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I am making a circuit using an LR8 voltage regulator, and because the current may go over the recommended 10ma I will be putting a pass transistor to carry a little more current. The one I see most used is the TIP50 ,and I can do that. I looked in my box of bits and can't find one , but I have a high-voltage high-current thyristor and I'm wondering if it would work and if not(which I suspect) why not? This may be obvious to those who understand transistors , but I am at a very basic level of experience and would learn something more if someone could enlighten me.

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You can't use a thyristor for the main reason that once it activates, it switches on and cannot be switched off until the DC power is removed. This is because a thyristor has a latching action i.e. it cannot linearly control current or voltage; it's a switch type operation.

The other side of the coin is that you may not be able to activate the thyristor and, it will "sit there" pretty much like an open switch and not perform any function.

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  • \$\begingroup\$ Hi , thanks for replying. I realise the thyristor can only turn on and off , but I imagined that in this application it would only need to turn on once when the power was switched on , and allow current through until the power was switched off. All it needs is a bit of current applied to the control pin at switch-on. \$\endgroup\$
    – Oli Senior
    Aug 6, 2023 at 12:31
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    \$\begingroup\$ No, that isn't the way transistors work when used to bolster a more lightweight voltage regulator; they still have to have control and linearity. \$\endgroup\$
    – Andy aka
    Aug 6, 2023 at 12:46
  • \$\begingroup\$ Thanks Andy , appreciate your help , I'll look into those things. \$\endgroup\$
    – Oli Senior
    Aug 6, 2023 at 12:50
  • \$\begingroup\$ @OliSenior if we are done here, please take note of this: What should I do when someone answers my question. If you are still confused about something then leave a comment to request further clarification. \$\endgroup\$
    – Andy aka
    Aug 6, 2023 at 13:18

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