Power conversion · Output current by cooling and ambient, surge and I²t, voltage class, packages and protection
A rectifier bridge converts alternating current to direct current with diodes in a bridge, from small single-phase packages to three-phase modules and heavy-current stacks on heatsinks. Ask three things first: the DC current at your cooling and ambient temperature, the reverse voltage class and surge (I²t) rating, and the protection and mounting it comes with.
Single-phase and three-phase rectifier bridges: packaged bridges, isolated bridge modules, high-voltage bridges and assembled stacks with heatsinks. Controlled thyristor bridges, alternator and generator rectifier spare parts, and complete power supplies are outside this page.
CNFX editorial research · Sources checked October 19, 2026 · 4 sources
Rate the current for your cooling and ambient temperature
GD Rectifiers' three-phase diode bridge (B6U) range lists maximum continuous output current at 30 °C and 40 °C ambient with natural (NAC) or forced (FAC) air cooling, device I²t and a VRRM of 1,800 V: for example 165 A at 30 °C and 155 A at 40 °C in natural air, 615 A and 565 A in a 34 kg natural-air stack, and 650 A and 600 A in a 10.5 kg forced-air stack. Options include line fuses, dv/dt and MOV overvoltage suppression, thermal trips, standby fans, water or oil cooling and IP20 enclosures. [1]
Editorial calculation: moving from 30 °C to 40 °C ambient cuts the 165 A rating by about 6%, and the forced-air stack carries a similar current to the 34 kg natural-air one at about a third of the weight, but it depends on its fans. [1] State your enclosure temperature and whether fans are acceptable.
Give the supplier the AC input (phases, voltage, frequency), DC load current and duty, overloads and inrush, ambient and enclosure temperature, cooling (natural, forced air, liquid), voltage class, protection required (fuses, suppression, thermal trips), isolation, mounting and approvals.
02
Check surge, I²t, voltage class and construction
Semikron's SKDH146/...-L140, a three-phase bridge module that also carries an IGBT braking chopper, gives in its datasheet a bridge output current of 140 A at 80 °C heatsink with inductive load, a surge current of 1,250 A and I²t of 7,800 A²s for a 10 ms half-sine, voltage classes of 1,200 V and 1,600 V VRRM, 3,000 V AC isolation for 1 minute through a DCB ceramic, and a maximum rectifier-diode junction temperature of 150 °C. [2]
Editorial calculation: for a 10 ms half-sine, I²t ≈ IFSM² × 0.005 s = 1,250² × 0.005 ≈ 7,800 A²s, matching the stated value. [2] Ask how fuses are coordinated with the device I²t.
Semikron's application manual explains that disk-type (capsule) diodes cooled on both sides have about half the thermal resistance of the same chip in a screw-mounted case, are used "mainly for high power applications (several 100A up to several kA)", reach reverse blocking voltages of more than 10 kV, need two heatsinks and a clamp, and remain safely shorted after a surge failure. Stud-screw diodes are robust and hermetic but their heatsink is at anode or cathode potential, not insulated. [3]
03
Derate a small single-phase bridge for load type and mounting
Diotec's GBU8A–GBU8M datasheet (version 2026-04-10) for a single-phase diode bridge in the GBU package shows how the rated current depends on mounting and load. Free-standing at 40 °C ambient, the bridge is rated 5.6 A with a resistive load and 4.5 A with a capacitive load; on a 300 cm² cooling fin at a case temperature of 100 °C it is rated 8.0 A resistive and 6.4 A capacitive. The series covers repetitive peak reverse voltages from 50 V (GBU8A) to 1,000 V (GBU8M), with maximum AC input voltages from 35 V to 700 V, a peak forward surge current of 180 A at 50 Hz (10 ms) or 200 A at 60 Hz (8.3 ms), an i²t of 162 A²s, a forward voltage below 1.0 V at 8 A, leakage below 5 µA at rated voltage, a −50 to +150 °C junction range, UL recognition under file E175067 and a mounting torque of 1 N·m. [4]
Cooling also changes the ratings of the three-phase bridges above, which are given for natural and forced air cooling, so state load type and cooling when asking for a current rating. [1][2][3]
Editorial calculation: the capacitive-load rating is 80% of the resistive rating in both mounting cases (4.5/5.6 and 6.4/8.0); fitting the 300 cm² fin raises the resistive rating by about 43%, from 5.6 A to 8.0 A, though the two ratings are given at different reference temperatures.
GBU8 rating (Diotec)
Resistive load
Capacitive load
Free-standing, TA = 40 °C
5.6 A
4.5 A
On 300 cm² fin, TC = 100 °C
8.0 A
6.4 A
Surge current, 50 / 60 Hz half-sine
180 A / 200 A
—
i²t (t < 10 ms)
162 A²s
—
VRRM range
50–1,000 V (GBU8A–GBU8M)
—
Give the supplier the input voltage, load current, load type (resistive or capacitor-input) and the heatsink or ambient condition, and ask for the current rating and surge rating under those conditions.
04
From GBU packages to 2,400 A forced-air stacks: where each linked maker sits
The current classes on this page span three orders of magnitude: Diotec's GBU8 is an 8 A single-phase package [4], Semikron's SKDH146 a 140 A isolated module [2], and GD Rectifiers' B6U stacks run from 37 A to 2,400 A [1]. Place each quotation in one of those classes before comparing prices.
Greegoo lists single- and three-phase bridge rectifiers and bridge modules with semiconductor fuses; LCTC lists rectifier bridges and bridge rectifier modules; Suly lists high-voltage rectifier bridges and silicon stacks; World and JSMicro list packaged bridge rectifiers with other diodes; Yunyi lists rectifier bridges alongside alternator rectifiers.
05
Diodes, DCB substrate, heatsink, clamp and protection in a bridge
Part
Role
Fix in the order
Diodes
Disk, stud or chip-in-module; set current and voltage. [3][2]
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
Why does a rectifier bridge's current rating change with temperature?
Ratings are given at a stated ambient and cooling; one published stack drops from 165 A at 30 °C to 155 A at 40 °C. [1]
What does I²t mean on a rectifier datasheet?
The surge rating for a short pulse, e.g. 7,800 A²s for a 10 ms half-sine, which matches that module's 1,250 A surge current; ask how fuses are coordinated with it. [2]
When are disk-type diodes used?
Semikron says disk cells are used "mainly for high power applications (several 100A up to several kA)"; two-sided cooling halves thermal resistance but needs two heatsinks and a clamp. [3]
Why is a bridge rectifier rated lower with a capacitor load?
Datasheets give separate ratings: Diotec rates its GBU8 bridge 5.6 A resistive but 4.5 A capacitive when free-standing at 40 °C, and 8.0 A versus 6.4 A on a 300 cm² cooling fin. [4]
Sources and what still needs a direct check
Sources checked 2026-10-19. GD Rectifiers and Semikron Danfoss are rectifier makers; their published data are used as worked examples, not recommendations.
