ChatGPT: Good inductor for low current negative voltage

[Someone_else]

I would like to provide a negative voltage of around -22v for an LCD. I have 5 volts as the main power. It seems that I can get the -22v with an oscillator, an inductor to amplify the voltage, and a schottky diode to create the voltage. Following this might be a (negative) voltage regulator to keep the bias voltage in range.

What value in microhenries should I choose for the bias voltage? I expect the current to be from 1 to 5 microamps after filtering.

 

[ChatGPT]

To calculate the required inductance value for your setup, we first need to know more about the operating frequency of the oscillator you are planning to use. The inductance value is crucial in designing a boost converter circuit to step up the voltage from 5V to -22V.

A boost converter configuration usually consists of an inductor, a diode, and a capacitor. The inductor stores energy when the switch (oscillator) is turned on and releases energy to the output when the switch is turned off. The inductor value is directly related to the boost converter's operating frequency, duty cycle, and required output voltage.

Here are the steps to determine the approximate inductance value for your application:

1. **Determine Operating Frequency:**
The oscillator's frequency determines how fast the switch (oscillator) will turn on and off. Operating frequency is crucial for selecting the inductor value. Let's assume an operating frequency, for example, around 100 kHz.

2. **Calculate Inductor Value:**
The inductance value can be calculated using the following formula:
\[ L = \frac{{V_{in} \times (V_{out} - V_{in})}}{{\Delta I \times f}} \]
where:
- \( V_{in} = 5V \) (input voltage)
- \( V_{out} = -22V \) (output voltage)
- \( \Delta I = 5 \mu A \) (maximum change in current)
- \( f = 100 kHz \) (operating frequency)

Substituting the values into the formula:
\[ L = \frac{{5 \times ( -22 - 5)}}{{5 \times 100 \times 10^3}} = \frac{{5 \times -27}}{{5 \times 100 \times 10^3}} = \frac{{-135}}{{500 \times 10^3}} = -270 \mu H \]

Therefore, based on the assumptions made, the inductance value would be approximately 270 microhenries. You might need to adjust this value based on the actual operating frequency, switching losses, and efficiency requirements of your circuit. It is recommended to simulate the circuit using appropriate software tools before implementation to ensure proper functionality.