solid state vibrator

ID: 219792
solid state vibrator 
05.May.10 13:04
10925
Jan Terranea (NL)
Articles: 62
Count of Thanks: 23
Jan Terranea

This design I have in use to replace a 120 hertz mechanical nonsynchronous vibrator in a small case to feed mobile radio-equipment from12 volts DC.

There are 2 vibrator types: series-drive with 3 pins connected, and shunt-drive with positive dc voltage at pin 4.

As the mulivibrator needs positive DC it must be connected as a shunt-drive vibrator.

(In case of a synchronous vibrator the ht-rectifying part is done by 2 HT-diodes.)

My previous solid state series-drive transistor vibrator got too hot after some time at a load of 60 mA.

 A friend advised me to try switching power mosfets and he gave me some HUF75345S3S.

These fets can stand to about 20 volts between gate and source, and to about 55 volts between gate and source.
So at 24 volts power input additional measures will be needed to protect these fets.
These switching fets do not consume any current at their gates, and their internal resistance between source and gate in the open-state is almost zero, so they only warm up during te period that the gate-tension is about 3 to 4 volts positive, and that is the reason why the switching transistors can be small, but they really need to have a high amplification.
1-2 must be 10 times ore more to the value of no. 3-4 to obtain good square waves,
1-2 togethet with 7-8 determine the switchting (vibrating) frequency (r-c time)
      to make about 120 HZ values are:1-2 = 12 k, 7-8=470 nF.
 5-6 are protecting diodes to the transistor bases at 12 volts DC-input.
13-14 are switchting Fets, that open at about 3-4 volts, so this vibrator does not work
      if the input voltage gets too low to firmly open the fets.
15-16 lead to the double LT-winding on the transformer, connected to vibrator-pin 1and 2;
      pin 3 is connected to –DC, pin 4 is connected to +DC.
 
Jan Terranea, may 2010.
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 2
solid state vibrator 
08.Jan.23 21:08
10925 from 11278
Christian ADAM (F)
Editor
Articles: 439
Christian ADAM

I did check your solid state vibrator design using the same switching power mosfets HUF75345S3S as recommended by you. For the the small transistors, I used BC337.

The result is very good. Most important point to be be highligted : the mosfets even without heat sink do not heat with a current of several amps...This allows a very compact card board: see hereunder ...

Thank you for this usefull tip !

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