Isolated DC/DC Converters: Implement a Discrete Solution or use an Integrated Module?

RECOM provides its DC/DC conversion technology not only in the form of fully integrated DC/DC modules, but also makes the underlying core components available as discrete building blocks. As a manufacturer of isolated DC/DC modules, RECOM therefore enables direct integration of identical primary-side controller ICs, transformer driver ICs, synchronous rectifier ICs, and magnetics into custom PCB designs.

This technical article analyzes the available technological options and serves as a structured decision guide for selecting between a pre-qualified, certified DC/DC module and an IC-based discrete power architecture. The use of an isolated module provides a fully validated design with defined EMC performance, verified isolation (functional or reinforced isolation), and minimal integration effort. Development risk, design complexity, and time-to-market are significantly reduced.

A discrete solution, in contrast, provides maximum flexibility in topology, transformer design, layout, and thermal integration. Particularly at high production volumes, optimized bill of materials and application-specific design can result in significant cost advantages.

An isolated DC/DC converter is fundamentally based on two functionally critical components: a primary-side transformer driver or controller IC and a galvanically isolating high-frequency transformer. The quality of these two elements largely determines efficiency, magnetic utilization, EMC behavior, and overall power architecture reliability.

RECOM offers a broad portfolio of discrete isolated transformer driver ICs and flyback controller ICs for common topologies such as pushpull, full-bridge, and flyback.

Push-Pull and Full-Bridge Transformer Driver ICs

Push-pull and full-bridge architectures operate with a primary-side square-wave drive of the transformer. The driver ICs generate precise complementary gate signals with defined dead time to prevent cross-conduction (shoot-through). The resulting high-frequency AC signal is stepped up or down according to the transformer turns ratio. On the secondary side, rectification is performed either by Schottky diodes or by a synchronous rectifier IC to reduce conduction losses. Output filtering is typically implemented using a capacitive or LC filter (C_OUT or LC).

For unregulated transformer driver ICs, the output voltage is primarily determined by:

• Input voltage
• Turns ratio
• Load condition
• Efficiency

In applications requiring higher output accuracy, a downstream LDO or additional regulation stage may be implemented.

Flyback Controller ICs

In contrast to pure transformer driver ICs, flyback controller ICs integrate closed-loop PWM regulation. Energy transfer occurs discontinuously or continuously through magnetic energy storage in the transformer (coupled inductor).

Depending on type, RECOM flyback controllers are equipped with:

• Integrated power MOSFET
• External MOSFET drive capability
• Primary-side regulation (PSR) or secondary-side feedback

The flexible choice between internal and external switching enables higher voltages and output power levels. The RVPW series supports both primary-side and secondary-side regulation concepts. In non-isolated configurations, direct current sensing is also possible. RECOM therefore covers both unregulated isolated transformer drivers for compact, efficient push-pull or full-bridge architectures, and fully regulated flyback controller ICs for power- and voltage-flexible applications.

RECOM offers a coordinated portfolio of isolated transformer driver ICs, flyback controller ICs, SMD transformers, and synchronous rectifier ICs (see Table 3). This enables consistent technological implementation of various isolated DC/DC architectures. The representative components RVP001, RVP010, and RVPW011 correspond to three established topologies in isolated power electronics:

• RVP001 – Full-Bridge Transformer Driver
• RVP010 – Push-Pull Transformer Driver
• RVPW011 – Regulated Flyback Controller IC

The RVP transformer driver ICs integrate a precise internal oscillator to generate complementary gate signals with defined dead time. Symmetrical drive ensures balanced magnetization of the transformer core and minimizes magnetic flux imbalance. The integrated dead time prevents cross-conduction (shoot-through) between switches. The RVPW series, by contrast, operates with integrated PWM regulation for driving a flyback transformer and enables primary-side or secondary-side regulation depending on configuration.

Push-Pull vs. Full-Bridge – Structural Difference

Push-pull and full-bridge topologies differ in both transformer construction and switch current stress. Push-pull designs require a transformer with a primary-side center tap. During each half-cycle, only one half of the primary winding is energized. Each MOSFET conducts only the current of its respective winding half. Full-bridge designs do not require a center tap. During each half-cycle, the entire primary winding is energized. Each switch must therefore be rated for the full primary current.

As a result:

• Push-pull architectures are advantageous at lower input voltages and higher currents
• Full-bridge topologies perform optimally at higher input voltages and lower currents

Both IC families are specified for an industrial temperature range of –40°C to +125°C.

The RVP001 (Figure2, left) implements a full-bridge topology with integrated 0.25Ω high-side P-channel MOSFETs and two 0.13Ω low-side N-channel MOSFETs. Due to the bridge structure, the entire primary winding is energized during each half-cycle, as shown in Figure2 (left, highlighted in red). The full-bridge architecture enables efficient utilization of the primary winding at a given input voltage, reducing the required number of turns. This positively impacts copper losses, leakage inductance, and ultimately transformer cost. However, each switch must be rated for the full primary current, which must be considered in thermal design.

The RVP010 (Figure2, right) is based on a push-pull topology with integrated 24V N-channel LDMOS MOSFETs with a typical RDS(on) of 0.1Ω. It is designed for output voltages from 3.3V to 24V. In push-pull configuration, only one half of the primary winding is activated per switching phase. Each MOSFET therefore conducts only the current of the corresponding winding half. The use of exclusively N-channel devices results in lower conduction losses compared to the P-channel high-side structure of the full-bridge variant. However, only one half of the primary transfers energy at a time, influencing magnetic utilization per switching period and requiring precise symmetrical drive to prevent core saturation.

The integrated dead time is intentionally kept very short, allowing an effective duty cycle close to 100%. As a result, the primary winding is driven for nearly the entire switching period, improving magnetic utilization and increasing transferable power per cycle. During dead-time intervals, however, no energy is transferred from the primary to the secondary side. The load current must be supplied entirely by the output filter during this phase.

An appropriately dimensioned output capacitor, typically in the range of 4.7µF to 10µF depending on load current, switching frequency, and allowable ripple voltage, provides this buffering function. Its dimensioning directly influences:

• Output voltage ripple
• Transient response
• Downstream load stability

Selection should consider ESR, RMS current capability, and temperature behavior.

Flyback topologies offer high power and voltage flexibility and are particularly suitable for applications with variable input voltage or multiple output voltages. Unlike unregulated transformer driver architectures, flyback controller ICs integrate closed-loop PWM regulation. Output voltage is sensed via a feedback path—either primary-side regulation (PSR) or secondary-side feedback—and processed internally.

The internal control structure enables:

• Precise voltage regulation over a wide load range
• Integrated cycle-by-cycle current limiting
• Protection functions such as OCP, OTP, and UVLO
• Controlled startup behavior (soft-start)

Due to energy storage in the transformer (coupled inductor), output power can be scaled via switching frequency, duty cycle, peak current limit, and transformer design. Flyback topologies are therefore particularly suitable for low- to mid-power applications requiring tight regulation and wide input voltage range.

The flyback topology differs fundamentally from push-pull and full-bridge architectures because it does not provide complementary drive signals with continuous energy transfer. Instead, power transfer occurs discontinuously in two distinct phases:

1. Primary conduction phase – Energy is stored in the magnetic field of the transformer.
2. Secondary conduction phase – Stored energy is transferred to the secondary side.

The resulting secondary current waveform is pulsed and directly dependent on PWM duty cycle and peak current. Continuous power transfer, as in push-pull or full-bridge, does not occur.

The output therefore relies on a properly dimensioned output filter. The output capacitor must:

• Supply load current entirely during the primary conduction phase
• Smooth pulsed energy transfer
• Maintain specified ripple voltage
• Support regulation stability

Dimensioning must consider load current, switching frequency, operating mode (DCM or CCM), ESR, and allowable ripple. At higher load currents or lower output voltages, RMS current rating becomes particularly critical.

Project managers, system architects, and design engineers will inevitably face a fundamental make-or-buy decision:
Use a standardized DC/DC module, or implement a discrete isolated power architecture? The answer is rarely purely technical. It results from a combination of performance requirements, isolation concept, time-to-market, production volume, mechanical constraints, and internal power design expertise. The following sections categorize the key decision parameters.

Power Supply Design Expertise

Even at single-digit watt levels, isolated DC/DC converter design requires multidisciplinary expertise:

• Magnetics design (core material, flux density, leakage inductance, winding topology)
• Control theory (stability analysis, compensation, load transients)
• EMC-optimized layout (loop minimization, dv/dt control)
• Thermal design (loss distribution, hot-spot analysis)

The transformer is not a commodity component but a functional core element. Switching frequency, maximum flux density, cooling conditions (natural convection or forced air), and isolation requirements (functional or reinforced isolation) must be coherently designed. If such expertise is not available internally, a certified DC/DC module often represents the lowest-risk approach, offering validated EMC performance and verified isolation.

Through close collaboration with RECOM’s applications and magnetics engineering teams, development risk in discrete designs can also be significantly reduced.

With aggressive project timelines, a DC/DC module is typically the pragmatic choice. Integration is limited to:

• Electrical connection
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