DIY Audio Projects Forum
 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

DIY Audio Projects Forum

Welcome to the DIY Audio Projects Message Forum. Use these forums to discuss Hi-Fi audio and to share your DIY Audio Projects. Registration is free and required to post messages and view the file attachments. Registration will only take a minute and registered users do not see any advertisements. After you have completed the online registration process, check your email (including spam/junk folder) for the verification email to activate your account. New members are under moderation - so your posts will not be visible until approved by a moderator. See the Read Me 1st, Forum RULES and Forum FAQ to get started on the forum.

It is currently 25 Sep 2018, 02:56

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 9 posts ] 
Author Message
PostPosted: 20 Nov 2016, 12:39 
Offline

Joined: 20 Nov 2016, 11:38
Posts: 4
Location: Germany
Hi Everyone!

Sorry for the offtopic here, but I have very typical ( from my understanding ) schematic with LR8 regulator. I burned 3 of them without any reason. I am using this design as PSU for PIC microcontroller, I need to regulate voltage came from moped alternator ( 0-200 Acv ) to 5v. Expected max current is 250ma. Could you please advise what can be the reason, why LR8 is not working properly. For the tests, instead of alternator, I was using UPS with AC regulator. Input voltage was 50v Ac.

Could you please advise what can be the reason, why LR8 is not working properly ? Thanks in advance for any suggestions.

Regards,
Vlad.

Image


Top
 Profile  
 
PostPosted: 21 Nov 2016, 00:39 
Offline
User avatar

Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
Hi,

The mods may split this into it's own topic. Who knows?

Why is your alternator kicking out 200V? Is the field regulator shorted?

Your circuit is failing due to SOA (Safe Operating Area) oopsies.

With such a wide input voltage, if you want to stay linear instead of switching, a pre-regulator is the way most all commercial builds do it with good reason - less stress on the regulator.

An alternator isn't 60Hz. It's frequency varies with the speed of your moped. A "1N" series of diode is a poor choice. The UF series is a better one because it's fast recovery, inexpensive and easily obtained.

The MOSFET is doing double duty as a pre-regulator and a power filter. Because of the large frequency variance and the inefficient half-wave rectification, you need a larger input capacitor and one with low ESR. Given the automotive application, I'd use a Nichicon LGR or LGX, long-life or the like.

The MOSFET shown has a Vgs of 4V. So for an 13V zener, you'll get 9V out. That's a 4V difference across the 7805 at 1/4 amp = 1 watt. Just a little set of "wings" on the 7805 will do, while the MOSFET will need more.

200V - 9V = 191V * 0.25A = just under 48 watts!

So, unless you're thinking of a large box, I'd think more of switchmode.


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.


_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


Top
 Profile  
 
PostPosted: 21 Nov 2016, 05:34 
Offline

Joined: 20 Nov 2016, 11:38
Posts: 4
Location: Germany
Geek wrote:

Why is your alternator kicking out 200V? Is the field regulator shorted?
An alternator isn't 60Hz. It's frequency varies with the speed of your moped. A "1N" series of diode is a poor choice. The UF series is a better one because it's fast recovery, inexpensive and easily obtained.


Thanks a lot for the answer.

Alternator voltage is 0 - 200 Vac and 20-150 Hz frequency varies with the speed of engine. Main purpose of voltage from Alternator is to power AC-CDI ignition. I just use PIC to time delay. Oldtimer mopeds has no 12V battery and I have no other way how to get power for it from the same coil. I see right now, big mistake in this design, if LR8 is fail, PIC controller will burn too. How I wrote, for the test purpose I am using stable source of AC 50V, with load 1K resistor. Expected current is very low. Why LR8 was burned in such kind of conditions, that is riddle for me. Do you think absolutely impossible to use LR8 for such kind of purpose with some mods of presented schematic ?


Top
 Profile  
 
PostPosted: 21 Nov 2016, 06:10 
Offline
User avatar

Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
Hi,

If you insist on an LR8, this is what I use successfully in tube circuits. But really, an LR8 is *not* a LV-output performer.

A little TO-92 sink on the LR8 keeps the voltage stable once warm - it's a pretty good "thermistor" and needs the bulk of the sink not for dissipation, but thermal inertia.

The PNP wraparound keeps the LR8's error amplifier in the loop - an NPN as you have it makes it clueless as to what's going on the load side.

Small cap on the output. Your large cap is most likely what cooked it (the pass transistor would have demanded base current to charge the cap that probably exceeded the LR8's ratings. They aren't short-circuit proof).

Cheers!


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.


_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


Top
 Profile  
 
PostPosted: 21 Nov 2016, 07:03 
Offline

Joined: 20 Nov 2016, 11:38
Posts: 4
Location: Germany
Hi,

Thanks a lot for your help, I will reduce cap to 1uF and let you know about result. About NPN. For me the same if not very clear how this typical LR8 design with NPN key is working and what's going on the load side. I have found other example, where author was using the same, but just with two NPNs. Post from stefa38 :
http://www.costruirehifi.net/forum/view ... 9&start=75
Internet full of such kind of solutions, based on LR8.


Top
 Profile  
 
PostPosted: 13 Jan 2017, 05:15 
Offline

Joined: 20 Nov 2016, 11:38
Posts: 4
Location: Germany
Big cap was a reason of issue. Reduced to 1uF solved my problem. Thanks a lot for your help !


Top
 Profile  
 
PostPosted: 08 Jul 2018, 13:47 
Offline

Joined: 08 Jul 2018, 13:38
Posts: 2
hi,
is your 230V Ac to 5V Dc power supply circuit using LR8 is working ok ?
i am asking because i am as well looking for 230v ac to 5V dc voltage converter for micro controller project .
any suggestion then please suggest.


Top
 Profile  
 
PostPosted: 09 Jul 2018, 18:22 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 3794
Location: Arizona, USA
Hi, I use LR8 regulators all the time...great when used properly. My sense regarding the last post 230 ac to 5 vdc is that using an LR8 is the hard and inefficient way to do it. use a small filament transformer and then something like a LM7805. A simple bridge rectifier and filter caps on both sides of the LM7805 and you have clean power. A whole lot less dangerous if there is a failure. Stuffing 230 vac into something that uses 5 vdc will not be pretty.

In the first postings I might consider an audio transformer as a step down device and use it in a similar manner. Also many filament transformers will work up to 400HZ and would be suitable. Why do things the hard and IMO less reliable way when simple works great?

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 10 Jul 2018, 02:58 
Offline

Joined: 08 Jul 2018, 13:38
Posts: 2
yes with transformer it is great but i have space issue i mean there is no space in enclosure. so looking for compact without transformer circuit solution.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 9 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
DIY Tube Projects :: DIY Tube Amp Kits :: DIY Speaker Projects :: DIY Solid State Projects :: DIY IC / Op-amp Projects :: DIY Phono Projects :: DIY Cable Projects :: Hi-Fi Audio Schematics
© diyAudioProjects.com - Terms of Service - Privacy Policy