What is the role of R3 and bipolar 2N3904 ?
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\$\begingroup\$ Google gives an excellent description: instructables.com/id/ARDUINO-SOLAR-CHARGE-CONTROLLER-PWM/…. \$\endgroup\$– jippieCommented Nov 9, 2015 at 19:13
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5\$\begingroup\$ I'm voting to close this question as off-topic because full circuit description (11 pages) was easily found using Google. \$\endgroup\$– jippieCommented Nov 9, 2015 at 19:15
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\$\begingroup\$ "The resistor R3 is used as a pull up resistor for gate." and "I used a simple MOSFET driver by using a NPN general purpose transistor.I used 2N3904 but you can use any general purpose transistors like 2N2222 or BC547 etc." \$\endgroup\$– got trolled too much this weekCommented Nov 9, 2015 at 19:33
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\$\begingroup\$ @jippie: How does that make the question off-topic? \$\endgroup\$– EM FieldsCommented Nov 9, 2015 at 19:41
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1\$\begingroup\$ @EMFields the explanation is in detail on the linked web page, OP doesn't supply any context. Simply by checking the circuit against Google's first hit it is explained that this is a PWM input of a solar charger and every single component is discussed. The question would substantially improve if the article text was quoted in the first place and specifically asked what part of the text is unclear. \$\endgroup\$– jippieCommented Nov 9, 2015 at 19:52
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Q1 is a P-channel MOSFET used to connect/disconnect the PV from the circuitry on the downstream side of its [Q1's] drain. R3 functions to pull Q1's gate up to its source, turning Q1 OFF when T1 is turned off by Cde being low, and T1 is used to pull Q1's gate down to ground, turning Q1 ON, when T1 is turned ON by Cde being driven high.
