The Appeal Of Low-noise Amplifier
페이지 정보
본문
I go into a bit more detail about MPPT in a post from a few weeks ago, but what matters this week is that a MPPT charge controller is fundamentally a variable buck (or, occasionally, boost) converter. The most common way of doing buck or boost conversions is with inductors, capacitors, a switch, and a diode. Each inductor is paired with a capacitor, as should be expected for a buck converter. Its a 60MHz capable 32-bit microcontroller with some analog-digital converters (voltmeters) and some high resolution, high frequency PWM (pulse width modulated) outputs that are perfect for driving things like buck converters. The inductors and capacitors, plus some switching transistors and diodes on the other side, make up a set of buck converters. If youre playing along at home, the top side has the inductors and capacitors, which means the bottom side must have the switching transistors and diodes. I cant decide if the top of this board is hand soldered or poorly machine soldered.
If I had to bet, though, Id say it was hand low-noise amplifier soldered, or at the very least, hand reworked after a machine went through. Id originally assumed that it was machine soldered on the top, but looking at it closer, theres a good chance its hand soldered. Theres a lot of flux residue on the board as well, and the microcontroller pins really look hand soldered to me (they remind me very much of the surface mount rework Ive done). Look at the picture below. What does a $150 Chinese MPPT unit look like on the inside? I probably wont have to replace these capacitors like I have with some electrolytic ones on an old mainboard. Plus, they dont dry out like electrolytic capacitors tend to do. Its always interesting to see what chip is used to control various devices, but this chip looks very well suited to being the brains of a MPPT unit like this. Which, I promise, doesnt go as well with Wizard of Oz as it sounds like it should. Things like the 103 chips in the lower left being flipped relative to each other, and the uneven solder blob size on the surface mount components makes me wonder.
This isnt a dirt cheap unit that would be using fake components. Using the whole case as a heatsink is a really good idea, though one might want to avoid mounting it firmly against a wall. The screws are actually well placed - they run through the switching transistors and help keep them pressed to the back of the case as a heatsink. Removing the board from the case is pretty simple: Remove all the screws. Remove the rubber plug in the firewall, next to the brake servo unit, and feed through the vacuum servo cable which attaches to the accelerator pedal assembly. Norbert Lehmann, seems very interested in equipping its products with better AC cords and I hope ANY HiFi designer in the World will start thinking at the mains cable like a COMPONENT of the unit itself which does affect the overall performance. These will make it more difficult for the amateur (and me) to assemble the board, but especially to service it. Theyre probably JTAG-ish, and with the right interface, you might be able to debug the unit, but reverse engineering a Chinese charge controller blind is a bit more effort than I really feel like putting in at this point.
A pair of electrolytic filter capacitors at either end are there to smooth the power out (theyre quite beefy units), and then there are some control electronics and a few transformers in the center, with a few connections for the controls on the lid. They took 10BASE-T and ISDN and ziptied them together, and then they put Iso in front of the name of everything. By rapidly switching how the circuit is configured (something, say, a high frequency PWM output is perfect for), these can convert a high voltage input into a lower voltage, higher current output (exactly what we want here). I did go ahead and convert my EasyEDA schematic into a PCB through JLCPCB. Bipolars are generally better when it comes to input voltage offset, and often have lower noise. The unit is rated for a maximum PV input voltage of 190V - and heres a 200V rated capacitor on the input side. This is a really, really good sign for something that claims to be a MPPT unit - and makes me believe that it actually is going to do the power conversion. Nothing too exotic so far, but definitely not just a rebadged PWM unit. A PWM charge controller, while far cheaper, doesnt do power conversion.
If I had to bet, though, Id say it was hand low-noise amplifier soldered, or at the very least, hand reworked after a machine went through. Id originally assumed that it was machine soldered on the top, but looking at it closer, theres a good chance its hand soldered. Theres a lot of flux residue on the board as well, and the microcontroller pins really look hand soldered to me (they remind me very much of the surface mount rework Ive done). Look at the picture below. What does a $150 Chinese MPPT unit look like on the inside? I probably wont have to replace these capacitors like I have with some electrolytic ones on an old mainboard. Plus, they dont dry out like electrolytic capacitors tend to do. Its always interesting to see what chip is used to control various devices, but this chip looks very well suited to being the brains of a MPPT unit like this. Which, I promise, doesnt go as well with Wizard of Oz as it sounds like it should. Things like the 103 chips in the lower left being flipped relative to each other, and the uneven solder blob size on the surface mount components makes me wonder.
This isnt a dirt cheap unit that would be using fake components. Using the whole case as a heatsink is a really good idea, though one might want to avoid mounting it firmly against a wall. The screws are actually well placed - they run through the switching transistors and help keep them pressed to the back of the case as a heatsink. Removing the board from the case is pretty simple: Remove all the screws. Remove the rubber plug in the firewall, next to the brake servo unit, and feed through the vacuum servo cable which attaches to the accelerator pedal assembly. Norbert Lehmann, seems very interested in equipping its products with better AC cords and I hope ANY HiFi designer in the World will start thinking at the mains cable like a COMPONENT of the unit itself which does affect the overall performance. These will make it more difficult for the amateur (and me) to assemble the board, but especially to service it. Theyre probably JTAG-ish, and with the right interface, you might be able to debug the unit, but reverse engineering a Chinese charge controller blind is a bit more effort than I really feel like putting in at this point.
A pair of electrolytic filter capacitors at either end are there to smooth the power out (theyre quite beefy units), and then there are some control electronics and a few transformers in the center, with a few connections for the controls on the lid. They took 10BASE-T and ISDN and ziptied them together, and then they put Iso in front of the name of everything. By rapidly switching how the circuit is configured (something, say, a high frequency PWM output is perfect for), these can convert a high voltage input into a lower voltage, higher current output (exactly what we want here). I did go ahead and convert my EasyEDA schematic into a PCB through JLCPCB. Bipolars are generally better when it comes to input voltage offset, and often have lower noise. The unit is rated for a maximum PV input voltage of 190V - and heres a 200V rated capacitor on the input side. This is a really, really good sign for something that claims to be a MPPT unit - and makes me believe that it actually is going to do the power conversion. Nothing too exotic so far, but definitely not just a rebadged PWM unit. A PWM charge controller, while far cheaper, doesnt do power conversion.