2CL77 Fast Recovery High Voltage Diode 20KV 5mA 80nS

A 20KV Axial Rectifier for Multiplier Stages

The 2CL77 is a fast recovery high voltage diode rated 20KV, and it holds the middle of the 2CL7 axial range. Its 5mA average forward current, 80nS recovery time and 0.5A surge rating are shared with the 16KV, 18KV and 30KV parts, so the four models differ in blocking voltage and in little else. Between 18KV and 20KV even the forward peak stays at ≥43.0V, which makes the extra two kilovolts a margin that costs nothing in conduction loss. Both blocking figures, repetitive peak and working peak, are quoted at 20KV with 2.0µA of reverse current flowing at 25 °C. Tying a rating to a leakage condition is what makes it usable in a design: the part is expected to hold the full 20KV in service, not only for an instant. The body is a moulded epoxy cylinder with two axial leads and a band at the cathode. It solders into a board, wires point to point into a multiplier ladder, or sits in an oil-filled or potted shell, and the leads form to the hole pitch without special tooling. Every step of the ladder is published by HVDIODE, Suly Electronics Co., Ltd., with its own rating table, test conditions and dimension drawing, in one table format from 16KV to 30KV — the property that lets the figures line up when high voltage diode manufacturers are put side by side. Step | Blocking voltage (Vrrm = Vrwm) | Forward peak voltage | What changes against the step below --- | --- | --- | --- 2CL75 | 16KV | ≥41.0V | Smallest blocking class in the family 2CL76 | 18KV | ≥43.0V | 2KV more blocking, 2V more forward drop 2CL77 | 20KV | ≥43.0V | 2KV more blocking, no change in forward drop 2CL82 | 30KV | ≥52.0V | 10KV more blocking, 9V more forward drop

Construction Details That Matter at 20KV

• Axial leads on a moulded epoxy body — The two leads suit a PCB joint, a point-to-point run in a multiplier ladder or a fixed position inside a potted shell, and they form to the hole pitch without extra hardware. - High thermal conductivity epoxy — The compound carries heat from the chip stack into the body and the leads, and seals the junction from humidity and surface contamination, which is what keeps the reverse characteristic steady as an assembly warms up. - Low internal resistance — Conduction loss stays small at 5mA, and the forward drop holds from one part to the next in a string, so the total drop along a multiplier can be added up from the datasheet figure. - Passivation over the chip surface — The passivation layer holds surface leakage down at 20KV, and surface leakage is the failure mode most high voltage diodes reach first in a warm, contaminated enclosure.

Where the 20KV Step Is Used

Imaging power supplies are the usual home for this voltage class. X-ray, DR, CT and dental panoramic generators rectify at high potential inside multiplier stages, and 20KV covers the intermediate stages of those stacks. Industrial high-voltage test and inspection equipment — NDT sets, DC high-voltage generators, HV test transformers — runs at currents the 5mA rating covers, and accelerator and radar supplies use series strings where a defined reverse margin at modest current counts for more than forward capability. Repair and maintenance is the other steady use. Where a stack has failed, the number on the old part is the place to start; the rest of the ladder shares the current, recovery and surge behaviour, so high voltage diodes one step either side of the original are a workable substitution once the reverse margin in the stack has been checked. Prototype and pre-production builds suit the axial format as well, because the leads are hand-solderable and a first article can be assembled without a reflow profile.

Working Inside the 5mA Forward Rating

The 5mA figure is an average forward current at 50Hz half-sine into a resistive load with Tbreak at 50 °C, and it is the continuous ceiling for this package. It fits the high-voltage side of a supply, where each diode in a multiplier carries only the stage current, but it does not fit a main power path: a design that needs hundreds of milliamps at a few kilovolts belongs in the SMD 5KV range, where a single footprint covers 100mA to 900mA at 75nS.

The other edge is voltage. The ladder stops at 30KV, so a stack that needs more reverse blocking gets more diodes in series rather than a different model, and the forward drops then add along the string.

2CL77 Ratings and Test Conditions

Fitting the Diode Into a High-Voltage Assembly

1. Form the leads before soldering: support the lead at the body, keep the bend clear of the epoxy seal, and set a stand-off so the body does not rest against the board surface.
2. Keep the cathode band facing the same way through the whole string, so a replacement goes in exactly as the part it replaces.
3. Solder with the lead supported and the heat brief; the body should carry no mechanical load from the joint.
4. Clean flux residue from the body and the leads afterwards. At 20KV the surface path between the leads is part of the insulation, and flux, dust or fingerprints shorten it.
5. Dress the lead junction with insulating adhesive once the joint has been inspected — sharp points are where corona starts, and this is the practice high voltage diode manufacturers recommend for oil-filled and potted stacks.
6. Choose the medium deliberately: insulating oil is the recommended environment, insulating gas is next, and open air needs insulated electrodes at both ends plus forced cooling.
7. In a potted shell, plan the thermal path: the surrounding compound becomes part of the insulation and carries the heat, so the electrical margins have to hold at the internal temperature.
8. Test the finished stack at working voltage before it is sealed, and again at working temperature if the design watches leakage.

Potting and Coating Materials

From Order to Dispatch

The same build is available at 16KV, 18KV and 30KV, so a change of margin mid-project does not change the package or the datasheet layout. The rating table and the dimension drawing go with the order. Delivery is by International express.

Technical Support & Model Matching

Selection starts with your circuit, not a catalogue number: tell us the working voltage, load current, switching frequency and ambient cooling conditions, and our engineers will match a model from our range and explain the margin left in the design. Each model ships with its datasheet, package drawing and installation guide, and we stay available for mounting and soldering questions, start-up checks and fault finding when an existing part runs hot or fails early. Orders run from about 7 days to 6 months depending on quantity, usually by international express.

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