some question about internal high-voltage linear regulator

i want to get the 7.5V DC volatage from the 20-400V supply could you give some paper about the internal high-volage regualtor

Wow, 400V to 7.5V is a lot of voltage drop. Even at just 100mA load current you will have to dissipate 39W as heat. Your main difficulties are dumping that much heat and the semiconductors withstanding the large voltage differential. The voltage differential will most likely require some external transistors outside of the regulator IC. The heat issue is a much bigger problem.

I would suggest a switching regulator in a buck configuration. It would much more efficient. At 400V input, less than 2% of the power is delivered to the load. The remainder is waste heat.

Re: some question about internal high-voltage linear regulat

banjo said:

Wow, 400V to 7.5V is a lot of voltage drop. Even at just 100mA load current you will have to dissipate 39W as heat. Your main difficulties are dumping that much heat and the semiconductors withstanding the large voltage differential. The voltage differential will most likely require some external transistors outside of the regulator IC. The heat issue is a much bigger problem.

I would suggest a switching regulator in a buck configuration. It would much more efficient. At 400V input, less than 2% of the power is delivered to the load. The remainder is waste heat.

Click to expand...

the 7.5V is VCC as the internal subblock power supply not the output of the circuit
the circuit is for constant current drivers

some one told me that can use the Nmos (deplation-mode) OR JFET to decrease the higt to low volatage in order to charge capacity to get the vcc=7.5v

I think the MOSFET parameter is Vdss or the max breakdown voltage from drain to source. A quick google search found IXKN 75N60C which is supposed to be a 600V device. Vgs max for this device is about 12V. Therefore you could control it from a simple op-amp without any problem.
However, the main issue is heat. This MOSFET is acting like a big variable resistor. In operation, it must adjust its on resistance until it drops 400V down to 7.5V.
How much current are the constant current drivers taking? Once you how that, apply Ohms Law and determine the power dissipated in the MOSFET. Most people fail to realize just how much heat linear regulators have to drop. I still remember an early design I did that severely burnt my fingers when I touched the output device.
While I know people dislike switchers because the feel that the output will be noisy, they are the best solution. If you must have a super quiet output, then I would suggest a switching pre-regulator that drops the voltage down to about 12V and then a 12V-7.5V linear regulator following that.

Re: some question about internal high-voltage linear regulat

thank you for your help
the output current of the circuit is about 300mA
if we choose the switching to regulator the volatage
it will be cost more at area,
oh My circuit have similiary as the Supertex HV9922
but we want to add some more function in our circuit
here is the block of hv9922


DRAIN is the input (20v-400v)
the VCC PIN only have the one capacity (0.1uF) no volatage sing in it.

can you give me some advice how to realize the 7.5V ?/

Added after 1 minutes:

here is application of the circuit

I really confused. The Supertex parts are constant current switching regulators. The VDD pins on these devices are for internal use within the part only. I do not think you can attach external loads to them. The only reason these have an external pin is to allow an external filter cap.

What are you trying to build? A constant voltage regulator or a constant current regulator? If you want a constant current regulator, then realize that the output voltage is totally dependent on the load. The regulator will force the necessary voltage to get the required current. If you need 300mA constant current, I would suggest contacting Supertex. You may be able to parallel several of their devices to get the current you need. (MOSFETs are much easier to parallel that BJTs because they will current share rather than current hog.)

thank you for help