How it works
Gate voltage creates a conducting channel. Once fully enhanced, a MOSFET acts approximately as a resistance; during switching it also charges capacitances and overlaps voltage with current. Planar, trench and shielded/split-gate designs trade conduction loss, switching charge and ruggedness differently. “Low voltage” is a catalog convention, so begin with the real bus and surge envelope.
The gate driver charges and discharges the MOSFET gate. Gate charge, drive voltage and loop inductance affect switching.
Parameters that matter
- Voltage stress
- VDS must cover the worst bus plus measured overshoot. Repetitive avalanche is not an automatic substitute for a clamp.
- Hot on-resistance
- Compare maximum RDS(on) at the actual VGS and hot junction. Threshold voltage only marks the onset of tiny test current; it is not a full-on drive voltage.
- Charge and recovery
- Qg/Qgd, Qoss and body-diode Qrr affect different loss mechanisms. Their test voltage, current and temperature must match the comparison.
- Thermal and SOA limits
- ID at a fixed case temperature is not a PCB current promise. Check SOA for startup/linear operation and transient thermal impedance for pulses.
A worked selection example
Illustrative calculation · not a product guarantee
Estimate two losses in a 24 V motor stage
Assume a rectangular 10 A current pulse at 50% duty. Hypothetical device inputs: hot RDS(on) = 8 mΩ at the real gate drive, Qg = 40 nC, gate swing = 10 V, switching frequency = 20 kHz. These are not measured specifications of a named part.
- Conduction loss is I² × RDS(on) × duty = 10² × 0.008 × 0.5 = 0.40 W.
- Gate-drive power per device is Qg × Vg × f = 40 nC × 10 V × 20 kHz = 8 mW.
- Do not treat 8 mW as total switching loss, or assume all gate-drive power is dissipated inside the MOSFET.
- Measure drain overshoot, dead-time body-diode conduction and temperature. Include switching and other losses before choosing the voltage class and package.
The calculations separate conduction and gate-drive budgets. They do not replace switching-waveform, SOA or board-thermal verification.
Where it fits
Suitable starting points
- Battery protection, low-voltage motor bridges, synchronous rectification and DC/DC switching.
Where to take extra care
- A switching-optimized device may be unsuitable for prolonged linear current limiting. Do not infer a 3.3 V gate rating from a low VGS(th).
Series directions to investigate
Investigate Silan planar/trench/split-gate lines and JSMC below-200-V catalog families. DFN/QFN-style power packages suit compact layouts; DPAK/TO-263 and leaded TO packages suit other thermal/mechanical constraints. Verify footprint, exposed-pad net and pin order.
What Chinese suppliers can offer
Where the opportunity lies
The concrete opportunity is several silicon processes and package routes for cost/thermal optimization in familiar battery and motor voltage ranges. Ask vendors to price the same electrical acceptance window and test workload; a lower unit quote can disappear after driver, copper and heatsink changes.
What still needs evidence
Confirm the exact manufacturing source, current datasheet, sample results and commercial terms before placing an order. Series availability does not establish qualification for your application.
Questions for the supplier
- 01
Hot RDS(on) and gate-charge curves at comparable drive conditions.
- 02
SOA/avalanche test details; exact die/package revision, leadframe and marking traceability.
- 03
Double-pulse or actual motor-bridge waveforms, PCB thermal result and change-notification terms.
Technical references
These references support the principles and catalogue directions discussed here. Public documentation is a different evidence level from a supplier reply, a lot document or an independent test. This guide does not claim those later stages have been completed.
- 1. Understanding MOSFET datasheets
- 2. Power Loss in Switching Power Supplies
- 3. Designing with power MOSFETs
- 4. Product catalog
- 5. MOSFET below 200 V selector
These guides explain selection principles. Final decisions require the current datasheet for the exact ordering code, operating conditions and appropriate application testing.