If you’re running a PCB power supply operation (like we are, as a small, reliable supplier that’s been in the game for over a decade) — you know that few things tank a project faster than a power supply that doesn’t pull its weight. I can’t tell you how many times we’ve gotten a panic call from a client who built their rig with two 12V 10A supplies wired in parallel, only to have one get way too hot and shut down. That’s the power supply output current sharing problem, and it’s not just a “nice to have” — it’s non-negotiable for stable, long-lasting PCB power systems. PCB Power Supply
First, let’s break this down in plain talk, no overengineering jargon. When you need more power than a single supply can deliver (say, 20A instead of 10A), the standard fix is to parallel multiple supplies. The goal? Split the load evenly, so every supply carries its share. If one supply is hauling 18A and the other is just 2A, the first one’s running way over its limit — it’ll fail early, drag the other down, and take your whole project with it. That’s why current sharing isn’t just a tech spec; it’s what keeps your PCB from turning into a fire hazard or a dead weight on the production line.
Now, what are the actual requirements here? Let’s start with the basics: current sharing accuracy. Most industrial and commercial apps I work with (think LED lighting, industrial control boards, consumer electronics) need a tolerance of 5% or less. Wait, 5% — that’s not a random number. Let’s say you have two 10A supplies: 5% of 10A is 0.5A. So each should sit between 9.5A and 10.5A when the load hits 20A. If your sharing is only 10% accurate, one might carry 11A and the other 9A — not terrible, but if you add more supplies, or if one supply drifts over time, that gap blows up. We’ve had clients come to us with projects where a 10% tolerance worked for a few days, but then temperature changes threw the supply output voltages off, and suddenly one supply was running at 12A, over its rated capacity, and frying. That’s why 5% is the sweet spot for most jobs — it keeps things steady without costing an arm and a leg.
Next up: dynamic current sharing. That’s the trickier part, because real-world loads aren’t static. Your PCB might have a motor that spikes to 20A for a second, or a microcontroller that draws 1A when waking up and 0.5A when idle. Static sharing (measured when the load is steady) is good, but dynamic is what matters when things move. Imagine you have two supplies, and the load jumps from 10A to 18A in 10 milliseconds. The supplies’ output capacitors and control circuits need to split that new load fast — within a few milliseconds — so neither has to handle the full 18A alone. Bad dynamic sharing leads to voltage dips, which crash microcontrollers, or overcurrent trips that shut down the whole system mid-operation. For our part, we test every parallel supply unit we ship with load ramps up to 10A per millisecond to make sure they pass this — we don’t cut corners here, because we’ve seen too many clients learn the hard way.
Then there’s the no-load current share. Wait, no-load? Yeah, that’s a thing. When your PCB is in standby mode — like a TV that’s off but still plugged in — the power supplies draw a tiny amount of current. If this doesn’t share evenly, one supply is drawing all the standby current, which means it’s working harder than it should. Over weeks or months, that extra wear shortens the supply’s lifespan. For standby loads (usually 10% or less of the rated output), we aim for a 10% max tolerance on no-load current share. It’s a small detail, but it’s what makes our supplies last longer than the cheap ones from the big box brands.
Now, let’s talk about why these requirements matter more for PCB-mounted supplies than for rack-mount or other types. PCB power supplies are tiny, right? They’re soldered right onto the main board, so there’s less space for big heat sinks, and the PCB traces carry the current. If current sharing is bad, the overloaded supply gets hot, and that heat transfers straight to the PCB — warping traces, damaging nearby components, and shortening the whole board’s life. We’ve had clients who used generic power supplies on their PCBs, and within 6 months, 15% of their boards failed because of heat-related damage. When they switched to our supplies with proper current sharing, that failure rate dropped to less than 1%. That’s the difference between a spec that’s checked on paper and a spec that actually works in the field.
Wait, also, there’s impedance matching. A lot of people forget this, but the PCB traces that connect the parallel supplies matter almost as much as the supplies themselves. If you route a 1oz copper trace to one supply and a 2oz trace to another, even two identical supplies will share current unevenly — the one with the thicker trace gets less resistance, so it carries more load. That’s why we always give our clients a simple routing guide when they buy parallel supplies: keep trace lengths as equal as possible, use at least 2oz copper for high-current paths, and avoid sharp bends that create extra resistance. We’ve had clients who did everything right on the supply specs, but messed up the PCB traces, so we offer free trace design checks for bulk orders — small step that saves them a ton of headaches.
Let me tell you about a recent example to make this real. We had a client who makes industrial sensor boards for food processing plants. They were using four generic 5A supplies in parallel, and their boards were failing at a rate of 12% per month. The problem? Their generic supplies only had a 15% current sharing tolerance, and they routed the traces unevenly, so one supply was carrying 6A, 20% over its rating. We swapped their supplies for our 5A units, which have 4% static sharing and 10ms dynamic response, and fixed their trace layout. Now their failure rate is less than 1% a year — that’s the power of meeting the right current sharing requirements, not just picking any supplies that add up to your total load.
Another common myth: if the supplies are the same brand and model, current sharing will work automatically. Nope, not true. We’ve tested same-model supplies from two different production runs, and even tiny differences in their internal components can lead to 8% sharing error. That’s why it’s not just about buying identical supplies — it’s about buying supplies that are binned (tested to have matching specs) for parallel operation. Bin grading is a big part of what we do here: every supply we ship for parallel use goes through a second test to make sure its voltage output at full load is within 10mV of the next one, which keeps current sharing accurate. No binning, no reliable parallel operation — simple as that.
So what do you actually need to look for when choosing a PCB power supply for parallel use? Let’s wrap it up with a quick checklist we give all our clients:
- Static current sharing accuracy of 5% or better at full rated load. Anything higher leads to overloading.
- Dynamic current sharing response time under 20ms for load transients — that way, spikes don’t overwhelm one supply.
- No-load current sharing tolerance of 10% max — even standby doesn’t have to mean one supply does all the work.
- Binned for parallel operation, so you don’t have to worry about small production variations messing things up.
- A simple routing guide for PCB traces, because even the best supplies fail with bad layout.
At the end of the day, current sharing isn’t just a technical requirement — it’s the difference between a product that ships on time and works for 5 years, and one that returns for warranty claims, damages your brand, and costs you money. We’ve been in this business long enough to know that cutting corners here is never worth it. If you’re working on a project that needs parallel PCB power supplies, don’t just go for the cheapest option — ask about their current sharing specs, test results, and whether they’re designed for parallel use. If you have questions, or if you want to chat through your project’s needs, reach out to our team for a no-obligation consultation. We’re here to help you get it right the first time, so you don’t have to deal with the same headaches we’ve seen hundreds of clients go through.
Enclosed Switching Power Supply References
- Texas Instruments, "Parallel Operation of Switching Power Supplies," Application Note SLVA685, 2018.
- International Electrotechnical Commission, "IEC 61204-3: Low-Voltage Power Supplies for Industrial Use," 2021.
- Analog Devices, "Design Considerations for Parallel Power Supply Systems," Technical Tutorial MT-037, 2020.
Guangzhou Kaihui Electronics Co., Ltd.
Guangzhou Kaihui Electronics Co., Ltd. is one of the most professional pcb power supply manufacturers and suppliers in China, specialized in providing the best customized service. We warmly welcome you to buy high quality pcb power supply made in China here from our factory.
Address: 2F BLDG8, Standard Ind.Park, Dongchong Town, Nansha District 511453, Guangzhou, Guangdong, China
E-mail: amy@gzkaihui.com
WebSite: https://www.kaihuipowersupply.com/
