How to connect a NPN transistor in place of an PNP - Page 1
Forum section: electronics / beginners

author: PillaDoubleG
author_rank: Newbie
timestamp: April 13, 2024, 12:02:32 pm
content: Hello, could someone maybe explain or give me a picture of how to connect a NPN transistor instead of a PNP transistor in this circuit?I've searched on the web but haven't found a super definitive answer.Here's a picture of the circuit.

author: xvr
author_rank: Frequent Contributor
timestamp: April 13, 2024, 12:10:22 pm
content: Very strange circuit. TV killer?> Hello, could someone maybe explain or give me a picture of how to connect a NPN transistor instead of a PNP transistor in this circuit?No way - there is no PNP transistor in this circuit

author: Gyro
author_rank: Super Contributor
timestamp: April 13, 2024, 12:11:30 pm
content: There isn't any PNP (or NPN) transistor in the circuit, just an N-Channel MOSFET.

author: MrAl
author_rank: Super Contributor
timestamp: April 13, 2024, 12:52:02 pm
content: Quote from: PillaDoubleG on April 13, 2024, 12:02:32 pmHi,Not only is there no PNP transistor in the circuit, but there is also a switch in series with the inductor L3 which is not a good idea because when it is opened the inductor could generate a huge voltage kickback and cause problems.I'd have to ask where you got this circuit and what is it supposed to be used for.

author: Gyro
author_rank: Super Contributor
timestamp: April 13, 2024, 01:03:20 pm
content: It also looks as if it may be powered directly from the mains (220V) making it extremely dangerous.

author: CaptDon
author_rank: Super Contributor
timestamp: April 13, 2024, 01:17:15 pm
content: Unless L1 and L2 are on the same core and that core also has another winding (secondary) that power is extracted from, that would be the most useless design I have ever seen. And why, when looking at that symbol did you guess it was a transistor? It is the industry standard symbol for a certain style of FET. N type devices in 99.999% of circuits can't be swapped with P type devices and vice versa unless the polarity of the power supply is also reversed. No fuse in the circuit = nice explosion when the FET shorts due to no snubbing circuit or failing to begin oscillation at all.

author: PillaDoubleG
author_rank: Newbie
timestamp: April 13, 2024, 02:00:12 pm
content: I'll try to answer all the questions here, to clear up confusion.Worded the original post very badly, and didn't fully understand the circuit. I was worried about the little arrow in the picture.I'm sure all of you know what that means, so I wont bother explaining it, but I have an IGBT that has the arrow going in the other direction, hence the current going in the other direction. Can i connect the IGBT same as the MOSFET, or differently? Or will an IGBT not work at all in this circuit?Quote from: MrAl on April 13, 2024, 12:52:02 pmThanks for mentioning the voltage spike when disconnecting the switch. Would it be better to go with no switch?Quote from: Gyro on April 13, 2024, 01:03:20 pmIt is supposed to be powered off 220v, which is super-super dangerous. For this reason if I ever run it, I will wear the proper protection.Quote from: CaptDon on April 13, 2024, 01:17:15 pmSadly, I don't know all of the symbols just yet, sorry about the confusion there. And thank you for recommending a fuse, which I will definitely add into the circuit. But if a snubber (I'm assuming that it would be a resistor and capacitor, parallel to the switch) were to be added, what should the values of the components be?Sorry for all of the confusion, I will try to understand and answer all of your answers as precisely as I can

author: Gyro
author_rank: Super Contributor
timestamp: April 13, 2024, 04:09:47 pm
content: I doubt you'll find any experienced people here willing to help you kill yourself. You're clearly too inexperienced.

author: xvr
author_rank: Frequent Contributor
timestamp: April 13, 2024, 04:31:52 pm
content: This is Solid State Tesla Coil. VERY unstable and worst behaving thing. Required a lot of experience to make it work. And quite dangerous too.I think Author with his experience could give 3 outcome : burn out a LOT of MOSFETs, short out power mains and finally kill himself.

author: Jwillis
author_rank: Super Contributor
timestamp: April 13, 2024, 09:19:29 pm
content: Quote from: PillaDoubleG on April 13, 2024, 02:00:12 pmA picture is worth a thousand words.Acronyms can often lead people to to confusion. BJT (Bi-polar JunctionTransistor), FET (Field EffectTransistor), or an IGBT(Insulated-Gate BipolarTransistor) are all Transistors.You can't put a resistor capacitor snubber on a switch for AC unless the 220V is rectified to DC first. A capacitor will pass AC but blocks DC. Just thought I would clarify that since the 220V hadn't been defined.I suggest you do a little more research into the project to get a better understanding of how things work, the components used, their limitations and hazards. I don't recommend any novice to dive into any high voltage applications without even the most basic understanding of this.

author: tooki
author_rank: Super Contributor
timestamp: April 14, 2024, 03:09:01 am
content: Quote from: PillaDoubleG on April 13, 2024, 02:00:12 pmThat’s not what the arrow means. Consider that in a zener diode, the device is normally operated with current flowing from cathode to anode.The arrow in a semiconductor symbol means one thing, and one thing only: a P-N junction. That means that the point of the arrow is N-type semiconductor and the shaft/tail of the arrow is P-type. That is, the arrow is always pointing at the N of a P-N junction. So in an NPN transistor, you see the arrow points away from the gate, so you know that gate-emitter is P-N, and because it’s a three-layer device, the remaining layer has to be N. In an N-channel MOSFET, the arrow points inwards, so the N-type semiconductor is in the middle, which is where the channel of a MOSFET is. (In other words, a symbol doesn’t have to showallthe P-N junctions in a device, it just shows enough for a knowledgeable user to tell it apart from other types.)

author: MarkT
author_rank: Frequent Contributor
timestamp: April 14, 2024, 07:58:07 am
content: Quote from: tooki on April 14, 2024, 03:09:01 amNot true, Schottky diodes don't use pn-junctions, nor do PIN diodes in a strict sense (or come to that hetero-junction LEDs and lasers).The arrow in a MOSFET corresponds to no junction come to that, as the doping of the channel is uniform relying on the field-effect to create an inversion layer.I'd say an arrow indicates polarity, usually...

author: tooki
author_rank: Super Contributor
timestamp: April 14, 2024, 10:28:56 pm
content: Quote from: MarkT on April 14, 2024, 07:58:07 amLook at the construction of a MOSFET, please.

author: MrAl
author_rank: Super Contributor
timestamp: April 16, 2024, 11:46:32 am
content: Hello,The construction of say a Schottky diode is different than a PN diode, as it only has one semiconductor layer. This makes it hard to say that the arrow-like shape indicates a PN junction.However, it is also difficult to say that that arrow-like shape indicates polarity also because that would be just a little misleading as well.Consider this: I draw an arrow on a piece of paper such as:--->or more like how a diode looks:--[>|--and now tell me which end (left or right) has positive polarity and which end has negative polarity.You can't do it, because for some devices the polarity has to be opposite to what some other devices require (reverse biased) in order for the device to work correctly, or at least in the normal way.This can only mean that the arrowhead means different things for different devices, both in the construction of the device and the proper (or normal) biasing of the device. Even the current flow can be negligible in some devices and very high in others. This means we have to know more about how the device itself works in order to be able to interpret the meaning of the portion that is indicated by the arrowhead correctly.

author: Zero999
author_rank: Super Contributor
timestamp: April 17, 2024, 08:42:21 am
content: I've always taken the arrow head to mean the direction of the conventional current flow, when the junction is forward biased. The symbol i.e. zener, J-FET or BJT, plain diode and surrounding components then indicates whether it's intended to be reverse or forward biased.