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I have a circuit in which the C aka 2SC transistor failed after many years. I Googled about, and tried to replace it with a BC The BC got kind of warm, and didn't work. So, is there something 'special' about the C trannies? I have seen them referred to as 'switching' transistors somewhere, I don't know what that specially means.
This is being used in a flyback circuit, which switches at approx ummm kHz or so. My previous, sort-of related question is here: What type of voltage booster circuit is this?
What could cause transistor to overheat? Well, it's whether excessive base current, or excessive product of Ic x Vce. This is your circuit:. Base current is not a problem, it is limited by R to 4.
So, transistor could overheat by high Vce or Ic. But it will be lower, say it is mA. Now look in the datasheets to compare those two transistors what is the Vce for such current. This is from 2SC datasheet:. This is from BC datasheet:. It is off the chart, it is a bad sign for this situation. Vce would be much higher than 1.
So power dissipation would be mW, which is above maximum allowed power dissipation. I do not say your circuit is drawing mA, peaks could be higher or lower. But you can see that in some situations there are differences between BC and 2SC Another relevant difference could be in hFE. It depends on your batch. There are huge differences: 2SC hFE from 90 to BC hFE from to Seeing that your circuit has no feedback resistor anywhere on the 2SC, I would suggest to try adding a 10R resistor in the base of the 2SC resp BC after the 22R resistor that goes to the feedback path and see whether that improves the situation.
If not, you have to take out a good oscilloscope and look at the waveforms. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Suitable replacement for 2SC transistor? BC doesn't seem suitable Ask Question. Asked 2 years, 8 months ago. Active 2 years, 8 months ago. Viewed 1k times.
Thanks, any help appreciated! Chalky Chalky 8 8 bronze badges. Is it possible that there is another problem which caused your transistor to fail and which makes your new transistor hot? When I replace it with a BC, the circuit doesn't work at all.
Active Oldest Votes. This is your circuit: Base current is not a problem, it is limited by R to 4. This is from BC datasheet: It is off the chart, it is a bad sign for this situation. Chupacabras Chupacabras 4, 2 2 gold badges 13 13 silver badges 44 44 bronze badges.
Edit: Adding schematic to show what I mean: simulate this circuit — Schematic created using CircuitLab. Attila Kinali Attila Kinali 1, 2 2 silver badges 10 10 bronze badges. Can you clarify position of additional 10R resistor? This would severely limit the lifetime of an already stressed component.
Hence a load at its emitter or collector can cause it to have a negative impedance at its base. The additional resistor dampens this oscillation. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog.
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