MEAN WELL LAD-120 Series 120W Security Power Supply with Battery Charger & UPS Function

Overview of MEAN WELL LAD-120 Series

The MEAN WELL LAD-120 Series combines regulated DC output, dedicated battery charging, UPS backup control and system status monitoring in a compact 120W AC/DC power supply. It is designed for security, fire alarm and backup power applications that require normal DC operation together with automatic battery-supported operation when AC mains power becomes abnormal.

During normal AC operation, the LAD-120 supplies power to the connected load while charging the external battery. If the AC input becomes abnormal, the built-in UPS function switches the power source to battery backup, allowing connected equipment to continue operating during mains interruption. The series also supports a forced UPS mode for battery maintenance and system testing.

The series includes four models. LAD-120A provides a 13.8V main output rated at 7.7A, LAD-120B provides 27.6V at 3.4A, LAD-120C provides 41.5V at 1.9A, and LAD-120D provides 55.2V at 1.21A. Each model also provides a dedicated 1A battery charging output, and the series is suitable for use with lead-acid and lithium-ion batteries.

For system monitoring, the LAD-120 Series provides TTL status signals for AC OK, battery disconnect or reverse polarity, battery low, battery full and discharge status. Built-in protection functions include short circuit, overload, overvoltage, overtemperature, battery low-voltage protection and battery reverse-polarity protection. With a compact 159 × 97 × 30 mm low-profile design and built-in AC and battery circuit ON/OFF switches, the LAD-120 Series is suitable for security systems, fire emergency and evacuation systems, public safety battery backup, DC UPS systems, central monitoring systems and industrial automation.

Features

• 120W AC/DC security and fire alarm power supply with dedicated main output and 1A battery charging output
• Universal 90–264VAC input with 127–370VDC input capability and up to 88% typical efficiency
• LAD-120A provides 13.8V main output rated at 7.7A
• LAD-120B provides 27.6V main output rated at 3.4A
• LAD-120C provides 41.5V main output rated at 1.9A
• LAD-120D provides 55.2V main output rated at 1.21A
• Built-in battery charger and automatic UPS backup operation during abnormal AC input
• TTL status signals for AC OK, battery disconnect or reverse polarity, battery low, battery full and discharge monitoring
• Forced UPS mode supports battery maintenance and system testing
• Short circuit, overload, overvoltage, overtemperature, battery low-voltage and reverse-polarity protection
• Suitable for lead-acid and lithium-ion batteries
• Compact 159 × 97 × 30 mm low-profile design with built-in AC and battery circuit ON/OFF switches

Need help selecting the correct output voltage for your system? Compare LAD-120A, LAD-120B, LAD-120C and LAD-120D below.

Model Selection Guide for LAD-120 Series

The MEAN WELL LAD-120 Series includes four 120W-class AC/DC power supply models with built-in battery charger and UPS backup function. Selection between LAD-120A, LAD-120B, LAD-120C and LAD-120D is primarily determined by the required DC output voltage, load current and battery charging requirements.

All four models share the same 90–264VAC / 127–370VDC input range, 1A battery charging output, UPS backup function, TTL status monitoring, forced UPS mode, battery reverse-polarity protection and compact 159 × 97 × 30 mm low-profile design. The main differences are output voltage, rated current, rated power, voltage adjustment range and battery low-voltage cut-off threshold.

LAD-120A – 13.8V Output

The MEAN WELL LAD-120A provides a 13.8V main output rated at 7.7A together with a 13.8V battery charging output rated at 1A. Rated power is 120W.

The main output voltage can be adjusted from 10.8V to 14.5V. Battery low-voltage cut-off is specified at 9.5V ±0.5V.

LAD-120A is generally selected when the connected load and battery backup architecture require the lowest output-voltage version in the LAD-120 Series.

LAD-120B – 27.6V Output

The MEAN WELL LAD-120B provides a 27.6V main output rated at 3.4A together with a 27.6V battery charging output rated at 1A. Rated power is 121.4W.

The main output voltage can be adjusted from 21.6V to 29V. Battery low-voltage cut-off is specified at 21.5V ±0.5V.

LAD-120B is suitable for systems requiring a 27.6V regulated output with integrated battery charging and UPS backup operation.

LAD-120C – 41.5V Output

The MEAN WELL LAD-120C provides a 41.5V main output rated at 1.9A together with a 41.5V battery charging output rated at 1A. Rated power is 120.35W.

The main output voltage can be adjusted from 32.4V to 43.5V. Battery low-voltage cut-off is specified at 32V ±0.5V.

LAD-120C is intended for higher-voltage backup power architectures requiring a 41.5V regulated output and integrated battery charging.

LAD-120D – 55.2V Output

The MEAN WELL LAD-120D provides a 55.2V main output rated at 1.21A together with a 55.2V battery charging output rated at 1A. Rated power is 121.99W.

The main output voltage can be adjusted from 43.5V to 58V. Battery low-voltage cut-off is specified at 43V ±0.5V.

LAD-120D is the highest-voltage model in the series and is suitable where the connected load and backup battery architecture require a 55.2V output.

How to Choose Between LAD-120A, LAD-120B, LAD-120C and LAD-120D

Start with the required DC output voltage. Choose LAD-120A for 13.8V, LAD-120B for 27.6V, LAD-120C for 41.5V or LAD-120D for 55.2V output.

Then confirm the required load current. LAD-120A provides up to 7.7A, LAD-120B up to 3.4A, LAD-120C up to 1.9A and LAD-120D up to 1.21A. All four models provide a dedicated 1A battery charging output.

When AC input is normal, the LAD-120 supplies the connected load while charging the external battery. When the AC input becomes abnormal, the built-in UPS function switches the system to battery backup operation.

Status Monitoring and UPS Control

All LAD-120 models provide TTL status signals for AC OK, battery disconnect or reverse polarity, battery low, battery full and discharge status. The TTL interface requires an external voltage source and supports up to 50VDC applied voltage with a maximum sink current of 30mA.

The series also provides a forced UPS mode through CN2 pins 7 and 8. Shorting these pins activates forced UPS operation, while leaving them open keeps the unit in normal operating mode.

Need help choosing the correct LAD-120 model? Start with the required output voltage, then confirm load current, battery charging requirements, backup operation and monitoring interface requirements.

Related MEAN WELL LAD, PSC and Security Power Supplies

For security systems, fire alarm systems, emergency power, central monitoring and battery backup applications, the following MEAN WELL power supplies can be compared with the LAD-120 Series according to required output power, output voltage, battery charging capability, UPS function, monitoring requirements and installation format:

• LAD-240 Series – Higher-power LAD Series security and fire alarm power supply with integrated battery charger, UPS backup function and system monitoring for applications requiring more output capacity than LAD-120.
• LAD-360 Series – Higher-capacity LAD Series power supply for security, fire alarm and battery backup systems requiring greater load power and charging capability.
• LAD-600 Series – High-power LAD Series security and emergency backup power solution for systems requiring substantially greater output capacity, battery charging and UPS operation.
• PSC-35 Series – Lower-power AC/DC power supply with integrated battery charger and UPS backup function for security and battery-backed DC applications with lighter load requirements.
• PSC-60 Series – Compact 60W power supply with battery charger and UPS function for applications requiring lower output power than LAD-120.
• PSC-100 Series – 100W battery charger power supply with UPS backup function for security, alarm and DC backup applications requiring lower output power.
• PSC-160 Series – Higher-power 160W AC/DC power supply with integrated battery charger and UPS backup function for systems requiring greater load and charging capacity.
• DRC-60 Series – DIN rail AC/DC power supply with integrated battery charger and UPS function for systems that require TS35 rail installation.
• DRC-100 Series – DIN rail security power supply with battery charging and automatic backup operation for higher-power DIN rail applications.
• DRS-240 Series – Intelligent DIN rail security power supply integrating AC/DC power, battery charger, DC UPS, status monitoring and communication functions for advanced backup power systems.

Need help selecting the right MEAN WELL security power supply?
Compare LAD, PSC, DRC and DRS Series based on required output voltage, load power, battery charging current, UPS backup operation, status monitoring, communication functions and installation format.

Battery Backup and Status Monitoring Functions

The MEAN WELL LAD-120 Series integrates battery charging, UPS backup control and multiple TTL status signals for security, fire alarm and DC backup systems that require continued operation and external status monitoring during AC mains interruption.

Battery Backup Operation

During normal AC operation, the LAD-120 supplies power to the connected load while charging the external battery. If the AC input becomes abnormal, the built-in UPS function switches the power source to battery backup so the connected load can continue operating.

The series includes four output versions: LAD-120A at 13.8V, LAD-120B at 27.6V, LAD-120C at 41.5V and LAD-120D at 55.2V. Each model also provides a dedicated 1A battery charging output.

TTL Status Monitoring

The LAD-120 Series provides multiple TTL status signals through the CN2 interface for external monitoring and control:

• AC OK: Indicates whether the AC input is normal or abnormal
• Battery Disconnect / Reverse Polarity: Detects battery connection status or reverse-polarity condition during initial power transmission
• Battery Low: Indicates a low-battery condition
• Battery Full: Indicates whether the battery is still charging or has reached full-charge status
• Discharge: Indicates whether the system is operating from battery backup

The TTL interface requires an external voltage source and supports a maximum applied voltage of 50VDC with a maximum sink current of 30mA.

Battery Low-Voltage Cut-Off Protection

To help prevent excessive battery discharge during extended backup operation, the LAD-120 Series includes battery low-voltage cut-off protection:

• LAD-120A: 9.5V ±0.5V battery cut-off
• LAD-120B: 21.5V ±0.5V battery cut-off
• LAD-120C: 32V ±0.5V battery cut-off
• LAD-120D: 43V ±0.5V battery cut-off

The series also provides battery reverse-polarity protection. If the battery is connected with reversed polarity, the unit is protected from damage and recovers automatically after the fault condition is removed.

Forced UPS Mode

For battery maintenance and system testing, the LAD-120 Series provides a forced UPS mode through CN2 pins 7 and 8.

When pins 7 and 8 are shorted, the unit enters forced UPS mode. When the pins are open, the unit operates normally. This function allows the battery backup path to be tested without waiting for an actual AC mains failure.

Need wiring and connector details? Continue below to review the LAD-120 mechanical drawing, CN2 TTL signal pin assignment, terminal assignment and installation information.

Mechanical Dimensions and Installation

The MEAN WELL LAD-120 Series uses a compact low-profile mechanical design intended for integration into security, fire alarm, battery backup and DC UPS equipment. The series has a height of only 30 mm, helping reduce enclosure space requirements in compact system designs.

Dimensions

The LAD-120 Series measures 159 × 97 × 30 mm (L × W × H) and uses Case No. 241.

The mechanical drawing identifies the mounting-hole positions, terminal block, CN2 signal connector, AC ON/OFF switch, battery connected/disconnected switch and airflow direction. The same mechanical platform is used across the LAD-120 Series.

TB1 Terminal Assignment

The main power and battery connections are provided through the TB1 terminal block:

• Pin 1: AC/L
• Pin 2: AC/N
• Pin 3: FG
• Pin 4: DC OUTPUT -V
• Pin 5: DC OUTPUT +V
• Pin 6: BAT –
• Pin 7: BAT +

CN2 TTL Signal Assignment

The CN2 connector provides status monitoring and forced UPS control signals:

• Pin 1: AC OK
• Pin 2: Battery disconnect / reverse polarity
• Pin 3: Battery Low
• Pin 4: GND
• Pin 5: Battery Full
• Pin 6: Discharge
• Pins 7 and 8: Open for normal operation; short for forced UPS mode

The specified CN2 mating components are TKP DH2 or equivalent for the housing and TKP DHT-1S(LF) or equivalent for the terminal.

Operating Environment and Derating

The LAD-120 Series is specified for operation from -20°C to +60°C. Output load should be reduced as ambient temperature increases beyond the full-load operating region.

The mechanical design also defines the required airflow direction. Adequate ventilation should be provided when the power supply is installed inside the final equipment enclosure.

Mechanical Drawing and Installation Reference

The LAD-120 mechanical drawing shows overall dimensions, mounting points, TB1 terminal locations, CN2 connector position, AC ON/OFF switch, battery connected/disconnected switch and airflow direction.

For final enclosure design and wiring, review the official LAD-120 Series datasheet and MEAN WELL installation manual to confirm mounting dimensions, connector details, wiring requirements and installation conditions.

Need complete installation details? Use the mechanical drawing above together with the installation documentation to verify mounting, TB1 wiring, CN2 TTL signal connections and forced UPS control.

Applications

The MEAN WELL LAD-120 Series is designed for security, fire alarm and backup power applications requiring regulated DC output, battery charging, UPS operation and external status monitoring.

With LAD-120A, LAD-120B, LAD-120C and LAD-120D covering 13.8V, 27.6V, 41.5V and 55.2V output versions, the series provides a flexible platform for systems that require continuous DC operation, battery-supported backup and TTL status detection.

• Fire emergency and evacuation systems requiring reliable DC power, battery charging and backup operation during abnormal AC input
• Security systems requiring regulated DC power together with battery backup and system status monitoring
• Public safety battery backup systems requiring continued operation from an external battery during AC mains interruption
• Uninterruptible DC-UPS systems requiring automatic transfer to battery-supported operation when AC input becomes abnormal
• Central monitoring systems using TTL signals for AC OK, battery status, battery low, battery full and discharge monitoring
• Industrial automation systems requiring regulated DC output, battery charging and backup power integration

Need safety and compliance details for your project? Continue below to review protection functions, safety approvals, EMC compliance and operating environment specifications for the LAD-120 Series.

Certifications and Safety

The MEAN WELL LAD-120 Series is designed as a 120W AC/DC security and fire alarm power supply with integrated battery charging, UPS backup and status monitoring functions for systems requiring continued DC operation during abnormal AC input conditions.

The series is approved to UL62368-1, BS EN/EN62368-1, AS/NZS62368.1 and EAC TP TC 004. Its design also refers to GB 17945-2010 system requirements.

Safety and EMC Compliance

The LAD-120 Series is specified with the following safety and EMC standards:

• UL62368-1 safety approval
• BS EN/EN62368-1 safety approval
• AS/NZS62368.1 safety approval
• EAC TP TC 004 safety approval
• GB 17945-2010 referenced in the product design requirements
• BS EN/EN55032 (CISPR32) Class A conducted and radiated EMC emissions
• BS EN/EN61000-3-2 Class A harmonic current requirements
• BS EN/EN61000-4-2, -4-3, -4-4, -4-5, -4-6 and -4-8 EMC immunity tests
• EAC TP TC 020 EMC requirements

Isolation and Electrical Safety

Withstand voltage ratings are:

• Input to output: 3KVAC
• Input to FG: 2KVAC
• Output to FG: 0.5KVAC

Isolation resistance is specified at 100MΩ between input-output, input-FG and output-FG when tested at 500VDC, 25°C and 70% RH.

Protection Functions

The LAD-120 Series includes protection against short circuit, overload, overvoltage, overtemperature, battery low voltage and battery reverse polarity.

Overload behavior depends on the operating condition. With a battery connected, the unit can enter UPS operation under CH1 overload conditions, while excessive combined CH1 and CH2 loading can cause hiccup protection. Without a battery connected, overload protection follows the applicable model and operating condition.

Overvoltage and overtemperature protection shut down the output and require the power supply to be re-powered after the fault condition is removed. Battery reverse-polarity protection prevents damage and automatically recovers after correct battery connection is restored.

Operating Environment and Final Equipment Integration

The LAD-120 Series operates from -20°C to +60°C, with output derating at higher ambient temperatures.

The power supply is intended for integration into final equipment. EMC performance is therefore also influenced by the completed system, including enclosure design, grounding, wiring and installation conditions.

System designers should verify wiring, grounding, enclosure layout, thermal conditions, airflow and EMC performance in the final installation.

Need more product details before sending an inquiry? Continue below to review model comparison, battery backup operation, TTL status signals, forced UPS mode, mechanical dimensions, installation guidance and application information for the LAD-120 Series.