The MEAN WELL LAD-120B is a 27.6 V security and fire-alarm power supply with a 3.4 A CH1 load output and a 1 A CH2 battery-charging output, sharing a 121.4 W total rating. It integrates DC-UPS backup, TTL status monitoring and AC / battery maintenance switches.
Product Datasheet
Download MEAN WELL LAD-120 Datasheet (PDF)
The LAD-120 section is on PDF pages 10, 11, 12, 13, 14, 15. Refer to the complete mechanical drawings and notes when planning installation.
Model and Output Ratings
| Full model |
LAD-120B |
| Series |
LAD-120 |
| CH1 output voltage |
27.6 V |
| CH1 rated current |
3.4 A |
| CH2 charge voltage |
27.6 V |
| CH2 rated charging current |
1 A |
| Rated total output power |
121.4 W |
| CH1 current range |
0–4.4 A |
| CH1 voltage adjustment |
21.6–29 V |
| CH1 ripple and noise, maximum |
150 mVp-p |
| CH1 voltage tolerance |
±1.0% |
| CH1 line regulation |
±0.5% |
| CH1 load regulation |
±0.5% |
CH1 supplies the load and CH2 charges an external battery. Both channels share the rated total output power; the charging channel is not an additional independent power allowance. Keep each channel within its rating and the combined load within the total power limit.
The CH1 VR adjustment covers the stated voltage range. Select a lead-acid or lithium-ion battery with a charging-voltage requirement and protection system suitable for this model. This model provides TTL status signals; UART communication and a buzzer are not specified for this version.
Input and Electrical Performance
| Input voltage range |
90–264 VAC; 127–370 VDC |
| Input frequency |
47–63 Hz |
| Typical efficiency |
88% |
| Typical AC input current |
2.5 A at 115 VAC; 1.5 A at 230 VAC |
| Typical cold-start inrush current |
30 A at 115 VAC; 55 A at 230 VAC |
| Leakage current |
0.5 mA at 240 VAC |
| Set-up / rise time at full load |
500 / 40 ms at both 115 and 230 VAC |
| Typical hold-up time at full load |
40 ms at 230 VAC; 9 ms at 115 VAC |
| Battery static discharge current |
Less than 100 µA |
| Switching frequency |
65 kHz |
The AC input accepts the continuous 90–264 VAC range without a 115 / 230 VAC selector.
Unless otherwise stated, specifications are measured at 230 VAC, rated load and 25°C ambient. Ripple and noise use a 20 MHz bandwidth, a 12-inch twisted pair and parallel 0.1 µF / 47 µF capacitors. Voltage tolerance includes set-up tolerance, line regulation and load regulation.
Battery Backup and Protection
| CH1 overload threshold |
105–135% |
| CH2 overload threshold |
90–110% |
| CH1 overvoltage threshold |
31–36 V |
| Battery cutoff voltage |
21.5 ± 0.5 V |
| Battery reverse-polarity protection |
No damage; automatic recovery after the connection is corrected |
| Overvoltage and overtemperature response |
Output shutdown; reapply input power to recover |
If the AC input becomes abnormal, the DC-UPS function transfers the load to the external backup battery. Built-in AC and battery circuit switches provide maintenance control. The battery is external and is not included with the power supply.
With a battery connected to CH2, CH1 overload around 105–160% causes the unit to enter UPS mode. When the combined CH1 + CH2 output reaches around 125–135%, the output enters hiccup protection and recovers automatically after the fault is removed.
Without a battery, CH1 overload uses hiccup protection with automatic recovery after the fault is removed.
CH2 uses constant-current limiting, recovers automatically after the fault is removed, and its fault does not stop CH1 operation. An external fuse in series with the battery is mandatory. Short-circuit, overload, overvoltage, overtemperature, battery undervoltage and reverse-polarity protection are provided.
TTL Status and Forced UPS Operation
| CN2 pin 1, AC OK |
Relative to pin 4: low = normal AC input; high/open = abnormal AC input |
| CN2 pin 2, battery disconnect / reverse polarity |
Relative to pin 4: low = disconnected or reversed; high/open = connected normally |
| CN2 pin 3, battery low |
Relative to pin 4: low = battery under undervoltage protection; high/open = normal battery |
| CN2 pin 4 |
GND |
| CN2 pin 5, battery full |
Relative to pin 4: low = fully charged; high/open = charging |
| CN2 pin 6, discharge |
Relative to pin 4: low = battery-backup discharge; high/open = main power working |
| CN2 pins 7 and 8 |
Short = forced-start UPS mode; open = normal operation |
| Status-output external voltage, maximum |
50 VDC |
| Status-output sink current, maximum |
30 mA |
| Status-output low level, maximum |
0.3 V at 30 mA |
Provide an external voltage source and pull-up resistor for the status signals. Observe the maximum applied voltage and sink current; the signal output is not an internal power source.
Battery-disconnected and reverse-polarity detection is available during the initial transmission at startup, rather than continuous detection at any time. Short CN2 pins 7 and 8 to force UPS operation for battery maintenance; opening them restores normal operation.
Terminal Connections and Mating Parts
| TB1 pin 1 |
AC/L |
| TB1 pin 2 |
AC/N |
| TB1 pin 3 |
FG |
| TB1 pin 4 |
DC OUTPUT −V |
| TB1 pin 5 |
DC OUTPUT +V |
| TB1 pin 6 |
BAT− |
| TB1 pin 7 |
BAT+ |
| CN2 mating housing |
TKP DH2 or equivalent |
| CN2 mating terminal |
TKP DHT-1S(LF) or equivalent |
DC OUTPUT −V and BAT− must not be shorted. Keep load and battery wiring on their assigned terminals and connect protective earth to FG. Follow the mechanical drawing for connector orientation and the AC / battery switch positions.
Select mating parts for the actual circuit count and wire assembly. The catalogue identifies the housing and terminal references without specifying an included signal harness.
Cooling and Derating
| Cooling arrangement |
Ventilated enclosure with free-air cooling |
| Working temperature |
−20 to +60°C, subject to derating |
| Horizontal temperature curve |
100% load from −20 to 50°C; 60% load at 60°C |
| Input-voltage load curve |
80% at 90 VAC; 100% at 115–264 VAC, 60 Hz |
| Working humidity |
20–95% RH, non-condensing |
| Storage temperature and humidity |
−30 to +85°C; 10–95% RH, non-condensing |
| Temperature coefficient |
±0.03%/°C, 0–50°C |
| Vibration |
10–500 Hz, 5 G; 10 minutes per cycle, 60 minutes along each X, Y and Z axis |
Apply the input-voltage and temperature load limits together. Above 2000 m, reduce allowable ambient temperature by 3.5°C per 1000 m for fanless models or 5°C per 1000 m for fan-cooled models. Keep ventilation paths and the marked airflow direction clear.
Safety and EMC
| Approved safety standards |
UL 62368-1; BS EN / EN 62368-1; AS/NZS 62368.1; EAC TP TC 004 |
| System design reference |
GB 17945-2010 |
| Withstand voltage |
Input–output: 3 kVAC; input–FG: 2 kVAC; output–FG: 0.5 kVAC |
| Isolation resistance |
Input–output, input–FG and output–FG: 100 MΩ at 500 VDC, 25°C and 70% RH |
| Conducted and radiated emissions |
BS EN / EN 55032 (CISPR 32), Class A; EAC TP TC 020 |
| ESD immunity |
8 kV air / 6 kV contact; criterion A |
| Radiated immunity |
BS EN / EN 61000-4-3: 10 V/m; criterion A |
| EFT / burst immunity |
BS EN / EN 61000-4-4: 2 kV; criterion A |
| Surge immunity |
BS EN / EN 61000-4-5: 1 kV line–line / 2 kV line–FG; criterion A |
| Conducted immunity |
BS EN / EN 61000-4-6: 10 V; criterion A |
| Magnetic-field immunity |
BS EN / EN 61000-4-8: 30 A/m; criterion A |
This is a component for installation in final equipment. Catalogue EMC tests mount the supply on a 360 × 360 mm metal plate, 1 mm thick. The completed installation must be checked against the relevant EMC requirements.
Harmonic-current testing to BS EN / EN 61000-3-2, Class A, is specified at 85% load.
Mechanical Installation and Reference Mass
| Catalogue dimensions, L × W × H |
159 × 97 × 30 mm |
| Drawing case number |
241 |
| Drawing dimensional tolerance |
±1 mm |
| Mass, catalogue PACKING reference per unit |
420 g |
| Catalogue packing |
0.42 kg; 30 units / 13.6 kg / 0.77 CUFT |
| Minimum MTBF, Telcordia / MIL-HDBK-217F |
1509.9K / 209.4K hours |
| Warranty |
3 years |
The 30 mm low-profile enclosure has three side M3 mounting points marked L = 5 mm and 3.5 mm mounting holes. Follow the case 241 drawing for mounting coordinates and switch access.
