Delta Pulse

[porkluvr]

The statement not the true. During flyback this diode is opened, is the small resistor, and does not do anything useful. It is easy for seeing by means of a simulator.
At the same time, this diod worsens the scheme - resistance of the diode is added to resistance of the transistor, and the power failure on it (0,7V) leads to additional losses.

Yes I did open my big mouth and make some somewhat exagerated claims, but no I'm not wrong*. Let me try to explain.
You are forgetting about PN junction capacitance.

A reverse biased diode is equivalent to an open switch at DC, but it has capacitance. That is why varactor (tuning) diodes work.
When you reverse bias the diode, there is essentially no DC current flow - but the junction capacitance varies with reverse voltage.
Without this effect FM radio technology would be in the stone age. There would be no CDMA cell phones or frequency hopping.
This capacitance is in series with the FET capacitance, and is useful because it reduces overall capacitance during flyback.
A typical Fast Recovery diode will have a whole lot less capacitance than the drain capacitance of an IRF740 FET.
The total capacitance seen looking back into the FET will be much lower when the diode is added in series.

Now, you are right about the 0.7V drop affecting charge time. But for target illumination we are mainly concerned with discharge time.
Exactly how much faster the flyback occurs will depend on several factor. Coil and FET used will affect how much difference adding a diode
will make, but I believe (from my limited testing) that you will see the most substantial decrease in flyback times when the coil current
is at relatively lower values. If you are pulsing three or four amps you will see little difference in flyback time, but if you pulse 1-1/2 amps
there can be a substantial difference. Of course I have not tested all coil and FET combinations, but I don't think adding a
FR diode will ever slow your flyback rate.

Then, also by adding a FR diode you can use a higher value of damping resistor. Again, the amount of difference depends on several factors,
but can be quite substantial. I have only run limited tests, but adding a FR diode ALWAYS allows a higher damper to be used from
what I've seen. This should increase receiver sensitivity, although I don't know how to quantify the difference.

The 0.7V diode drop can be overcome by slightly lengthening the TX pulse. A very small change in timing resistance will maintain
the same coil current.

*I need to temporarily withdraw my claim of decreased battery supply current because I cannot remember my test setup to make that
conclusion. When I remember what I did I will reassert the statement and come back with proof. "I'll be back". (I just remembered.)

[Andy_F]

The diode becomes reverse biased during flyback and therefore acts as a capacitor in series with FET capacitance. Series capacitance is reduced, by the formula CT=(C1XC2/(C1+C2)).

The statement not the true. During flyback this diode is opened, is the small resistor, and does not do anything useful. It is easy for seeing by means of a simulator.
At the same time, this diod worsens the scheme - resistance of the diode is added to resistance of the transistor, and the power failure on it (0,7V) leads to additional losses.

[rajesh]

build to delta pule

Hi Ivconic. This time i am very busy so i can not answer to you or to do experiment with my XR71. The second results are good and better than mine. If you have free time you can do some experiments and to tell the results.
1. Change R21 with 200k to increase the gain 4 times.
2. Change R17 with 270k to increase the gain 2.25 times.
3. With an extra pcb you can change LF357 (or 356) and connect a 5534 with current offset and larger R17 (1Mohm is ok).
If all changes work then the DP will be a very very sensitive detector.
Btw who is the inductance of the 42 cm coil?

regards

hi geo i"m planing to build this pi so i need p.c.b. layout can you provide me pcb and schematic and all part list ....rajesh

[porkluvr]

Holding the reset line low during initialization should prevent the long "on" signal that otherwise occurs at startup that could fry the FET. The component values I show are probably a little bit of over-kill but should be no harm in that.

Now, about what I said earlier about a fast recovery diode being so great.
Up until earlier today I thought it was ALWAYS good. After running further tests I'm not so sure.

Maybe I'm just having one of those Twilight Zone days when the laws of physics seem to take a vacation - or else it is an over-simplification to state flatly that a fast recovery diode between the FET and coil will increase performance.

I have some more tests to run but it's looking to me like there could be some exceptions. I'll leave it at that for now but I'll probably be back because it looks like I may have some explaining to do. (Damn, why couldn't I just mind my own business?)

[Aziz]

Hi kt315,

hi Aziz. what do the diode and the resistor give that you added?

tia

I was asked about a thermal problem of the MOSFET (getting hot). The main problems were observed with the NE555 chip during startup. He stated, the 7555 chips were difficult to get and would not cause any problems. But he would like to use the NE555 variant.
I proposed the above trial without looking deeper into details. As porkluvr mentioned, the flyback voltage gets faster into its maximum value with less coil power, which would reduce thermal problems.

Aziz

[porkluvr]

hi Aziz. what do the diode and the resistor give that you added?

tia

Hello KT315. Sorry, I'm not Aziz. I once asked Aziz the same question about the diode so maybe you won't mind if I answer. The diode becomes reverse biased during flyback and therefore acts as a capacitor in series with FET capacitance. Series capacitance is reduced, by the formula CT=(C1XC2/(C1+C2)). This reduces flyback time and allows using a higher value damping resistor.
The resistor? I think that is a 10k pulldown resistor. The LM556 already has a fast trailing edge in this circuit - but if you use one of the CMOS versions having reduced output drive (ICM7556, GLC556, etc.) a pulldown would be beneficial.

edit: Any increase in speed to the flyback pulse should equate to more energy transmitted. Adding the diode should definately result in noticably higher coil current for a given transmit pulse. So, the transmit pulse could be shortened if you don't want more coil current. If you do shorten the transmit pulse you should see an increase in battery life because of increased efficiency.

[kt315]

hi Aziz. what do the diode and the resistor give that you added?

tia

[Geo]

Hi. Do you replace the D7 (1N4001)???
It is the first that destroying with reverse power. Also D8... D9 from big current. Normaly nothing else is destroying...
I dont read all the articles, so sorry if you have made same reply.

Ivica, i will not stay long time. I will return from Budapest and i will go to Sofia via Beograd. We will stay at Beograd only some Hours. I will try to phone you
Regards

[Aziz]

Merhaba arkadas,

aziz abi delta puls'ta şöyle bir sorunum var power açınca fet aşırı ısınıyor. lm556 (ne556, ka556) yerilerine icm7556 takınca normal çalışıyor. sence ne yapmam gerekiyor icm7556 hem pahalı hemde zor bulunuyor. birde ben pulsdetektor.de sitesindeki miner'in çıkış katını nasıl uygularım ne yapmam gerekir. ben birebir miner2 nin çıkış katını uygulaya çalıştım ama hcpl3120 tetikleyemedim nasıl bir modifiye yapabiliriz yardımlarınızı bekliyorum..
thank you all's forum..

Delta pulse'nan hic ilgilenmedim simdiye kadar. Ama altindaki gösterdigim deneyi yap. FET'in isinmasini biraz indirir belki.

Miner'nen hic ilgilenmedim. Su anda kendi yaptigim deneylernen cok ilgeleniyorum.
Bol selamlar,
Aziz

merhaba aziz abi

aziz abi delta puls'ta şöyle bir sorunum var power açınca fet aşırı ısınıyor. lm556 (ne556, ka556) yerilerine icm7556 takınca normal çalışıyor. sence ne yapmam gerekiyor icm7556 hem pahalı hemde zor bulunuyor. birde ben pulsdetektor.de sitesindeki miner'in çıkış katını nasıl uygularım ne yapmam gerekir. ben birebir miner2 nin çıkış katını uygulaya çalıştım ama hcpl3120 tetikleyemedim nasıl bir modifiye yapabiliriz yardımlarınızı bekliyorum..
thank you all's forum..

[ivconic]

Giasou Geo!
Not only to phone me, but visit me! Looking forward!

This guy obviously need help refering blowed DP. Reversed batt. poles and busted it. I never had simillar case. Also i estranged latelly from this subject. First thing came to my mind was TL062 and virtual gnd. But he replaced it already. Also D8 and D9 need to be replaced....what else?

[Geo]

" I accidentally reversed battery poles at DP. Something blowed. Already replaced : tl062 , irf840 , 1n4001 , 1n4148 , bc546 , lm556 and still not working. What else should i check and replace? "

Hahahaha ..... where are you Ivica???
How are you and your family?????
Long time to read about you. What about the beautiful Servia????
Maybe after 3 weeks to go again to Beograd, so i will phone you again.
Se xereto Geo

[ivconic]

povezao sam pogresno polove na akomulatoru i delta pulse je crko
Zamenjeno : tl062 , irf840 , 1n4001 , 1n4148 , bc546 , lm556 i dalje ne radi
sta bi moglo da bude i gde i sta treba da merim unimerom radi provere

" I accidentally reversed battery poles at DP. Something blowed. Already replaced : tl062 , irf840 , 1n4001 , 1n4148 , bc546 , lm556 and still not working. What else should i check and replace? "

[labtec1]

povezao sam pogresno polove na akomulatoru i delta pulse je crko
Zamenjeno : tl062 , irf840 , 1n4001 , 1n4148 , bc546 , lm556 i dalje ne radi
sta bi moglo da bude i gde i sta treba da merim unimerom radi provere

[nelson]

Excellent Geo. I ll try 1.5 mm electrical wire and for the frequency i ll try first to connect my meter to the pins you said.
Take care
Nelson

With 0.85 maybe to work. I know many people that made the coil with 1.5mm with very good results.
Here at Greece, we use the PI detectors only with Big coils (1x1 or 2x2 m)