GS 5 THRESHOLD PROBLEM

[dbanner]

Now to do some actual testing to see what the cut out voltages are on this particular one. Well, I learn something more everyday. I like tearing things apart to see what little treasures can be found.

[Ferric Toes]

Here is the picture promised in post 78.



The MC3608 converter sits in a PVC box to isolate it from the metal screening box. The added 4.7uF ceramic capacitors (blue) are across the input and output. Also inside the screening box is the linear regulator to give the -12V rail for the TX etc. This regulator is also fitted with similar ceramic capacitors. The TX/RX board sits under the larger metal plate which is connected to the ground on the coil connector, which is out of sight on the right hand end of the outer box. In this instance the battery supply consists of 6 x 1.2V rechargeable NiMh AA cells. Two 3.7V Li-ion cells would also suit, although NiMh were preferred as they are less likely to fail if the unit is inadvertently left on.
As mentioned previously, a -15V linear regulator could be used and the converter output set to -18V by means of the on-board preset. The screening box is RS part no.627-6304.

Eric.

[kt315]

thank you Eric. you show all i wrote from start in this thread. now he will think WHO IS RIGHT.
low drop low drop low drop bla bla.

[ivconic]

Here is the picture promised in post 78.

[ATTACH]44714[/ATTACH]

The MC3608 converter sits in a PVC box to isolate it from the metal screening box. The added 4.7uF ceramic capacitors (blue) are across the input and output. Also inside the screening box is the linear regulator to give the -12V rail for the TX etc. This regulator is also fitted with similar ceramic capacitors. The TX/RX board sits under the larger metal plate which is connected to the ground on the coil connector, which is out of sight on the right hand end of the outer box. In this instance the battery supply consists of 6 x 1.2V rechargeable NiMh AA cells. Two 3.7V Li-ion cells would also suit, although NiMh were preferred as they are less likely to fail if the unit is inadvertently left on.
As mentioned previously, a -15V linear regulator could be used and the converter output set to -18V by means of the on-board preset. The screening box is RS part no.627-6304.

Eric.

I've been using such dc-dc step up converters for quite a while. Mostly with success. To supply various battery operated audio&music equipment. At few detector models too.
Additional filtering is mandatory, of course. Sometimes i add choke in series too.
I experienced huge problems only once, trying to supply 2.5GHz audio TX. There was a constant "whistle" in the background, completely spoiling the output.
No matter what i tried; i couldn't get rid of the whistle. With more complex filters i achieved only to lower the level of the whistle. But it was there all the time.
At the end i gave up and redesigned the circuitry.
As for the use at PI detectors; i haven't experienced any troubles so far. Even simple filtering like that will do the job just fine.

[ivconic]

Ah yes! One good hint for you Eric!
Remove the trimmer and put small SMD resistor instead.
You'll notice significant difference if you monitor the output on scope.

[daverave]

i decided to make a separate -10v circuit which has a drop out voltage of about 500 mV to try and correct the threshold drift when the supply voltage drops below 13 volts...but alas it has not cured the problem so i guess the when the supply votage dips below the 13 volts then it must affect more than the -10v on the audio pcb.