I am looking to test an embedded system for its behavior during power interruption soon after power on. The system is supplied with 15V DC power with a steady state draw of <500mA

The power transient is shown below - 1ms on, 1ms off, and then on again for steady state, simulating the action of a specific mechanical interrupter to turn the device on. The turn-off and turn-on time is <10us . When the power is turned off the supply line is left floating


simulate this circuit – Schematic created using CircuitLab

Mechanical relays are not quick enough to do this, I have considered solid state relays but their behavior is load dependent. Programmable Power supplies are usually with a resolution no better than 1ms.

Since the total load is under 1A peak I have considered using a Power MOSFET as the switching device and this is my current approach.

Is there anything else that you can suggest to test these conditions in a controlled, repeatable manner?

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    \$\begingroup\$ (1) Is the power AC or DC [the question sounds like DC, but let's make sure]? What's the supply voltage that you need to switch? (2) When you interrupt the power, do you need the DUT power input floating, or do you have to connect this input to ground? (3) You've mentioned that this is to simulate the action of a mechanical interrupter, can you use the actual interrupter in the test fixture? \$\endgroup\$ – Nick Alexeev Jun 11 '18 at 16:45
  • \$\begingroup\$ What is meant to happen during the first and last 1 ms on periods? What happens during the 1 ms off period? \$\endgroup\$ – Andy aka Jun 11 '18 at 16:52
  • \$\begingroup\$ @NickAlexeev @AndyAka I have addressed your questions and updated my post. In summary - DC Power @15V, the input can be left floating. This is an attempt to simulate interrupter "bounce", so it is a ~1ms transient (brownout) on power on. \$\endgroup\$ – crasic Jun 11 '18 at 17:23
  • \$\begingroup\$ sounds like a MOSFET would be ideal for this. \$\endgroup\$ – dandavis Jun 11 '18 at 17:30
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    \$\begingroup\$ @crasic When you say "turn-off and turn-on time under 10us", what do you mean? Do you mean that your DUT should start-up (or shut-down) within 10us? Or, do you mean that the raise and fall time for the supply voltage should be under 10us? The raise and fall time, in turn, is dependent on load capacitance. So, the next question in that direction would be: "turn-off and turn-on time under 10us" with what for a load? \$\endgroup\$ – Nick Alexeev Jun 11 '18 at 19:14

Your load likely has decoupling caps which must be charged very fast due to contact low R and low ESR of load caps.

Thus Ic= C * ΔV/Δt= ΔV/(R+ESR) for decaying duration Δt. This can be many Amps if available from 15V supply caps.

So the real task is how to simulate a 10m Ω typical contact with random interruptions from 10us to 20 ms that simulate typical contact bounce with aging contacts.

You are correct to use a FET . It can be a high side or low side (-) voltage switch around 10mΩ rated at some Vgs like logic levels you plan to use. Nch FET for low side , Pch for high side rated for your logic level or >2.5x Vgs.

How you mix pulse noise with the DC step voltage depends on your ingenuity and rigor as a Test Engineer . First there should be explicit design specs or some unconditional practical limit. Second you can inject noise with repeatability or random pulse pattern. 3rd you should NOT limit yourself to one condition and search for the worst case. You can synthesize patterns with a shift register and variable clock with preset and clock inputs and this gives a wide range using a pot controlled Schmitt Trigger Relaxation Osc clock and a PISO register with dip switches and can be rigged up in a couple hours to switch between 15v source and load. If you are using a Pch then a transistor common emitter or CD4xxx 15V logic is needed.

Try to keep power & gnd wires twisted to reduce EMI from surge current or use coax. and make it small neat and professional looking.


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