HV37-15F Fast Recoveryhigh voltage diode 15KV, 250mA, 75nS

Product Overview

A 15 kV fast recovery diode in an axial package, this part is built for rectifier circuits in high-voltage supplies. The body is a black cylindrical moulding about 15 mm long and 4.5 mm across, with a white band at the cathode end and two straight leads; inside, the chip sits under a passivation adhesive layer and the whole assembly is encapsulated in a high-thermal-conductivity epoxy compound. That combination — small body, protected chip, heat-conducting encapsulant — is what makes a 15 kV part practical to mount on a board or drop into an oil-filled tank.

Within the HV37 family this is the highest-voltage member, and the trade-off shows up in the current ratings: as reverse voltage rises, the average current the same body can pass falls. Designs that need the full 15 kV of margin sit here. Designs that need 350–500 mA usually step down to the 10 kV or 6 kV models and accept a lower reverse voltage, or move to a larger rectifier assembly.

High voltage diodes of this class work in the rectifier stages of medical imaging generators, industrial NDT and X-ray equipment, HVDC and electrostatic supplies, high-voltage test sets and radar modulators. The same part is the usual replacement when a legacy axial diode on an existing high-voltage board fails or goes obsolete: the axial format, the lead arrangement and the cathode band are the familiar ones, so a substitution is a question of ratings rather than of re-machining the mounting.

Key Features

• In a high-frequency high-voltage supply that shows up as lower recovery loss and less heating inside the device. - High-thermal-conductivity epoxy moulding — the encapsulant carries heat from the chip to the body wall and on into oil, gas or air, which is why a body this small can pass a useful current at all. - Passivation adhesive over the chip — an insulating adhesive layer covers the chip surface before moulding and holds back surface leakage and breakdown at high field. A part this compact leans on that layer for its voltage hold. - Surge headroom — the surge rating covers the inrush pulse of a capacitor charging through the rectifier, so the diode rides out the switch-on event that a marginal part fails on. - Stable discharge behaviour — characterised for discharge duty as well as rectification, so capacitor-discharge and pulse-forming circuits do not see an unpredictable recovery tail. - Marked cathode, straight axial leads — the white band identifies the cathode end, and the straight leads suit through-hole and point-to-point wiring without special tooling.

Specifications

Package & Dimensions

• Body diameter (φ1) — 4.5 mm (0.18 in) with a ±0.2 mm tolerance, so allow for the moulding when you set clearance to nearby metal.
• Body length (L1) — 15 mm (0.59 in), ±0.2 mm.
• Lead diameter (φ2) — 0.8 mm (0.03 in), ±0.2 mm; a standard through-hole drill and a normal soldering iron will handle it.
• Lead dimension (L2) — 25 mm (0.98 in). This one carries the wider ±0.5 mm tolerance, so set your mounting centres from it rather than from the body length.
• Package code HVD-415, straight-lead outline — the drawing shows the straight-lead form with the cathode band at one end. Keep parts in their labelled packaging until assembly; a high voltage diode this small is easy to mix up on a bench.
• No type number on the moulding — apart from the cathode band the body is unmarked, so identify a loose part by its packaging or by measuring it, never by reading the body.
• Lead forming — support the lead between the bend and the body seal, bend once, and avoid repeated flexing at the same point.

Operating Medium & Insulating Adhesive

Choosing the medium

The two current ratings on the datasheet are not a like-for-like pair, and reading them as one is the most common mistake with a part this size. Oil immersion lets the diode live in a hotter environment, but the higher ambient costs current — so decide the medium first, then read the rating that goes with it. Four arrangements are used in practice. Immersing high voltage diodes in insulating oil is recommended, and so is mounting them in insulating gas; both media suppress corona and carry heat away from the body. Secondary packaging — potting or encapsulating the assembly — also works, but it leans harder on the diode's own heat path, so leave more current margin. Running in exposed air is the least forgiving option: a small high-voltage part in air discharges easily and sheds heat poorly, so add forced air cooling where you can, fit insulated electrodes at both ends, and keep the working voltage below the rated 15 kV with real margin. Treat 125 °C as a design limit rather than a target: the epoxy encapsulant and the passivation layer are what set it. Choosing the insulating adhesive

Most assemblies bond the diode body or its leads down with an insulating adhesive, and the material changes how that joint behaves over life. Silicone cures to a clear, elastic rubber. It absorbs shock and rides out the severe stress of large hot-cold swings, and it is the natural choice where the assembly will see temperature excursions. Acrylic cures clear and hard, takes up little moisture, sets quickly and gives strong wear and insulation performance. Urethane also cures clear and hard, wears well and resists moisture; it is particularly stable at low temperature but less tolerant of heat. Epoxy is the rigid option — usually opaque, very sturdy, resistant to moisture, chemicals and wear, with good dielectric properties. Match the adhesive to what the joint has to survive: thermal cycling supports silicone, a fast rigid bond to acrylic, low-temperature service to urethane, and chemical or moisture exposure to epoxy. Cure it fully before the first high-voltage test.

Installation Sequence

1. Inspect before assembly — check the leads are straight and the body free of cracks or chipped epoxy. On a fast recovery diode this small the leads are the only mechanical interface, and a lead bent hard against the seal is a leak path waiting to happen.
2. Set the orientation from the cathode band — the band marks the cathode, which in a rectifier leg faces the DC output side. Reversed, the diode conducts on the wrong half cycle and fails at the first full-voltage event.
3. Form the leads with support — grip the lead between the bend and the body, bend once, and keep the radius outside the seal area.
4. Keep high-voltage clearance — in a high voltage diode this small, distance is insulation. Hold the body and leads away from earthed metal and from other high-voltage nodes; tight layouts are where discharge starts.
5. Bond with the insulating adhesive — apply it to the body or the board as your assembly drawing requires and let it cure fully before test. A partly cured adhesive insulates far less than a cured one.
6. Fit insulated electrodes if the part runs in air — where the assembly is not oil- or gas-filled, terminating both ends with insulated electrodes keeps corona at the lead exits under control.
7. Bring it up on a current-limited supply — raise the voltage in steps and watch reverse leakage at the working temperature, not just cold. A part that leaks more than expected when warm is telling you the thermal path is wrong.

HV37 Series Range

Ordering & Delivery

1. Start from the ratings — reverse voltage, forward current at your medium and ambient, recovery time and the L2 mounting dimension. If you are replacing an existing part, quote the number printed on it; high voltage diode manufacturers can match a part from that number far more reliably than from a photograph of the board.
2. Ask about sample availability and lead time — your sales contact will confirm whether samples of this model are available and what the current lead time is for the quantity you need.
3. Confirm the packing for your line — tell us whether the parts will be hand-soldered from a bag, fed from tape or presented in a tray, and we will confirm what is available for this model.
4. Shipping — International express. Confirm the destination, consignee and any labelling your goods-in team needs at quotation stage.
5. Payment and documents — payment terms and the paperwork you require are agreed with your sales contact when the order is placed.
6. Inspect on arrival — check lead straightness, body condition and the quantity against the packing list before the parts go into stores. Axial leads can bend in transit; catch it before assembly rather than at the test bench.
7. Keep the technical contact open — the same contact handles questions on mounting, adhesive choice or a diode that runs hot after commissioning. Raise it there rather than guessing at a fix.

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.

FAQ