Hi Everyone..
I produced a pwm circuit comprising of a 555 timer astable at a frequency of 10Hz which switches a Darlington transistor (tip120) { collector connected to another supply different from that of the 555 ic} {base connected through a 10k resistor to the output pin of the 555} the emitter is connected to a Lm7806 to give a stable output voltage of 6v... the idea is to distribute a voltage of approximately 7V at the input of the voltage regulator .... and then regulate the noisy voltage supply to a clearer one.
thus an efficient supply of 6v is taken from say 18Volts supply...
unfortunately this doesn't work...can anyone help me.Thanks in advance.
555 / Darlington output (split from control circuit "and gate"?)
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williamjems
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Re: 555 / Darlington output (split from control circuit "and gat
Hi
Firstly 7V input to the LM7806 is too low to give a regulated 6V output - the input needs to be at least 2V higher than the output. If you can't raise the input voltage you could use an LDO (low drop-out) regulator.
Check which bits of the circuit work - do you have the expected output from the 555 into the transistor? If not disconnect the transistor and check the 555 output on it's own. Beyond this a circuit diagram would help explain things better.
If I understand correctly and the purpose of the circuit is to step 18V down to 6V without wasting too much power in the regulator you could use a switching regulator. I think switching equivalents for the conventional LMxx linear regulators exist, although I don't have part numbers to hand.
Firstly 7V input to the LM7806 is too low to give a regulated 6V output - the input needs to be at least 2V higher than the output. If you can't raise the input voltage you could use an LDO (low drop-out) regulator.
Check which bits of the circuit work - do you have the expected output from the 555 into the transistor? If not disconnect the transistor and check the 555 output on it's own. Beyond this a circuit diagram would help explain things better.
If I understand correctly and the purpose of the circuit is to step 18V down to 6V without wasting too much power in the regulator you could use a switching regulator. I think switching equivalents for the conventional LMxx linear regulators exist, although I don't have part numbers to hand.