# Two questions about astable multivibrators and transformers

Here's something that confuses me: The output on an astable multivibrator will be shown on a multimeter as half the input voltage (for example we have 9V-0V-9V-0V...and the multimeter averages it out and displays 4.5V). But then if I put that output to a voltage doubler, the voltage should be 18V, not 9V right? Since the voltage doubler will output in DC.

Second question is basically me being stupid: I've tried hooking up a transformer (9V to 230V, 0.5A) to an astable multivibrator (which operates at 671Hz) but something starts to smell burnt and the components of the astable multivibrator get hot. How do I fix this? (the components still work, I checked) Here's the circuit:

But then if I put that output to a voltage doubler, the voltage should be 18V, not 9V right?

Correct. Voltage doublers are easy enough that if you sorta-kinda understand how a capacitor and a diode works you can work this out for yourself, on paper. Nothing does a better job of understanding circuits than working it out yourself.

...but something starts to smell burnt and the components of the astable multivibrator get hot...

1. transformers are inductive components, and inductors "want" to have zero average voltage on their terminals. When you put your 0V/9V power to the thing, it sees a -4.5V/+4.5V signal added to a 4.5V signal. It steps up the square wave, but it tries to short the 4.5V signal to ground. That's going to cause an inordinate amount of DC current to flow. The easiest way to deal with this is to put a capacitor between ground and the transformer -- it'll charge up to 4.5V, and everything will be fine in that regard. Make sure your cap is big enough so that there isn't significant ripple, and that it can handle the current.
2. Your transformer is rated for 1/2 an amp at 9VAC. A 555 can possibly drive that much, but it'll get hot. Even if your transformer is unloaded, just the magnetizing inductance of the transformer is going to require a hefty current. You really need a power stage there, that can safely drive an inductive load.
• Thanks. I'll have a look at what a power stage is. Is there an easier way? Commented Aug 20, 2019 at 15:33
• A power stage is an amplifier that is designed to deliver power, not just generate a signal. Commented Aug 20, 2019 at 17:02
• Are you telling me the only way to make 1500V (and very low current) from a 9V battery is using giant transformers and power stage devices? I searched every god damn corner of the internet and I can't find a single schematic that does what I need.... Commented Aug 20, 2019 at 17:24
• Your question is about driving a 9V to 230V transformer from a 555. I answered it. If you want to generate 1500V from 9V, that's a separate question. And no, you don't need "giant transformers" -- you can make a flyback boost converter. Commented Aug 20, 2019 at 17:38
• Ahh, thank you Tim, I'm sorry if I've been a bit rude. I'll try reddit. Commented Aug 20, 2019 at 17:43