Trying to understand this biasing circuit for the voltages

[FreshmanNewbie]

In this link, can someone explain how the circuit in Figure 1 on page 3 works?



source: Texas Instruments TIDU683, "LCD Bias Power Reference Design with TPS61085"

 

[D.A.(Tony)Stewart]

This is a boost regulator 3.3 to 10 V where the switched output pulses (SW) feed above two linear regulators using pulse rectified doublers to emitter followers after Zeners.

The left side uses D5 as an AC coupled +ve clamp and doubler to get -20 V to drive the 7.5 V zener low to get -7 V out for a low current load.

The right side is similar but uses D4 to create a negative clamp and doubler to create +20 V to drive the 18 V Zener to get 17.5V out. The load is just a constant bias for the LCD to define black / white thresholds or similar effect.

Design details are in the datasheet.

 

[BlackHelicopter]

The left side uses D5 as an AC coupled +ve clamp and doubler to get -20 V to drive the 7.5 V zener low to get -7 V out for a low current load.

The left charge pump doesn't double the voltage to -20 V. The left charge pump inverts the input voltage to -10V. That -10 V (across C2) is applied to a series regulator formed by a zener diode and PNP pass transistor.

When you take into account the zener voltage and Vbe of the transistor you get around -7 V.

 

[D.A.(Tony)Stewart]

The left charge pump doesn't double the voltage to -20 V. The left charge pump inverts the input voltage to -10V. That -10 V (across C2) is applied to a series regulator formed by a zener diode and PNP pass transistor.

When you take into account the zener voltage and Vbe of the transistor you get around -7 V.

I missed that the right side rectifier clamp D4 was referenced to the +10V rectified pulses output added 10V to the output to get 20 another way.
yes left side is not a doubler.

--- Updated Nov 9, 2023 ---

In this link, can someone explain how the circuit in Figure 1 on page 3 works?



source: Texas Instruments TIDU683, "LCD Bias Power Reference Design with TPS61085"

Which part do you not understand?
The Boost Reg?, The pulse Clamp and rectifiers? or the Zener regulators?