if you see this as spam !

I would have to read the total article ,beginning with the not existant "red arrow" in your offered diagram but in the other Class schemes !

" Red arrow now shows current flowing in opposite direction."

This is high fidelity spectrum ! Like https://translate.google.com/translate?sl=de&tl=en&u=https://www.abacus-electronics.de/
Title: Re: Help me understand complementary push pull amp
Post by: nix85 on March 09, 2021, 01:47:39 PM
Pardon,if you see this as spam !

I would have to read the total article ,beginning with the not existant "red arrow" in your offered diagram but in the other Class schemes !

" Red arrow now shows current flowing in opposite direction."

This is high fidelity spectrum ! Like https://translate.google.com/translate?sl=de&tl=en&u=https://www.abacus-electronics.de/

No worries, it's just that saying a lot of stuff without really saying anything doesn't help.

Yes, red arrow shows current flowing in opposite direction.

Someone around here should know this. I guess it will be answered within day or two max.

Title: Re: Help me understand complementary push pull amp
Post by: AlienGrey on March 09, 2021, 02:40:04 PM
Here is an article on push pull amps.

https://www.electronics-tutorials.ws/amplifier/amp_6.html

Second diagram shows two NPN transistors back to back and you can see how current flows for each halfcycle as nicely drawn.

But i don't understand NPN PNP combination, first diagram, shown below.

During positive halfcycle TR2 is off, TR1 conducts and current flows through it and through load to ground.

All sweet, but...http://overunity.com/Smileys/default/cool.gif

During negative halfcycle TR1 is off, TR2 is on and.....? How does the circle close?

TR1 is off, Vcc is disconnected.

Red arrow now shows current flowing in opposite direction.

Something's missing in these diagrams (they are all like this).
The problem with this circuit is as a half an H bridge you only get half the power of a hakfl H bridge ! shock horror  :'(

Be aware if you use 2x N channel  Mos fets as per IR2184 totem pole driver, and you pull up the Drain to the supply rail you have a problem!
as that top supply Mosfet cant get an up to 12 volt turn on bias unless you use a an extra pull up bias power supply.

The same applys to bipolar circuits too but at a lower bias voltage.

Also you need to use a pair of charge capacitors between the half bridge - load - split supply or you blow up or over heat
one of the transisters thus blowing them both up.

And my name is (Alen > Alien) close aim it not Adrian, Adrian is some onme else.
Title: Re: Help me understand complementary push pull amp
Post by: forest on March 09, 2021, 02:42:24 PM
I cannot help much because PNP transistors are difficult to me also but.... maybe there is something missing like -VCC source ?
https://d2vlcm61l7u1fs.cloudfront.net/media%2F5bd%2F5bd89220-5060-45e9-844b-de518d8e6073%2FphphnBCzU.png
Title: Re: Help me understand complementary push pull amp
Post by: AlienGrey on March 09, 2021, 02:48:44 PM
I cannot help much because PNP transistors are difficult to me also but.... maybe there is something missing like -VCC source ?
https://d2vlcm61l7u1fs.cloudfront.net/media%2F5bd%2F5bd89220-5060-45e9-844b-de518d8e6073%2FphphnBCzU.png
the transistor QI reacts to over heating of the two transistors mount it as close to them as possible.

Note there is no over currenrt protection ! :'(
Title: Re: Help me understand complementary push pull amp
Post by: nix85 on March 09, 2021, 03:31:06 PM
The problem with this circuit is as a half an H bridge you only get half the power of a hakfl H bridge ! shock horror  :'(

Be aware if you use 2x N channel  Mos fets as per IR2184 totem pole driver, and you pull up the Drain to the supply rail you have a problem!
as that top supply Mosfet cant get an up to 12 volt turn on bias unless you use a an extra pull up bias power supply.

The same applys to bipolar circuits too but at a lower bias voltage.

Also you need to use a pair of charge capacitors between the half bridge - load - split supply or you blow up or over heat
one of the transisters thus blowing them both up.

And my name is (Alen > Alien) close aim it not Adrian, Adrian is some onme else.

So i guessed right, half of the H bridge is missing.

I'd appreciate the diagram of whole H bridge push pull amp.
Title: Re: Help me understand complementary push pull amp
Post by: citfta on March 09, 2021, 05:20:58 PM
So i guessed right, half of the H bridge is missing.

I'd appreciate the diagram of whole H bridge push pull amp.

For a full H bridge circuit just create a mirror image of the two transistors on the opposite side of the load with the output connecting to the load instead of the load connecting to ground.  The full H bridge can be used for controlling a motor in either direction or for applying an AC signal to the load.  For the H bridge to work correctly the top transistor on one side is turned on at the same time as the bottom transistor on the other side.  And vice versa to change the direction of current through the load.

The half bridge can also supply an AC signal to the load if you connect an appropriate capacitor between the load and ground.  The cap can charge during the first half cycle and discharge during the last half cycle thus supplying an AC current to the load.
Title: Re: Help me understand complementary push pull amp
Post by: nix85 on March 09, 2021, 05:43:58 PM

For a full H bridge circuit just create a mirror image of the two transistors on the opposite side of the load with the output connecting to the load instead of the load connecting to ground.  The full H bridge can be used for controlling a motor in either direction or for applying an AC signal to the load.  For the H bridge to work correctly the top transistor on one side is turned on at the same time as the bottom transistor on the other side.  And vice versa to change the direction of current through the load.

I know how full H bridge looks and works from an inverter, still, i want to see push pull amp version.

Quote
The half bridge can also supply an AC signal to the load if you connect an appropriate capacitor between the load and ground.  The cap can charge during the first half cycle and discharge during the last half cycle thus supplying an AC current to the load.

That wouldn't work. Cap would start to discharge as soon as charging voltage starts falling from the peak, not when it reaches zero.

Also, you can't assume halfcycles are mirror replicas and even if they were cap would not mirror the original pulse.
Title: Re: Help me understand complementary push pull amp
Post by: AlienGrey on March 10, 2021, 01:33:00 AM
I wouldnt let the above comments bother you as in this type of circuit that has inductance coils it will still end up as a sine wave
when its in RESONANCE, way back in the 60's and 70's early transister amplifiers used this cap coupling in the Clive Sincleair
amplifiers and you would never know the difference, and any way Adrian Gusker used the Stalker circuits he uses this type of circuits.

However note in this circuit the top transistor has no full gate bias and will never fully turn on and if a p channel device is used it will add
further complications with the driver circujit.
;D ;D ;D ;D ;D

SIL
Title: Re: Help me understand complementary push pull amp
Post by: AlienGrey on March 10, 2021, 01:44:45 AM
One solution would be to change the top totemnpole transister drive to an over  current device or and run the bottom device
as a rail to rail biased device and just limit the current to it's availability.

SIL
Title: Re: Help me understand complementary push pull amp
Post by: nix85 on March 10, 2021, 08:52:47 AM
I got trouble understanding how EXACTLY you imagine half bridge creating AC.

(Let's ignore the fact that you cannot just recreate the missing halfcycle and call it HiFi)

Now you are mentioning resonance and inductors.

Let's first get some basics out of the way...

We all know no electrons pass through a cap, but a changing electric field, displacement current..

We also know reactance of the cap is XC= -1/2πfC

So, higher the frequency and capacitance, more it looks as if cap is not there.

We also know in purely capacitive or inductive circuit voltage and current are 90° out of phase.

Any changing waveform passes "through" a cap, be it pulsed DC or AC.

So halfsinewave passes through a cap as easily as a whole sinewave does.

In other words, when the halfsine ends, with slight delay, voltage would pass through the cap leaving it uncharged.

So let's bring in resonance. If we are talking LC tank instead of a cap alone, then it depends if it's in series of parallel.

Series LC tank at resonance is short circuit, in parallel open circuit..

So, how exactly is other half of the sinewave produced.

Title: Re: Help me understand complementary push pull amp
Post by: AlienGrey on March 10, 2021, 10:28:06 AM
It sounds like you dont experiment  a capacitor is an insulator so how can it pass currevt ?
it charges and discharges it's size demnds on its time and frequency and how it's charged

Also if the cap is in series your DC content is lost.

Also if you bias a semiconducter on its on off slope your moving its DC swing in your circuit.
Title: Re: Help me understand complementary push pull amp
Post by: nix85 on March 10, 2021, 11:40:23 AM
It sounds like you dont experiment  a capacitor is an insulator so how can it pass currevt ?
it charges and discharges it's size demnds on its time and frequency and how it's charged

Also if the cap is in series your DC content is lost.

Also if you bias a semiconducter on its on off slope your moving its DC swing in your circuit.

I do experiment and build but you clearly don't know the basics.

You don't know what displacement current aka capacitor current is, google it.

"Wire has inductance" sooo? Unless it's coiled inductance is negligible.

Everything i wrote is COMMON ELECTRONIC KNOWLEDGE.

Everything you crossed and called wrong is correct.

"It depends on slope bias set up", no it doesn't, you can't recreate the missing halfcycle and call it HiFi.

All changing voltage waveforms indeed pass through a cap, be it pulsed DC or AC... even pulsed DC squarewave signal will pass through a cap at the moment of the change.

Back to school.

Title: Re: Help me understand complementary push pull amp
Post by: antijon on March 10, 2021, 03:02:58 PM
The first image that you posted wouldn't work. As it is nothing would happen on the neg half cycle.

Just saying it's more likely that they forgot to add the label for -VCC at the bottom rail.

Otherwise, you could replace the "ground" at the load with the center tap of a voltage divider. e.g. if you had 12V from VCC rail to bottom rail, when the top transistor closes the load would see 6V+ from VCC to center tap. When the bottom transistor closes the load would see 6V- from center tap to bottom rail. (Don't really know if this would work because I don't do electronics but it seems feasible in my head lol)
Title: Re: Help me understand complementary push pull amp
Post by: nix85 on March 10, 2021, 03:10:07 PM
They did not forget it is implied and most often symbolized that bottom is also "ground", that is, Vcc-.

Of course "ground" does not always have to be Vcc-, it's just a circuit wide reference point.

Here is the first diagram on google images for push pull amp

Looking at these diagrams one would conclude that during negative halfcycle current flows from ground to ground, lol.
Title: Re: Help me understand complementary push pull amp
Post by: nix85 on March 10, 2021, 05:46:34 PM
This guy is "explaining" it and of course does not address the issue.

And then we wonder why ppl don't understand shit. Almost nothing is explained right.
Title: Re: Help me understand complementary push pull amp
Post by: AlienGrey on March 10, 2021, 10:05:18 PM
If you understand sh would that be a hallo of some sort ? ;D ;D

If you conect the lower transister to a -12 Volts it will go bang !

Do you know why ?
Title: Re: Help me understand complementary push pull amp
Post by: antijon on March 10, 2021, 11:45:49 PM
AlienGrey, is that why they sometimes put a capacitor before the input? I don't know about with a square wave, but a sine would pass through the cap. and show a pos. and neg. value.

Nix, I can see why that would work in the video, at least the diagram with the capacitor before the output load. The cap. charges during the pos. half wave, and negative half wave discharges the cap. through the bottom transistor. The load after the cap. should see a forward and reverse current
Title: Re: Help me understand complementary push pull amp
Post by: nix85 on March 11, 2021, 10:23:19 AM
Nix, I can see why that would work in the video, at least the diagram with the capacitor before the output load. The cap. charges during the pos. half wave, and negative half wave discharges the cap. through the bottom transistor. The load after the cap. should see a forward and reverse current

Capacitor before the input is to remove any dc.

Yea, that's what i assumed too. Keep in mind

all changing voltage will pass through the cap.

Only the dc bias 1/2 Vcc can remain on it to

discharge in opposite direction.
Title: Re: Help me understand complementary push pull amp
Post by: nix85 on March 11, 2021, 10:24:45 AM
If you understand sh would that be a hallo of some sort ? ;D ;D

If you conect the lower transister to a -12 Volts it will go bang !

Do you know why ?

LOL i see you are still confused,
have you at least learned what displacement current is
and that all changing signals pass through a cap ? ;D ;D
Title: Re: Help me understand complementary push pull amp
Post by: nix85 on March 11, 2021, 11:16:30 AM
Only way i can see it really make sense, the way he describes in the video

is with another resistor that forms voltage divider with load resistor

that biases Ve at 1/2 Vcc when both transistors are off. So as Q1 turns on Ve

can swing from 1/2 Vcc up to Vcc and when Q1 is off and Q2 on from 1/2 Vcc to 0.
Title: Re: Help me understand complementary push pull amp
Post by: nix85 on November 09, 2021, 03:07:46 PM