Hi,
I just want to tell you about my story with transistors, because i really do feel stupid now.
I've been using various transistors for a long time. I always put them most of the time before the load because it seemed logical and that's how i've seen it elsewhere. I also supplied the gate/base with a voltage equal or smaller than the supply voltage. This became a habit and although i knew about the difference between potentials and voltage, the use of transistors this way seemed so straightforward that i never thought about it more deeply. So, until now i believed those 0.7 V or in case of MOSFETs 1-3 V losses were perfectly normal and couldn't be dealt with. I thought about it as a fact, something that can only be solved with a relay.
Though i had doubts, I really didn't think the circuit design was wrong. Maybe I'm just not using the correct MOSFET suited for the task, that's why they have slightly bigger losses (and i still thought that even better ones should have a voltage drop of at least 0.3-0.7 V). I've been using my transistors this way for at least 5 years with this belief. I used many simulators and i built many real circuits this way. It was not really a problem in signal processing and in some cases transistors do need to be used this way, but it caused massive losses in power applications.
I only noticed today that something is wrong. I started designing a PWM circuit that drives a motor. Because the electricity comes from the 230 V AC network, i had to do a lot of things with it first and as a result i had a quite few different potentials, which served as a reminder that potentials really are relative. As usual, i've been struggling with the voltage drop in my simulation program and this time it was really big, so i was playing around with the circuit. Eventually I increased the voltage at the gate/base of the transistor, which decreased the voltage drop. At first, I didn't understand why this is happening since i already supplied it with a quite high voltage. It is only then that the gears in my head started to turn. I had positive voltages on all sides of the transistor when it was on, so i had to think about it again, what voltage is really responsible for switching the transistor. Then I finally realized the error.
Thinking now about it, this behaivour is really self-explanatory, I don't even know how i didn't notice this until now that my transistors were only partially switched on. This is kind of embarrassing but it is also a pleasant suprise. I can now make improvements to power efficiency.
I just want to tell you about my story with transistors, because i really do feel stupid now.
I've been using various transistors for a long time. I always put them most of the time before the load because it seemed logical and that's how i've seen it elsewhere. I also supplied the gate/base with a voltage equal or smaller than the supply voltage. This became a habit and although i knew about the difference between potentials and voltage, the use of transistors this way seemed so straightforward that i never thought about it more deeply. So, until now i believed those 0.7 V or in case of MOSFETs 1-3 V losses were perfectly normal and couldn't be dealt with. I thought about it as a fact, something that can only be solved with a relay.
Though i had doubts, I really didn't think the circuit design was wrong. Maybe I'm just not using the correct MOSFET suited for the task, that's why they have slightly bigger losses (and i still thought that even better ones should have a voltage drop of at least 0.3-0.7 V). I've been using my transistors this way for at least 5 years with this belief. I used many simulators and i built many real circuits this way. It was not really a problem in signal processing and in some cases transistors do need to be used this way, but it caused massive losses in power applications.
I only noticed today that something is wrong. I started designing a PWM circuit that drives a motor. Because the electricity comes from the 230 V AC network, i had to do a lot of things with it first and as a result i had a quite few different potentials, which served as a reminder that potentials really are relative. As usual, i've been struggling with the voltage drop in my simulation program and this time it was really big, so i was playing around with the circuit. Eventually I increased the voltage at the gate/base of the transistor, which decreased the voltage drop. At first, I didn't understand why this is happening since i already supplied it with a quite high voltage. It is only then that the gears in my head started to turn. I had positive voltages on all sides of the transistor when it was on, so i had to think about it again, what voltage is really responsible for switching the transistor. Then I finally realized the error.
Thinking now about it, this behaivour is really self-explanatory, I don't even know how i didn't notice this until now that my transistors were only partially switched on. This is kind of embarrassing but it is also a pleasant suprise. I can now make improvements to power efficiency.