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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 23rd May 2020, 1:42 pm   #21
Trigon.
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Default Re: Low voltage indicator for 90v circuit

BC547 has a max Vceo of 45v.

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Old 23rd May 2020, 2:41 pm   #22
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Default Re: Low voltage indicator for 90v circuit

Quote:
Originally Posted by Trigon. View Post
BC547 has a max Vceo of 45v.

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That is the same as the SMD SOT23 specified. Thanks for pointing it out. What would you device suggest ?

John.
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Old 23rd May 2020, 2:44 pm   #23
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Default Re: Low voltage indicator for 90v circuit

Brilliant, I am rather chuffed that it works when built. You are stretching the voltage rating of the BC547 (rated 45V) a bit, modern components are so good that I am not surprised it is OK. 78V, the simulation was smack on.
 
Old 23rd May 2020, 7:43 pm   #24
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Default Re: Low voltage indicator for 90v circuit

Many people seem to keep MPSA42 (npn) and MPSA92 (pnp) devices on hand as general purpose higher voltage transistors.

Both Vceo= 300v, with gain good enough for many purposes.

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Old 23rd May 2020, 9:16 pm   #25
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Default Re: Low voltage indicator for 90v circuit

Quote:
Originally Posted by Trigon. View Post
Many people seem to keep MPSA42 (npn) and MPSA92 (pnp) devices on hand as general purpose higher voltage transistors.

Both Vceo= 300v, with gain good enough for many purposes.

Cheers

Thank you, I have just ordered 10 of each, I may only use one but look handy just in case I need any more. While looking for a suitable transistor I found an interesting Diode, I had better start another thread about it.

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Old 29th Jun 2020, 12:02 pm   #26
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Default Re: Low voltage indicator for 90v circuit

I'm very pleased with the above circuit and wonder if it can be done for a 9v circuit ? light on at about 7v. I have been playing with my bread board but not making much progress. I have 3.3v 4.7v and 10v Zener diodes available. Please can anyone help.


TIA John.
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