Narrow-Bandwidth Television Association

After my video-driver is working, I continue with the automatic speed control circuit. I would like to use the circuit from the NBTV handbook, p. 14 (if nobody has a better idea).

My motor is a 6 V so I have to recalculate the 4k7 resistor. How? What are the values I have to put into my calculation?

Another problem: The circuit needs 12 Volt. Can I take it simply from the video-driver 12 V output? For the motor I have a variable transformator (3 V - 12 V), currently set to 6 V. Or could I better use an extra 12 transformator for both and put an extra resistor for the motor?

And my last question: Wouldn't it a good idea to sell PCBs for that circuit in the club shop?

I was shopping today, and the bad news are that the IRF 510 and all its recommended substituts are no longer available due to stronger laws (RoHS). I've got an IRFZ34N, I hope it will do it, otherwise I have to look for a completely other circuit, or I have to ask at the "Scientific Museum in Munich", as the man in the shop said.

And I still don't know what to do with my 6 Volt motor and the capacitor and the resistor in that circuit. Maybe I have to look for an alternative circuit.

Volker, can't you buy a BUZ11?

And there are Philips Power MOS-fets called BUK and then some long number, that are almost identical.

The differences are the very high currents, much higher than you are going to use, and the high voltages that they can withstand, much higher than you are goint to apply.

There is a long list of Power FET's in the Conrad catalogue (www.conrad.de)

I'll try that on friday (tomorrow I'm not at my work, and on thursday it's a bank holiday here. Conrad costs time, and an order only for one part about 1 EUR, I don't think it's possible? the next Conrad shop is in Essen, I think about 50 km from here. I have to look if there is a shop like this in Venlo. (Maar niet op donderdag met al de Duitsers... )

There is a RoHS compliant version of the IRF510 called the IRF510PBF, it's stocked in the UK by Farnell, but I know that doesn't help you. There are many that can be used as a replacement, there's nothing particularly special about the IRF510.

I think Andrew used an IRF540 if my memory is correct. The BUZ11 that Klaas mentioned should be fine too.

Others that should do fine are the BUZ71, IRF520, IRF610/620/630/640. If you really get stuck give Klaas or I a shout. The differences between those above is primarily current rating, but they're all OK for this job.

Steve A.