Designing your own power supply: The PWM controller and cooking your own
Here you can find the TL494 datasheet. I don't think that the TL494 requires any more presentation. If you think it does then read this and try for yourself.
On page 2 of the datasheet you can see the block diagram of the TL494. As you can see, it's not a complicated device. The heart of the chip is the PWM comparator (which actually makes the pulses) and the error amplifiers (which allow you to implement voltage/current regulation). The rest isn't important - all that logic is only for the clean switching of the outputs, nothing more.
From now on i will only discuss about voltage mode controllers. Current mode controllers like the UC3842 are different. They can be somewhat easier to implement but the theory is harder to understand and they pose their own set of problems. The current mode camp always cites pulse-by-pulse current limiting as their greatest advantage, but IMO pulse-by-pulse limiting is just an excuse to use wimpy parts.
But what if you don't want to use the TL494, or you don't understand how it works? Well... you can roll your own controller. Sure, it involves three chips instead of one, but hey. We will be making a different type of controller - instead of PWM we will be making a pulse skipping controller. This is the simplest type of them all - no need for output = no pulse. It is also very efficient but due to its nature (variable-frequency switching) it produces more ripple than the fixed-frequency PWM type.
For it we will be using three ICs. The NE555 timer will be the oscillator and driver, the LM311 will be the comparator, and a good choice for an error amplifier would be the TL082. You will also need a 12v power supply for the controller and an idea of some sort of power supply you want to be controlling. I already hear you. "A power supply based on the 555 timer? Seriously?".
Well, yup. It won't drive a half or full bridge since it has only one output, but it works great for single-ended supplies like buck, boost or forward converters. And you can have as many error amps as you want, i will be using a dual opamp but there's no reason why you can't use a quad. In a PWM controller the opamps are used as comparators but the reason opamps are used instead of dedicated comparators is because their gain characteristic can be shaped.
I will be posting a PCB design, but if you think it sucks you can make your own. But my PCB will try to cover everything that you can do with this controller and have room for extra parts. In the meantime you're free to think about how in the world could a 555, a comparator and an opamp make a power supply controller.
On page 2 of the datasheet you can see the block diagram of the TL494. As you can see, it's not a complicated device. The heart of the chip is the PWM comparator (which actually makes the pulses) and the error amplifiers (which allow you to implement voltage/current regulation). The rest isn't important - all that logic is only for the clean switching of the outputs, nothing more.
From now on i will only discuss about voltage mode controllers. Current mode controllers like the UC3842 are different. They can be somewhat easier to implement but the theory is harder to understand and they pose their own set of problems. The current mode camp always cites pulse-by-pulse current limiting as their greatest advantage, but IMO pulse-by-pulse limiting is just an excuse to use wimpy parts.
But what if you don't want to use the TL494, or you don't understand how it works? Well... you can roll your own controller. Sure, it involves three chips instead of one, but hey. We will be making a different type of controller - instead of PWM we will be making a pulse skipping controller. This is the simplest type of them all - no need for output = no pulse. It is also very efficient but due to its nature (variable-frequency switching) it produces more ripple than the fixed-frequency PWM type.
For it we will be using three ICs. The NE555 timer will be the oscillator and driver, the LM311 will be the comparator, and a good choice for an error amplifier would be the TL082. You will also need a 12v power supply for the controller and an idea of some sort of power supply you want to be controlling. I already hear you. "A power supply based on the 555 timer? Seriously?".
Well, yup. It won't drive a half or full bridge since it has only one output, but it works great for single-ended supplies like buck, boost or forward converters. And you can have as many error amps as you want, i will be using a dual opamp but there's no reason why you can't use a quad. In a PWM controller the opamps are used as comparators but the reason opamps are used instead of dedicated comparators is because their gain characteristic can be shaped.I will be posting a PCB design, but if you think it sucks you can make your own. But my PCB will try to cover everything that you can do with this controller and have room for extra parts. In the meantime you're free to think about how in the world could a 555, a comparator and an opamp make a power supply controller.
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