Re[6]: Question about auto coil -

[Guest guest]

Hi Andy,

If you use the correct MOSFETs the heatsink will not need to be very

large. Try using IRFP150N. These have an on-state resistance of only

0.03 Ohms (and increased voltage rating - 100V). The ones used by

Aubrey are 0.014 Ohms (even better, but only 50V). This can make a

huge difference.

The IRFP150N also has a lower gate, and output capacitance than most.

Will help with high freq response (as did the original HUF75337P3,

50V MOSFETs).

If your MOSFETs are rated around 0.05 Ohms or higher, they are going

to get hot. Don't know why Don used such huge caps (and so many).

Maybe they are extremely old (much smaller these days).

--

Best regards,

Bil Green

2001 TV VCR

Mammoth Lakes, CA 93546

mailto:tv.vcrrepair@...

Sunday, December 21, 2003, 5:23:16 AM, you wrote:

AS> Hi Bil, Thanks for the link to Don Maloneey's device. I note that he is

using different Mosfets ( I cant read the number) and a very susbstantial cap

bank for bypass- these must be rated at 100v

AS> or over, judging by their size ; with 6v I am using the (much smaller) 4x

5000UF 35VW mini caps which take up a fraction of the space and still work fine

with the original mosfets. My only need

AS> is a much more effective heatsink than I am using at present.

AS> Could I reiterate my query about the driver you are using?

AS> Andy

[LONG QUOTE REMOVED BY THE MODERATOR]

[Guest guest]

The large caps are there because that was my original variable supply.

If you look at the other pictures there are different supplies and voltages.

All the best.

Don

[Guest guest]

Hi Bil, Aubrey, Alvin, Dave,

Thank you for your various valuable inputs regarding the construction of

Aubrey's experimental device. As Aubrey pointed out the circuit is only

experimental and needs refining. From what he says, if the parameters are

correct his circuit should do what is necessary without the need for large heat

sinks etc. However, to extract greater power and to increase the upper frequency

range, some modifications, such as those suggested, as well as others clearly

need to be made. In my case overheating is probably due to insufficient gate

voltage - this uses 9v (in my portable unit) rather than the 12v + specified,

which may be insufficient to turn the mosfets on fully.

Looking through the lists of mosfets available from RS components, one can see

that as working voltage and current handling increase so does drain-source

resistance and gate capacitance, so that one would have to go for either rather

expensive (or difficult to obtain- eg from the US) mosfets or use several in

parallel, with attendant gating problems. One advantage of the mosfets that

Aubrey selected is that they are quite cheap and easily replaced. The ferrite

toroids used were obtained from RS components, the larger one being identical to

that specified by Aubrey; the smaller (portable unit) one having the same

permeability characteristics.

Andy

Re[6]: Question about auto coil -

Hi Andy,

If you use the correct MOSFETs the heatsink will not need to be very

large. Try using IRFP150N. These have an on-state resistance of only

0.03 Ohms (and increased voltage rating - 100V). The ones used by

Aubrey are 0.014 Ohms (even better, but only 50V). This can make a

huge difference.

The IRFP150N also has a lower gate, and output capacitance than most.

Will help with high freq response (as did the original HUF75337P3,

50V MOSFETs).

If your MOSFETs are rated around 0.05 Ohms or higher, they are going

to get hot. Don't know why Don used such huge caps (and so many).

Maybe they are extremely old (much smaller these days).

[Guest guest]

Hi Bil, Aubrey, Alvin, Dave,

Thank you for your various valuable inputs regarding the construction of

Aubrey's experimental device. As Aubrey pointed out the circuit is only

experimental and needs refining. From what he says, if the parameters are

correct his circuit should do what is necessary without the need for large heat

sinks etc. However, to extract greater power and to increase the upper frequency

range, some modifications, such as those suggested, as well as others clearly

need to be made. In my case overheating is probably due to insufficient gate

voltage - this uses 9v (in my portable unit) rather than the 12v + specified,

which may be insufficient to turn the mosfets on fully.

Looking through the lists of mosfets available from RS components, one can see

that as working voltage and current handling increase so does drain-source

resistance and gate capacitance, so that one would have to go for either rather

expensive (or difficult to obtain- eg from the US) mosfets or use several in

parallel, with attendant gating problems. One advantage of the mosfets that

Aubrey selected is that they are quite cheap and easily replaced. The ferrite

toroids used were obtained from RS components, the larger one being identical to

that specified by Aubrey; the smaller (portable unit) one having the same

permeability characteristics.

Andy

Re[6]: Question about auto coil -

Hi Andy,

If you use the correct MOSFETs the heatsink will not need to be very

large. Try using IRFP150N. These have an on-state resistance of only

0.03 Ohms (and increased voltage rating - 100V). The ones used by

Aubrey are 0.014 Ohms (even better, but only 50V). This can make a

huge difference.

The IRFP150N also has a lower gate, and output capacitance than most.

Will help with high freq response (as did the original HUF75337P3,

50V MOSFETs).

If your MOSFETs are rated around 0.05 Ohms or higher, they are going

to get hot. Don't know why Don used such huge caps (and so many).

Maybe they are extremely old (much smaller these days).