# Zener Diodes in series as Voltage Regulators

#### Gumnuts

Joined Apr 26, 2024
35
I’m attempting to confirm my approach to this project circuit. I’m wondering if the 2 halves of the circuit (as shown) would work well to drive the Load, or even work together well at all. (It’s been a while since I was designing circuits (30+ years) and I’m a bit rusty.)
I’ve done a preliminary drawing but many of the details like Current and Component values are still either missing or a best guess at this point.
I have 3 questions really:
1. Is using Zener Diodes as I have done an appropriate approach for regulating/providing the 4 different voltages I need? (as shown) I am yet to work out the values but I want to check my approach is correct first.
2. Are the Amplifiers needed in addition to the Buffers (Emitter Followers) after the Frequency Generators? I suspect that the amplitude of the signals may be sufficient without them.
3. Is there a better approach I should use instead?

Circuit Purpose
To generate a variable frequency of approx. 10KHz (±50%), at a variable range of amplitudes. An isolated circuit is the Load. (See circuit)
Regulate 36V DC to generate 5v (Circuit Vcc), 12v DC, 24v DC & 36v DC.
The 12v, 24v & 36v circuits each provide an approx. 10K Hz, 50% Duty Cycle wave. I’ve used Hex Inverters with Schmitt-Trigger Inputs to achieve a really square wave. (See circuit)
The Load is an Isolated Circuit that contains a step-up transformer (1 to 10) that feeds a large capacitor in a very poor dielectric solution. The diode D12 stops the capacitor from discharging during operation. Once charged, the current in the Isolated circuit is very low.
Only one signal is connected to the Load at a time so I’ve used 4 x switch DIPs to select the appropriate connections. Changes to switches would be made only when the power is off.
The same earth is used throughout.

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#### ericgibbs

Joined Jan 29, 2010
19,118
Hi Gum,
Welcome to AAC.
You cannot power HC logic from those higher voltages.
The device is designed for operation with a power supply range of 2.0V to 6.0V.
E

Update:
2. Are the Amplifiers needed in addition to the Buffers (Emitter Followers) after the Frequency Generators? I suspect that the amplitude of the signals may be sufficient without them.

Without isolation buffers, the loading imposed by the circuit you are driving could change the frequency and amplitude of the signal.

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#### Gumnuts

Joined Apr 26, 2024
35
Are you referring to the series Zener/resistor part of the Voltage Regulator circuit at left?
I'm generating the signal (Vcc is 5v) so the max amplitude of the HC circuit is 2 to 5v.
Use it as an input to the Base of the Amplifier (with a Collector Voltage at say 12V.) so the HC circuit is separate excluding the ground.

#### Gumnuts

Joined Apr 26, 2024
35
I haven't chosen the correct component values a yet. Choosing the perfect Zener according to its Breakdown Voltage and choosing the right resistor values is key, but I'm not there yet.

#### ericgibbs

Joined Jan 29, 2010
19,118
hi G,
This circuit section shows the high voltages I noted.
E

#### Gumnuts

Joined Apr 26, 2024
35
OMG - I found the error. A new version is attached

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#### BobTPH

Joined Jun 5, 2013
9,284
A Zener diode is a very poor regulator that wastes more power than even linear regulators. Three pin linear regulators are simple to use, cheap, and very accurate. Why would you not use them?

#### Gumnuts

Joined Apr 26, 2024
35
Thank you. This is a great idea! I'll look into it.
And the other part of the circuit? How does that look?

#### BobTPH

Joined Jun 5, 2013
9,284
And, looking at your circuit, it has serious problems. Your output voltages do not have a common ground. With respect to ground, the one labelled 5V will actually be at least 31V.

Also, even if you fixed this (by reversing the order if the outputs), the series resistors will prevent the Zeners from doing their job. The voltages will vary with the total current drawn from each output voltage. This is no regulator at all!

Have not looked at the rest of the circuit.

#### Gumnuts

Joined Apr 26, 2024
35
Yes. I thought there were some issues.

Is this the type of regulator you were suggesting?

#### Gumnuts

Joined Apr 26, 2024
35
The Data Sheet

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#### MisterBill2

Joined Jan 23, 2018
19,461
Certainly the zener diode/resistor stack is an interesting concept, but it does not work if any current is drawn.
What I missed was a description of the intended purpose of the whole project. The description in post #1 does not mention the overall purpose, but only the intent of the portions discussed.

My guess is that the ultimate intent is to apply different voltage pulse strings to the capacitor not described, but shown, in post #1.
Aside from the issue of the different voltages to the CMOS oscillator circuits, I did not see any serious goofs.
But certainly the system could be much less complex.
At the 10 KHz frequency the transformer driving the capacitor charging circuit will not be a common, iron cored device, if efficiency is any consideration. And quite likely the amplifier circuit will be more complex.

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#### BobTPH

Joined Jun 5, 2013
9,284
That is an adjustable one. A fixed regulator is simpler. You need one for each output voltage.

#### Gumnuts

Joined Apr 26, 2024
35
In my original post?

#### Gumnuts

Joined Apr 26, 2024
35
Yes but I need an adjustable amplitude in the output to the transformer, and that amplitude is derived from Vc (in my circuit) directly so I could use that adjustment for that or not.

#### Gumnuts

Joined Apr 26, 2024
35
I would still 3 regulators I suspect. The currents in each circuit are voltage-dependent and selecting them for the entire range of voltages would be difficult if not almost impossible. Yes?

#### BobTPH

Joined Jun 5, 2013
9,284
Yes but I need an adjustable amplitude in the output to the transformer, and that amplitude is derived from Vc (in my circuit) directly so I could use that adjustment for that or not.
One adjustable regulator would give you the ability to set the output the output voltage anywhere within a range. As far as current goes, only the max is relevant, it can always supply less.

#### Gumnuts

Joined Apr 26, 2024
35
Yes, true but I would have to manually adjust the output voltage each time I wanted to move to a much higher value before connecting the correct circuit (to match the component values), wouldn't I?

#### LowQCab

Joined Nov 6, 2012
4,309
What is this project supposed to measure ?
Shades of Stan Meyer come to mind.
Are You looking for the "Resonant-Frequency" of your "Capacitor" ?
An Output Transformer adds all kinds of complexities.
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