I've come across this symbol in the datasheet (link below) of a transistor for a halogen "electronic transformer" that uses two in a half-bridge operating at about 35KHz. The datasheet mentions nothing special about the transistor, a regular fast-switching bipolar NPN.

enter image description here

Now I understand the presence of the diode, but what is the box connected to all three terminals? I can only think of it as a biasing network, perhaps even resistive. I have searched images on the net for NPN symbol variants and have not seen anything like it.

Link to BLD135D datasheet

Can anyone shed light on this?

  • \$\begingroup\$ Whatever it is, it's not mentioned in the datasheet. It's not a particularly good datasheet anyway. Not enough information. It could be a biasing network that is not mentioned (a glaring omission), or it could simply be a resistor that is drawn on the wrong side and not mentioned (also a glaring omission), or it could be a copy-pasted symbol from something else that has it and describes it, while this one doesn't actually have it. Given the brevity and lack of other details that would certainly apply to this one and are not mentioned either, I would look for a better datasheet. \$\endgroup\$
    – AaronD
    Commented Jun 18, 2022 at 15:38
  • \$\begingroup\$ Agreed the documentation is terrible. And the site I linked is the only one to have the datasheet... Cheap chinese products. I want to build an more rugged version of this transformer as a high voltage power supply and looking for equivalents. If it is a biasing network it is not needed in the circuit, since I can simulate in LTspice using a regular BJT and anti-parallel diode without biasing network and the output is ecactly the same as the unit's as seen on my scope... \$\endgroup\$
    – Joe
    Commented Jun 18, 2022 at 16:13
  • \$\begingroup\$ MJE13003 and friends are likely equivalents; the series offers parts with higher voltage and current ratings too. \$\endgroup\$ Commented Jun 18, 2022 at 16:20
  • \$\begingroup\$ @TimWilliams That's exactly the one I found so far, you are confirming my choice, thanks!. Also FJPF13007 looks a good option in isolated TO-220F package. \$\endgroup\$
    – Joe
    Commented Jun 18, 2022 at 16:29
  • \$\begingroup\$ Transistor decorations like this sometimes associate cooling options or requirements. \$\endgroup\$
    – Jens
    Commented Jun 18, 2022 at 23:31


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.