my first pcb any mistake

[pomme]

Just make them thinner. If resistance is high enough, large current can’t happen, right?

if the traces are thin enough electrons won't have place to pass through

Indeed. That fragment does not deliver any significant power. It’s there only to pass signal.

I'm really happy I understood it.
does the resistance of diode or transistor play a big role in preventing big amount of current to pass through ? and if yes
how do we determine the resistance ? is it in the datasheet or do we calculate it

I'm talking about a capacitor, likely two or three of them... Maybe 47uF next to the inductor and 100nF ceramic next to the heater connector. The circuit would work without them, but they should reduce the EMI produced.

do you recommend me puting them ?

[pigrew]

I'm talking about a capacitor, likely two or three of them... Maybe 47uF next to the inductor and 100nF ceramic next to the heater connector. The circuit would work without them, but they should reduce the EMI produced.

do you recommend me puting them ?

I do recommend adding places to mount capacitors on the output, however you might not need them. It's always better to add places to put a component, in case you need them (at least for initial designs).

You may also want a capacitor in parallel to your Zener diode (where you had circled). As it is, you'll see a triangle-wave on the voltage-output pin. If that's your intention, great. If you want the average voltage, then you'll need to add a capacitor in parallel to the Zener, to form a lowpass filter.

[pomme]

You may also want a capacitor in parallel to your Zener diode (where you had circled). As it is, you'll see a triangle-wave on the voltage-output pin. If that's your intention, great. If you want the average voltage, then you'll need to add a capacitor in parallel to the Zener, to form a lowpass filter.

I didn't understand every thing but I'll keep that in mind and make some research

[golden_labels]

does the resistance of diode or transistor play a big role in preventing big amount of current to pass through ? and if yes
how do we determine the resistance ? is it in the datasheet or do we calculate it

For resistor: Ohm’s law.

For diodes: diodes do not exhibit resistance understood in that manner. While each real-world diode has some ohmic resistance, in this case it’s negligible and you may assume in this circuit the diode has no resistance above 3V and does not conduct at all below 3V.

[pomme]

okey thanks
for example in the case of R1 and D3 I know that R1 is 10kΩ so ohm's law : I = 24V/10kΩ = 0.0024A
so I know that I don't need thick traces right ?

[golden_labels]

The short answer: yes. 2.4mA is very low current.

A longer answer: it’s even less than 2.4mA: the voltage drop on the resistor is around 21V, as the rest is taken by the diode. ATMega328P inputs in practice take no current. And even without calculating the current, you have a 10kΩ resistor there. With such a huge resistance and low voltages, track width becomes irrelevant, as it will always be orders of magnitudes smaller.

The proper answer: judging by this thread, you are at the very beginning of the adventure with electronics. While being a newbie is not a problem, not doing one’s homework will be. You are embarking at a project that can’t be easily designed or understood by an EE student halfway through their first semester. But so far it is clear you miss any knowledge in the topic. Like, literally, any. Nothing wrong with trying things out and learning by experimentation, but there is an enormous gap between what you know and what you try to do. Perhaps try with something simpler first? Something that will let you grasp the basic principles.

[pomme]

I understand what you mean and I agree with you but this is how my brain understand things (with a project) I tried a classical path but it was so boring that I give up
but with this project I have really learned so much from your feedbacks
sorry if my questions were too simple and I appreciate your help until now

[pigrew]

The zener D1 (protecting the gate) might overheat.

When the pFET switch is ON, DRIVE will be about 0.7 V. If the input is a little high (25 V),  D1 may have 18.5 V on it, so GATE is 6.5 V. The Zener's current is (6.5 - 0.7 volts )/(100 ohm) = 58 mA.

The Zener's power would then be I*V = 58 mA * 18.5 V = 1.1 watts. This seems to be too much, since the max power is about 0.35 watts.

You may want to run a simulation of this circuit (such as in LTSpice), and verify that all the components are within their power envelopes and that the circuit functions as desired.

[pomme]

this schematic is not from me it's from a youtuber called sasiskas and from what I have seen his soldering station works
I don't know if I can put a the link of his video or if it's against the rules of the forum

[pigrew]

this schematic is not from me it's from a youtuber called sasiskas and from what I have seen his soldering station works
I don't know if I can put a the link of his video or if it's against the rules of the forum

My understanding is that it's perfectly fine to post links to YouTube videos (unless it's done as advertising).



and these are the design files.

I'm not saying it wouldn't work. I'm not even saying that it must be changed. I'm saying that there are design issues that should be considered as you are working on the design, and I hope that my comments will help you understand the design.

With this overheating issue, in particular, the PWM duty cycle might be low enough that the part will never overheat. Or maybe, it'll cause moderate overheating, and only cause failure after 10,000 hours. It is a design issue that should be considered. It may also point you into investigating other issues, like how V_gs=-18.5 V is probably bad for the MOSFET (its max rating is Vgs = 20 V, and only shows data down to Vgs=-15). A zener closer to 15 V would be safer.

[pomme]

My understanding is that it's perfectly fine to post links to YouTube videos (unless it's done as advertising).

I'll keep that in mind

I'm not saying it wouldn't work. I'm not even saying that it must be changed. I'm saying that there are design issues that should be considered as you are working on the design, and I hope that my comments will help you understand the design.

With this overheating issue, in particular, the PWM duty cycle might be low enough that the part will never overheat. Or maybe, it'll cause moderate overheating, and only cause failure after 10,000 hours. It is a design issue that should be considered. It may also point you into investigating other issues, like how V_gs=-18.5 V is probably bad for the MOSFET (its max rating is Vgs = 20 V, and only shows data down to Vgs=-15). A zener closer to 15 V would be safer.

Oh I see I'll try doing like you suggested and check out the issue you pinpointed
I'll take my time to understand an search, I'm not in a hurry anyway
thanks

[golden_labels]

sorry if my questions were too simple and I appreciate your help until now

It’s not that they are “too simple”. The problem is: no one is going to explain you the most absolute basics in a project, that requires a decent grasp of them.

What I meant is that you may try something simpler first. To get the feel of how stuff works. Play with some trivial circuits to learn the fundamental concepts before combining many of them in a single project.

When the pFET switch is ON, DRIVE will be about 0.7 V. If the input is a little high (25 V),  D1 may have 18.5 V on it, so GATE is 6.5 V. The Zener's current is (6.5 - 0.7 volts )/(100 ohm) = 58 mA.

The Zener's power would then be I*V = 58 mA * 18.5 V = 1.1 watts. This seems to be too much, since the max power is about 0.35 watts.

I believe it’s not.

Notice that, using free_electron’s schematic version, both Q4 and Q3 operate as voltage followers. So DRIVE will see about the same voltage as PWMDRIVE. That gives additional 5V of margin. 23V is needed for R2 and D1 to even see any current. At 24V and above they would see about 10mA/V increase, with theoretical 180mW/V power on D1. But there is negative feedback from the power supply line: R3.

Of course you noticing a potential issue there is still a good thing! 👍

[pigrew]

Notice that, using free_electron’s schematic version, both Q4 and Q3 operate as voltage followers. So DRIVE will see about the same voltage as PWMDRIVE. That gives additional 5V of margin. 23V is needed for R2 and D1 to even see any current. At 24V and above they would see about 10mA/V increase, with theoretical 180mW/V power on D1. But there is negative feedback from the power supply line: R3.

I completely missed R6. With it in mind, the design is fine.

With 5V digital IO, SINK goes between 4V and 24V (not 0V and 24V as I mistakenly thought). With 3.3V logic levels, SINK would alternate between ~11V and 24V.

I threw together a LTspice simulation, assuming nominal parameters. I believe it's a 5V Arduino being used. When the PWMDRIVE is active, the Zener is at 180 mW, so within the safe range. Even with 25V input and 5.5V I/O, it's within the power limit of the zener.

(I couldn't find the RF107 diode model, so I arbitrarily choose the RF071 model... it's an anagram, so maybe it's close?)