r/Fotovoltaico_FaiDaTe

Hi everyone! I was sick of having to manage three or four different power supplies on my workbench every time. So I designed this 6-stage multi-rail linear power supply and it is running perfectly. The goal was to obtain six stable DC voltage lines plus a raw line, starting from a single standard 12V AC (11.9V RMS) laminated transformer, without having to modify or rewind the secondary.

🔍 How it works (The 6 power stages):
To make everything work with a single winding, I implemented a Delon voltage doubler in the input stage. This configuration allows me to have a total differential voltage of about 32V DC across the main filter capacitors, split into two raw symmetrical branches of about +16V and -16V relative to the central ground.

Unregulated DC Stage (~16V): Taken directly from the doubler and the beefy filter capacitors (XMM2), perfect for heavy loads or raw DC inputs.

+15V Line (LM7815 / XMM1): Ideal for analog and audio circuits. To avoid dropout problems related to the single +16V line (too low for a standard 7815), I connected the COMMON pin of the chip to the lowest negative line (-16V). In this way, the regulator "sees" all 32V at the input and pulls out a solid +15V relative to ground.

+12V Line (LM7812 / XMM6): The standard for relays, fans, and LED strips. It is connected in cascade from the +15V output, taking the central ground as reference.

+5V Line (LM7805 / XMM3): Rock-solid 5V for legacy TTL logic, sensors, and Arduino boards (or any other similar logic). It is put in cascade from the 12V regulator to distribute the thermal dissipation load over multiple components.

-5V Negative Line (LM7905 / XMM4): The secret weapon. A negative voltage regulator connected to the negative side of the Delon doubler. In combination with the +5V line, it creates a dual-line supply essential for correct bipolar biasing of operational amplifiers without virtual grounds.

+3.3V Line (LM1117-3.3 / XMM5): The latest addition! A clean LDO output in cascade from the 5V line, inserted specifically to power an entire series of ESP32 modules and modern low-consumption ARM microcontrollers.

🛠️ Notes for the physical prototype.
Mounting: Thermal dissipation: The LM7815 will undergo the greatest voltage drop (from 32V to 15V), so I will mount a dedicated and generous aluminum heatsink.

Pin isolation (CRITICAL): Since the metal tab of the LM7905 is connected to the INPUT pin (negative voltage) and NOT to ground, I will strictly use mica/silicone insulating pads to avoid short circuits if it should share the chassis or the same heatsink with the 78xx series.

Stability: I will add 100nF ceramic decoupling capacitors very close to the pins of each regulator on the real board to prevent high-frequency self-oscillations.

Here's the maximum current draw (available from the chips) I calculated for the final circuit:

~16V raw: Limited only by the diodes and transformer (great for heavy loads).

+15V line (LM7815): Max 1.5A (total). Note: Since all subsequent positive regulators are cascaded from here, the current drawn from 12V, 5V, and 3.3V will be drawn on this chip.

+12V line (LM7812): Max 1.5A (can be drawn if the 15V stage isn't already fully loaded).

+5V line (LM7805): Max 1.5A (ideal for Arduino, TTL logic, and similar).

-5V line (LM7905): Max 1.5A independent (being on the negative line of the regulator doubler, it doesn't affect the cascade of positive regulators).

+3.3V rail (LM1117-3.3): Max 800 mA (more than enough for the peak Wi-Fi transmission of the ESP32 or other Arduinos and sensors).

Cascading the 3.3V LDO from the 5V was the ideal choice for thermal reasons: the voltage jump is only 1.7V (from 5V to 3.3V). With an ESP32 drawing an average of 100-200mA, the LM1117 will need to dissipate very little heat (~0.3W), remaining remarkably cool!

Dopo aver fatto una selezione mirata, dopo test su test , ho finalmente chiuso il design dell'hardware per la scheda madre primaria della mia centralina solare.

Il sistema dovrà gestire la logica delle soglie delle batterie e commutare carichi pesanti (scaldabagno, forno, servizi, eccetera) senza bloccarsi mai, e quando dico mai, dico mai... ma non solo, requisito fondamentale, consumi a riposo vicini allo zero.

Invece di usare schede moderne già pronte, ho deciso di affiancare al mio fidatissimo core PIC16F876 una squadra di integrati eccezionali, ottimizzando i pin del PIC attraverso un bus parallelo a 8-bit condiviso a configurazione industriale.

Ecco la configurazione definitiva degli "eletti" che vedete sul tavolo:

1. 👁️ AD7582KN (Analog Devices): Un convertitore ADC industriale a 12-bit (4096 passi). Sostituisce l'ADC interno del PIC, garantendo una precisione chirurgica nella lettura dei millivolt delle batterie, eliminando i falsi scatti causati dal rumore elettrico.
2. 🎛️ MM74C154N (National Semiconductor): Decoder/Demultiplexer da 4 a 16 linee in pura tecnologia CMOS. Con soli 4 pin del PIC gestisco i segnali di Chip Select (CS) di tutte le periferiche con un consumo statico pari a zero.
3. 💾 6x Hitachi HM62256LP-12: Due SRAM statiche da 32 KB ciascuna (192 KB totali) in versione Low Power. Servono come macro-buffer per calcolare medie mobili stabili sulle letture dei pannelli ed evitare che i relè "ballino" quando passano le nuvole.
4. 💪 M82C55A (OKI): L'interfaccia periferica programmabile (PPI) in tecnologia CMOS. Gestisce i 24 pin di I/O digitali dedicati interamente a pilotare le schede relè optoisolate per scaldabagno, forno e servizi, luci giardino eccetera...
5. 🗃️ ATmega16 (Il Guardiano / Scatola Nera): Collegato ai pin RX/TX del PIC 16F876, questo chip a 40 pin fa da supervisore indipendente. Il PIC gli invia continuamente i log degli eventi e lo stato dei carichi. L'ATmega memorizza tutto e monitora il PIC tramite un Watchdog seriale. Se il PIC si blocca a causa di un forte disturbo elettromagnetico generato dai teleruttori, l'ATmega interviene, isola i relè di potenza per sicurezza e resetta forzatamente il PIC, ripristinando i dati di configurazione al millisecondo precedente al crash.

La telemetria verso l'esterno è delegata a un ESP32 (collegato all'ATmega), che gestisce solo il WiFi. Se lo stack di rete dell'ESP si blocca, la logica di controllo e la scatola nera hardware rimangono isolate e totalmente operative.