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Insulation Tester power supply - del50001Description.With these circuits you can make an insulation tester going upto one tera ohm (2 Tera ohm max). hence currents will be in pico amps, great care required in design. Also 1000 Volts DC is generated which can cause injury. take great care. the above circuit is for the advanced instrumentation hobbyist only, do not try it at home.The parts list which is not in the circuit is listed below, the circuit is 15 years old. but you may get some idea on high resistance measurement.
the above list is from my memory, hence it may be wrong, i have forgotten this circuit, this circuit was scanned by a hp photosmart and resized and optimized by irfanview. also note the technology may be obsolete, but basic idea is still the same today. |
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Theory of Operation.IC7 555 as an Astable chops the DC with T2 NPN transistor. TR2 was a Russian U Core High-Freq Transformer. The secondary was insulated with mylar, layer to layer and impregnated in Mica-Lacquer or varnish. The 723 Chip along with T1 is The closed loop regulator which changes the DC which is chopped.This is part of an old product of mine, it is a megger, a tera ohm meter or call it an insulation tester. IC8 is LM723 - Voltage Regulator and then see a good application of that here Build A 10 Amp 13.8 Volt Power Supply and Small Variable power Supply. The LM723 works like a closed loop Regulator but its DC output from T1 is chopped by a 555 and T2. This is stepped up by a small transformer (Russian U Core, with layer to layer insulation) as it has to meet with near 2KV spikes at output at times. Two diodes are used as 1K is the limit of 1N4007. A switching diode like FR105 may be better. Diodes - General Purpose - FR105. The caps are piled up due to the high voltage. The feedback is an attenuated sample of HV output thru the R8 4.7M. The high voltage current is low for safety reasons, but great caution has to be taken. TR1 must be a 1 A, 10-0-10 V Transformer. The high voltage is attenuated and that is the feedback to 723 chip which by comparing to a reference, controls the output. The diodes and caps are in series to withstand 1000V and above. Data sheets and Information. |