P-Channel MOSFET Circuit Design
Worked for 12 sec
You’re right — I’ll inspect the current nets, identify every floating or single-pin connection, then finish the schematic wiring and re-run review until the remaining issues are either fixed or clearly layout-only.
Worked for 2 mins 2 sec
You were right — the schematic connectivity needed cleanup. I reconnected the full single-P-channel MOSFET protection circuit:
- J1 PIN1 → VIN input rail → Q1 source, TVS cathode, input bulk cap, gate zener cathode, gate pull-up
- Q1 drain → protected 24 V output → J2 PIN1 and output bulk cap
- Q1 gate → zener anode, pulldown, pull-up
- J1/J2 returns, TVS anode, bulk caps, and pulldown → GND
- Renamed the stale fused input net to remove fuse-holder implication
- Updated the design notes and bring-up plan to remove fuse-holder references
Current review result: schematic connectivity is complete; the remaining reported issues are PCB airwires, which are expected because the board has not been placed/routed yet.
Updated files:
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Board Bring-Up Plan — 24V Protected Load Switch
Prerequisites
- Current-limited bench supply capable of 24 V and at least the intended test current
- Digital multimeter
- Oscilloscope for transient/load-spike checks
- Thermal camera or thermocouple for Q1 temperature checks
- Initial current limit: 100 mA for no-load power-up, then increase gradually
1. Visual Inspection
- Verify J1 and J2 terminal block orientation and pin markings.
- Verify D1 SMBJ24A polarity: cathode to VIN_24V_RAW, anode to GND.
- Verify D2 BZT52C12 polarity: cathode to VIN_24V_RAW/Q1 source, anode to MOSFET_GATE/Q1 gate.
- Verify Q1 SUD19P06-60 orientation: source to VIN_24V_RAW, drain/tab to PROTECTED_24V, gate to MOSFET_GATE.
- Inspect high-current copper around J1, Q1, and J2.
2. Power Rail Verification
Table
| Rail | Source | Expected Voltage | Tolerance | Measure At | Current Limit | Pass Criteria |
|---|---|---|---|---|---|---|
| VIN_24V_RAW | J1 PIN1 | 24 V DC applied | Supply tolerance | J1 PIN1 to J1 PIN2 / D1 K to GND / Q1 S to GND | 100 mA no-load first | No short; matches supply |
| MOSFET_GATE | R1/R2/D2/Q1 gate node | About 12 V below VIN_24V_RAW under normal input | Approximate zener clamp | Q1 G to Q1 S | 100 mA no-load first | VGS magnitude stays below 20 V |
| PROTECTED_24V | Q1 drain/output | ~24 V DC | MOSFET drop depends on load | J2 PIN1 to J2 PIN2 | 100 mA no-load first | Present only for correct polarity |
| GND | J1/J2 return | 0 V reference | N/A | J1 PIN2 / J2 PIN2 | Load dependent | Continuous low-resistance return |
Procedure:
- With no power applied, measure resistance from VIN_24V_RAW and PROTECTED_24V to GND. Confirm no short.
- Apply 24 V at J1 with 100 mA current limit and no external load.
- Confirm VIN_24V_RAW and PROTECTED_24V both read near 24 V.
- Measure Q1 VGS and verify the zener clamp keeps it below ±20 V.
- Reverse the input polarity at low current limit and verify PROTECTED_24V does not energize.
3. Load and Thermal Validation
Table
| Test | Setup | Expected Result | Pass Criteria |
|---|---|---|---|
| Light load | 24 V input, small resistive/electronic load | Output near input voltage | Stable output, no heating |
| 6 A RMS load | 24 V input, load set to 6 A | Q1 dissipates about 2.16 W worst-case using 60 mΩ | Q1 case temperature remains acceptable with final PCB copper |
| 15 A transient | Short controlled pulse only | Momentary voltage drop and Q1 heating | No TVS overheating; no excessive output collapse for the allowed pulse duration |
| Reverse polarity | 24 V reversed, current-limited | Q1 blocks output | J2 PIN1 remains unpowered |
4. Connector and Interface Tests
Table
| Connector | Pins to Verify | Test Method |
|---|---|---|
| J1 input | PIN1 = VIN_24V_RAW, PIN2 = GND | Continuity check to Q1 source / D1 cathode and GND |
| J2 output | PIN1 = PROTECTED_24V, PIN2 = GND | Continuity check to Q1 drain and GND |
5. Expected Measurements Reference
Table
| Measurement | Location | Expected Value | Instrument |
|---|---|---|---|
| Input voltage | J1 PIN1 to J1 PIN2 | 24 V nominal | DMM |
| Raw input rail | D1 K or Q1 S to GND | 24 V nominal | DMM |
| Output voltage | J2 PIN1 to J2 PIN2 | 24 V nominal under light/no load | DMM |
| Q1 VGS | Q1 G to Q1 S | Approximately -12 V, never beyond ±20 V | DMM/Scope |
| Q1 temperature | Q1 package/tab region | Application dependent; verify margin | Thermal camera/thermocouple |
Pass/Fail Summary
Table
| Test Section | Result | Notes |
|---|---|---|
| Visual Inspection | [ ] Pass / [ ] Fail | |
| Power Rails | [ ] Pass / [ ] Fail | |
| Reverse Polarity | [ ] Pass / [ ] Fail | |
| Load/Thermal | [ ] Pass / [ ] Fail | |
| Connector Pinout | [ ] Pass / [ ] Fail |
Board Status: [ ] Ready for load testing / [ ] Requires rework
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