thermal pads for TDA7264 - Page 1
Forum section: electronics / beginners

author: hummusdude
author_rank: Regular Contributor
timestamp: June 18, 2020, 04:27:20 pm
content: I'm building a gain clone amp with this chip but I'm having a hard time finding a mica sheet made for it. I'm guessing that's because it's easy to cut mica paper to size and mica paper is easy to find. Am I close or is the grade of mica paper used for microwave ovens not appropriate for this application?

author: Vovk_Z
author_rank: Super Contributor
timestamp: June 18, 2020, 05:29:54 pm
content: I'm not sure (haven't used it) but if it is mica and if it slices into thin enough slices then why not?

author: hummusdude
author_rank: Regular Contributor
timestamp: June 18, 2020, 07:17:28 pm
content: I guess because I don't want to blow up my amp or electrocute myself if the material doesn't provide sufficient thermal conduction and electrical isolation. There are a lot of people selling pre-cut mica insulators for TO-072 and TO- 03 but none for this package type...that I can find anyone. So it would seem reasonable that it's easy to make one from the right material otherwise there would be a market and people supplying that market.

author: wraper
author_rank: Unknown
timestamp: June 18, 2020, 07:24:03 pm
content: Why do you need it to begin with? Tab is connected to GND.

author: hummusdude
author_rank: Regular Contributor
timestamp: June 18, 2020, 08:12:33 pm
content: Good point. The design I'm using has an optional ground loop protection circuit to prevent hum. The designer is specific in noting that if the circuit is used than all inputs and outputs must be electrically isolated from the chassis. Would not the ground of the op amp be considered part of the output?

author: Vovk_Z
author_rank: Super Contributor
timestamp: June 18, 2020, 08:22:02 pm
content: Quote from: wraper on June 18, 2020, 07:24:03 pmIt depends on bipolar or single polarity power supply is. Tab is connected to negative Vdd (as usual for power IC), so it can be either "minus" or Gnd.

author: hummusdude
author_rank: Regular Contributor
timestamp: June 18, 2020, 08:38:09 pm
content: In this case it will be -VCC.

author: Vovk_Z
author_rank: Super Contributor
timestamp: June 18, 2020, 08:48:58 pm
content: 20-25 VDC can't electrocute usually, but it is definitely unsafe with possibility to make a short circuit with a large radiator.

author: hummusdude
author_rank: Regular Contributor
timestamp: June 18, 2020, 09:18:56 pm
content: Safety is one concern. The author also points out that if any of the input/output get grounded than the ground loop circuit is bypassed anyway.

author: thm_w
author_rank: Super Contributor
timestamp: June 18, 2020, 09:50:55 pm
content: Thin sil-pad would be fine too and they are non-conducting. Just a question of where to buy them without paying a fortune. If you can salvage some from old electronics it would work.From what I can see the "microwave oven mica" is ~0.45mm. The stuff on digikey is 0.08mm. So I think its going to be too thick.https://www.digikey.ca/en/products/filter/thermal-pads-sheets/218

author: sahko123
author_rank: Frequent Contributor
timestamp: June 19, 2020, 12:47:10 am
content: Yeah silicon pads should be perfectly fine for this as long as you find some way to screw on the heatsink without using something conductive otherwise it would undo all the effort

author: hummusdude
author_rank: Regular Contributor
timestamp: June 19, 2020, 10:12:46 pm
content: Cool... I found some silicon stock at Mouser that I can trim to size.Thanks!!