I can't understand/see the difference between a push-pull and a totem-pole output.
Push-pull:
Totem-pole:
Do these circuits have a transistor in the input for something like "double amplification?"
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asked Feb 24, 2018 at 17:42
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2\$\begingroup\$ A Totem-Pole output is often used for logic gates and some op-amps because it allows the output to approach ground potential, or zero volts. The Push-Pull output cannot approach either power rail due to a Vbe drop of .6 to 1.2 volts. That is just a comment, not an answer to your question. \$\endgroup\$– user105652Feb 24, 2018 at 20:59
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2\$\begingroup\$ This line from a website I have forgotten the address says it all: "Totem-pole and push-pull I/O are functionally the same, but the former require inputs of opposite polarity for same polarity transistors, while the latter uses transistors of opposite polarity driven by the same input." Be aware that the terms are somewhat loosely used and sometimes people call push-pull a totem pole and vice versa. \$\endgroup\$– Sredni VashtarFeb 25, 2018 at 2:42
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\$\begingroup\$ As for the double amplification, with a single transistor you usually place the operating point in the middle of the characteristics to accommodate both positive and negative swings of the output signal, while when using push-pull, you can place it at the cut-off border and make the output swing only in one 'direction' for each transistor, achieving double the swing with a single transistor. \$\endgroup\$– Sredni VashtarFeb 25, 2018 at 2:47
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3 Answers
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You'll notice in the push pull stage that you need a PNP and an NPN transistor, whereas the totem pole driver uses only NPN transistors. This is useful because NPN type transistors are usually easier to make, and support higher current for a given size than PNP type transistors.
To address your question on "Double amplification", a push pull driver doesn't necessarily give more amplification, but is used because it is more efficient than a single transistor amplifier because (ideally) only one transistor is on at a time, and all the current goes through the load.
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\$\begingroup\$ Your final (incomplete?) paragraph ignores the existence of Class A. \$\endgroup\$ Feb 25, 2018 at 1:09
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Some of the explanations above confuse ideas.
You shouldn't mix push-pull, totem pole & bootstrap circuits.
Only push pull mode gets alternate signal on the output load starting from a half wave.
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I’ve always thought of push pull as a type of output realized by many different configurations and a totem pole is one of the configurations as is compound, complementary.
