I see, double isolated🙂
regulation gets worse but youll have a Variac to compensate.
buy a small panel variac and couple of big analog meters and mount the whole mess in a box.
DIY test equipment, don't forget to use an input fuse 2A slow blow
regulation gets worse but youll have a Variac to compensate.
buy a small panel variac and couple of big analog meters and mount the whole mess in a box.
DIY test equipment, don't forget to use an input fuse 2A slow blow
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I am not sure what the PE brings to extra safety when equipment is fed from an isolating transformer.
If the "in test" equipment is genuinely "isolated", then there is no voltage trying to return fault current back to the distribution board.
If that is the case then PE does not increase the safety of the user/operator/tester while at the test bench.
As I see it, an isolated piece of electrical equipment would need TWO points of contact for electricity to flow through the body parts of an operator/tester.
This is VERY DIFFERENT from a normal PE protected piece of mains powered electrical equipment, where one needs only ONE point of contact to electrocute the user.
If the "in test" equipment is genuinely "isolated", then there is no voltage trying to return fault current back to the distribution board.
If that is the case then PE does not increase the safety of the user/operator/tester while at the test bench.
As I see it, an isolated piece of electrical equipment would need TWO points of contact for electricity to flow through the body parts of an operator/tester.
This is VERY DIFFERENT from a normal PE protected piece of mains powered electrical equipment, where one needs only ONE point of contact to electrocute the user.
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not for safety, it can be useful as a ground reference for EMI filters. I also ground the metal bench top. that way a ground plane can be rigged between the instruments and test article. eg common mode noise at the scope or SA,
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i have a smps im looking at right now that has an issue on the 15v control voltage line. its a voltage that is created by big resistors dropping the rectified mains. right now it is only showing 5.7v instead of 15v. its what starts the switching circuit. so because i only get 5v it does not start.
since this is all in the primary, could i remove the transfo's primary switching mosfets to feel safer about things exploding if theres a malfunction? that is untill i find what is dropping that 15v to 5v.
since this is all in the primary, could i remove the transfo's primary switching mosfets to feel safer about things exploding if theres a malfunction? that is untill i find what is dropping that 15v to 5v.
on a voltage divider I use an ohm meter, may have to resort to disconnecting suspected bad guy?
IDK depends on your troubleshooting methods,
note > housekeeping supplies from the mains are usually only designed to operate for a short time
IDK depends on your troubleshooting methods,
note > housekeeping supplies from the mains are usually only designed to operate for a short time
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well. at the moment if i power up the smps and leave it powered for more then 30 second. a 25k 1w resistor goes up in smoke.
it is in series with a 75k 1w resistor that are together paralleled with about 300vdc(rectified mains). the center point of that divider is what goes to a 17v regulator circuit (paralleled transistors with a 17v zener on the base)
it is in series with a 75k 1w resistor that are together paralleled with about 300vdc(rectified mains). the center point of that divider is what goes to a 17v regulator circuit (paralleled transistors with a 17v zener on the base)
use a bench supply and a resistor to run the controller?
note the current it should be in low 10's mA
note the current it should be in low 10's mA
its a zener eg shunt regulator circuit, if the load takes too much current it wont regulate, find the increased load
you can calculate the zener current right?
you can calculate the zener current right?
that was my reasoning as well. from reference to 15v "ouput" the is no resistance at all. so it seems to be something active
i had trouble understanding the tone from the guy in the video but, after a moment i have.
the zener is mmbz5247b
it is spec'd at
VZ:17v
IZT : 7.4ma
IZK: 0.25ma
the zener is mmbz5247b
it is spec'd at
VZ:17v
IZT : 7.4ma
IZK: 0.25ma
x Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
here is a copy of the schematic of the smps
here is a copy of the schematic of the smps
i think the 17v zener diode is at fault, the 15v ctrl line is regulated by the zener controled transistor voltage regulator, im getting 22v at the collector of the transistor, theres 6v standing at the base of the transistor(kathode of zener) and 6v on the emitter after their resistors. and that is after i cut the trace after the transister emitter resistors (10ohms because 3 transistors in parallel) to any load that could be
EMI filters operate at VHF.
As such the PE connection back to the distribution board is very high impedance at VHF and will not help an EMI filter to operate effectively.
The EMI filter connects to Chassis and that Chassis is capacitively coupled to the 12720km diameter conductive ball we commonly refer to as "Earth".
It is the capacitive coupling to "Earth" that allows the EMI filter to operate at VHF.
You gain nothing in the way of interference attenuation by coupling the bench to PE and back to the Distribution board.
H.Ott's diagrams show this repeatedly through his "ELECTROMAGNETIC COMPATIBILITY ENGINEERING".
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remember EMI filters use largish mains capacitors tied to chassis. best not leave a big chunk of metal on a bench floating yes?
keep the research going! common mode is always referenced to earth ground.
(BTW you ignored ground plane and test instruments ) ever wonder why they connect earth ground to commercial RF screen rooms?
what does H. Ott recommend, does he consider 1" metal conduit a bad ground?
keep the research going! common mode is always referenced to earth ground.
(BTW you ignored ground plane and test instruments ) ever wonder why they connect earth ground to commercial RF screen rooms?
what does H. Ott recommend, does he consider 1" metal conduit a bad ground?
While 1 inch metal conduit is an excellent low resistance Safety Ground/Protective Earth, many question the long term reliability of the connections/joints.
Common mode has a different definition in the AC power generation industry than in electronics area.
The connection to Mother Earth has little to do with EMI/RFI problems.
****************************
Jim Brown writes:
Shunting Common Mode RF to Earth Earth connections are almost never a solution to RFI problems,
but there is one important exception. We know that RF induced by antenna action on cables
entering or leaving equipment is coupled into the equipment by pin 1 problems, and by poor common
mode filtering on balanced circuits. We can attack this kind of RFI by diverting that current
away from the victim equipment. We do this by giving it connection to the shielding enclosure of
the interference source, or to the shielding enclosure of the victim equipment, or to the earth.
Common mode has a different definition in the AC power generation industry than in electronics area.
The connection to Mother Earth has little to do with EMI/RFI problems.
****************************
Jim Brown writes:
Shunting Common Mode RF to Earth Earth connections are almost never a solution to RFI problems,
but there is one important exception. We know that RF induced by antenna action on cables
entering or leaving equipment is coupled into the equipment by pin 1 problems, and by poor common
mode filtering on balanced circuits. We can attack this kind of RFI by diverting that current
away from the victim equipment. We do this by giving it connection to the shielding enclosure of
the interference source, or to the shielding enclosure of the victim equipment, or to the earth.
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