Dear all.
I hope everybody is ok.
I have a small problem in this circuit. The circuit is designed to switch off the load when the input voltage decreases under 12V, this is set by R3 pot. and to regulate the voltage at output when the input voltage exceeds 24V, so when the input voltage is in between 24V and 30V (which will be the maximum input voltage) the IRF5305 will be off and the current will drain across the leaner voltage regulator circuit (U3, TIP35C...), the 24V is set by R1 pot.
Now as I said, the circuit is working fine but there is a small problem facing me. U1A's output is used to sink current in order for the PNP transistor to work, LM358 needs a minimum sink current of 10mA and maximum of 20mA, I think the 2N2906 is a good choice. U1A sinks current as it's set, when the supply voltage is 24V or lower, calculating at maximum voltage (24V) for RB will give approximately (24V-10V)/0.015A=933Ω.. so I used 1KΩ resistor...
Now IC will be approximately 150mA, which means 0.15Ax24V = 3.6W, when calculating the values of RC and RE I found that they should be about 100Ω and 60Ω, 2 to 5 watt resistors.. this is my problem. So as I need the PNP transistor for only switching the p-channel ON and OFF, I need to dissipate that power and use high wattage resistors, and this seems to be ridiculous!
It seems that I need an "inverse darlington" here
Any idea?
Regards,
Hazim
I hope everybody is ok.
I have a small problem in this circuit. The circuit is designed to switch off the load when the input voltage decreases under 12V, this is set by R3 pot. and to regulate the voltage at output when the input voltage exceeds 24V, so when the input voltage is in between 24V and 30V (which will be the maximum input voltage) the IRF5305 will be off and the current will drain across the leaner voltage regulator circuit (U3, TIP35C...), the 24V is set by R1 pot.
Now as I said, the circuit is working fine but there is a small problem facing me. U1A's output is used to sink current in order for the PNP transistor to work, LM358 needs a minimum sink current of 10mA and maximum of 20mA, I think the 2N2906 is a good choice. U1A sinks current as it's set, when the supply voltage is 24V or lower, calculating at maximum voltage (24V) for RB will give approximately (24V-10V)/0.015A=933Ω.. so I used 1KΩ resistor...
Now IC will be approximately 150mA, which means 0.15Ax24V = 3.6W, when calculating the values of RC and RE I found that they should be about 100Ω and 60Ω, 2 to 5 watt resistors.. this is my problem. So as I need the PNP transistor for only switching the p-channel ON and OFF, I need to dissipate that power and use high wattage resistors, and this seems to be ridiculous!
It seems that I need an "inverse darlington" here
Any idea?
Regards,
Hazim
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