current draw of a chipamp - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 13th July 2007, 10:25 AM   #1
jarthel is offline jarthel  Australia
diyAudio Member
 
Join Date: Jan 2002
Location: somewhere in Australia
Default current draw of a chipamp

I need current draw of an lm3785, lm3886 and lm4780 (as used in PCBs sold by Peter and Brian). I want to use a CLC filter in the supply but I do not know how much current is required by the chip.

Thank you

ps. I looked at the datasheet and I cannot find it.
  Reply With Quote
Old 13th July 2007, 11:14 AM   #2
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
the input current is roughly equal to the output current.

If your amp is capable of 50W into 8r0 then peak voltage is 28.3Vpk.
The peak output current is based on the effective impedance of the load and the shape of the drive signal.
Continuous sinewave signals will send Ipk=Vpk/Z
for a normal speaker then Z can vary from about 60% of nominal impedance to about 10times nominal impedance.
For discontinuous signals with fast stopping or fast starting the effective impedance can drop as low as 35% of nominal impedance.

The worst case current is Vpk/nom imp/0.35=28.3/8/0.35=10Apk
The worst case input into that 50W amp is about 10Apk from either supply rail. Most of this peak will be met by discharging the main smoothing caps fitted to the supply rails. Any added resistance between the amp and the rectifier will reduce the peak current ability.
Your CRC will rely on the last C to supply the peak demand with a little help from any on board decoupling.
__________________
regards Andrew T.
  Reply With Quote
Old 13th July 2007, 12:45 PM   #3
jarthel is offline jarthel  Australia
diyAudio Member
 
Join Date: Jan 2002
Location: somewhere in Australia
Quote:
Originally posted by AndrewT
Hi,
the input current is roughly equal to the output current.

If your amp is capable of 50W into 8r0 then peak voltage is 28.3Vpk.
The peak output current is based on the effective impedance of the load and the shape of the drive signal.
Continuous sinewave signals will send Ipk=Vpk/Z
for a normal speaker then Z can vary from about 60% of nominal impedance to about 10times nominal impedance.
For discontinuous signals with fast stopping or fast starting the effective impedance can drop as low as 35% of nominal impedance.

The worst case current is Vpk/nom imp/0.35=28.3/8/0.35=10Apk
The worst case input into that 50W amp is about 10Apk from either supply rail. Most of this peak will be met by discharging the main smoothing caps fitted to the supply rails. Any added resistance between the amp and the rectifier will reduce the peak current ability.
Your CRC will rely on the last C to supply the peak demand with a little help from any on board decoupling.

thank you very much for the extensive reply Andrew. helpful as always

ps. I wouldn't have figured that out myself
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
calculating total current draw woodturner-fran Tubes / Valves 3 9th March 2008 12:11 PM
Current rating and tube current draw cbutterworth Tubes / Valves 1 13th October 2006 05:42 AM
Do CLC filters work well at low current draw? leadbelly Solid State 2 28th March 2004 01:51 PM
current draw on a gainclone? cowanrg Chip Amps 9 9th August 2003 07:58 AM
Opamp current draw 5th element Solid State 2 21st July 2003 01:11 AM


New To Site? Need Help?

All times are GMT. The time now is 03:54 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2