Buzzer Circuit help needed

AlbertHall

Joined Jun 4, 2014
12,116
Is 'no' the correct answer?
It looks as if the cathode of D4 also connects to something else?
What does the red writing around the MOSFET drain mean?
 

Thread Starter

mishra87

Joined Jan 17, 2016
966
Is 'no' the correct answer?
It looks as if the cathode of D4 also connects to something else?
What does the red writing around the MOSFET drain mean?
D4 cathode is connected to source of M1, no other connection.
Red wire is Buzzer .

Trying to drive buzzer at the same time short circuit protection needed.
 

AnalogKid

Joined Aug 1, 2013
10,112
Without the connection from D4 to the M1 source, C3, D4, and D5 form a charge pump, a low-power type of dc/dc converter. To the right of D4, off the page, there probably is a capacitor to GND to filter the ripple. The circuit is getting double duty out of transistor M1, driving both the buzzer and the charge pump. The buzzer acts as the pull-up for driving the pump. The output of the pump will be something less than twice the input voltage, so 5 V minus two diode Vf drops.

With standard silicon diodes, a charge pump running on 5 V is not very efficient because the diodes eat up a lot of the boosted voltage. Changing D4 and D5 to Shottkey diodes will increase the output voltage by approx. 0.5 V.

ak
 
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