PWM control circuits for chargers and power converters · Current-mode PWM controller ICs, UVLO thresholds for off-line versus DC-DC use, maximum duty cycle, oscillator setting, current limiting, and ready-made PWM charger and converter boards
A PWM control circuit is the controller IC, gate driver and feedback network, or a ready-made board built around them, that switches a power stage at a fixed frequency and varies the on-time (duty cycle) to regulate the output voltage or current of a rectifier, battery charger or DC-DC converter. Ask three things first: whether it runs from an off-line (rectified mains) or DC supply, what duty-cycle range, switching frequency and control mode it uses, and what current limiting, regulation and temperature range the application needs.
PWM control circuits for power conversion and charging: PWM controller ICs with their feedback and gate-drive circuits, and PWM converter and charger boards. Complete power supply units (see industrial power supply unit), rectifier bridges and stacks, UPS systems and motor PWM drives are outside this page.
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01
TI's UCx84x data sheet (SLUS223H, revised October 2024) describes current-mode PWM controllers for off-line and DC-DC fixed-frequency converters, with start-up current under 1 mA, undervoltage lockout with hysteresis, pulse-by-pulse current limiting, a totem-pole output for driving N-channel MOSFETs and operation up to 500 kHz. Its device comparison table gives 16 V turn-on and 10 V turn-off for the UCx842 and UCx844, suited to off-line supplies, and 8.4 V and 7.6 V for the UCx843 and UCx845, suited to DC-DC, with a maximum duty cycle of up to 100% for the UCx842/3 and up to 50% for the UCx844/5. [1]
The data sheet sets the oscillator frequency as f = 1.72 / (R × C) with R in ohms and C in farads, says the timing resistor should never be below 5 kΩ, and states that the UCx844/5 output switches at half the oscillator frequency. The UC184x is specified for −55 to 125 °C, the UC284x for −40 to 85 °C and the UC384x for 0 to 70 °C. [1]
Editorial calculation: with R = 10 kΩ and C = 3.3 nF, f = 1.72 / (10,000 × 3.3 × 10⁻⁹) ≈ 52 kHz; a UCx842 would switch at about 52 kHz and a UCx844 at about 26 kHz with its duty cycle limited to 50%. [1]
Duty-cycle limits matter because of how current-mode control behaves. Ricoh's US patent 7,876,073 B2 (Switching regulator with slope compensation and control method therefor) states that a current-mode controlled switching regulator can fall into subharmonic oscillation and become uncontrollable when the PWM duty cycle exceeds 50%, and that slope compensation is added to the PWM control to prevent it. For a step-down regulator it sets the slope of the compensation ramp at not less than half the slope of the inductor current while the switch is off, which is Vout/L (the on-time slope being (Vin − Vout)/L), and it varies the ramp slope with input voltage (step-down) or output voltage (step-up) so the compensation stays adequate across a wide voltage range. [4]
Editorial calculation: for a buck stage with an assumed 12 V output and 22 µH inductor, the off-time current slope is 12 / 22 µH ≈ 0.55 A/µs, so the patent's rule calls for a compensation ramp of at least about 0.27 A/µs referred to the current-sense signal. A controller limited to 50% duty, such as TI's UCx844/5, stays below the 50% point the patent identifies; a 100%-duty part (UCx842/3) used above 50% needs the slope compensation designed in. Ask the supplier how slope compensation is set and at what duty cycle the circuit was tested. [4] [1]
Give the supplier the input (AC mains via rectifier, or DC range), output voltage and current, charge profile for batteries (CC/CV, termination), topology, switching frequency, duty-cycle limit, control mode, current-limit and protection functions, regulation and ripple targets, efficiency target, operating temperature, size limits, isolation needs and quantities.
02
Creatall lists an XL4015-based constant-current, constant-voltage module for LED driving and lithium battery charging with 5–32 V input, 0.8–30 V output, adjustable current, conversion efficiency up to 95%, 300 kHz switching, 50 mV output ripple at 20 MHz bandwidth, ±0.5% load regulation, ±2.5% voltage regulation, −40 to +85 °C operation and a 51 × 26.3 × 14 mm board. [2]
Editorial note: board-level modules quote peak efficiency and adjustable ranges; ask for efficiency and temperature rise at your input voltage and output current, the current-limit accuracy, and whether the board terminates charging or only holds a constant voltage.
The chip maker's data sheet does not match the board listing on every point. XLSEMI's XL4015 data sheet (Rev 2.0) describes a 180 kHz fixed-frequency PWM buck converter with an internal power PMOS, 8–36 V input, 1.25–32 V output set by VOUT = 1.25 × (1 + R2/R1), 5 A output, duty cycle adjustable from 0 to 100%, 0.3 V minimum dropout, and frequency foldback to 48 kHz under output short circuit. Its electrical table gives a feedback voltage of 1.225–1.275 V, oscillator frequency 144–216 kHz, switch current limit 7 A, PMOS on-resistance 60–80 mΩ, quiescent current 5 mA, and efficiency of 87% at 12 V in, 5 V/5 A out and 93% at 24 V in, 12 V/4 A out. The TO263-5L package has a junction-to-ambient thermal resistance of 30 °C/W with no heatsink, a junction range of −40 to 125 °C, and ESD above 2,000 V HBM. [3]
Editorial calculation: at 12 V in and 5 V/5 A out, 87% efficiency means about 3.7 W of loss (25 ÷ 0.87 − 25); at 30 °C/W with no heatsink that would be a 112 °C rise if all of it fell in the chip, so a board claiming 5 A continuous needs copper area or a heatsink, and its listed 300 kHz and 5 V minimum input differ from the chip's 180 kHz and 8 V; ask which chip and ratings the board actually uses. [3] [2]
03
Suppliers linked to this page list PWM converter and charger boards; each card links to the page reviewed.
Listings include buck and boost DC-DC modules, CC/CV charging and LED driver modules and USB charging boards.
04
This is a functional reference built from the sources cited; it is not one maker's design.
| Part | Role | Fix in the order |
|---|---|---|
| PWM controller IC | Sets frequency and duty. [1] | UVLO, duty limit, frequency. |
| Timing R and C | Set oscillator frequency. [1] | Values, tolerance. |
| Gate driver output | Drives the MOSFET. [1] | Peak current. |
| Current sense | Pulse-by-pulse limiting. [1] | Sense resistor, limit. |
| Feedback network | Regulates voltage or current. [1] [2] | CC/CV set-points. |
| Power stage | Converts power. [2] | Topology, efficiency. |
05
A PWM control circuit quotation needs values for your converter. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.
| Field | What it means and published values | Ask the supplier for |
|---|---|---|
| Input Voltage (V AC) | Off-line or DC; 5–32 V DC on one board. [1] [2] | Input range. |
| Output Voltage (V DC) | 0.8–30 V on one board. [2] | Range and set-point. |
| Output Current (A) | Adjustable on one board. [2] | Maximum continuous current. |
| Switching Frequency (kHz) | Up to 500 kHz controller; 180 kHz (XL4015 chip) vs 300 kHz on one board listing. [1] [3] [2] | Frequency. |
| PWM Duty Cycle Range (%) | Up to 100% or 50% by controller variant. [1] | Limit. |
| Line Regulation (%) | ±2.5% voltage regulation on one board. [2] | Value and conditions. |
| Load Regulation (%) | ±0.5% on one board. [2] | Value and conditions. |
| Efficiency (%) | 87% (12→5 V, 5 A) and 93% (24→12 V, 4 A) on chip data; up to 95% on one board. [3] [2] | Efficiency at your load. |
| Operating Temperature (°C) | 0–70, −40–85 or −55–125 °C by controller grade; −40 to +85 °C on one board. [1] [2] | Range. |
| Storage Temperature (°C) | e.g. −65 to 150 °C (chip). [3] | Range. |
| Relative Humidity (% RH) | Environment. | Range or coating. |
| Ingress Protection | Open board or enclosed. | Enclosure. |
| Dimensions (L×W×H) (mm) | 51 × 26.3 × 14 mm for one board. [2] | Drawing. |
| Weight (g) | Mounting. | Weight. |
06
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Input: [AC mains; DC range] Output: [voltage; current; CC/CV; charge termination] Control: [frequency; duty limit; mode] Protection: [current limit; UVLO; temperature] Performance: [regulation; ripple; efficiency] Supply: [size; quantity]
These companies list PWM converter and charger boards.
Lists PWM buck and boost converter modules, CC/CV charging modules and USB charging boards.
Product scope checked 2026-10-11
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
In TI's UCx84x family, the UCx842 and UCx844 with 16 V turn-on and 10 V turn-off are described as suited to off-line supplies. [1]
For the UCx84x, f = 1.72 / (R × C), with the timing resistor not below 5 kΩ. [1]
One lists 5–32 V input, 0.8–30 V output, 300 kHz switching and up to 95% efficiency. [2]
XLSEMI's XL4015 data sheet lists 87% at 12 V in and 5 V/5 A out, and 93% at 24 V in and 12 V/4 A out, below the 95–96% headline figures. [3]
Ricoh's US patent 7,876,073 B2 states that above 50% duty a current-mode regulator can go into subharmonic oscillation; a compensation ramp of at least half the inductor's off-time current slope prevents it. [4]
Sources checked 2026-10-12. TI's data sheet describes its own controller family and is used here to show what a PWM controller specification covers; Creatall describes its own module. Values for your design must come from the component data sheets and the supplier's test data. Ricoh's US patent 7,876,073 B2 explains the duty-cycle limit and slope compensation of current-mode control.
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