I am trying to understand the internal circuit schematic of the LM565 phase locked loop IC, on page 6 of this datasheet: PDF Datasheet for LM565 from TI website

In the upper middle, there is a strange little symbol labeled "Q13". Here is a screenshot: screenshot fo strange symbol

It looks like a PNP BJT, but I am not sure what it is exactly. Can anyone give me a pointer.

Also, this schematics has quite a few BJT with unconnected pins. I assume that this is when a BJT is used as a diode, but if someone could shed some light I'd appreciate it.

  • \$\begingroup\$ Tetrode transistor. \$\endgroup\$
    – Majenko
    Feb 28, 2015 at 12:23
  • \$\begingroup\$ The data sheet that you linked from the TI web site does not have any chip level schematic. The page has been rendered blank. \$\endgroup\$ Feb 28, 2015 at 12:26
  • \$\begingroup\$ That's probably your viewer - it displays perfectly fine in evince. \$\endgroup\$
    – Majenko
    Feb 28, 2015 at 12:37
  • \$\begingroup\$ @MichaelKaras : I'm using Chrome to view it, and it works fine. Might there be a problem with your PDF viewer ? \$\endgroup\$ Feb 28, 2015 at 12:58

1 Answer 1


This is a multi collector transistor. More common is the multi emitter transistor used in TTL integrated circuits.

enter image description here

  • \$\begingroup\$ I can see how that can indeed be a multi-collector transistor, but then what is that wire coming out of the base and ... is it connected to one of the collector then ??? \$\endgroup\$ Feb 28, 2015 at 13:05
  • \$\begingroup\$ @blondiepassesby: It's a third collector that's tied to the base. \$\endgroup\$ Feb 28, 2015 at 14:00
  • \$\begingroup\$ @blondiepassesby Looks like its internally connected as a diode to me. If you look at the circuit they have several transistors connected in this fashion. \$\endgroup\$ Feb 28, 2015 at 14:03

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