Problem with swithing power supply

Hi to everybody!

I think to have a problem with switching power supply.

When I use this kind of power supply my circuit begins very sensitive to the electro-static discarge.

I use 2 Voltage regulator to lower the Voltage of power supply from 24V to 5 V.
The first one lowers the voltage from 24 V to 12 V.
The second one lowers the voltage from 12V to 5 V.

When a ESD happens, the tension on the output of second voltage regulator is lowered and its temperature begins to increase.



You have some council in order to resolve my problem ?

Thx

Are these 12V and 5V voltage regulators linear or switch mode?

What do you mean by ESD? These discharges have very low charge. The bypass and filtering capacitors on your circuit and the regulator output should absorb this charge without making any significant voltage change. Do you have low value capacitors (nanofarad range) as well as large ones (mcirofarad range) on your circuits?

When a ESD happens, the tension on the output of second voltage regulator is lowered and its temperature begins to increase. What you mean please clarify clearly for further explaination.

Inkwaterman said:

I think to have a problem with switching power supply.

Click to expand...

What do yo mean? Is it a problem when you switch power supply (say, switch it ON and OFF), or is it a problem with a switch mode power supply?

Inkwaterman said:

When I use this kind of power supply my circuit begins very sensitive to the electro-static discarge.

Click to expand...

Was your circuit insensitive to ESD when you used another kind of power supply? Which power supply did you yse originally? My guess is that your circuit was OK while you used linear power supply, but it became sensitive to ESD when you started using switch mode power supply. Is it true? :?:

Inkwaterman said:

I use 2 Voltage regulator to lower the Voltage of power supply from 24V to 5 V.
The first one lowers the voltage from 24 V to 12 V.
The second one lowers the voltage from 12V to 5 V.
When a ESD happens, the tension on the output of second voltage regulator is lowered and its temperature begins to increase.

Click to expand...

Where ESD happend? Did you discharge ESD probe to the 5V power supply circuitry, or to 5V rail, or to another circutry which is powered from 5V?

IanP said:

Are these 12V and 5V voltage regulators linear or switch mode?

Click to expand...

Both linear voltage regulator.

selvaraja said:

When a ESD happens, the tension on the output of second voltage regulator is lowered and its temperature begins to increase. What you mean please clarify clearly for further explaination.

Click to expand...

The voltage regulators are 78xx type.

For example, when I charge myself with electrostatic voltage and touch my cirtuit ,
the voltage output of the second voltage regulator, a 7805, is lowered of approximately 1.5 V , and its temperature begins to increase.

You need to separate the problem between the circuit being powered drawing too much current and the regulator being damaged. Can you take the failed board and while it is still powered cut the trace from the regulator to the circuit being powered by it? If the 5V returns the powered circuit was damaged. If it stays at 1.5 V there is still the possibllity of the load being damaged causing the regulator damage.

Next power a good board from a lab supply for the 5 V and do the ESD thing again. From the above set of experiments you should be able to converge on the problem. Then finding the solution (esd protection) is the next step.

Are you esd testing properly? The offiial test is on the whole product inside the enclosure. Only the exposed connections like socket pins are zapped. Parts of the circuit that are not accessable because of the enclosure are not zapped.