I'm looking for a simple 38 - 40v 150ma P/S built around an LM7824.
I thought a 15v Zener on the centre pin with an 8k2 from the o/p pin, to make sure the reg. is not starved, should jack it up to 39 volts as I have all the parts lying around.
But, the LM7824 is rated for a max i/p of 40v. - Am I correct in assuming this refers to the max i/p voltage between i/p & centre pin, & as long as it is below 40v here, it should be OK.
The total input voltage I'm feeding to it is about 46 volts which should leave about 31 volts between the i/p & centre pin.
Comments please.
I thought a 15v Zener on the centre pin with an 8k2 from the o/p pin, to make sure the reg. is not starved, should jack it up to 39 volts as I have all the parts lying around.
But, the LM7824 is rated for a max i/p of 40v. - Am I correct in assuming this refers to the max i/p voltage between i/p & centre pin, & as long as it is below 40v here, it should be OK.
The total input voltage I'm feeding to it is about 46 volts which should leave about 31 volts between the i/p & centre pin.
Comments please.
There is normally one or more large capacitors on the output.
At turn-on, these caps are ZERO volts. With 46V on the IN pin. Poof.
At turn-on, these caps are ZERO volts. With 46V on the IN pin. Poof.
Thanks PRR. I was intending to put a 10 ohm resistor on the Reg. o/p in series with the cap. (& the load), which hopefully will reduce the in-rush.
An engineer friend in the Philips lab told me this about 40 yrs. ago, explaining that these regs were similar to an amplifier and you certainly would'nt put a large cap straight on an amp. o/p.
An engineer friend in the Philips lab told me this about 40 yrs. ago, explaining that these regs were similar to an amplifier and you certainly would'nt put a large cap straight on an amp. o/p.
TL783, you need two windings for this setup, i have gerbers for dual LM317/TL783 just wire the outputs together and you have the bipolar +-40V supply you're looking for.
Gerbers are available for free in the free gerber thread.
Gerbers are available for free in the free gerber thread.
Over-voltage breakdown does NOT need "large current".
Altho 43V and 10r is 4+ Amps. Even some power transistors don't have that much SOA. IC regulators are wimpier.
There are high-voltage reg chips, and boosted regulators. Go ahead and try your plan, but in 1 or 1,000 start-ups you may be looking for another plan.
Thanks for your replies.
I don't need + - 40v. Only +40v.
Also, I forgot to mention that before the regulator there is R/C filtering, (390r/330uf), so there won't be a sudden 46 volts applied after switch-on.
Hopefully, it'll be OK, - agree - ??
Thanks again.
I don't need + - 40v. Only +40v.
Also, I forgot to mention that before the regulator there is R/C filtering, (390r/330uf), so there won't be a sudden 46 volts applied after switch-on.
Hopefully, it'll be OK, - agree - ??
Thanks again.
Apparently the LM317HV is still available. Ease of use typical of 3 terminal regs, basic overcurrent protection built in, runs at your voltage with minimal support components.
You could make a 7824 work safely by adding some support components (including another power transistor), but by the time you add all that you’ve already spent the two and a half bucks the proper regulator costs.
You could make a 7824 work safely by adding some support components (including another power transistor), but by the time you add all that you’ve already spent the two and a half bucks the proper regulator costs.
Another vote for the LM317HV - you'll end up with roughly the same number of passsive components in the design anyway and compared to the 7824 you'll be sure that nothing should blow up 🙂
Remember to check the power dissipated in the second adjustment resistor, because if you run 5-10mA though the first resistor the the dissipation in the resistor used to set the voltage will be quite high.
Remember to check the power dissipated in the second adjustment resistor, because if you run 5-10mA though the first resistor the the dissipation in the resistor used to set the voltage will be quite high.
Thanks again. I have not heard of the LM317HV & none of my local suppliers have it but it's good to know about it.
However, with all the filtering before the reg. & output with 10 ohm in series, plus having all the parts on hand, Iv'e built it up & it seems to perform very well.
However, with all the filtering before the reg. & output with 10 ohm in series, plus having all the parts on hand, Iv'e built it up & it seems to perform very well.