Short answer: Yes—2 MOSFETs is OK if you use a synchronous buck and your panel voltage stays above the battery voltage during charging.
What that means
Topology: A 2‑MOSFET synchronous buck (high‑side switch + low‑side synchronous rectifier) is appropriate for ~18 V panel -> 12 V lead‑acid charging. If you want to keep charging when panel voltage drops below the battery (e.g., dawn/dusk), you’d need a buck‑boost (4 MOSFETs).
Duty example: With 14.4 V absorb target from an 18 V panel, duty ≈ 0.8.
Power/current: A 500 W panel could deliver up to ≈ 41.7 A at 12 V; your 12 V 15 Ah lead‑acid typically can’t take that. Limit charge current (commonly 0.1C–0.3C ≈ 1.5–4.5 A unless your battery’s datasheet allows more).
Design tips (apply exactly as stated)
Include a switching regulator IC, an inductor, and input/output capacitors to avoid unstable or non‑functional output.
Inductor: ripple target 20–40% of full load; saturation current ≥ 1.2× peak load; low DCR and low core loss.
Example inductor for 5 A bulk at 50 kHz, 30% ripple, 18 V -> 14.4 V: about 38 µH.
MOSFETs: choose adequate VDS margin (for 18 V input, 40–60 V class is typical), low RDS(on), and thermal headroom for your limited charge current.
Lead‑acid charging: implement bulk/absorption/float with temperature compensation; add polarity protection, battery protection, and simple charge status indicators.
If you confirm your intended max charge current (e.g., 3 A, 5 A), I can size the inductor and suggest MOSFET/diode ratings and initial capacitor values accordingly.
Wirelessly connects nets on schematic. Used to organize schematics and separate functional blocks. To wirelessly connect net portals, give them same designator. #portal
General Purpose Thick Film Standard Power
and High-Power Chip Resistor
47 kOhms ±5% 0.125W, 1/8W Chip Resistor 0805 (2012 Metric) Automotive AEC-Q200 Thick Film
Features:
- RMCF – standard power ratings
- RMCP – high power ratings
- Nickel barrier terminations standard
- Power derating from 100% at 70ºC to zero at +155ºC
- RoHS compliant, REACH compliant, and halogen free
- AEC-Q200 compliant
Non-Isolated Synchronous 4-Switch Buck-Boost DC-DC Converter for PV Optimization (JKM610N-78HL4, 45.39 V @ 9.23 A MPP to 85 V, 50 kHz) with TI C2000 PI Control, Integrated Sensing, and Full Protections
Properties
A
mm
kHz
mm
mm
mm
V
mm
mm
V
mm
mm
oz
V
Diagram
Pricing & Availability
Distributor
Qty 1
Arrow
$15.09–$52.36
Digi-Key
$21.59–$86.17
LCSC
$30.48–$30.73
Mouser
$42.39–$44.72
TME
$9.03
Verical
$15.92–$54.82
Controls
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