Linear regulator, 8-100Vin, 4mA output at 7.5V with HV9910B?

[treez]

Hello,

I wish to design a linear regulator which can provide a 7.5V output, with maximum output current being 4mA.

The input voltage is between 8V-100V.

Can the HV9910B do this job?.....surely it will provide my required output from its VDD pin if i connect the Vin pin to the mentioned input voltage?

HV9910B datasheet:
**broken link removed**

 

[tpetar]

Yes, on page 4 they say:

"The HV9910B can be powered directly from its VIN pin and can work from 8.0 - 450VDC at its VIN pin. When a voltage is applied at the VIN pin, the HV9910B maintains a constant 7.5V at the VDD pin. This voltage is used to power the IC and any external resistor dividers needed to control the IC. The VDD pin must be bypassed by a low ESR capacitor to provide a low impedance path for the high frequency current of the output GATE driver."

 

[betwixt]

I don't think it will work as you want it. The VDD pin is brought out of the package so the capacitor can be connected but it isn't intended to be used as a voltage source for anything outside the IC. It *might* be possible to draw 4mA from it but I don't think it's a design feature.

Brian.

 

[treez]

It *might* be possible to draw 4mA from it but I don't think it's a design feature.

On page 3 of the HV9910B datasheet it says that "Iin,max" is 5mA when Vin = 8V.

Surely this means that as long as Vin is above 8V, it can supply 5mA from its VDD pin?

Presumably, if Vin is greater than 8V, then the Vdd pin can supply more than 5mA?

 

[betwixt]

That's not how I read it. The VDD pin is the internal supply to the circuits brought out so a filter capacitor can be connected. The data a sheet says it can be used to connect an external potential divider but doesn't suggest it's a regulated output to anything else. This means you COULD draw some current from it but it isn't intended to be used as a regulated supply to other devices. Please also read the notes on power dissipation regarding high voltage drops.

Brian.

 

[treez]

page 3 definetely says "5mA when Vin = 8V"......the internal circuitry takes 1mA......so i make it thats 4mA can be drawn from the Vdd pin to supply whatever else is external to the hv9910b.

I realise that VDD may not stay at 7.5V when its supplying 5mA...but youve gotta think that vdd will stay above the uvlo of 6.7V when supplying 5mA?