Bridging transistors

Hi! Title might seems confusing but I want to connect two seperate transistors' outputs - bridging them.

Main question: Would there be a short circut if I connect +V(voltage from another transistor output) to transistor output (Emiter if NPN, Collector is PNP)?

I didn't have such a problem with briding relays but now Im confused. Thanks in advance

by MateuszX
June 22, 2020

As shown, I don't see a possibility to have a short. On the other hand, if BOTH are turned ON, one of them will probably get warmer than the other (due to difference in the fabrication) and so, will conduct better, getting more current, getting warmer, getting more current... (thermal runaway). That is a reason why we don't often see bi-polar transistors in parallel. You should select the transistors such that ONE transistor could handle ALL the current by itself (including power dissipation considerations).

by vanderghast
June 24, 2020

This circuit is shown with one transistor on and the other off so it should be a case of either tr on lights both LEDs and I don't see a problem. If both are on for an appreciable time (overlap) then vandergast's comments apply. However you would normally have a resistor in series with each LED and this would improve load sharing in case of overlap.

by Foxx
June 24, 2020
Add comment...

Please sign in or create an account to comment.


No Answers

No answers yet. Contribute your answer below!


Your Answer

You must log in or create an account (free!) to answer a question.

Log in Create an account


Go Ad-Free. Activate your CircuitLab membership. No more ads. Save unlimited circuits. Run unlimited simulations.

Search Questions & Answers


Ask a Question

Anyone can ask a question.

Did you already search (see above) to see if a similar question has already been answered? If you can't find the answer, you may ask a question.


About This Site

CircuitLab's Q&A site is a FREE questions and answers forum for electronics and electrical engineering students, hobbyists, and professionals.

We encourage you to use our built-in schematic & simulation software to add more detail to your questions and answers.

Acceptable Questions:

  • Concept or theory questions
  • Practical engineering questions
  • “Homework” questions
  • Software/hardware intersection
  • Best practices
  • Design choices & component selection
  • Troubleshooting

Unacceptable Questions:

  • Non-English language content
  • Non-question discussion
  • Non-electronics questions
  • Vendor-specific topics
  • Pure software questions
  • CircuitLab software support

Please respect that there are both seasoned experts and total newbies here: please be nice, be constructive, and be specific!

About CircuitLab

CircuitLab is an in-browser schematic capture and circuit simulation software tool to help you rapidly design and analyze analog and digital electronics systems.