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I want to PWM-switch neon bulbs.

The power supply delivers about 220V DC. And I have to switch the bulbs in the "positive" section, so this means PNP, I can't switch them NPN because a NPN Transistor is used to switch on and off specific bulbs, the PWM is for regulating the overall brightness.

So I'm looking for a solution to switch the voltage PNP. Device should be able to switch 220V DC and 50mA at least.

The PWM control signal is 800Hz, level 5V DC out of an ATMEGA328. If there is a SMD solution that would be great, but doesn't need to be.

What could I try to use here?

What I tried to search for:

1) Optocoupler : Sadly no PNP Optocoupler found

2) Relais: Not Possible, too slow

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2 Answers 2

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1) Optocoupler : Sadly no PNP Optocoupler found

That's actually not relevant. The switching input is not emitter-referenced, so the same voltage requirements a NPN BJT has regarding its B-E junction don't exist here.

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  • \$\begingroup\$ vishay.com/docs/83682/sfh640.pdf Would this work? \$\endgroup\$
    – sgt_johnny
    Commented May 16, 2015 at 14:11
  • \$\begingroup\$ @sgt_johnny it's going to be slow and quite variable in speed with the number of lamps that are 'on' at 800Hz. It won't fail (assuming very low collector current), but I don't think it will work well. \$\endgroup\$ Commented May 16, 2015 at 14:45
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It sounds like your actual question is how to achieve level shifting in order to control a PNP transistor. There are lots of suitable PNP transistors such as the venerable MPSA92 and its SMT equivalent.

You can use a high-voltage NPN transistor to switch a high-voltage resistor to control the PNP base. For example, if you allowed 1mA that would require a 220K 1/4W resistor. Use a resistor such as 10K from base to emitter of the PNP. A suitable NPN would be the complement of the MPSA92- MPSA42.

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  • \$\begingroup\$ Oh okay. Thank you. So i need 2 Transistors and 2 Resistors. Well if it works i will use it !! I thought maybe there would be a single part solution \$\endgroup\$
    – sgt_johnny
    Commented May 16, 2015 at 14:47
  • \$\begingroup\$ @sgt_johnny There might indeed be a single part solution, but it might be $10 rather than $0.20. That's engineering... \$\endgroup\$ Commented May 16, 2015 at 16:18
  • \$\begingroup\$ I don't care if its $.20 , $10 or $100. If its working and will fulfill my need, then its fine. =) \$\endgroup\$
    – sgt_johnny
    Commented May 16, 2015 at 17:55
  • \$\begingroup\$ @sgt_johnny Then it is arguably not really engineering because sensible constraints are not present. As the saying goes "An engineer is someone who can do for 10 pence what any fool can do for a quid”. \$\endgroup\$ Commented May 16, 2015 at 17:59

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