![]() ![]() If I recall correctly, LTspice also has this (or an equivalent) shunt reference in its library. The LM431 has a threshold of 2.5V, so, keeping in mind Iref, you can calculate R1B and R2B to get 2.5V when the HV becomes 60V. This can be solved by adding a resistor parellel resistor (R p) to the LM431 and optocoupler's LED, so it makes a voltage divider with the current limiting resistor.Ĭhoosing the value of this parallel resistor equal to the current limiting resistor, limits the voltage to max 30V (because then the LM431 starts working). Because the HV can become 10x as big (60V to 600V) I'd choose an optocoupler with min CTR > 100% and a resistor (R lim) that limits forward current from 1 mA 60V (that's what the LM431 needs as well!) and so 10 mA 600V.ĭrawback is this resistor still dissipates 6W at 600V.Īs Jasen points out, the cathode voltage should be limited. The LED represents the LED from the optocoupler. I'd use a LM431 as comparator in the HV lines.īecause my phone doesn't support the editor, below a modified schematic: Simulate this circuit – Schematic created using CircuitLabįigure 3. +DC (left), -DC (center), AC (right) supplied to NE-2 type neon lamps. It's going to flicker so you would need to address that in your software.įigure 2. Connect the neon indicator across the capacitor and make your own opto-isolator by attaching the light sensitive receiver of your choice to the neon. The lamp glow discharge lights at its striking voltage.įrom memory these breakdown at about 60 V which would suit you.ĬircuitLab won't load for me right now but the idea is to make a series RC circuit with R connected to V+ and C connected to ground. The gas is typically a Penning mixture, 99.5% neon and 0.5% argon, which has lower striking voltage than pure neon, at a pressure of 1–20 torrs (0.13–2.67 kPa). The lamp glow discharge lights at its striking voltage.Ī small electric current (for a 5 mm bulb diameter NE-2 lamp, the quiescent current is about 400 ♚), which may be AC or DC, is allowed through the tube, causing it to glow orange-red. Ī small electric current (for a 5 mm bulb diameter NE-2 lamp, the quiescent current is about 400 ♚), which may be AC or DC, is allowed through the tube, causing it to glow orange-red. NE-2 type neon lamp powered by alternating current (AC). My question is whether the converter can share a ground with the HV line (ie HV- connected to converter ground)? And should you have time and/or are willing, suggest alternative solutions to this issue?įigure 1. ![]() I was hoping that an isolated DC/DC converter (such as ) could be used to supply an IC (such as a comparator) to reduce the current through any voltage divider used between the HV lines, as shown in Fig 2. The main issue with this circuit is the large amount of power (~43W) burnt across R1 (be it a single large resistor or several smaller ones) once the input voltage reaches 600V. The value of R1 is set so that once the input voltage V1 reaches 60V, enough current (5mA) gets through to meet the forward current requirement of the opto-isolator diode. R2 and D2 are modelling the opto-isolator. My initial idea was to use a 12v zener diode voltage divider with an opto-isolator as shown in Fig 1. ![]() The output side of the sensing circuit (and if used the 12v and 5v supply) must be galvanically isolated from the high voltage lines. A seperate supply of 12v and 5v is available for use. I'm designing a circuit to detect when the voltage across two DC input lines (HV+ and HV-) is greater than 60V. ![]()
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