Implementing a DC/DC Single-Ended Forward Converter with the NCP1216A - Application Note

Oct 12, 2026

Explains how to use the NCP1216A controller to design a DC/DC single-ended forward converter for telecommunication needs, outlining electrical requirements such as 36–72 VDC input, >30 W continuous output power for a 12 V output, compact PCB footprint, >85% efficiency, and 1500 V input-to-output isolation. Details why NCP1216A is suitable, covering 50% maximum duty cycle, Dynamic Self-Supply, 500 mA peak current capability, current-mode control, direct optocoupler feedback, low no-load power, and short-circuit protection. Provides converter connection description and design considerations including transformer operation principles.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages10

Reading Time25 min

AccessFree to download

Requirements and application overview

Key features of the NCP1216A controller

35 W DC/DC converter board specifications

Converter connection description

Input filter and primary clamping

Primary current sensing and switching stages

Isolated feedback and output regulation

Output filtering and snubber network

Design considerations

Transformer design principles

AND8161/D Implementing a DC/DC Single-Ended Forward Converter with the NCP1216A Prepared by: Roman Stuler APPLICATION NOTE This document describes how the NCP 1216A controller can be used to design a DC/DC single−ended forward converter suitable for telecommunication applications. The requirements for the converter are as follows: − Input voltage range from 36 V to 72 VDC − Continuous output power greater than 30 W for a 12 V output voltage − Small PCB dimensions − Efficiency greater then 85% − Input to output isolation voltage of 1500 V The NCP1216A controller is an attractive solution for this application, due to the following features: • 50% Maximum Duty Cycle Operation Forward converters usually limit the maximum duty cycle to 50% . Since the voltage reset is constrained tobe equal to the input voltage (1:1 reset ratio), it is not desirable to exceed 50% DC to avoid saturating the transformer core. • No Auxiliary Winding Operation The DSS (Dynamic Self−Supply) function allows the NCP1216A derive power directly from the HV line without having to supply V CC either from the secondary output inductance (creepage distance and isolation issues) or via an auxiliary winding delivering a variable voltage of N x Vin. • 500 mA Peak Current Capability The NCP1216A can drive a MOSFET directly without any additional driver stage. If the selected MOSFET gate charge would overload the DSS capability, then an auxiliary winding could be used solely to supply the driver pulses. • Current−Mode Operation Cycle−by−cycle primary current monitoring eliminates any overcurrent situations, e.g. resulting from a secondary short−circuit. • Direct Optocoupler Connection In applications where the input to output isolation is required, a direct connection eases the design stage, saving external components. • Extremely Low No−Load Power Consumption Extremely low consumption in no−load operation is a great advantage of the NCP1216A controller. Today’s maximum stand−by consumption standards can be easily met if this function is used. • Short−Circuit Protection By monitoring the activity on the feedback line, the NCP1216A simplifies the task of secondary side short−circuit protection. Coupling problems are eliminated thanks to this feature and the DSS implementation. The 35 W DC/DC Converter Board Specifications The schematic of the proposed converter is shown in Figure 1. This converter has the following specifications: Minimum Input Voltage Maximum Input Voltage Output Voltage Continued Output Current Operating Frequency No−load Consumption at 48 V Maximum Ambient Temperature 36 VDC 72 VDC 12 VDC 3.0 A 100 kHz 1.8 mA 70°C 􀁗 Semiconductor Components Industries, LLC, 2004 May, 2004 − Rev. 0 1 Publication Order Number: AND8161/D [http://onsemi.com](http://onsemi.com) 2 F igure 1. +12 V AND8161/D AND8161/D Description of Converter Connection Capacitors C1, C2, C3 and inductor L1 form the input filter. Diode D3, capacitor C5 and resistor R5 provide the primary clamping network which combats leakage inductance between the reset winding and the primary winding. The link between both windings occurs via D2 when the switch is off. Transformer T2 with diode D1 and resistors R2, R3 serve as the primary current sensing circuit. Thanks to low insertion losses, the final efficiency of the converter benefits greatly from this configuration. IC1 is the main driving circuit of the power converter. The secondary circuitry has D4A as the forward diode and D4B as the freewheeling diode. Capacitor C6 offers a path for common−mode (CM) currents circulating via the various transformer stray capacitances during switching events. Resistors R7, R8, R9, and R10 together with capacitor C12, shunt regulator IC3, and optocoupler IC2 form an isolated feedback circuit for output voltage regulation. A snubber network (R6, C7) is connected across inductor L2 in order to damp high frequency oscillations

FAQs

What input and output specifications must the forward converter meet?

The converter targets an input range of 36–72 VDC and a 12 V output delivering continuous power greater than 30 W. The design also targets high efficiency (>85%) and 1500 V input-to-output isolation.

Why is the NCP1216A suitable for this single-ended forward converter application?

It supports 50% maximum duty cycle operation, uses Dynamic Self-Supply to derive power directly from the HV line, can drive a MOSFET with 500 mA peak current capability, and offers current-mode primary current monitoring and short-circuit protection via feedback activity.

How does the document describe transformer magnetization and core flux reset?

It explains that applying Vin on the primary side ensures core magnetization and flux linkage, using Faraday’s law to relate generated voltage to turns and flux. When the switch is off, the transformer core must be reset using a dedicated reset circuit so internal flux returns toward zero.

Oct 12, 2026

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