Hi,
I have some bushes for the TO-220 package, and these fit no issue to the backplate of the transistor.
The BD139/BD140 is a TO-225 package, and the hole in the transistor is not large enough for the TO-220 bush.
The rear of the BD139/140 has the collector electrical connection, and the 3mm hole seems to be insulated.
Can anyone confirm that using an M3 screw to secure the transistor to the heatsink, with the thermal insulation in place, is acceptable.
I am unable to locate any M2.5 bushes from Farnell, RS Electronics, Mouser, Digikey etc., which leads me to believe that they are not generally available since TO-225 packages do not require them since they have the necessary insulation around the hole.
Thanks and regards,
Shadders.
I have some bushes for the TO-220 package, and these fit no issue to the backplate of the transistor.
The BD139/BD140 is a TO-225 package, and the hole in the transistor is not large enough for the TO-220 bush.
The rear of the BD139/140 has the collector electrical connection, and the 3mm hole seems to be insulated.
Can anyone confirm that using an M3 screw to secure the transistor to the heatsink, with the thermal insulation in place, is acceptable.
I am unable to locate any M2.5 bushes from Farnell, RS Electronics, Mouser, Digikey etc., which leads me to believe that they are not generally available since TO-225 packages do not require them since they have the necessary insulation around the hole.
Thanks and regards,
Shadders.
Last edited:
No,just do not trust this!
Just yesterday i had an issue using 3mm screw to fix a bd139Vbe multiplier.
Yes, the hole seems isolated but screw easy destroy the isolation.
Hi,
Thanks - i did locate some 3mm out diameter and M2 inner diameter bushes. When you search bush on the internet, a lot of non-electronic engineering results are returned.
https://uk.farnell.com/c/fasteners-...xings/spacers-feet/spacers?outer-diameter=3mm
Regards,
Shadders.
Hi,
Thanks - i located them from Farnell UK. I did just try bushings, and similar to bush, but the range of products on Google refers to too many false hits.
I am surprised, that if people have had issues with te TO-220 package, that their availability is not more prolific.
The bushes ordered from Farnell are a perfect fit, aside from a slight reduction in the length for 3mm, which needs to be trimmed.
Regards,
Shadders.
Thanks - i located them from Farnell UK. I did just try bushings, and similar to bush, but the range of products on Google refers to too many false hits.
I am surprised, that if people have had issues with te TO-220 package, that their availability is not more prolific.
The bushes ordered from Farnell are a perfect fit, aside from a slight reduction in the length for 3mm, which needs to be trimmed.
Regards,
Shadders.
The TO126 is specifically designed to be used with 3mm screws and provide isolation.
It is however good practice to use a belleville or compression washer between the screw head and the transistor body, for two reasons:
1 It spreads the pressure on the whole body
2 Many screws have an uncontrolled diameter or burrs very close to the head, and this can damage the plastic
I wanted to share a number of parts that fit the BD139 and BD140 regulators. The shoulder washer protects the device package when a screw is used to mount it to a heatsink.
Keystone Shoulder Washer #4 (Insulator bushing). Accepts a fastener up to 2.97mm diameter.
Mouser P/N: 534-3049
Wakefield-Vette Deltapad Thermal Interface (thermally conductive/electrically isolating, footprint for 220 devices)
Mouser P/N: 567-173-7-240A
Keystone Shoulder Washer #4 (Insulator bushing). Accepts a fastener up to 2.97mm diameter.
Mouser P/N: 534-3049
Wakefield-Vette Deltapad Thermal Interface (thermally conductive/electrically isolating, footprint for 220 devices)
Mouser P/N: 567-173-7-240A
You have all forgotten that those early partly insulated transistor packages needed a flat washer and a spring washer to take up the thermal cycling so that the insulation does not crack.
The fully insulated TO220F packages also need the washers.
The fully insulated TO220F packages also need the washers.
BD139/140 come in two different packages, to-225 with exposed metal tab and a isolated to-126
You do not need a shoulder washer ( bushing) for the to-225 because it’s not like the to-220, where as the to-225 is like the to-3p where there is plastic insulation between the hole and the metal.
You do not need a shoulder washer ( bushing) for the to-225 because it’s not like the to-220, where as the to-225 is like the to-3p where there is plastic insulation between the hole and the metal.