2CL71 Fast Recovery High Voltage Diode 8KV 5mA 80nS

Eight Kilovolts at the Top of the 2CL7 Range

Eight kilovolts is the top of the 2CL7 axial family, and the 2CL71 is the step that lets a rectifier string hold its margin without adding another body to the stack. Average forward current is 5 mA, reverse recovery is 80 nS, and the package is a molded epoxy cylinder with straight leads and a banded cathode — a through-hole part of the kind high voltage diode manufacturers build for the secondary side of an imaging or industrial supply, where the voltage is high, the current is small and nothing can be serviced once the tank is closed.

In circuit it has two jobs. Forward, it should conduct with a small and predictable loss. At the switch-off edge it has to stop conducting quickly, because reverse current that lingers becomes heat at the junction; the 80 nS recovery figure is what separates this family from an ordinary mains rectifier and what makes it usable in the switching stages of an X-ray generator supply.

Every rating is published with the condition behind it: blocking voltage at 2.0 µA of reverse leakage, average current into a 50 Hz half-sine wave with a resistive load at Tbreak = 50 °C, and reverse leakage at 25 °C and again at 100 °C. That turns a design review into arithmetic and shows how the part behaves hot before anything is frozen on a drawing.

8 kV Against the 6 kV and 4 kV Steps

The 2CL69 at 4 kV, the 2CL70 at 6 kV and the 2CL71 at 8 kV share one body, one lead form, one 5 mA current class and one 80 nS recovery time. What changes is blocking voltage and forward peak voltage: ≥16.0 V, ≥18.0 V and ≥23.0 V respectively. The choice between them is therefore a question of headroom against conduction loss, not of speed or footprint.

Headroom is what the extra kilovolts buy. A multiplier string, a tank that sees mains regulation swings, or a chain of devices in series all accumulate tolerances, and the larger class keeps the string clear of its leakage knee under worst-case conditions rather than nominal ones. It also shortens the string: fewer bodies, fewer joints, less accumulated forward drop and a shorter assembly where the tank has no room to spare.

The cost is forward drop. In a potted stack with no airflow, every extra volt of forward peak voltage becomes junction temperature, so if the peak reverse voltage on the device — including the overshoot a multiplier or a tank circuit throws at it — sits comfortably below 6 kV, the 6 kV step runs cooler at the same current and speed, and the 4 kV step runs cooler again for the lower-voltage stages of a long string.

Blocking voltage is specified at 2.0 µA of leakage, which makes it a working rating rather than a destruction limit: it is the voltage the part holds while leaking that much. Leakage is also ten times higher at 100 °C than at 25 °C, so a string balanced on the bench drifts as the tank warms, and equalising resistors or leakage-sensitive sensing have to be sized on the hot figure. Because all three steps are published against the same test conditions, the comparison can be finished on paper — the kind of documentation high voltage diode manufacturers should give a designer before a stack is committed.

How the Molded Body Handles 8 kV

• Axial leads, through-hole mounting — straight leads sit in a conventional footprint, can be formed to suit a compact stack, and leave every joint visible for inspection after soldering; the banded cathode stays readable once the part is in place.
• High thermal conductivity epoxy — heat leaves the junction through the molding instead of collecting at the die, which is what matters in oil or inside a potted module where there is no airflow to help.
• Low internal resistance — forward loss stays modest at the 5 mA rating, so the body runs cooler and does not heat the insulation around it from the inside.
• Passivation glue chip protection — the chip surface is treated before encapsulation, and that surface is where the field concentrates at kilovolt levels; protecting it is what lets the part sit at its rated blocking voltage without surface effects creeping in over time.
• Discharge behaviour — capacitor-discharge and multiplier circuits hit the diode with short, sharp pulses rather than a smooth sine wave, and the 0.5 A surge rating for 0.01 s covers that case, which the steady-state current figure says nothing about.

Mounting in Oil, Gas or Potted Modules

1. Decide the medium first. Insulating oil or an insulating gas is the recommended environment for this part: both hold off the field along the outside of the molding and carry heat out of the body. A small body in open air discharges easily but sheds heat by convection alone, so treat exposed air as the case that needs airflow.
2. Give the body clearance. On a high voltage diode the molded surface and the lead length are part of the insulation, so keep neighbouring components, board edges and bends clear of them.
3. Form and trim with the bend supported away from the body, never flush against the epoxy. Bending against the seal stresses the lead-to-chip joint, and that sort of damage shows up months later rather than at first power-up.
4. Solder at the joint, not at the body. Keep the heat on the lead, let it cool between two nearby joints, and treat the molding as the seal it is.
5. Clean before the assembly moves on. Flux residue and fingerprints are the usual cause of surface tracking across a kilovolt molding; a wipe with a suitable solvent removes both.
6. If the part is potted, allow for the hotter running that encapsulation brings, and check that the compound is compatible with the epoxy body and with the passivation layer beneath it.
7. Test at assembly level before the tank is closed. A leakage or hipot reading at the working voltage exposes a contaminated surface or a cold joint while it is still rework rather than a scrapped assembly.

Where the 8 kV Step Is Used

Most of these parts end up inside a sealed high-voltage assembly. In medical imaging the 2CL71 sits in the rectifier stack of an X-ray generator tank, in the high-voltage section of a DR or CT supply, and in the compact head of a portable dental panoramic unit, where the voltage is split into fewer, larger stages to save space and an 8 kV body keeps both the part count and the joint count down. Industrial inspection brings the same requirement to non-destructive testing generators, which run long shifts and care about continuous forward loss and a steady thermal path more than about peak capability.

Outside imaging, the part appears in DC high-voltage generators and in accelerator or radar supplies, in multiplier and rectifier stages built from high voltage diodes where the higher-voltage stages are the ones that need the 8 kV class. Repair work is the other steady user: the through-hole footprint, the banded cathode and the published leakage figures make a like-for-like swap practical on a board that will not be relaid, and the 8 kV rating covers equipment originally built around a higher-voltage part.

Rated Parameters and Test Conditions

Ordering and Dispatch

• Quantities from prototype to production — a few pieces for a repair or a pilot build, or a scheduled production pull; tell us the quantity and the date you need and the reply comes back with availability.
• Shipping — orders go by international express, which suits the small, high-value cartons this product travels in. Confirm the destination and any duties with your sales contact when the order is placed.
• Documentation — the data sheet and the mounting notes travel with the parts, so the ratings and the test conditions behind them are on hand at the bench.
• More than one voltage step — a build that uses several steps of the family can be quoted together; send the full list of high voltage diodes you need so the quantities line up.
• Replacement checks — if you are swapping an existing part, send its markings or its data sheet and we will compare blocking voltage, current, recovery time and lead form before you commit.

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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