MEAN WELL DBUF20-24 is a DIN rail electrolytic-capacitor buffer module for regulated 24 VDC systems, with a maximum buffer output current of 20 A. At 22 VDC and 20 A it provides 350 ms typical and 250 ms minimum buffering. It supports selectable fixed or dynamic trigger thresholds and status monitoring; duration depends on the load and operating conditions.
Product Datasheet
Download MEAN WELL DBUF20 Datasheet (PDF)
The DBUF20 section is on PDF pages 1, 2, 3, 4, 5, 6, 7. Refer to the complete mechanical drawings and notes when planning installation.
Model and Operating Principle
| Complete model |
DBUF20-24 |
| Product type |
DIN rail buffer module for a regulated 24 VDC power supply. Energy is stored in electrolytic capacitors instead of lead-acid batteries. |
| Model code |
DBUF identifies the DIN rail buffer family; 20 is the 20 A maximum buffer output; 24 is the nominal system voltage. |
| Use |
Supplementary short-duration support for industrial controls, semiconductor fabrication equipment, factory automation and electromechanical apparatus. |
The module charges from an existing DC supply and releases stored energy when the selected voltage threshold is reached. It is not an AC-input power supply or a battery UPS with unlimited hold-up time.
Charging and DC Buffer Ratings
| Nominal system voltage |
24 VDC. |
| Charging voltage |
23–30 VDC. |
| Charging / standby current |
900 mA maximum during charging; 100 mA maximum in standby. Allow for this additional demand when sizing the upstream supply. |
| Charging time |
15 s typical; 25 s maximum. |
| Buffer operating range |
22–29 VDC. Fixed mode uses 22 VDC; dynamic mode follows the Vin−1 V setting described below. |
| Maximum buffer current |
20 A per DBUF20-24, subject to the finite buffering time and installation conditions. |
| Buffer time at 20 A |
At 22 VDC: 350 ms typical; 250 ms minimum. |
| Buffer time at 10 A |
At 22 VDC: 700 ms typical; 500 ms minimum. |
| Buffer time at 0.1 A |
At 22 VDC: 45 s typical; 30 s minimum. |
| Additional curve reference |
The typical 22 VDC buffering curve marks approximately 1.4 s at 5 A. Use the complete curve for intermediate loads; do not treat a typical curve value as a guaranteed minimum. |
| Ripple and noise, maximum |
200 mVp-p. Measured at 20 MHz bandwidth using a 12-inch twisted pair terminated by parallel 0.1 µF and 47 µF capacitors. |
Charging and buffering have different voltage ranges. All three tabulated buffering cases apply to this same complete model; they are operating points, not separate output-channel or power-supply variants.
Mode Selector and Status Indication
| Fixed mode — factory setting |
With the switch at Fix 22Vdc, buffering starts when terminal voltage falls below 22 VDC. |
| Dynamic mode |
With the switch at Vin−1Vdc, buffering starts when the input terminal voltage decreases by 1 VDC. |
| LED continuously on |
Ready: the capacitors are fully charged. |
| LED off |
The capacitors are discharged. |
| LED flashing at 1 Hz |
The capacitors are charging. |
| LED flashing at 10 Hz |
The module is buffering and its capacitors are discharging. |
The operating diagram shows charging, standby and buffer states separately. After the upstream supply loses AC input, its own hold-up interval precedes the module’s illustrated buffering interval.
Control and Monitoring Signals
| Signal supply +Vs |
10–35 VDC / 10 mA as specified. Supply +Vs from the module’s +V or from an external voltage source using the corresponding application wiring. |
| Inhibit input I |
Buffer module ON when +Vs−V(I) <6 VDC; buffer module OFF when +Vs−V(I) >10 VDC. Maximum: 35 VDC / 4 mA. The intermediate region is not assigned a guaranteed state. |
| Ready output R |
Charged-ready state: V(R) >+Vs−2 VDC. Unready state: V(R) <1 VDC. Maximum: 35 VDC / 10 mA. |
| Buffering output B |
Buffering state: V(B) >+Vs−2 VDC. Other modes: V(B) <1 VDC. Maximum: 35 VDC / 10 mA. |
| Signal interface |
The block and signal diagrams show optocouplers for I, R and B. These monitoring outputs are not specified as potential-free relay contacts. |
Follow the complete application circuit for signal return paths, external indicators or relay loads and the inhibit switch. The diagrams show both a signal supply taken from the DC rail and a separate external signal supply; do not substitute an AC connection at these signal terminals.
Protection
| Overvoltage |
31–37.5 V: output-voltage shutdown. |
| Overload in buffer mode |
105–125% of rated output power as specified; output-voltage shutdown, re-power to recover. This is a protection threshold, not an additional continuous-output rating. |
| Short circuit |
Output-voltage shutdown; re-power to recover. |
| Reverse polarity |
Internal MOSFET protection; automatic recovery after the fault is removed. |
| Signal TVS rating |
35 V maximum, as listed in the protection table. |
Use the charging, buffer and signal-terminal limits for their respective circuits. Protection does not replace correct polarity, wiring or load sizing.
Connection and Parallel Applications
| Main DC wiring |
Connect the regulated DC supply, load and buffer module to the same DC rails with the polarities shown in the general wiring diagram. The module’s main terminals are +V and −V; there are no AC L/N input terminals on this module. |
| Parallel buffer units |
The catalogue allows parallel buffer modules to increase output capacity or extend buffering time and provides a two-unit example. Follow the illustrated main-rail and signal wiring for each unit. |
| Parallel selection limits |
The assigned catalogue pages do not state a numerical maximum unit count or a guaranteed combined buffer-time formula. Keep each unit within its own ratings and size the upstream supply for charging demand as well as the load. |
| External application components |
The diagrams show a power supply, load, Ready/Buffering relay or signal loads, an inhibit switch and an optional external signal-voltage source. Complete order codes and included quantities for these external items are not specified. |
The illustrated application parts are not a promise that relays, indicators, switches or another power supply are supplied with the DBUF20-24.
Cooling and Environment
| Cooling / working temperature |
Free-air convection; −25 to +75°C. The vertical-installation load curve shows 100% through this range, subject to the other catalogue conditions. |
| Working humidity |
5–95% RH, non-condensing. |
| Storage temperature |
−25 to +80°C. |
| Temperature coefficient |
±0.03%/°C over 0–75°C. |
| Operating altitude |
Up to 5,000 m; overvoltage category II. Above 2,000 m, reduce the permissible ambient temperature by 3.5°C per 1,000 m for this fanless design. |
| Shock test |
IEC60068-2-27; 30 G (300 m/s²), 18 ms, one time per direction and two times in total as listed. |
| Vibration |
Component: 10–500 Hz, 2 G, 10 minutes per cycle, 60 minutes each along X, Y and Z. Mounting clip: compliance with IEC60068-2-6. |
Apply the installation orientation, altitude and DC operating limits together; the ambient-temperature endpoint does not remove the finite-energy buffering limit.
Dimensions, Terminals and Mounting
| Dimensions, W × H × D |
63 × 125.2 × 114.9 mm; drawing tolerance ±1 mm; case 979E. |
| TB1 main terminals |
Pins 1 and 2: DC +V. Pins 3 and 4: DC −V. |
| TB2 signal terminals |
Pin 1: FG; pin 2: Inhibit (I); pin 3: Ready (R); pin 4: Buffering (B); pin 5: supply voltage (+Vs). |
| Front elements |
The main terminal block, mode selector and status LED are above the lower signal terminal block, as shown in the mechanical drawing. |
| DIN rail |
Fits TS35/7.5 or TS35/15. The rail illustrated is for reference and is not included with the unit. |
Mount vertically and follow the supplied installation instructions. The catalogue does not specify terminal torque, conductor size or a separate complete mounting-accessory order code in these assigned pages; select and install these items using the applicable installation documentation.
Safety, EMC and Measurement Conditions
| Safety approvals |
IEC62368-1 and UL62368-1 are listed as approved. |
| Withstand voltage |
Combined input/output circuit to FG: 2.2 kVDC; signals to FG: 2.2 kVDC. No input-to-output isolation rating is inferred. |
| Isolation resistance |
Greater than 100 MΩ for input/output-to-FG and signals-to-FG, tested at 500 VDC, 25°C and 70% RH. |
| EMC emissions |
Conducted and radiated emissions: BS EN/EN55032 Class B. No harmonic-current or flicker test level is listed for this DC buffer module. |
| EMC immunity framework |
BS EN/EN55035 and BS EN/EN61000-6-2. The following listed tests use criterion A. |
| ESD / radiated immunity |
BS EN/EN61000-4-2: 15 kV air and 8 kV contact discharge. BS EN/EN61000-4-3: 10 V/m. |
| EFT / surge immunity |
BS EN/EN61000-4-4: 2 kV. BS EN/EN61000-4-5: 1 kV line-to-line and 2 kV line-to-FG. |
| Conducted / magnetic-field immunity |
BS EN/EN61000-4-6: 10 V. BS EN/EN61000-4-8: 30 A/m. |
| Default measurement conditions |
Unless stated otherwise: normal input, rated load and 25°C ambient. |
Reconfirm compliance of the completed equipment and the whole system with the applicable EMC requirements.
Weight and Reliability
| Single-unit catalogue weight |
1,062 g (1.062 kg), explicitly stated in the PACKING entry. This is a single-unit catalogue reference, not a shipping-package weight or measured net-weight claim. |
| Packing reference |
12 pieces / 12.8 kg / 0.74 CUFT. |
| MTBF estimates at 25°C |
164.8 thousand hours minimum by MIL-HDBK-217F; 1,510.0 thousand hours minimum by Telcordia TR/SR-332 (Bellcore). |
| MTBF estimates at 40°C |
108.6 thousand hours minimum by MIL-HDBK-217F; 765.8 thousand hours minimum by Telcordia TR/SR-332 (Bellcore). |
| Catalogue warranty |
The catalogue lists a 3-year manufacturer warranty, subject to the applicable terms. |
MTBF figures are statistical estimates under the named methods, not guaranteed service life.
