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Author Topic: Zener diode in place of voltage regulator IC  (Read 1396 times)

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effdub

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Zener diode in place of voltage regulator IC
« on: January 04, 2011, 03:54:18 PM »
I just looked at the datasheet for the Holtek ht8950 (vibrato and robot voice on a chip), and I saw that the operating voltage was min 2v max 4v. And all of the application schematics have a 3.6v zener diode between VCC (which is listed as 4.5v) and ground.

I wonder why that isn't done more in effects circuits? Seems like it would be an easier way to regulate voltage than using an IC and a filter cap, or a voltage divider and filter cap (since 4.5v zeners are available).

Oh, and would you still need the filter cap? It seems logical that you'd still want it, but I'm often wrong about that sort of thing.

Interesting page on the topic:
http://www.reuk.co.uk/Zener-Diode-Voltage-Regulator.htm

According to the above page, the app note in the HT8950 might not have sufficient input voltage for the zener.
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CountryBoyAtHeart

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Re: Zener diode in place of voltage regulator IC
« Reply #1 on: January 04, 2011, 05:17:45 PM »
The main issue is overheating the IC. Although, for smaller pedals this isn't of too much of a concern. A voltage divider with proper limiting resistor can prevent this though. You'd want a cap paralleled to reduce noise from the diode switching as well.
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earthtonesaudio

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Re: Zener diode in place of voltage regulator IC
« Reply #2 on: January 05, 2011, 01:57:45 PM »
Resistive voltage dividers work well in stompboxes (in general) because often you want a reference voltage that is some fraction of the total power supply, and the power supply is not always known.  It can be a battery (whose voltage changes over time) or some random wall wart from 9V to 18V or higher.  Two equal resistors will give you a reference that is always exactly half of *any* supply.

Diode voltage references work best where you want the voltage to always be *exactly* such-and-such volts, no matter what the power supply is doing.

I think of a Zener reference as being a cheap and not as good alternative to a regulator IC.  The IC regulator performs better in most categories (power consumption, output current, noise, etc) except purchase price.   You can add a constant current source and a big cap to a zener voltage reference to improve the standby current and noise specs, but by that time many regulator ICs are cheaper and take up less board space.
Wow. Looks like you've got all the parts you need to make a thermostat right there buddy. Cool! Hot!
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effdub

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Re: Zener diode in place of voltage regulator IC
« Reply #3 on: January 05, 2011, 03:52:21 PM »
Resistive voltage dividers work well in stompboxes (in general) because often you want a reference voltage that is some fraction of the total power supply, and the power supply is not always known.  It can be a battery (whose voltage changes over time) or some random wall wart from 9V to 18V or higher.  Two equal resistors will give you a reference that is always exactly half of *any* supply.

Right, that makes sense.

Quote from: earthtonesaudio
You can add a constant current source and a big cap to a zener voltage reference to improve the standby current and noise specs, but by that time many regulator ICs are cheaper and take up less board space.

Wouldn't the IC also need a filter cap? Something like a 78L05 seen in 2399 delay circuits usually has a 10uf or so cap.

Either way I suppose a diode + cap or IC + cap would take up about the same space.


Perhaps the best use of a zener in effects is as over-voltage protection. Seems like I've seen them in series with the power supply, but not generally in parallel.
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CountryBoyAtHeart

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Re: Zener diode in place of voltage regulator IC
« Reply #4 on: January 06, 2011, 04:34:26 PM »
http://sound.westhost.com/articles/soft-clip.htm

Ran across this, the "assisted zener" should be good enough for any small pedal if you're worried about response. But, which has a lower output Z, the assisted zener or the regulator?
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earthtonesaudio

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Re: Zener diode in place of voltage regulator IC
« Reply #5 on: January 07, 2011, 10:27:34 AM »
Did you mean this page:
http://sound.westhost.com/appnotes/an007.htm
?

The "assist" is in the form of increased power handling.  So yes you can get a lower output impedance, but at the cost of higher current consumption.  The output Z of a regulator will generally still be lower because it's an active device that uses negative feedback.
Wow. Looks like you've got all the parts you need to make a thermostat right there buddy. Cool! Hot!
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CountryBoyAtHeart

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Re: Zener diode in place of voltage regulator IC
« Reply #6 on: January 07, 2011, 04:49:16 PM »
http://sound.westhost.com/miscc.htm

This is what I meant to post.  :-[ Whoops, damn Safari and multiple tabs.

Same schematic, but the new link shows a graph of the response change.

For an application, do zeners or assisted zeners work when wanting to "regulate" a negative voltage? Do I maintain the cathode to the positive voltage (ground) and the anode to the negative voltage?
-Jared

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