Zener Heat

146.4 (at test conditions there's 149 >V across them, which is close enough for me).

Oh!, 12-6volt and 6-12 volt = 144volt

So you have about 6v across 165 ohms or about 3.6 milliamps through the string at no load.

If you connected a 40ma load at the 72 volt junction the voltage at the top of the string would start to drop below the 155volt supply voltage and the string would stop functioning properly. I'm sure your running this close to keep heat low in the string.This would happen even if you spread out the load among several zener junctions. The 12volt zener at the top of the string would have about a half watt across it, which is ok. Well Tim, now that I've went through this I think you need to find a way to cool your zeners (sorry, I guess you new that ;-). If it's a one of unit, you might bend a thin u shaped piece of alum. around each diode. Such as, poor ascii art. l_o_l The vertical sections will help get rid of the heat.

I'm curious why you need such high voltages for ICs.

I don't have any ideas other than heat sinking. Mike

From what you have told us so far this is either a top secret product for the military or you have but a limited idea of what you are doing. Be careful - 150Vdc is dangerous - and get someone in to do whatever it is you are playing with before you harm yourself.

I read in sci.electronics.design that Tim M wrote (in ) about 'Zener Heat', on Sat, 12 Feb 2005:

This is not a good design. You would do far better to derive your 5 V supply from a 9 V wall-wart.

If you are putting the zener string in series with your regulator, it simply won't work, nor will it work if you put the regulator across a 12 V zener at the ground end of the string. Your zener current of 3.6 mA is the maximum you can draw from the regulator.

--
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

You need to get rid of the zeners and put that power dissipation in a component built to take it, like a power resistor, and you can parallel two 6.2V zeners so as to cut their temperature rise by half with Tj at a maximum of 22oC above ambient. None of the semiconductors get warm:

View in a fixed-width font such as Courier.

In addition, you should follow the resistor with a transient suppressor.

J

When I don't want two power cords, what I've done is carefully saw open a small (

You can make it safer by using two identical transformers back to back such as this;

pri-TRANSFORMER-sec=sec TRANSFORMER-pri

this way you get isolation and still have your 155v or 170v output. Mike

So the series line capacitor is a no-no?

You seem to get a big turn-on slapping people's shit. What I "need" ain't what you got.

That's the problem with the series line capacitor method which is incomprehensible and misused by nearly every hack and hobbyist who ever used it. A transformerless power supply that is perfectly safe when double insulated would be something this- cheap small 1.5ARMS ripple e-caps will work well, and line transient suppression follows naturally:

View in a fixed-width font such as Courier.

Fred Bloggs wrote: [..snip wrong diagram..] View in a fixed-width font such as Courier.

Only if you need to be told why there is a resistor in series with the capacitor, why there is one in parallel with the capacitor, why a transient suppressor is necessary, what is the difference between X and Y rated capacitors, and what class ll means.

Otherwise there are millions of successful products out there with reactive ballasts.

The problem comes with rating the capacitor and handling surges. For example, when the LINE is first applied, and it happens to be 170V max when you flip the switch, there will be a helluva surge through the cap throwing the full 170V onto the load until it charges up. Now that I have looked up these NIXIE tubes, it seems they don't require a doubled line voltage, 180VDC is the required anode voltage. In a pinch you can stack a primary with the secondary with an international type transformer with dual primaries and keep the end circuit grounded. It will be important to fuse both legs of the line and MOV it at 300V between L-N and L/N-GND. The transformer is not safety rated for this but it will provide isolation. The LV can plug directly into a 7805, and the HV goes to the NIXIE anodes.

View in a fixed-width font such as Courier.

. .. . .. .. ,----------------------|>|---------------------+-->HV .. | 1N4007 | .. | 131VAC |+ .. | TERM 1 -8 |300V .. ,---------------. === .. | | | 10U .. | o----. | | .. | 1 | | | .. | o)|| | | .. | )|| --o | .. | )||(o 5 | .. | )||( | .. | )||( 6 | .. | 2 ||| --o | .. '----o----.|| | | .. || | 1A .-----|--->LV .. >--------o----.|| | 50V | | .. 3 ||| | --FWB-- | | .. o)|| --o----------------|~ + |----+ + | .. )||(o 7 | | | 16V | .. LINE 115VAC )||( 8VAC | -|>|- | === | .. )||( 8 | | |470U | .. )|| --o----------------|~ - |----+ | .. 4 | ------- | | .. >--------o----. | | .. T1 | | .. | | .. GND >-------------------------------------------------+-----' .. | .. --- .. /// . .. .. T1 TRIAD POWER p/n 553-FS16-150 . .. 2.5VA DUAL PRIMARY 16VAC @ 0.15A CT . .. 1.2 x 1.125 x 1.375 inches . ..

. ..

glad you are so sure

*That* you will not get:

Eventually, one zener will fail stressing the others a bit more so one of those fail - and directly on the mains too. At least the eventual explosion of the entire stack and the group-suicide of the IC's should be impressive!

Use a wall-wart and a custom switcher to generate the special voltages - how hard can it be?

Planar transformers can be *very* small - even with mains isolation.