FAQ
TL;DR: Design uses 230 VAC → buck to 221 VDC with 1% ripple; “output ripple = 1% of the output voltage.” [Elektroda, Charith Mendis, post #21660807]
Why it matters: Engineers searching “how do I build a tiny high‑voltage buck from mains” get constraints, pitfalls, and thread‑verified context fast.
Quick Facts
- Specs: Vin 230 VAC, Vout 221 VDC, Iout 20 mA, non-isolated brief stated by OP. [Elektroda, Charith Mendis, post #21660807]
- Ripple target: 1% of Vout (≈2.21 Vpp at 221 V). [Elektroda, Charith Mendis, post #21660818]
- Topology request: Buck converter; designer noted increased difficulty. [Elektroda, Charith Mendis, post #21660808]
- Mandates: DCM operation and N‑channel high‑side MOSFET switch. [Elektroda, Charith Mendis, post #21660807]
- Intermediate bus used by OP: ≈325 VDC after rectifier and smoothing. [Elektroda, Charith Mendis, post #21660816]
What’s the simplest high-level architecture for 230 VAC to 221 VDC at 20 mA?
Use a rectifier and bulk capacitor to create a high-voltage DC bus, then a non‑isolated buck stage in DCM to 221 V. This mirrors the thread’s requested buck approach and maintains low output current with manageable magnetics. Keep clearances consistent with high voltage practices. [Elektroda, Charith Mendis, post #21660808]
Why not just use a linear regulator here?
A participant suggested SMPS might be overkill, but constraints include high output voltage and controller power challenges. Linear drop from a rectified bus would waste heat and still not solve auxiliary Vcc. “We’re talking a mere 5th of a watt, here!” reflects skepticism, not a final design choice. [Elektroda, Steve Lawson, post #21660811]
How do I meet the 1% ripple requirement at 221 V?
Target about 2.21 Vpp ripple. In DCM buck, size the output capacitor and switching frequency to keep the inductor current fully discontinuous while meeting ripple. Validate with simulation and measure at load. “Output ripple = 1% of the output voltage.” [Elektroda, Charith Mendis, post #21660818]
Is isolation allowed for this supply?
No. The requester explicitly disallowed an isolated topology. That restriction drives the choice toward a non‑isolated rectified bus plus buck stage and complicates safe referencing and measurements during development. [Elektroda, Charith Mendis, post #21660814]
What intermediate DC voltage should I expect after rectifying 230 VAC?
Expect about 325 VDC from a smoothed bridge (230 VAC RMS × √2). The OP confirmed using this intermediate node before the buck stage. Ensure components are rated for this bus. [Elektroda, Charith Mendis, post #21660816]
Can I power the controller Vcc from the high output if no external supply is allowed?
The OP notes Vcc generation is difficult due to the high output voltage and the no‑external‑supply rule. Plan startup and housekeeping power early, since this constraint impacts driver selection and reliability. [Elektroda, Charith Mendis, post #21660812]
Why mandate an N‑channel high‑side MOSFET in DCM—what’s the impact?
Mandating an N‑channel high‑side device in DCM narrows driver choices and startup strategies. The OP flagged the requirement, which increases design effort for a small‑power supply. Choose parts and topology with this constraint in mind. [Elektroda, Charith Mendis, post #21660807]
What MOSFET driver and controller ICs were recommended in the thread?
The designer asked for specific MOSFET drivers, controller ICs, and PSpice models but none were named in‑thread. The open request highlights parts selection and simulation models as a blocker. [Elektroda, Charith Mendis, post #21660815]
Is using off‑the‑shelf AC‑DC modules acceptable here?
One reply proposed splitting the job into two parts and considering AC‑to‑DC modules. That can reduce risk and speed development if specifications and budget allow. [Elektroda, Cody Miller, post #21660810]
What do other engineers think about using a buck here?
One respondent asked why a buck would be harder, since bucks normally step down. This underscores that perceived difficulty stems from the high voltage, Vcc generation, and high‑side drive—not the step‑down action itself. [Elektroda, Todd Hayden, post #21660809]
How tightly regulated must the output be?
The thread clarifies the requirement as 1% ripple at the output voltage level. Treat this as a hard target during simulations and component selection. [Elektroda, Charith Mendis, post #21660818]
What special constraints did the requester impose beyond specs?
The designer couldn’t use an external power source for controller Vcc, and isolation was disallowed. These constraints directly affect driver choice and startup circuitry. [Elektroda, Charith Mendis, post #21660812]
Who asked for the N‑channel high‑side switch, and why?
A participant questioned the mandate’s purpose. The designer said it was a favor for a faculty member, acknowledging the requirement may be arbitrary. [Elektroda, Todd Hayden, post #21660819]
Did the OP simulate the buck stage successfully?
Yes. The OP reports a working buck design in PSpice, though hardware driver/controller selection remained unresolved. Use simulation to verify ripple and DCM boundaries before prototyping. [Elektroda, Charith Mendis, post #21660813]
Quick 3‑step plan to de‑risk this design?
- Rectify 230 VAC to a smoothed HV DC bus and verify ≈325 V.
- Implement DCM buck to 221 V with mandated N‑channel high‑side switch.
- Validate 1% ripple and address Vcc without external supply.
[Elektroda, Charith Mendis, post #21660816]
What’s an edge case to watch out for during bring‑up?
With no external Vcc and a high‑side N‑MOSFET, startup and driver biasing can stall progress. The OP explicitly struggled with driver and controller selection; plan this path early. [Elektroda, Charith Mendis, post #21660813]
