Pulse-stress testing power discretes
Power semiconductor discretes have to be qualified against extreme electrical stress, and some of that qualification is deliberately destructive-looking. Under specific conditions a power discrete is hit with pulse current up to 100 A, mainly to prove it can carry that current without failing. The same setup exposes a weak die attach — poor attachment to the substrate shows up immediately under high-current pulse stress — and it is used to read withstand voltage. Typical devices under test are TVS diodes, power MOSFETs, surge protectors and power transistors.
The switch has to isolate tests and survive the duty cycle
Each device runs several tests at different voltages and currents with different instruments, so the tests have to be isolated from one another by switching hardware. The binding constraint is cycle count: in a production tester the switches see hundreds of millions of operations, which makes switch lifetime the dominant design variable. The two usual choices each miss a requirement:
- An electromechanical relay carries current comfortably, but a pivoting armature is generally worn out near one million operations.
- A semiconductor switch ages slowly but rarely combines high current and high voltage in a single device.
The HVFR family of high-voltage, high-insulation reed relays is SHR AUTOSENSOR’s answer to that gap.
HVFR-HI series figures
- Switching voltage to 1 kV, with transient capability to 2 kV
- 1 A switching current; pulse current options of 5 A, 10 A or 20 A
- Dielectric strength above 3 kV; insulation resistance above 100 TΩ
- Switching time under 1.2 ms; life above one billion operations
One family across low-level and pulse duties
The HVFR uses vacuum reed switches, which is how it reaches 1000 V switching with dielectric above 3000 V in the same part. It switches low-level signals for billions of operations and carries high-current pulses on the same contacts: 3 A continuous, and a 5 A pulse of 5 ms passes through without distorting the leading or trailing edge. Pulse edge shape is not cosmetic — the current pulse is what reveals die integrity and substrate attachment, so a distorted edge weakens the test. The timing rule is to energize the coil and wait at least 5 ms before applying the high-current pulse so the blade has settled.
Scaling from 5 A to a 100 A pulse with parallel contacts
A relay rated for a 5 A pulse cannot take 100 A directly, so the current is divided. Twenty reed relays are paralleled, each contact in series with one leg of a power-resistor network; the network splits the 100 A pulse evenly across twenty paths and each contact sees only its rated share. The result is a high-current pulse tester built from long-life reed relays rather than short-lived contactors, with every channel still fully isolated between tests.
Two design rules that protect contact life
First, hold the timing discipline — coil on, wait at least 5 ms for the blade to settle past the bounce window, then pulse; firing during actuation is the quickest way to erode the contacts. Second, keep the parallel network symmetric: matched resistor legs and matched relay batches hold an even current split so no single contact carries above its 5 A share. A per-leg fuse or current-limiting element is a cheap backstop against a leg that drifts out of balance.
Typical applications
- Pulse testing power discretes such as TVS diodes
- Power MOSFET and power transistor test
- Surge and overvoltage-protection component test
- Die-attach integrity verification under pulse stress
About SHR AUTOSENSOR
SHR AUTOSENSOR TECH LIMITED (SHR AUTOSENSOR) manufactures high-voltage reed relays, mercury wetted relays and high-voltage DC contactors. Contact: [email protected] | +86 13761571029 | www.reed-relay.com