Typically, BJTs can be more reliably operated in parallel if balancing resistors are placed in series with the emitter, rather than the base. Even a small resistance here will strongly counteract the tendency for imbalance, because an increase in current flowing through any one transistor causes the applied base-emitter voltage to decrease. This in turn reduces the amount of base current that flows, and therefore the portion of the shared current that the affected transistor carries.
In practice, matching the resistor values and transistor characteristics including temperature is just as important to achieving an accurate balance as the value of the resistance chosen. I was on a team that tried that in my first job, I was only an apprentice then but none of the grown ups could make it work.
I still remember the pings as they went one after another. In those days just one of these 5A power transistors cost the same as my weeks wages. No that is the maximum voltage it will take before you damage it. However you do need 10V to turn this FET on fully. Look at the Rds on conditions. Will this work? A small resistance in series with the emitter would be far more effective and would balance the load on each transistor naturally through adjusting the base current.
In a previous life I was part of a team that designed DC motor drives. The biggest I worked on was a 10KW drive that used banks of over a hundred 2Ns with. I believe some of them are still in service today.
Thanks Grumpy Mike. Im still studying about FETS. To prevent this from happening, you must integrate a low-rated resistor connected in series with every emitter. For example, if the load equates to 50 Ohms, then a 1 Ohms resistor will perform well. It provides negative feedback that keeps the current moderated because of the voltage increase in its emitter resistor.
However, these do not distribute current under linear mode. Then, conductance will increase in frequency. It provides a worse problem compared to BJTs in parallel. It allows more current control in linear operation. To conclude, this article mainly focuses on the correct implementation of transistors in parallel. For example, BJTs should contain a resistor in series for current sharing.
Additionally, you can integrate transistors in parallel with a heat sink, a more efficient approach compared to BJTs. If you have any questions regarding transistors in parallel, feel free to contact us! File Upload. It can switch mA. It's a sunday, the store is closed, so suggestions to go and buy something are not helpfull at this point :p. Transistors don't match that well when in parallel - one of them always gets a greater amount of current - a small resistor in each collector will help - the value depends on the voltage headroom.
Yes, you can put transistors in parallel. Connect the collectors together, the bases together, and put a resistance in the emitter line of each transistor not just one resistor for the pair that will drop 0. This will create negative feedback to help balance the current through the transistors.
Jokerman wrote: FETs are better for using in parallel - but like you say it's Sunday :. If you can afford CMOS transistors they cost more usage instead of bipolar, you can connect them in parallel without ballast resistors I am talking about additional ballast resistors for transistors current alignment, not about LED ballast resistors - those you need anyway.
Another good thing about CMOS transistors is, that voltage drop across drain-source can be lower with appropriate type selection then in bipolar transistor, so less power you will waste with CMOS.
Just make sure you will use "logic level" with lover gain opening voltage type if you are connecting them directly to the MCU. Look in the datasheet, it will usually have a max pulsed current, or something along those lines - and tell you under what conditions you can hit that peak.
Like others say, if you can use FETs instead, you're set.
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