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Author Topic: Help me understand complementary push pull amp  (Read 4558 times)

Offline nix85

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Help me understand complementary push pull amp
« 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).

Offline lancaIV

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Offline nix85

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Re: Help me understand complementary push pull amp
« Reply #2 on: March 09, 2021, 12:25:29 PM »
How is the circuit closed during negative halfcycle?

Offline lancaIV

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Re: Help me understand complementary push pull amp
« Reply #3 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

Offline nix85

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Re: Help me understand complementary push pull amp
« Reply #4 on: March 09, 2021, 01:23:20 PM »
Please, if you don't know the answer, don't spam.

Offline lancaIV

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Re: Help me understand complementary push pull amp
« Reply #5 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/

Offline nix85

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Re: Help me understand complementary push pull amp
« Reply #6 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.

I read the whole article, it never addresses the issue.

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.


Offline AlienGrey

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Re: Help me understand complementary push pull amp
« Reply #7 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.

Offline forest

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Re: Help me understand complementary push pull amp
« Reply #8 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

Offline AlienGrey

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Re: Help me understand complementary push pull amp
« Reply #9 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 ! :'(

Offline nix85

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Re: Help me understand complementary push pull amp
« Reply #10 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.

Offline citfta

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Re: Help me understand complementary push pull amp
« Reply #11 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.

Offline nix85

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Re: Help me understand complementary push pull amp
« Reply #12 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.
« Last Edit: March 09, 2021, 08:00:43 PM by nix85 »

Offline AlienGrey

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Re: Help me understand complementary push pull amp
« Reply #13 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

Offline AlienGrey

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Re: Help me understand complementary push pull amp
« Reply #14 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