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I have been trying to simulate high voltage regulator LR8 on the MINDI software.

I first ran this circuit which came as is in the "examples" folder, and just changed the input to our need. It worked properly and gave a constant 5V output as expected.

We want a 60V/10V/18V output, however, so we tried manipulating the resistors R1 and R2 to get our required Vout= 60V (as stated by the formula in the data sheet of LR8) but the software refused to simulate this iteration. We tried several such iterations, but none worked.

Please guide me on how we can get our required output voltage of 60V/10V/18V.

enter image description here enter image description here enter image description here enter image description here

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  • \$\begingroup\$ What error did the software give you? \$\endgroup\$
    – JRE
    Commented Sep 3, 2020 at 5:43
  • \$\begingroup\$ Actually when the ckt is correct it shows a graph of the output and when there is some error no ouput is shown. You can refer the above pictures \$\endgroup\$ Commented Sep 3, 2020 at 6:36
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    \$\begingroup\$ Can you please provide us the calculation involved in getting the 5W power dissipation across the voltage divider? \$\endgroup\$ Commented Oct 27, 2020 at 5:38
  • \$\begingroup\$ A warm welcome to the site. I think you're using 'Answer' on this Q&A site like 'Reply' is used on discussion sites. Although well-intended, this is a comment and not a detailed Answer. I appreciate that you don't yet have sufficient Reputation points to have posted this as a comment. It will most likely be deleted, though you can delete it yourself before any downvotes reduce your Reputation. Thanks. \$\endgroup\$
    – TonyM
    Commented Oct 27, 2020 at 6:17
  • \$\begingroup\$ @ShubhamKarekar I converted your 'answer' to a comment. When you get slightly more reputation points you'll be able to post comments. \$\endgroup\$
    – Russell McMahon
    Commented Oct 27, 2020 at 7:11

2 Answers 2

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Although it can be calculated, here are the modeled (optimized) values ​​with 1% resistors. lr8

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  • \$\begingroup\$ Actually when i was simulating it it was showing an error so can you help me with were you simulated this \$\endgroup\$ Commented Sep 3, 2020 at 3:38
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    \$\begingroup\$ Here, with this program. \$\endgroup\$
    – csabahu
    Commented Sep 3, 2020 at 6:33
  • \$\begingroup\$ Is LR8 available on TINA-TI as it is a microchip prodct \$\endgroup\$ Commented Sep 3, 2020 at 6:35
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    \$\begingroup\$ You can use anything in it that has a PSpice compatible model. \$\endgroup\$
    – csabahu
    Commented Sep 3, 2020 at 6:38
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Got it.

The problem lies in the voltage divider and which simulation model of the LR8 you use.

With your high value voltage divider, the LR8_SIMETRIX model fails to simulate - the simulation stops and says "DCOP failed." With the LR8_SIMPLIS model,the simulation completes and shows you that the regulator doesn't regulate properly with the low current (and voltage) available through your voltage divider.

When I did my simulation, I accidentally used the LR8_SIMPLIS example instead of the LR8_SIMETRIX example you started with.

The different models use different simulation methods. One just fails outside of the required operating conditions, and the other manages to complete the simulation.

You'll need to modify your input voltage divider as described below in order to get the LR8_SIMETRIX model to work - or switch to the LR8_SIMPLIS model.

I can't tell you what other drawbacks you may encounter when using the different model.


Original answer:

I had never heard of Mindi, so I downloaded it to give it a try.

It was easy enough to use, and it simulated your circuit properly.

With your voltage divider at the input, the output can't reach the desired 60V. Your voltage divider limits the current to the regulator to the point that VIN is less than 60V.

The resistor values for your divider need to be much smaller. I reduced them to 10k and 45k, and got a regulated 60V on the output using csabahu's voltage select resistors.

This circuit:

enter image description here

produced this output:

enter image description here

Using your original voltage divider:

enter image description here

produces this output:

enter image description here

The output isn't what you wanted, but the simulation clearly works.

I can't tell you why it isn't working for you. I used the latest version (8.20) and went straight from the (working) example for the LR8 to your circuit with the voltage divider.

All I can suggest is that you update to the newest version and start over from the LR8-Startup_SIMPLIS example.


Your voltage divider will need to use resistors with a fairly high power rating.

I got good simulation results using 10k and 45k in the divider. Given an input voltage of 550V, the divider will dissipate (waste) over 5 watts of power.

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  • \$\begingroup\$ Ohh thank you very much. Can you help me with the current required by LR8 as it is not mentioned anywhere so that i can choose an appropriate resistor of higher powwer rating. 5W resistor would be very bulky on the PCB. \$\endgroup\$ Commented Sep 3, 2020 at 13:16
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    \$\begingroup\$ The 5 watts will be consumed by the voltage divider by itself. If you had nothing but the two resistors connected to 550 volts, then those two resistors would have to dissipate over 5 watts of power. \$\endgroup\$
    – JRE
    Commented Sep 3, 2020 at 13:19
  • \$\begingroup\$ The LR8 isn't a good choice for an input voltage of 550 volts. I don't know of a good regulator for your case. The voltage divider is wasteful, but you can't expose an LR8 to 550V. \$\endgroup\$
    – JRE
    Commented Sep 3, 2020 at 13:21
  • \$\begingroup\$ There aren't many voltage regulators used for a voltage greater than 500V so had to use LR8. Also there are some voltage regulators for higher voltage applications but the circuitry used is very bulky and complex. \$\endgroup\$ Commented Sep 3, 2020 at 13:23
  • \$\begingroup\$ If you want to make 60V out of 550V, there is another solution if you meet Zener stability. \$\endgroup\$
    – csabahu
    Commented Sep 3, 2020 at 22:38

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