XL4015 5A CC/CV Adjustable Buck Converter – Setup, Current Limit & Troubleshooting
This XL4015 module is an adjustable DC-DC buck converter with separate constant-voltage (CV) and constant-current (CC) controls. It can be used as an adjustable step-down power supply, a current-limited supply, a CC/CV charging source for suitable batteries, or a constant-current LED driver.
This guide applies to the no-display version with two blue multi-turn adjustment trimmers, IN+/IN− and OUT+/OUT− terminals, and onboard status LEDs. It explains an important feature of this module: the CC control sets a maximum current limit; it does not force a load to draw the selected current.
XL4015 Module Overview
The complete module is sold with a 4–38V input and 1.25–36V output specification. The XL4015 IC manufacturer's datasheet specifies an 8–36V operating input range and 1.25–32V adjustable output range for the IC itself. For conservative operation, keep the input within 8–36V DC and provide adequate input-to-output voltage headroom.
The module cannot increase voltage. The input must be higher than the required output, with enough additional margin for regulation, wiring losses and the module's current-sensing path.
Understanding CV, CC and Actual Load Current
The voltage trimmer establishes the maximum regulated output voltage. When the load is drawing less than the selected current limit, the module normally operates in constant-voltage mode.
The current trimmer does not command a fixed current regardless of the load. It sets the point at which the module starts reducing its output voltage to prevent the current rising further.
For example, if the current limit is set to 2A but the connected device only requires 300mA, the module supplies approximately 300mA. Turning the CC control higher will not make that device draw 2A.
If a load attempts to draw more than the selected current limit, the converter reduces its output voltage as required and enters constant-current operation. The red CC indicator is associated with this current-limiting state.
Connections & Controls
| Module Marking | Connect To | Function |
|---|---|---|
| IN+ | DC supply positive | Positive power input |
| IN− | DC supply negative | Input return |
| OUT+ | Load / battery positive | Regulated positive output |
| OUT− | Load / battery negative | Output return through the module's current-sensing path |
Adjustment Trimmers
| Control | Function | Clockwise Adjustment |
|---|---|---|
| Voltage / CV | Sets maximum output voltage | Increases voltage |
| Current / CC | Sets maximum output current | Increases current limit |
The controls are multi-turn trimmers. Several complete rotations may be required before a noticeable change occurs, particularly if a previous user has adjusted the control close to one end of its range.
This module measures output current using a low-value current-sampling resistor in the output-negative path. An external connection between IN− and OUT− can bypass this sensing resistor, preventing the CC circuit from measuring and regulating output current correctly.
An unintended connection can occur through a common-ground power supply, chassis, USB-connected equipment, oscilloscope ground, test equipment or another part of the circuit. This should be one of the first checks if the voltage adjustment works but the CC adjustment appears not to work.
The instruction not to bridge IN− and OUT− externally does not mean the converter provides galvanic isolation. The two returns are electrically related through the module, with the current-sensing circuitry intentionally located in the return path.
This module does not include input reverse-polarity protection. Reversing IN+ and IN− can damage the module.
Setting the Output Voltage
Set the output voltage before connecting a battery, LED or sensitive load.
- Disconnect the normal load from OUT+ and OUT−.
- Connect a suitable DC power supply to IN+ and IN−.
- Set a multimeter to DC volts.
- Connect the multimeter across OUT+ and OUT−.
- Apply input power.
- Turn the voltage/CV trimmer until the required output voltage is displayed.
- If the output will not adjust normally and the red CC indicator is active, turn the CC trimmer clockwise to increase the current limit.
- Switch the input supply off and on and confirm the output voltage again before connecting the load.
The current-limit setting normally does not affect the no-load output voltage unless the CC control has been adjusted extremely low or there is another fault or unintended current path.
Setting the Current Limit with a Multimeter
The supplier documentation for this module specifies a direct short-circuit-current method for presetting the CC limit with a multimeter on its high-current DC range. In this test the meter itself provides a very low-resistance current path across the output.
The red probe must be connected to the meter's high-current A or 10A socket and the meter must be set to its appropriate high-current DC range. Do not perform this test using the normal voltage/resistance socket or a low-current mA/µA range.
- Disconnect the battery, LED or other normal load.
- Connect the module to a suitable input supply.
- Set the required output voltage using the CV adjustment.
- Turn the CC trimmer anti-clockwise through several turns to begin with a low current limit.
- Switch off the input supply.
- Move the multimeter's red probe to its high-current A or 10A input.
- Select the appropriate high-current DC current range.
- Check the meter manufacturer's current and time limits for that range.
- Connect the meter directly between OUT+ and OUT−.
- Apply input power.
- Slowly turn the CC trimmer clockwise until the meter displays the required current limit.
- Switch off the input and disconnect the meter promptly after adjustment.
- Return the red probe to the normal voltage/resistance socket before making later voltage measurements.
In current mode the meter places its low-resistance current-measuring path across the module output. The XL4015 module then supplies current into that path up to the selected current limit, input-supply capability and module limits.
If the direct-output test shows only a tiny current and turning the CC control makes no difference, confirm the selected range, probe socket and high-current input path. Depending on the meter, the high-current range may have its own fuse or protection. Follow the meter manufacturer's instructions.
Alternative CC Functional Test with a Known Load
A known load is a useful second test because it demonstrates how current limiting works without intentionally shorting the output. An electronic load is ideal, but a suitable power resistor can also be used.
Example Test: 12V Input, 5V Output, 10Ω Load
A 10Ω resistor connected to 5V would normally draw approximately 0.5A and dissipate approximately 2.5W. Use a resistor rated for at least 5W and allow for it to become hot.
- Connect a regulated 12V supply to IN+ and IN−.
- With no load connected, adjust the output to 5.0V.
- Configure the multimeter to measure DC current on a suitable range.
- Connect the multimeter in series with a 10Ω, 5W or higher power resistor across the module output.
- Turn the CC adjustment anti-clockwise until the module enters current limiting and the measured current falls below approximately 0.5A.
- Slowly turn the CC trimmer clockwise.
- While the module is current-limiting, the measured current should increase as the CC setting is increased.
- Once the current limit rises above what the 10Ω load naturally requires, the current should stop increasing at approximately 0.5A and the module should return to normal constant-voltage regulation.
Expected Result
While current limiting is active, changing the CC setting should change the measured current and the output voltage may fall below the 5V CV setting. Once the selected current limit exceeds the current required by the resistor, further clockwise CC adjustment should no longer increase load current.
If a connected load needs less current than the selected limit, actual current is determined by that load. The CC adjustment only becomes active when the load tries to exceed the selected limit.
Keep the resistor away from plastic, wiring insulation and other heat-sensitive material, and allow it to cool before handling.
Using the Module for Battery Charging
The module can provide constant-current / constant-voltage behaviour when the correct charging voltage and current are already known for the battery being charged.
Use the battery or pack manufacturer's specified maximum charge voltage and permitted charge current. Do not choose the charging current from a generic example or assume that all rechargeable battery chemistries use the same charging method.
- Leave the battery disconnected.
- Set the required maximum charging voltage using the CV adjustment.
- Set the required maximum charging current using the CC adjustment and a suitable current-test method.
- Recheck the output voltage after setting the current limit.
- Switch off the module input.
- Connect battery positive to OUT+ and battery negative to OUT−.
- Check polarity again.
- Apply input power and monitor charging voltage, current and battery temperature during initial operation.
If the battery initially tries to draw more than the selected charging current, the module operates in constant-current mode. As the battery voltage approaches the CV setting, the charging current normally falls and the module transitions into constant-voltage operation.
A lithium battery pack may require over-voltage, under-voltage, over-current and temperature protection plus cell balancing appropriate to its construction. The XL4015 module only regulates its overall output voltage and current.
Nickel-based rechargeable batteries normally require chemistry-specific charge termination and monitoring rather than a simple fixed CC/CV supply.
The module can regulate power from a suitable DC source, including a solar source in some applications, but it does not provide maximum-power-point tracking or battery-management functions.
Using the Module as a Constant-Current LED Driver
The CC function can also be used to limit current through a suitable high-power LED or LED string.
- Check the LED manufacturer's rated operating current and voltage requirements.
- Leave the LED disconnected.
- Set the CV adjustment to an appropriate maximum voltage for the LED or string.
- Set the CC adjustment to the required LED current.
- Switch off the module input.
- Connect the LED to OUT+ and OUT− with correct polarity.
- Apply power and confirm the actual operating current.
- Provide suitable cooling for the LED and the XL4015 module.
The red CC indicator may remain on continuously in a correctly configured constant-current LED application because current regulation is the intended operating mode.
Status LEDs
The supplier documentation shows red, blue and green status indicators. The translated descriptions for the charging indicators are not especially clear, so use the LEDs as status aids rather than precision measurements.
| LED | Supplier-Described Function |
|---|---|
| Red | Indicates that constant-current regulation is active |
| Blue | Associated with charging / higher charging-current operation |
| Green | Associated with the low-current / full-charge indication |
An LED can tell you that a state has changed, but it does not replace measurement of output voltage and current when setting up a charger, LED driver or current-limited supply.
Whether charging should stop, continue at constant voltage or move to another charging stage depends on the battery chemistry and manufacturer's requirements.
Power, Current Sensing & Cooling
The supplier documentation describes an approximately 0.05Ω current-sampling resistor in the output return path. This allows the external CC circuitry to measure load current.
A small load-dependent voltage difference through the current-sensing path is normal. At 5A, 0.05Ω corresponds to approximately 0.25V across the sense resistance.
Connecting IN− and OUT− together externally can provide an alternative current path around the sensing resistor. The current-regulation circuit can then receive an incorrect measurement and may fail to limit the load as intended.
The product is advertised for output currents up to 5A and power up to 75W, but those values should not be treated as guaranteed continuous operating points under all conditions. Actual safe output depends on input voltage, output voltage, load current, wiring, ambient temperature, airflow and cooling.
This is specifically recommended for this module. Monitor the temperature of the regulator, diode, inductor, current-sense components, PCB and screw terminals during initial high-current operation.
A converter that survives a short bench test can become considerably hotter after operating continuously or when installed in an enclosure. Reduce current or improve cooling if temperatures continue to rise.
Troubleshooting
Voltage adjustment works but CC adjustment does nothing
- Remember that CC is a current limit, not a command for the load to draw a particular current.
- If the load is drawing less than the selected limit, adjusting CC may have no visible effect.
- Use the documented high-current multimeter method or the known-load test above to force the module into current limiting.
- Turn the multi-turn CC trimmer through several complete rotations if necessary.
- Confirm IN− and OUT− are not joined externally anywhere in the system.
Direct current-limit test shows only a tiny current
- Check that the multimeter is set to DC current, not DC voltage.
- Check that the red probe is plugged into the meter's high-current A or 10A socket.
- Confirm that the correct high-current range has been selected.
- Check the meter's high-current fuse or protection path if applicable to that meter.
- Confirm the input power supply is actually supplying the module and is capable of providing the test current.
- Turn the CC trimmer clockwise through several complete rotations while watching the current reading.
- If the result is still abnormal, perform the known-load CC test rather than assuming the module is defective.
Meter reads around zero or a few milliamps across OUT+ and OUT−
- A correctly configured high-current meter should provide a low-resistance path that makes the converter enter current limiting.
- A very small reading can indicate the wrong probe socket, wrong range, an open high-current fuse/path, insufficient input power or an incorrectly configured test.
- Take clear photos of the meter display, selected range, probe sockets and complete module wiring when requesting support.
CC works on the bench but not in the finished project
- Check for an external connection between IN− and OUT−.
- Look for a return path through USB cables, computer-connected equipment, oscilloscopes, chassis grounds, power supplies or another circuit board.
- Disconnect other equipment and test the XL4015 module as a standalone circuit.
Output voltage drops when the load is connected
- If the red CC indicator is active, the load is attempting to draw more than the selected current limit.
- Increase the current limit only if the load, module, wiring and power supply can safely handle the additional current.
- Check whether the input supply is sagging or entering its own current limit.
- Allow for the small voltage drop associated with the module's output current-sensing path.
Output cannot reach the selected voltage
- Confirm the input voltage is higher than the desired output voltage.
- Allow additional voltage headroom rather than operating at the converter's dropout limit.
- Check whether the red CC indicator is on; the converter may be current-limiting.
- Measure the input voltage directly at IN+ and IN− while the load is connected.
No output
- Check input voltage and polarity directly at the module terminals.
- Disconnect the load and measure the output again.
- Turn the CC adjustment clockwise in case the current limit has been set extremely low.
- Check for an output short circuit or incorrect wiring.
Module becomes very hot
- Reduce the load current and check whether the temperature stabilises.
- Add airflow or other suitable cooling, particularly above approximately 3A or 35W.
- Check for loose screw-terminal connections and undersized wiring.
- Confirm the converter is not continuously operating in overload or short-circuit conditions.
- Do not assume the advertised 5A / 75W figures are continuous ratings under every operating condition.
Before requesting a replacement for a CC fault
- Record the input supply voltage.
- Identify the load being powered and its expected current draw.
- Record the multimeter make and model.
- Photograph the selected meter range and display.
- Photograph which meter sockets the probes are connected to.
- Photograph the complete wiring between the power supply, module, meter and load.
- Check for any connection between IN− and OUT− outside the module.
- Try the known-load CC test described in this guide.
This is a non-isolated adjustable DC power converter with no input reverse-polarity protection. Do not externally connect IN− and OUT− together, as this can bypass the module's current-sensing path and prevent correct constant-current regulation. Verify output voltage, current limit, polarity, battery or LED requirements and multimeter configuration before connecting valuable equipment. High-current operation requires suitable wiring and thermal management, and the module is not a replacement for a battery BMS, cell balancer, MPPT controller or chemistry-specific charging system where those functions are required.