Reverse Polarity Circuit Fix
1:34
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U1
U2
V1
Below is a suggestion to update your schematic with the additional EMI filtering components for CISPR 25 compliance on both the power and signal domains. The changes include:
-
Power Input EMI Filtering:
- Common Mode Choke ([CM1]):
• Insert a common mode choke in series with the output of the PTC fuse ([PTCCL05H181DBE U1]).
• This choke will filter common-mode noise from the power supply. - RC Filter ([R2] and [C2]):
• Place a resistor ([R2]) in series after [CM1] and connect a capacitor ([C2]) from the node following [R2] to Ground.
• This RC low-pass filter attenuates high-frequency noise on the power rail before it reaches your load. - TVS Diode ([TVS3300DRV U2]):
• Connect the TVS diode’s IN terminals to the EMI-filtered power rail (i.e. the node after [R2]/[C2]) and its GND terminals to system Ground.
• It will clamp voltage spikes (load dump conditions) without interfering with normal operation.
- Common Mode Choke ([CM1]):
-
Signal Line EMI Filtering:
- Ferrite Beads (e.g. [FB1]):
• On any sensitive signal lines leaving or entering the load, add a ferrite bead in series.
• This bead reduces high-frequency interference on those lines. - Optional RC Filters:
• If further attenuation is needed, small RC filters can be added on signal lines.
- Ferrite Beads (e.g. [FB1]):
-
Retention of Existing Protections:
- The PTC fuse ([PTCCL05H181DBE U1]) remains on the input side to protect against reverse polarity and overcurrent situations.
- The DC Supply ([V1]) continues to supply power, with its negative terminal ([V1 CATHODE]) tied directly to Ground via the proper Ground component.
Summary of Proposed Schematic Changes:
Table
| Component/Node | Current Setup | Suggested Revision |
|---|---|---|
| V1 (DC Supply) ANODE | Connected to [PTCCL05H181DBE U1] | No change – continue feeding the PTC fuse input with V1 ANODE |
| [PTCCL05H181DBE U1] | In-series PTC fuse for reverse polarity protection | No change – remains in series. Its output (pin 2) now feeds into the EMI filtering chain |
| [CM1] (Common Mode Choke) | Not present | Add a common mode choke in series between the output of [PTCCL05H181DBE U1] and the EMI-filtered power rail |
| [R2] and [C2] (RC Filter) | Not present | Add [R2] in series after [CM1] and then [C2] connected from the node after [R2] to Ground. This RC network further attenuates high-frequency noise on the power rail |
| [TVS3300DRV U2] | Connected across the load (post fuse) | Connect the IN terminals of [TVS3300DRV U2] to the filtered power rail (after the RC network) while keeping its GND terminals tied to Ground – ensuring it clamps transient spikes (load dump) effectively |
| Signal Lines | Not filtered | For any sensitive signal paths, add a ferrite bead (e.g. [FB1]) in series. Optional RC networks might also be added if further filtering is desired |
| V1 (DC Supply) CATHODE | Tied to Ground | Remains connected to Ground using the Ground component |
How This Works:
- Protection:
- The PTC fuse limits currents during reverse polarity or overcurrent events, shielding both the TVS and downstream load.
- The TVS diode remains quiescent under normal conditions but clamps voltage transients (load dump) on the filtered power rail.
- EMI Filtering:
- The common mode choke and RC filter work together to suppress high-frequency noise on the supply line.
- Signal lines are further cleaned up by adding ferrite beads (and optionally RC filters) to comply with CISPR 25 requirements.
You can use the Apply changes button to update your project schematic with these adjustments.
348 days
0:20
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Project
The changes I described are currently only suggestions. They haven't been applied to your schematic yet. Please click the Apply changes button to update the schematic with the new EMI filtering components and connections.
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348 days
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R1
Resistance
12 Ω
V1 ANODE - U1 2
V1 ANODE - U1 2
U1
V1 ANODE - U1 2
V1
U2
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