Shunt Regulator circuit

[David HK]

In the Otherpower amgazine there is a shunt regulator circuit based on a LM 723 (Chris Greacen author/designer)

The final part of the circuit indicates the use of a FET - IRF Z40 N Channel.

I have searched high and low through all the electronic shops in Hong Kong and cannot find this FET on sale here.

Can anyone suggest an alernative in the form of a power transistor suitable to handle 4 ohms @250 watt to 3 ohms to 80 watts - as per the article. If the load spec is wrong please correct me.

Regards,

Dave

[Flux]

Any N channel mosfet with 40A or greater rating should do.

Anything with IRF or IRZ 44  or 48 should do such as IRFZ48R.

STP55NF06 or STP55NF10     HUF75369P3

Or you could use 2 smaller ones in parallel such as IRF540N

Don't try to use bipolar transistors, it must be N channel mosfet.

Hope you can find one of these.

Flux

[David HK]

Dear Flux,

Thank you very much for your reply, it was most helpful.

The problem is that FET's do not seem to be very popular items in Hong Kong for hobbyist electronics people and I doubt if I could find any of the alternatives you recommend.

I was rather hoping to look at something like a 2N3055 or similar along those lines.

Still hopeful.

Dave HK

[Flux]

Dave

That does make life difficult.

You would have to use a complimentary darlington pair to use bipolar transistors, there will not be enough base drive to run a power bipolar transistor direct.

If you use a darlington pair you may get away with it, such as TIP 41 driving 2N3055. The saturation will be poor and you will need a large heatsink. Tip 41 driving 2N 2955 as a complimentary would be better if you know how to do it.

It will need a bit of knowledge and experimenting but certainly it could be done.

Personally I think it would be easier to use Hugh's circuit with relays, the bits for that seem to be available most places.

Flux

[David HK]

Flux,

Many thanks indeed. I will follow your first suggestion and see what my local Aladdins Cave has in stock to come close with your recommendations.

After that I will fall back to your second response.

Dave

[coldspot]

When checking local supply shop for this part

# IRFZ40

The number that it crossed to in their book

was

# NTE 2395 031H

just my $.02

if that helps

I have a couple of DC PM Motors ready to fly and lack only "control"

So I am very interested in other peoples ways of doing it!

[dinges]

Hi David,

You're having trouble finding MOSFETs in Hong-Kong ?! What is the world coming to... Next thing you'll know, we'll have trouble finding oil in Saudi-Arabia ;-) They should be quite easy to find, over here in NL several Pop&Mom electronics shops have various typenumbers on stock. They can order just about everything that is made.

As others have said, most any old MOSFET should do the trick; try to find one with as low  Rds as possible; as high a current rating (Id) as possible; and a voltage rating that is high enough. It's a reason why I like MOSFETs: they're so easy to exchange for other typenrs, with better/other ratings. Much easier than bipolar transistors, for example.

You could also try to find an old VCR or colour tv; in the powersupplies usually are one or two MOSFETs. Look for part.nrs like 'RFP' or 'IRF' or 'IRFP'. Hmm, have you tried TV repairshops in your area? They should definately have the item you want, it's so common...

Good luck,

Peter,

The Netherlands.

[dinges]

And of course, old PC power supplies have at least one MOSFET in them. Come to think of it, I'm having trouble thinking up a piece of electronis that doesn't have one in them ;-)

I wouldn't bother with 2n3055s or other modifications; just search for the MOSFET, if necessary take apart the PC :-)

BTW, after more careful reading your mail I noticed that you can find it nowhere 'on sale'. That may be true, I've never seen electronics components on sale, but for sale was never the problem ;-)

Easy for me to say though, as I've just walked to the electronics components rack, got out the drawer with MOSFETs and looked for the right part. Too bad Hong-Kong is such a long way to drive, else you could have it...

Peter,

The Netherlands.

[Dzisko]

It is not necessary  to replace FETs with FETs, NPNs with NPNs, etc.

Everybody can easy replace almost all parts with almost all parts, ICs with NPNs, MOSFETs with PNPs, so simply give me list of parts you do have and I will rebuild the whole circuit under these parts.

Of course, give me a link to the circuit.

[David HK]

Success!

After trudging around town this morning and ransacking a few electronic shops I finally located some FETS namely - IRFZ 44 and IRFZ 48. IRFZ 40's are nowhere to be found.

So I am pleased to report that the IRFZ 44 works well and I am indebted for all the help given to suggest this FET as an altenative option.

I am also hopeful that none of you have attacked your computers to locate this vital part and send it to me for Christmas.

Regards to all from a fairly warm and sunny Hong Kong.

Dave