Anti-backflow protection prevents such a reverse current failure and allows the healthy supplies to maintain the DC bus or to shut down gracefully if at over-current. Power ORing is the preferred anti-backflow method of protecting parallel DC supplies. Power ORing combines the current from multiple supplies while preventing any reverse current.
For decades, engineers have relied on Schottky or p-n diodes for reverse-current protection. However, as current demands increase and efficiency targets tighten in telecom, data center, and industrial DC distribution, designers are increasingly turning to more efficient active ORing solutions built around MOSFETs and ideal diode controllers.
Diode ORing: Simple Design with Higher Conduction Loss
A diode ORing circuit places a diode in series with each source, with cathodes connected at the common output. Each diode conducts when its source voltage equals or exceeds the bus and blocks reverse current if its source falls below the bus voltage. This simple design works well in low-power and/or cost-sensitive systems.
The downside is power loss. Schottky diodes typically exhibit a forward voltage drop of 0.35V to 0.6V at rated current. P-N diodes can drop more than 1V. This voltage drop translates to direct power loss. At 10A, for example, a 0.45V Schottky will dissipate 4.5W on a 5V rail. That’s a 9% efficiency loss from the protection circuit alone. As current scales, loss increases linearly, raising the thermal burden.
Larger packages, copper pours, or forced air become necessary to keep junction temperatures in check. Each thermal mitigation step increases the cost, occupies board space, and adds potential failure points. Moreover, diode ORing solutions offer limited or no diagnostic visibility, as a degraded or shorted device usually goes undetected until the redundant power supply path is required.
Active ORing: MOSFET-Based Reverse Current Protection
Active ORing replaces each diode with an N-channel MOSFET driven by an ideal diode controller. The controller monitors the drain-to-source voltage (VDS) and keeps the MOSFET fully on while its source is supplying power. It switches it off rapidly in the event of a reverse current fault.
The MOSFET’s power loss comes from its RDS(on) parameter, rather than a specific voltage drop across the diode. Therefore, conduction loss is dramatically lowered. For example, a power MOSFET with 3mΩ RDS(on) carrying the same 10A as the Schottky dissipates only 0.3W and produces a forward drop of about 30mV. That is more than an order-of-magnitude improvement. Lower conduction loss directly improves thermal headroom, which reduces heat sink and airflow requirements, frees up board space, tightens rail regulation, and enables higher current handling. Active ORing also enables automated fault detection and alerting.
Key benefits of Active ORing:
- Significantly lower voltage drop
- Automated fault detection and alerting
- Superior thermal performance
Ideal Diode Controllers for Efficient Power Path Control
The ideal diode controller is crucial in every active ORing solution. It emulates near-perfect diode behavior by regulating the MOSFET’s gate to deliver minimal forward voltage drop (typically 15mV to 30mV at light load). Most active ORing controllers, including the RECOM
RACPRO1-RD series, feature:
- Fast reverse-current detection and turn-off (100-200 ns typical)
- Low forward voltage drop (15mV to 140mV typical)
- Undervoltage and overvoltage protection
- Status outputs and reverse-current fault flags
- Optional periodic MOSFET health checks
The fast response time delivers robust performance in the face of sudden source loss, hot-plug events, and downstream faults. Active ORing delivers fast, efficient protection, with diagnostics and lower losses than diode ORing.
Side-by-Side Comparison of Active ORing vs. Diode Oring
| Forward voltage drop |
0.35V to 0.6V at rated current |
15mV to 140mV, scales with current |
| Power dissipation at 10A |
~4.5W |
~0.3W |
| Thermal management |
Heat sink and airflow are typically required |
Passive cooling often is sufficient |
| Reverse current turn-off |
Tens to hundreds of nanoseconds |
~100ns to 200ns plus FET delay |
| Fault diagnostics |
None native |
Status pin, flags, optional self-check |
| Component count |
One diode per source |
Controller + MOSFET per channel, or self-contained module (RD40) per two sources |
| Best fit |
Low-power, cost-sensitive, low-current rails |
High-current, high-efficiency redundant systems |
Table 1: Comparing Diode ORing with Active ORing
Choosing the Right DC Anti-Backflow Strategy
Modern datacenters, telecom installations, and industrial complexes require the maximum possible efficiency from power supply equipment. Hundreds or thousands of unit deployments amplify the efficiency-derived power savings. MOSFET-based active ORing is the right choice for these settings. For low-current consumer or instrumentation rails, where a few hundred mW of loss is inconsequential and board area is plentiful, a Schottky diode is often still the right answer.
RECOM RACPRO-1 Redundancy Module
The
RACPRO1 redundancy module integrates a pair of MOSFETs with control circuitry configured as high-efficiency gating diodes. At 40A, the RACPRO1-RD40 produces 5W of conduction loss compared to roughly 18W loss from an equivalent Schottky ORing circuit.
Key Specifications:
- Wide input voltage range: 9-56V (nominally 12/24/48V)
- 20A per channel in N+1 redundant operation (where one redundant supply is added to N supplies, all sized for full load)
- 40A continuous (60A peak for 5s) in parallel current-sharing mode
- Maximum forward voltage drop: 140mV at full load
- ~99.5% efficiency at 40A
- Convection cooled from -40°C to +70°C
- No-load power consumption of ~200-400mW
The
RACPRO1-RD40 module also features a 43mm DIN-rail width, tool-less mounting, and 25° push-in connectors. As a result, the redundancy stage can drop into an existing panel without dedicated copper, custom fasteners, or a separate thermal solution. This module is certified to IEC/EN/UL/CSA 62368-1 with EN 61000-6-4 Class B emissions and EN 61000-6-2 immunity.
