Saturday, March 12, 2016

Baofeng UV5R accu eliminator part2

Received 2 very small DC-DC converters from China.
How is it possible 1€ free shipping from China?

Decided to break open  the  "accu eliminator" I payed 15€ local prize 
 loosing warranty but this type adapter does not work. 
  From China 5€ for the cartridge and power cord and 1 €  for the dc-dc regulator still is a bargain
The plastic case had to be forced open with a knife
Inside as expected a linear regulator with a 7808
A much too small heath sink  for 6W heath loss and  thermal protection trips after a minute with a UV5R.  I did not hear about problems with this adapter? must have  been
 first one sold?

The dc-dc converters need minimum 470uF elco on the output to filter switching ripple 
  
 I did not have a suitable 9V suppressor TVS diode for over voltage protection.  

like a  Unipolar Transient Voltage Suppressor Diode 5kW

Break Down: 8,33V...10,2V 5mA
Max Clamping: 14,3V  350A
DO204

10+€ 0,30  5KP7.5C    but crazy 7.5€ shipping  


The smaller regulator performs even better at low input Voltage.
10V -20V  input   8V out   drop 20-30 mV  with 1A load 
Impressive performance,  much better then I could get with the emitter follower regulator.
at 1A the the switching IC off the smaller became hot 50C-70C about
the total conversion loss is 100-400 mW estimated
Precaution  is needed these regulators have no short circuit-  reverse polarity- over voltage- or thermal protection 

  

For the UV5R  I used the bigger regulator
with the original Cap's  used with the UA7808
over the output extra  470u  and input 100u


the original  useless 7800 regulator


this tiny regulator performed best but heats up a bit at 1A
a tiny heat sink on the regulator IC would be enough or a very small PC fan


first result was okay had a long talk over the local repeater
No problem . the 7808 would trip thermal after 1 minute.


the small type uses the  MPS  MP2307N   claimed to be better then the LM2596
 the 1.5MHz switching frequency that was in some specs is a misprint
it's around 340kHz in the MPS specs.  chip seems to have  no internal protection.

http://www.datasheet4u.com/pdf/MP2307-pdf/596551

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