KD1047 npn epitaxial power transistor REPLACEMENT

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Kaloudis stefanos

Joined Sep 3, 2018
3
Hello guys,I recently bought A DIY power supply from ebay https://www.ebay.com/p/Red-0-30v-2ma-3a-Continuously-Adjustable-DC-Regulated-Power-Supply-DIY-Kit-PCB/514101507?iid=201751652278.
I patched eveything together,everything worked fine until i burned up the power transistor KD1047 from heat cause i used a very small heatsink (genius).The problem is that im searching a similar or the same and im not sure that i found the correct one, Can you tell me the difference on KD1047 to KTD1047? is it the same or even better? or worse? can i use it as a replacement?

MOD Note: Bad language has been deleted, please do not repeat.
 

bertus

Joined Apr 5, 2008
20,773
Hello,

The given page states that the input voltage is 24 Volts AC, that is about 33 Volts on the input of the transistor.
When the ouput voltage is near 0 Volts, there will be almost 33 Volts accross the transistor.
When you draw 3 Ampere in this state, the pass transistor will have to dissipate almost 100 Watts.
As the maximum allowed power is 100 Watts, it is no wonder the transistor could blow.

KTD047_maximum ratings.png

Bertus
 

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digsys

Joined Jun 27, 2018
27
Agree with Bertus .. at low volts / high amps .. that is a heck of a lot of heat !!! I would seriously consider using a much bigger heatsink to mount
the KD1047 and even a fan (w/ thermister?). Those types of cheap kits are made to be upgraded / modified ... that's why they're so cheap :)
In many cases as well - the semis are not to spec, often counterfeits or 2nds. If you check comments in some of the kits, you'll find plenty that
had to buy replacement semi parts. If you buy these replacements from a reputable source, you should be fine.
I've bought many kits / modules over the years for testing, and rarely found any that were 100% as specified. They'll likely still work ok, but maybe
not as expected.
 

MisterBill2

Joined Jan 23, 2018
7,034
It may also be that a totally different series pass transistor would work much better. AND, as other have mentioned, the heat sink capability is VITAL!!! In a series regulator all the power wasted is spent in the series pass transistor. That can be a whole lot of heat to spread and radiate.
 
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