Better solution for heat?

Thread Starter

Miracletech

Joined Nov 15, 2019
160
Its been long since I've been here :)
So, I made a boost converter that converts 3.7v to 5.3V(Is this too much?) To charge my phone. It works well, But...
The switch I'm using(2SC3807) Is getting warm while charging my big phone. Tried TIP41C and it blew on the spot. Its drawing 1A of current, So its normal.
My question is: Should I add a parallel transistor or go for a heatsink? Which would do the job?
By the way, Base drive current is 200ma at 3.6v, Everything is ok, Charges very fast.
It feels like its dissipating more than 500MW of heat.

Switching frequency is unknown, Because I don't have a scope, But its above 300Khz.
 

DickCappels

Joined Aug 21, 2008
6,659
If it is above 300 kHz as you said don't use this transistor:
It's too slow.
Turn-on time 0.14 us
Storage time 1.35 us
fall time 0.1 us

If your input is 1 amp on average as stated you may be marginal compared to the maximum current test.

You might want to try a MOSFET for that frequency and if you really need to use this part, try a large heatsink and if possible drop the frequency.
 

Thread Starter

Miracletech

Joined Nov 15, 2019
160
Oh my God.... Humpty dumpty... So I lowered frequency, But its still heating up, and TIP41C just Died, MJE13003 and 5 Died, logic level fets are not available, But If its any Good BJT, I can get it on hand. Or, Is a darlington pair worth it?

The device consumes 1A, while its on charge, Not the circuit. My bad. ;-)
 

panic mode

Joined Oct 10, 2011
1,865
well... why don't you show your circuit? how is transistor biased? i would NOT use darlington due high Vce voltage which explains your heat (Vce*Ic is about 1W in your case).

you should use separate small signal transistor to drive high current output transistor but... do NOT connect their collectors together. collector of driving transistor should go to V+ (so Vc1 is not pulled down when output transistor is on...). this will ensure that output transistor Vce is lower and dissipated heat will be reduced due smaller Vce (should be lowered significantly, some 3-4 times).
https://forum.allaboutcircuits.com/threads/1v-saturated-on-darlington.111088/
 
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Thread Starter

Miracletech

Joined Nov 15, 2019
160
Hahahaha, I don't go to pharmacists, I go to doctors :)
I'm using a PNP transistor to drive the NPN's , But its still misbehaving, The signal is coming from the PNP transistor.
 

bertus

Joined Apr 5, 2008
20,889
Hello,

Show us the complete schematic.
That way we can see how there can be made an improvement on your circuit.

Bertus
 

Thread Starter

Miracletech

Joined Nov 15, 2019
160
Ok. This is it.
electronics-diy.com/transformerless-joule-thief.php
In my own, I changed some things.
Emitter resistor is 56 ohms,
Pnp base resistor and capacitor is 470PF and 15Kohms,
Output diode is SR260, output cap is 10V100UF,
I'm using feedback to regulate output voltage.
PNP is S8550 and NPN.... You should Know.

So, Its something I had in mind. Inductor is unknown, 11 turns on medium sized ferrite core with medium sized wire.
 

Thread Starter

Miracletech

Joined Nov 15, 2019
160
I'm using my pc with a 10GB HDD, So can't install simulators.
So, I have to post pictures. I apologize for the inconvenience.
Darlingtons have high gain, meaning lesser base drive current, so .....?
 

Thread Starter

Miracletech

Joined Nov 15, 2019
160
Let's just imagine that I'm making a boost converter with an external switch, whereby an PNP transistor drives An NPN.
Let's say pwm is coming from an RC circuit, with adjustable frequency.

"Let's use our imagination to achieve a solution."
Miracletech.
 

bertus

Joined Apr 5, 2008
20,889
Hello,

I have already merged several posts made within in a couple of minutes.
You can edit posts to add some more info.

Bertus
 

Thread Starter

Miracletech

Joined Nov 15, 2019
160
Thanks so much bertus.
So, let's focus on the external switch. Its possible to use a heatsink, But adding another in parallel would be more efficient. So, I may have to add another in parallel, or would MR. Heatsink save me space?
 
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