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Registered Member #2115
Joined: Fri May 08 2009, 01:17PM
Location: Singapore
Posts: 46
Hello,
I want to interrupt an SSTC with a 555 independently variable circuit. The SSTC uses antenna feedback with 74HC14, and its design is mainly from Steve Ward's SSTC5.
I have only used the UCC37322/21 gate driver chips before, so I don't know how to interrupt without the "Enable" pin. So far, I can only think of 3 ways to do so:
Directly tie the feedback and 555 outputs together.
Make the 555 output drive a MOSFET in series with the 5v supply to the 74HC14.
Make the 555 output drive a MOSFET in series with the 74HC14 output signal.
Can I ask, if there is any other way to do so, and which method of interrupting the signal is best?
Registered Member #883
Joined: Sat Jul 07 2007, 01:02PM
Location:
Posts: 16
You could also use AND gates in series with the driver chips but i think without the TI chips you might need a free running "startup" oscillator. The inverting TI chip automatically sends out a short pulse when enabled, negating the need for a startup oscillator.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Curtis wrote ...
Why all the inverters in series. That would just add a lot of delay.
The delay is not going to hurt you. If your only switching at say 300kHz (3333ns period), then (4) extra gates (44ns), is nothing. If you were switching at 10MHz, then that would be a different story.
Registered Member #2115
Joined: Fri May 08 2009, 01:17PM
Location: Singapore
Posts: 46
Thank you all for the informative replies. So I have chosed to interrupt it by putting a bc107 transistor at the output of the 555 disable signal, and connect it to the antenna signal.
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Interrupting SSTCs with TC4421/22
