Push Button Voltage Regulator Failed!! - Page 1
Forum section: electronics / beginners

author: hpibmx
author_rank: Regular Contributor
timestamp: June 01, 2022, 03:53:11 am
content: Hi,I'm trying to make this adjustable voltage regulator with IRFZ44 push button, however it stopped working.this worked only once I've changed all elements but no luck at all.It's driving me crazy why didn't work anymore.I'm following the first picture exact same circuit.Or if you have any other simple design where I can refer please do share.Thank you all.

author: james_s
author_rank: Super Contributor
timestamp: June 01, 2022, 04:11:27 am
content: Can you provide a schematic? I have a hard time following a rat's nest of wires and components. What is the function of the button?

author: hpibmx
author_rank: Regular Contributor
timestamp: June 01, 2022, 05:06:06 am
content: Sorry for bad drawing.I have tried both circuits no result only once

author: james_s
author_rank: Super Contributor
timestamp: June 02, 2022, 12:40:53 am
content: What is the purpose of the circuit? That doesn't look like a voltage regulator to me, it looks like a push on, push off switch? A bit of an odd way of doing one. Or does it vary the voltage by running the mosfet in linear mode?

author: hpibmx
author_rank: Regular Contributor
timestamp: June 02, 2022, 02:23:14 am
content: Quote from: james_s on June 02, 2022, 12:40:53 amyou may have llok on these links,

author: ledtester
author_rank: Super Contributor
timestamp: June 02, 2022, 05:23:52 am
content: I think this is the basic idea:Falstad simulationPress the UP button to increase the load current and the DOWN button to decrease it.The scope at the bottom shows the load current.And here is the schematic from the first video (at around 1:27 in the video):Doesn't look like the MOSFET is being used correctly -- at the very least the source and drain need to be swapped if I'm not mistaken.

author: hpibmx
author_rank: Regular Contributor
timestamp: June 02, 2022, 09:58:05 am
content: Quote from: ledtester on June 02, 2022, 05:23:52 amThank you for the simulation exactly that's what I want, however I did swap the drain and source still didn't get any changes

author: janoc
author_rank: Super Contributor
timestamp: June 02, 2022, 11:47:48 am
content: Quote from: hpibmx on June 02, 2022, 09:58:05 amAre you sure you didn't blow your MOSFET?I wouldn't be too surprised if it has failed short because IRFZ44 isn't really meant to operate in linear mode and that LED you are showing likely draws some non-trivial current. Also, in the second photo with the 3 LEDs in series I don't seem to see any current limiting resistor. You are running this from 2 Li-ion cells (a really really really BAD idea unless you enjoy some impromptu fireworks), so a lot of current is to be had for anything that could want to blow ...You are also likely blasting the gate of that transistor with ESD. Granted, it is a relatively chunky device with a zener protected gate (assuming it is a genuine IRFZ44 and not some eBay/AliExpress special/fake) but it isn't going to survive that forever.If it doesn't work, you need to start to debug. Throwing hands up in the air isn't a valid debugging technique.Use a current limited power supply, not a battery that can supply hundreds of amps (and blow up in your face doing so!) in case of an accidental short! If you don't have one, put at least a current limiting resistor in series!Put a current limiting resistor in series with the LED - that MOSFET has a very low resistance when it is fully conducting. That is likely to blow your LEDsMeasure the voltage on the MOSFET gate - if it is constantly above the threshold voltage (about 3-4V for IRFZ44), it will be conducting and the LED will be on. If that is so, you may have a shorted switch, for exampleRemove the capacitor and verify that you can actually both turn the MOSFET on by putting positive voltage on the gate and turn it off by grounding it. If you can't, you have either wired something wrong (e.g. the MOSFET is reversed and the body diode is conducting) or the transistor is shorted.

author: CMTan
author_rank: Contributor
timestamp: June 02, 2022, 01:56:32 pm
content: I think you trying to design a switch with memory. 1 button to ON and the, and 1 button to OFF.My first comment, is that this is a very bad design. I explain later why I commented that.To get the basic concept to work, you have to make some change according to the put I suggested circuit.Note, even with this, functionally it can work, but there are serious flaws.1. It works if you press the switch one at a time, but not at the same time.2. If you press both switches together, there will be a short circuit to the supply. The solution to this problem is to have the 2 resistors (high values say 10K) on the switching path as shown3. There is a another problem, the capacitor is acting as a memory holding the voltage. but it will discharge slowly over time. So if you press switch to OFF the light, the light will go OFF, but the capacitor will slowly discharge and over some time (depends on the capacitor leakage and gate leakage current), the switch will turn on again.Solution, please find a circuit with a proper memory circuit instead of relying on the capacitor.4. Also note that the symbol for the MOSFET is incorrect. IRFZ44N is a NMOS, but you are using a PMOS symbol which is incorrect.5. You can also use the circuit suggested earlier by Ledtester. The basic concept is the same.

author: hpibmx
author_rank: Regular Contributor
timestamp: June 06, 2022, 02:57:53 am
content: Quote from: janoc on June 02, 2022, 11:47:48 amThank you pointing out.If you have read, I mentioned I have tried so many other mosfets same number so I'm confident they work.I'm using Riden PSU of course I'm aware not to blow anything up!

author: janoc
author_rank: Super Contributor
timestamp: June 06, 2022, 08:33:30 am
content: Quote from: hpibmx on June 06, 2022, 02:57:53 amThat wasn't clear from your messages. I don't see you mentioning that anywhere above.Quote from: hpibmx on June 06, 2022, 02:57:53 amI have assumed that first photo you have posted (which clearly shows what looks like two 18650 cells) was yours.If you want meaningful help it would bevery helpfulto post both the schematic and pictures of your actual setup, not something that is almost completely unrelated to whatyouhave in front of you.

author: hpibmx
author_rank: Regular Contributor
timestamp: June 07, 2022, 03:51:02 am
content: Quote from: janoc on June 06, 2022, 08:33:30 am

author: janoc
author_rank: Super Contributor
timestamp: June 08, 2022, 12:28:07 pm
content: Quote from: hpibmx on June 07, 2022, 03:51:02 amYou wrote:QuoteI guess my English is really not good enough to recognize how this implies that you have actually verified that your MOSFET isn't blown (or destroyed all of them).Quote from: hpibmx on June 07, 2022, 03:51:02 amSo you show a picture that has a battery and second picture that isn't showing any power supply but alligator clips - and we are supposed to figure out what is that clip connected to somehow and that it isn't the battery?Right, makes sense ...Quote from: hpibmx on June 07, 2022, 03:51:02 amI didn'twatchthe videos. If you can't formulate your question clearly without us having to resort to piecing together what your problem actually is (like what Ledtester did) and watching unrelated youtube videos, maybe the problem is not on our side?Maybe less attitude and more thought before hitting the keyboard would be advisable.

author: hpibmx
author_rank: Regular Contributor
timestamp: June 10, 2022, 05:48:37 am
content: Quote from: janoc on June 08, 2022, 12:28:07 pmyes definitely next time will be more clear on my question,maybe you could tell to your self before aboutattitude!! You haven't read nor watched anything, and commenting criticizing people's knowledge!Anyway I'm done long ago before you, Big thanks to 'ledtester' so helpful with falstad simulation.kindly don't waste anyone's time.peace.