You could just use a voltage divider with resistors, select a resistor with the appropriate wattage to handle your power needs, this would dissapate power as heat, but so does a linear regulator.
Ahh, yes... back to my days as a power supply designer when a customer requests a design and one of the design conditions is that you can not use the only possible circuit that meets the requirement.
A switcher of some type is the only way to drop a voltage down with decent efficiency. If you use diodes, resistors, transistors or any other passive/active linear device to lower the voltage, the total power lost is the same which is:
(12 - 5) X IL which is 7V x 0.8A = 5.6W in your design.
Any linear circuit will burn this amount of power. You can shift the power between diodes, resistors, transistors but the total power burned is constant.
It will melt with 5.6W of power. You would need a 7805 in a TO-220 package attached to a heatsink whose thermal resistace is less than about 12C/W which is reasonably sized.
If you really need the efficiency you could probably use a low noise switcher design such as from Linear Technology Linear Technology - Ultralow Noise Regulators. It requires a carefull layout and good filtering but you can get a switching regualtor with 10's of microvolts noise, which is good enough for most low noise applications.
If you really need the efficiency you could probably use a low noise switcher design such as from Linear Technology Linear Technology - Ultralow Noise Regulators. It requires a carefull layout and good filtering but you can get a switching regualtor with 10's of microvolts noise, which is good enough for most low noise applications.
I can't get that link to open, but if those are their switched capacitor buck converters then they can have very low noise. They are very good for low power conversion with low noise because they have no inductors.
I can't get that link to open, but if those are their switched capacitor buck converters then they can have very low noise. They are very good for low power conversion with low noise because they have no inductors.
No, the devices I referred to are not the switched-cap converters, they are switching regulators with inductive filtering.
Inductors have nothing to do with the noise in a switching regulator. The noise comes from the switched currents which are rapidly being switched between the transistor and the flyback diode. The inductors just serve to filter and smooth the switching currents. The Linear Tech devices get their low noise primarily by controlling the transistor current rise and fall times to minimze the harmonic noise.
You could just use a voltage divider with resistors, select a resistor with the appropriate wattage to handle your power needs, this would dissapate power as heat, but so does a linear regulator.
Say for instance he was trying to get 6 volts from 12 and set up a voltage divider of two 1 ohm, high wattage resistors...high enough to handle the power they are subjected to. Obviously your circuit load will tap into the 6 volts created by the divider, probably from zero volts to the 6 volt point. Well, the load will be parallel to that resistor, thus the overall resistance at that point will decrease, thus dropping more of the voltage across the other resistor in the divider....by how much depends on the impedance of the load.
For this to be workable you would have to have a stable, known load impedance and calculate the value of the divider resistors accordingly.
I tried this a long time ago with a circuit I was playing with and that's when I truly learned about series/parallel circuits. I'm not saying it can't work, but generally it will only work in very specific applications and the voltage divider will either waste a lot of power, impede so much current as to not properly feed the circuit, or be too unpredictable a voltage source as I described.
Nope, you are wrong about that. Inductors ring when the switch gets turned off abruptly. Switching transformers also have leakage inductance and self resonance that tends to ring in the 50 - 100 MHz range. You wouldn't believe how many years of my life I spent fighting the noise that comes from those.
Actually, the problem is that the catch diode is not ideal which means it has a finite turn on and turn off time (off is worse) and the inductor rings while the diode gets it's act in gear.
No, not true at all: in nearly every buck (step down) switcher, the inductor is the energy storage element in the converter: it releases stored energy during the transistor's off time. You may add L-C filters after that output, but somewhere in the heart of the converter is the inductor that stores and dumps energy.
Basic buck regulator operation is covered in the switcher section of a book I wrote for customer training some years back. Check page 34 of attached document.
That's a bogus approach IMHO because it increases switching losses. We used it when we absolutely had to, but it wastes power. BTW: it's not "harmonic" noise that's the real problem, it's the very high frequency ringing at the switch turn off that generates the most obnoxious EMI. The fundamental frequency of that ring is not a harmonic of the switch frequency, it's dependent on parasitic R-L-C values in the assocuiated switch components.