The problem of slow power-off of negative voltage circuit

lhjsol

The problem of slow power-off of negative voltage circuit [Copy link]

ELVDD outputs positive voltage. After 20V is disconnected, the output quickly drops to 0V.

ELVSS outputs negative voltage. After 20V is disconnected, the output power is lost for more than 5 seconds and there is still power. How to solve it?

maychang

Presumably your negative power supply load is very light (low current), so C24 discharges very slowly after 20V is disconnected. The positive power supply load is heavy and discharges quickly.

Solution: One way is to increase the negative power load (connect a resistor in parallel with C24), which will waste some current in normal operation. Another way is to reduce the capacity of C24, but the negative power output ripple may increase after the capacity of C24 is reduced.

lhjsol

maychang posted on 2020-1-10 14:53 Presumably your negative power supply load is very light (low current), so C24 discharges very slowly after 20V is disconnected. The positive power supply load is heavy and discharges quickly. Solution: One...

When both positive and negative pressure are no-load, the power-off speed is very different

maychang

lhjsol published on 2020-1-10 14:59 When both positive and negative pressure are no-load, the power-off speed is very different

When both the positive and negative power supplies are unloaded, the output voltage drops at a very different rate. I can't figure out what the reason might be.

maychang

I would like to ask: TPS54561 can output current up to 5A, do you really need such a large current? If both the positive power supply and the negative power supply are not fully loaded, you can use a TPS54561 to achieve positive and negative power output.

lhjsol

maychang published on 2020-1-10 20:04 I would like to ask: TPS54561 output current can reach 5A, do you really need such a large current? If both the positive power supply and the negative power supply are not fully loaded, you can...

The ± power supply currently requires 4A current, but even if I need ±1A, a single IC should not be able to output both positive and negative voltages at the same time, right? Can you give a schematic diagram?

maychang

lhjsol Published on 2020-1-10 22:43 Currently, the ± power supply requires 4A current, but even if I need ±1A, a single IC should not be able to output both positive and negative voltages at the same time? Can you give me a demonstration...

This picture is the picture in the chip datasheet.

This figure shows that based on the negative power supply output, a winding is added to the inductor, and then rectified and filtered to obtain a positive power supply.

Of course, it is also possible to add a winding to the inductor based on the positive power supply output to obtain a negative power supply.

maychang

lhjsol Published on 2020-1-10 22:43 Currently, the ± power supply requires 4A current, but even if I need ±1A, a single IC should not be able to output both positive and negative voltages at the same time? Can you give me a demonstration...

However, in this method of adding a winding to the inductor based on the Buck circuit to obtain another output, the output of the additional winding is limited by the output of the main winding.

lhjsol

maychang published on 2020-1-11 08:41 However, this method of adding a winding to the inductor on the basis of the Buck circuit to obtain another output, the output of the additional winding is limited by the output of the main winding...

The output voltage value of this method should be the same. I need two different values of ± voltage.