It just crossed my mind. If a mosfet used in switch mode should or
could a thyristor also work. Do manufacturers make them already
for high frequencies ?
Because a power mosfet is far too expensive to hobby around with.

Hi,

Early TV's used them in their power supplies. Some used a SCR, others used
fancier devices.

MOSFET's give a higher efficiency and are a lot easier to drive, so they
were pretty much abandoned.

Cheers!

D. v. Bilt wrote:

It just crossed my mind. If a mosfet used in switch mode should or
could a thyristor also work. Do manufacturers make them already
for high frequencies ?

I've done it in the past, but they're not really capable of high frequencies
(mine was at 173 kHz).

Because a power mosfet is far too expensive to hobby around with.

What? The IRF730 (for example) is capable of 50 Watts at up to 25 MHz for
very little drive, and costs under $1!

Bob

Bob wrote:



Because a power mosfet is far too expensive to hobby around with.


What? The IRF730 (for example) is capable of 50 Watts at up to 25 MHz for
very little drive, and costs under $1!

Bob

Hams is cheap! If it ain't free, it's too expensive to bother with

Scott
N0EDV

"Bob"

Because a power mosfet is far too expensive to hobby around with.

What? The IRF730 (for example) is capable of 50 Watts at up to 25 MHz for
very little drive, and costs under $1!

Bob

Agreed. But now the 150 W and up versions for 2 meters..

b.t.w. since when did the u.s. agree to go metric ? (1888?) not only for hams.

"D. v. Bilt" wrote in message
...


It just crossed my mind. If a mosfet used in switch mode should or
could a thyristor also work. Do manufacturers make them already
for high frequencies ?
Because a power mosfet is far too expensive to hobby around with.

The main problem I see is the fact that they are generally designed to lock
into the on state, until the load current drops to zero. For a switch mode
power supply, the switching device has to be able to break full current. If
you used an SCR it would lock on, and things would melt under most
conditions.

The only switching circuits they can be used in is circuits that are
designed to drop to zero on it's own for the SCR to unlatch. Like AC load
control, where the sine wave drops to zero at a 120 times a second.

Like the old computer line printers. They had a bank of SCRs driving the
printing heads. The inductive rebound would bring the current to zero and
allow the SCR to unlatch after triggering. But If one stuck on, you better
shut the system down quick, or the thing was going to burst into flame.

On Mar 1, 3:53*am, "D. v. Bilt" wrote:
* * It just crossed my mind. If a mosfet used in switch mode should or
* * could a thyristor also work. Do manufacturers make them already
* * for high frequencies ?
* * Because a power mosfet is far too expensive to hobby around with.

They are relaatively slow, You might could build a VLF transmitter
using them.

Jimmie

"D. v. Bilt" wrote in message
...


It just crossed my mind. If a mosfet used in switch mode should or
could a thyristor also work.

Yes they would however the circuit complexity is higher. Other than the
frequency issue the problem is turning off the SCR. This requires some
careful design techniques to commutate the SCR off once it is turned on.
That's where the complexity comes in to play. Various methods are used to
accomplish this. Also SCR's have other problems too such as turn-on di/dt
limits, dv/dt limits at turn off (which can cause retriggering), recovery
time requirements, high recovered charge etc making snubber circuit design a
challenge.

http://nptel.iitm.ac.in/courses/Webc...)NPTEL)%20.pdf

http://forum.vtu.ac.in/~edusat/Prog6...niques.ppt#113

--
Regards,
Leland C. Scott
KC8LDO


Do manufacturers make them already
for high frequencies ?
Because a power mosfet is far too expensive to hobby around with.

On Mar 1, 12:37*pm, "D. v. Bilt" wrote:
"Bob"

* * Because a power mosfet is far too expensive to hobby around with.

What? *The IRF730 (for example) is capable of 50 Watts at up to 25 MHz for
very little drive, and costs under $1!

Bob

* Agreed. But now the 150 W and up versions for 2 meters..

* b.t.w. since when did the u.s. agree to go metric ? (1888?) *not only for hams.

I wonder what the cost would be on an SCR that oprates at 150 Mhz.

Jimmie