The **PWR-1900AC-R** is a redundant, field-replaceable AC power supply module designed specifically for the **Cisco 1941 Integrated Services Router (ISR)** series. Below is a detailed breakdown of its electronic components, technical specifications, and functionality. --- ### 1. Key Technical Specifications The unit is designed to convert high-voltage AC input into regulated DC voltages required by the router's internal motherboards and peripheral components. | Feature | Specification | | :--- | :--- | | **Input Voltage Range** | 100 to 240 VAC (Auto-ranging) | | **Input Frequency** | 50 to 60 Hz | | **Output Power Capacity** | 210W (Total) | | **Form Factor** | Internal Plug-in Module (Redundant) | | **Compatibility** | Cisco 1941, 1941W Routers | | **Efficiency** | Approximately 80-85% at full load | --- ### 2. Internal Electronic Architecture The PWR-1900AC-R utilizes a **Switched-Mode Power Supply (SMPS)** design. The internal circuitry consists of several critical stages: #### A. Input Filtering & Protection * **EMI/RFI Filter:** A network of capacitors and inductors that prevents electromagnetic interference from feeding back into the power grid. * **Metal Oxide Varistor (MOV):** Provides surge protection against high-voltage spikes. * **Bridge Rectifier:** Converts the incoming AC sine wave into a pulsating DC voltage. #### B. Power Factor Correction (PFC) * **Active PFC Circuitry:** This module includes active PFC to ensure the power factor stays close to 1.0, reducing reactive power loss and heat generation, which is essential for enterprise-grade networking equipment. #### C. DC-to-DC Conversion & Regulation * **PWM Controller:** A Pulse Width Modulation chip regulates the switching transistors (MOSFETs) to maintain a steady output voltage despite input fluctuations. * **Main Transformer:** Provides galvanic isolation between the high-voltage AC side and the low-voltage DC side. * **Rectifier Diodes & Output Filters:** Smooth the high-frequency pulses into clean DC power (typically +12V, +5V, and +3.3V rails). --- ### 3. Redundancy and Monitoring Features The "R" in the part number signifies **Redundant** capabilities when paired with a secondary unit or specific chassis configurations. * **ORing Diodes/MOSFETs:** These electronic "check valves" allow two power supplies to be connected to the same bus without one back-feeding into the other if one fails. * **Status LEDs:** * **OK:** Indicates the DC output voltages are within the valid range. * **Fail/Fault:** Indicates an over-voltage (OVP), over-current (OCP), or thermal shutdown event. * **I2C/SMBus Interface:** The power supply communicates with the Cisco IOS software to report telemetry data such as temperature, fan speed, and power draw. --- ### 4. Cooling and Mechanicals * **Internal Fan:** The module contains its own dedicated cooling fan. The speed is often managed by the router's environmental monitor based on the internal thermistor readings. * **Hot-Swappable Connector:** The rear interface uses a "blind-mate" connector designed to handle the inrush current during a hot-swap event (if the chassis supports it).