| Electronics > Projects, Designs, and Technical Stuff |
| My Very first fully custom PCB looking for Schematic Input and maybe any errors. |
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| jaycee:
--- Quote from: poorchava on May 14, 2020, 08:38:08 am ---I don't recommend the LM2575. Yes, they are jellybean and are made by countless Chinese companies. I would recommend something more modern. The likes of TI, Diodes, Microchip, ST, NXP, ONsemi each offer loads of integrated synchronous switch mode regulators. Most of them require only input and output caps, feedback resistors (or not if u use a fixed version) an inductor and sometimes a bootstrap capacitor. --- End quote --- Thats pretty much all the LM2575 requires. Whats the problem with using them ? |
| SirAlucard:
--- Quote from: jaycee on May 14, 2020, 03:54:35 am --- --- Quote from: SirAlucard on May 14, 2020, 03:36:49 am ---ok, so a little bit more detailed information.The power draw on the 5v rail is max 234mAh, with my source voltage set to 13.7 max draw with everything connected is 380mAh. Without any solenoids connected it only draws 45mAh to power the ATMEGA and an led on the 5v rail. My main focus right now is to try to get rid of as much heat as I can, cause this is meant to be a controller you can hold, so it can't be running hot. Which I realize now, I should have gone with a switching regulator. Does anyone have a suggestion as to which to use? Or have experience with one they like. Would the best course of action be to get a single 5v switching regulator? or a regulator that has dual output of 12v and 5v? I'm really quite lost in the vast quantities of options. --- End quote --- Does the 12V rail really need regulating if you are using 13.8V input ? Your 12V regulator is also having to deal with the current drawn by the 5V rail, due to how you have put the two regulators in series. The 5V regulator doesnt need to be LDO as you have quite a head of voltage. As for what regulator to use, LM2575 - about as simple as you get, available in fixed 5v versions. --- End quote --- Yes, for the application that I'm using it for it does, I require the motor to be at a constant and controllable speed. This would be for something that can be used in the car and in the home, so especially in the car when the voltage can varry I want my 12v rail to be constant. Which is why I added a motor controller, so that the only way the motor speed changes is if a pot was turned to change it. |
| Buriedcode:
--- Quote from: SirAlucard on May 15, 2020, 09:24:21 pm ---Yes, for the application that I'm using it for it does, I require the motor to be at a constant and controllable speed. This would be for something that can be used in the car and in the home, so especially in the car when the voltage can varry I want my 12v rail to be constant. Which is why I added a motor controller, so that the only way the motor speed changes is if a pot was turned to change it. --- End quote --- Generally, for fixed, repeatable, speed, some sort of feedback is used with a control loop which greatly increases complexity in terms of software.. Relying on power voltage, is perhaps one way, but a car's battery can drop below 12V, and go significantly higher than it (its a bit of a nightmare). An LDO is all well and good, but it will still require some headroom - as well as a possible input diode because a car's power supply will happily destroy an LDO without adequate protection. What is the current this motor needs? The motor driver you have is rated for 3A (3.5A max) so we can assume it is much lower than that. That's good, because there are 3A and 5A LDO's, but if you're drawing say 2.5A from the motor regularly, and your LDO - assuming your input voltage is high enough - drops 1V that still 2.5W of heat that has to go somewhere. A switched mode supply, can solve multiple issues (power input voltage variation, using buck/boost, sufficient output current, more efficient etc..) but adds more complexity. It can't hurt to try one of the cheapo "simple switchers" and test if it can keep the motors speed fixed with varying input voltage, but beware the advertised current rating on prebuilt modules, often they are just lies. As you've found the sheer vast number of switching controllers/devices is daunting, even when you narrow it down by package, type (buck, boost, buck/boost) and current rating. It can also be quite critical in terms of layout. But there are ones that only require an inductor and IO caps that shouldn't be difficult to add to your PCB. |
| wraper:
LDO circuit is totally wrong. Instead of connecting a capacitor directly to the output as shown in the datasheet, for some reason there are inductors in series. This circuit likely will be unstable and may oscillate. D1 and D2 have little use, especially connected before those stupid inductors. If you want protection, place TVS diodes onto power rails. Also I don't think that dumping voltage spikes through D4 and D5 into unprotected 5V rail is such a great idea. 680nF/10k values for C8/R8 snubber make no sense. |
| bson:
--- Quote from: jaycee on May 14, 2020, 03:45:23 am ---What happens if they get stalled ? You'll probably find the current goes a lot higher, and your MMBT3904's will evaporate. Look for something in a SOT-89 or SOT-223 package. --- End quote --- My experience breadboarding with TO-92's is they don't even evaporate. They get slightly warm, then turn into diodes without smoke or other warnings... |
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