Nations Technologies NS1KW48VB2B2: 1kW Single-Stage Bidirectional 9-15V to 48V Conversion at 95.1% Peak Efficiency

A 9–15V battery, a 48V bus, and energy that has to move both ways between them. That combination is common to e-bikes, e-motorcycles, electric tricycles, quadruped robots, powered wheelchairs and large low-voltage battery packs such as 314Ah units. NS1KW48VB2B2, released by Nations Technologies on 29 October 2026, is a 1kW non-isolated bidirectional DC-DC reference design that folds the whole conversion into a single power stage with 95.1% peak efficiency. The interesting part is not the kilowatt rating. It is the topology that removes the isolation transformer.

Why 9–15V to 48V is a topology problem

These systems run their batteries at 9–15V while motor drives, communications and auxiliary loads want a 48V rail or higher. Discharging means stepping up; charging means stepping down. A conventional boost converter is bounded by a gain of 1/(1-D), and pushing the duty cycle toward unity degrades efficiency and loop stability at the same time. Two other routes exist — add an isolation transformer, or add a dedicated charging power stage — and both raise cost, volume and thermal complexity.

The NS1KW48VB2B2 takes a third route. It swaps the roles of the main switches and synchronous rectifiers across two MOSFET groups inside one power stage, so step-up on discharge and step-down on charge share the same silicon. Direction is decided by the control loop rather than by rewiring. According to the technical note published by Nations Technologies, the full charge-to-discharge transition runs without any change to the harness, and the system stays stable through complete charge and discharge cycles.

Power stage and key specifications

• Input 9–15V, output 48V, tested up to 53.5V; bidirectional conversion up to 1kW.
• Peak efficiency 95.1% at 285W, Vin = 12V, Vout = 53.5V.
• Twelve 150V MOSFETs (AGM15T13A) and two 22μH / 40.6A power inductors form a two-phase, non-interleaved, synchronous bidirectional boost stage.
• Control and protection run on an N32DP474 series MCU with an ARM Cortex-M4F core.
• Two PCBs joined by an 80-pin connector: the main board carries the power stage, auxiliary supply, isolated gate drive and communication circuits plus voltage, current and temperature sensing; the core board holds the MCU, on-board supply and transceivers and handles bidirectional conversion control, status monitoring and protection.

"Non-interleaved" here means the two phases switch in phase rather than 180° apart. Paralleling the phases splits the current stress per leg, and the margin implied by twelve 150V devices and two 40.6A inductors is the physical basis for 1kW bidirectional throughput at 95.1% peak efficiency.

Where the (1+D)/(1-D) gain comes from

A classic boost stage gives 1/(1-D), which diverges as D approaches one and leaves a narrow usable window. This design adds one more series contribution along the energy-transfer path, so the gain becomes (1+D)/(1-D). For the same duty cycle the output is higher; equivalently, the duty cycle needed to reach 48V is lower. Nations Technologies states that duty cycle varies between roughly 52.4% and 68.4% across the full operating range.

That window deserves attention on its own. A conventional boost converter going from 12V to 48V needs a theoretical duty cycle of 75%, and in that high-gain region switching loss, inductor ripple current and loop gain all deteriorate together. Operating between 52.4% and 68.4% keeps the devices and the magnetics away from the edge of the duty-cycle range and leaves more room in the compensation network. That is the practical meaning of the "ultra-high step-up ratio" claim: not how large the gain can be made, but how far the operating point sits from the region where the converter becomes hard to control.

95.1% and 9V answer different questions

The 95.1% figure is a peak measured at 285W with a 12V input and a 53.5V output. It is neither a full-load number nor a system-level number. What it shows is that the loss structure along this power path is sound at a mid-load operating point. The release states that efficiency stays flat across the load range, but it does not publish the individual points, so the curve itself has to come from the vendor.

The deeper constraint for two-wheelers and quadruped robots is the low end of the battery. With roughly 10% charge left and the low-voltage side at about 9V, the design still holds a regulated 48V output — a step-up ratio above 5:1. That is the condition where internal resistance is rising and the bus still has to be maintained, and it is the condition users actually encounter. Peak efficiency answers whether the converter is frugal; 9V-output capability answers whether the vehicle still moves when the pack is nearly empty. The two cannot substitute for each other.

Two further results come from the same lab environment: output voltage stays regulated and input current stays smooth from 1% to 100% load, and the power direction is detected automatically when charge and discharge swap. Together they indicate no significant bus droop or current surge at the moment of reversal.

Digital control is the reusable layer

The N32DP474 runs an ARM Cortex-M4F core at 240MHz with 300DMIPS and includes Cordic and FMAC hardware acceleration. What determines whether this design can be reused, however, is how much of the control loop it fits into one chip.

• 125ps PWM resolution with 200ns dead-time insertion, used to smooth the output waveform and reduce ripple.
• 16 PWM channels in 8 complementary pairs, plus four 4.7MSPS 12-bit ADCs with differential input. This design uses only four complementary PWM channels and eight differential sampling channels to control the entire system, with no external ADC.
• An ADC analog watchdog trips through on-chip hard wiring (ADC2_AWD1 → EXEV4 → TxRST) to reset the output cycle by cycle, giving cycle-by-cycle current limiting and hardware-level protection without consuming comparator pins.
• External events, any comparator, UART and CAN-FD can be mapped to any IO, so a derivative design is a matter of software rerouting.

Firmware runs on the in-house HunterWave OS: non-preemptive time-slice polling combined with hardware interrupt handling. The release notes that this is the first design to support full-range waveform visualization for tuning PID parameters in place of conventional JTAG debugging, with a host tool for online parameter configuration, waveform analysis and protection-policy management. With the three earlier 3kW-class designs — NS3KW420VP2, NS3KW53V5L2 and NS3KW53V5P2L3 — the portfolio now spans 1kW to 3kW from AC/DC through DC/DC.

HSY Perspective

What this reference design changes is the bill of materials of a low-voltage battery system, not a number in an efficiency table. Once step-up and step-down share one power stage and the isolation transformer is gone, more disappears than a single magnetic component: the dedicated charging stage, its magnetics, its thermal path and the mechanical space around it go with it. For a product built on a 9–15V platform, that is a reallocation of cost and volume, and the efficiency gain is a side effect.

Three published figures support that reading. Duty cycle moving between 52.4% and 68.4% means the devices are not parked in the extreme-gain region and both the loop and the magnetics retain margin. A regulated 48V at a 9V input means deep-discharge gain is a design target rather than an edge case. Peak efficiency at a 285W point means the loss structure is controlled at mid load. Together they form a parameter set that transfers to other power levels, not just a board that works. The market scale points the same way: Nations Technologies cites a Chinese e-bike installed base above 400 million units by the end of 2025, a segment with low voltage platforms, high volume and acute sensitivity to the cost of every component.

The boundary is equally clear. This is a reference design, not a production module: what a customer receives is a topology and a set of control parameters, and production consistency, thermal design and EMC still have to be validated in-house. No derating curve is published, so the 1kW bidirectional rating and the 95.1% peak both need to be re-established against actual ambient and duty profiles. If the 3kW platforms adopt the same topology and control layer, the cost of porting falls further; if a target system is bound to an isolated architecture by its safety certification, the case for removing the transformer has to be rebuilt from scratch.

Source: Nations Technologies (300077.SZ / 02701.HK), technical note published 29 October 2026, "Digital Power | 1kW non-isolated bidirectional DC-DC reference design: ultra-high step-up ratio, 95.1% peak efficiency", original article.