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flyback driver circuit

vitom001

Aug 12, 2015
5
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Aug 12, 2015
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I'm trying to construct a simple flyback driver circuit using a single BU-508D transistor. In my circuit,
the base (pin 1) is connected to the (+) 0-48v DC input, the emitter (pin 2) is connected to pin 1 of
my flyback (HR 7839, http://www.donberg.ie/pics/h/hr7839.gif), and the collector is connected to the
neutral of the DC input and ground. For the flyback, pin 2 is connected to the (+) 48v DC input, and pin 8
to ground. When I run the circuit I can hear the flyback working but there is no output on the HV wire.
What am I doing wrong?
 

duke37

Jan 9, 2011
5,364
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Jan 9, 2011
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5,364
Show us a circuit. If looks as if the BU508 (npn) is upside down but then it shouldn't work at all.
 

Colin Mitchell

Aug 31, 2014
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Aug 31, 2014
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1,416
The transistor has to be connected as shown in the diagram and the waveform has to be suitable to get the transformer to produce a high voltage under fly-back conditions.
 

vitom001

Aug 12, 2015
5
Joined
Aug 12, 2015
Messages
5
I'm using a step-down transformer from the mains (230v, 50Hz) to 48v and a bridge rectifier for DC. Pictures of my setup are attached below. Note: if we count the pins from the transistor from left to right as 1-3, then 1 is connected to the positive DC terminal, 3 is connected to the negative DC terminal, and pin 2 goes to pin 1 on the flyback (diagram shown above). Pin 2 from the flyback goes to the positive DC terminal, and pin 8 goes to ground.
 

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