Introduction — The Project Brief
This case study covers the design of a compact brushless DC (BLDC) motor controller developed for direct integration into a pump assembly, where the entire controller had to fit within a 20mm diameter circular footprint while running a single-pole BLDC motor at 24V, 2A. The brief called for a low-cost, high-volume-manufacturable controller that could be built directly into the customer's product — not housed separately — while still offering a genuine range of programmable performance options.
Unlike many compact controller designs that trade away performance for size, this project required both: a controller small enough to disappear inside the pump housing, and sophisticated enough to deliver sinusoidal commutation, programmable fixed-speed options, closed-loop speed control, and startup optimisation.
Project Background and Objectives
The client needed a controller that their own production staff could integrate directly into the pump assembly during manufacture — not a separately housed unit wired in afterwards. That single requirement shaped almost every design decision that followed, because it meant the controller had to succeed on three fronts simultaneously: physical space, thermal performance, and ease of handling on someone else's production line.
Key objectives for the project included:
- Delivering a fully functional BLDC controller within a 20mm diameter circular board outline
- Supporting a single-pole BLDC motor at 24V / 2A running current
- Implementing sinusoidal commutation to maximise motor performance and minimise audible noise and torque ripple
- Providing programmable fixed speed options, variable speed control, and startup optimisation, so the same hardware platform could serve multiple product variants
- Ensuring the design could be manufactured to ISO 9001 standards and reproduced reliably at volume
- Making the controller genuinely easy for the client's own assembly staff to integrate, without specialist equipment or risk of handling damage
We had produced 20mm controllers before but these been limited to 0.5A peak
The Core Engineering Challenge: Space
A 20mm diameter footprint leaves very little room for a controller that still needs to deliver 2A of continuous drive current, handle sinusoidal commutation, and provide multiple programmable modes. Every component on the board had to justify its footprint.
The most significant space-saving decision the custom design team made was the use of tantalum capacitors in place of conventional electrolytic or MLCC types. Tantalum capacitors offer a much higher capacitance-to-volume ratio than electrolytics of equivalent value, which made it possible to meet the controller's decoupling and smoothing requirements without the board-area penalty that electrolytic capacitors would have demanded. In a design where every square millimetre was accounted for, this single component choice was one of the decisions that made the rest of the layout achievable.
The Core Engineering Challenge: Thermal Management
Fitting a 2A-capable drive stage into a 20mm circular board would be straightforward if thermal performance weren't a constraint — but with so little surface area available for heat dissipation, thermal management became just as critical as the physical footprint itself.
Rather than relying on heatsinking or forced airflow — neither of which was realistic given the size and the pump-integrated installation — the design team's approach was to engineer the controller's efficiency to be as high as possible, minimising the heat generated in the first place rather than trying to manage it after the fact. This meant careful attention to switching losses in the drive stage, conduction losses through component selection, and control-loop design that avoided unnecessary current draw during normal operation.
The result is a controller that runs well within safe thermal limits at full rated current, despite having almost no thermal mass or dissipation area to work with.
Motor Control Strategy
The application required accurate control of a single-pole BLDC motor across its full speed range — including, critically, at the lower end of the speed range, where BLDC control is typically at its most difficult. Low-speed BLDC control is a well-known challenge: back-EMF signals are weak at low RPM, making accurate rotor position sensing and smooth commutation harder to achieve than at higher, more electrically "comfortable" speeds.
This was addressed through careful design of the control stage itself, tuned specifically to maintain stable, accurate control at low speed without sacrificing performance at the top end of the range. Combined with sinusoidal commutation — rather than simpler trapezoidal switching — the controller delivers smoother torque output and quieter running than a standard six-step BLDC drive would achieve, which matters directly for pump applications where noise and vibration are often as important to the end customer as raw performance.
Tantalum capacitors are more expensive than their electrolytic alternatives but in small footprint designs like this the space savings are essential
Programmability
Rather than build a single fixed-function controller, the platform was designed to support a range of programmable performance options from the same hardware base:
- Fixed speed options — allowing the same board to be configured for different product variants without a hardware redesign
- Variable speed control — for applications requiring dynamic flow or pressure adjustment
- Startup optimisation — tuned specifically to the mechanical characteristics of the pump, ensuring reliable starts without excessive inrush current or stalling
This programmability turns a single physical design into a flexible platform, letting the client cover multiple product tiers or configurations without maintaining several different controller designs. It is however important to note that, given the size of the controller, such programming has to be done pre-installation. In this case, the client was supported with a range of programme options to enable them to operate directly from power-up or via speed control inputs such as PWM inputs.
Designed for Manufacture Twice!
One of the most easily overlooked aspects of a project like this is what happens after the electrical design is finished. It is one thing focusing on our own electronic manufacturing facility and the DFM requirements there but this project required a further consideration. Namely, can the client's own staff actually fit it, safely, at production speed? For a controller integrated directly into a pump rather than supplied as a boxed unit, this matters as much as any electrical specification.
The board's solder points were specifically designed to make installation straightforward and low-risk for the client's assembly team — accessible, good thermal relief, well-spaced, and tolerant of manual soldering without fine-pitch precision requirements that would demand specialist equipment or training. This is a good example of a broader principle in bespoke motor control design: a controller isn't just an electrical component, it's a physical object that has to survive someone else's manufacturing process, and designing for that reality from the outset avoids costly rework or damaged units further down the line.
Quality, Compliance, and Longevity
The controller was manufactured under Zikodrive's ISO 9001-certified quality management process, ensuring that what was validated in prototype form is what gets reproduced, unit after unit, at volume. This matters particularly for a design this compact and thermally constrained — small manufacturing variances can have an outsized effect on a board with so little margin, so process control was as important to the outcome as the original design work.
The controller was also designed to meet the compliance standards expected of a product destined for long-term field use: safe, predictable thermal behaviour, robust power handling, and built-in protection features to guard against fault conditions over the product's working life. Full programmability also means individual units can be reconfigured or repurposed for different applications rather than discarded, and all components used are compatible with end-of-life recycling once a unit does eventually reach the end of its service life.
Outcome
The completed controller met every constraint of the original brief: a working, sinusoidal, programmable BLDC drive fitted within a 20mm diameter footprint, running reliably at 24V/2A without dedicated cooling, and simple enough for the client's own production staff to install without risk of damage. It stands as a clear example of how far a controller's footprint can be pushed down when space, thermal, and manufacturing considerations are treated as first-class design constraints from day one — rather than problems to solve after the electronics are already finished.