Variable power supply
Variable power supply
(OP)
Hello,
I'm trying to build a variable DC power supply, I'm using TL494 for PWM and a NPN transistor as the switch.
I'm using a Buck topology, and my problem is that my voltage is fine without any load applied to it, but when I connect a simple led with a resistor the voltage drops a lot.
I'm not using any feedback on the TL494.
Thanx in advance, Carlos Cardoso
I'm trying to build a variable DC power supply, I'm using TL494 for PWM and a NPN transistor as the switch.
I'm using a Buck topology, and my problem is that my voltage is fine without any load applied to it, but when I connect a simple led with a resistor the voltage drops a lot.
I'm not using any feedback on the TL494.
Thanx in advance, Carlos Cardoso





RE: Variable power supply
either the drive current to the pass transistor is not enough to turn it on or
feedback is less than needed.
You said you do not use feedback, A regulated power supply mainly is a FEEDBACK circuit, it compairs output sample agains a reference voltage then control a pass element.
How this control is done gives the circuit its name.
The data sheet has few nice examples up to 1 amps and a thorough explanation of how it works
http://www.alldatasheet.com, then type your chip part number
you are then directed to this link
http:/
I am typing both links because some sites will only allow access to files through its main home page, even they are free...
Any more help I will be glad
RE: Variable power supply
RE: Variable power supply
And without any additional components. ;)
RE: Variable power supply
RE: Variable power supply
In a buck configuration, it will not work with an NPN. Use a PNP instead with base resistor, the output of the TL494 pulling the base to ground when on. You'll need a base-emitter resistor to help turn off the switch transistor.
Benta.
RE: Variable power supply
I'm attempting to control the power output of a resistive heater using PWM. I intend to use a TL494 IC and hope to use a varistor to alter the output but am not sure how to achieve it. My original thought is to use the varistor to vary the signal input to the deadtime control pin, not sure if this is the best way.
Any ideas would be greatly appreciated.
Vultan
RE: Variable power supply
If you want to control the heat, you must do some circuit with a temperature sensor. ;)
RE: Variable power supply