I am helping someone out with building a PWM controller using a 555 timer IC and a MOSFET. He wants to use the controller to regulate the voltage being outputted by the circuit (from 0-15v but will really be 0-12v due to power supply limit). The circuit will need to take upto 10A of current.
P = IV = 10 * 12 = 120watts it will need to support also.
I searched on google and all I found were circuis for PWM for servos or fans which only require like 500mA at max…
Does anyone have any schematics that I may use? One with a pot to control the voltage would be best.
As Zoomcat said, a PWM system doesn’t “control” a voltage per se, it just turns it on and off rather quickly. The amount of power going to the device is related to how much time is spent ‘on’ vs ‘off’.
I don’t know how a Peltier device really works, but it’s not guaranteed that PWM is an appropriate way to control it. Some devices may need an actual voltage change.
I’m probably not as advanced in EE as some here, but what is the difference between “actual” voltage control and say a fast PWM with a suitable large enough capacitor? I mean that’s essentially how all switching regulators work, right?
I would suggest a variable switching regulator perhaps? It would probably be a lot easier and efficient than making your own with a 555, unless you want to make it for the point of learning how.
If that’s the case, try an astable 555 circuit, like the one here: kpsec.freeuk.com/555timer.htm with R1 or R2 as a pot. Then connect the output to a suitable array of FETs, then put a large and small capacitor in parallel and you’re set. You’d probably have to do some experimenting to get the voltage to go between the values you want. There are ways to calculate it from the size of the output capacitor, and the 555 equations, but probably easier to just experiment. An oscilloscope would really help here to make sure you’re 555 is behaving the way you think it should.
I don’t have a lot of time to burn writing today so I’ll take the easy question.
Direct voltage control generally refers to a linear regulator with a pass element such as a transistor that a control circuit varies the impedance of to regulate the voltage on a particular load. As with all linear regulators you must realize that whatever current is flowing in the load is passing through the pass element, and the difference between the source voltage and regulated voltage is presented across the pass element. A little PIE will reveal it is quite possible to be dissipating more power from your pass element than your load, especially at high currents and large voltage differentials.
Switching regulators apply nearly the full source voltage across the load for a period of time. The non-resistive characteristics of the load determine how much energy is stored in the load while the source voltage is removed. For a FAN circuit, especially one driven by a brushless motor controller, you almost must use a switching circuit as there is often an undervoltage lockout that will keep the fan from turning until some minimum input voltage threshold is reached. Modern PC fan speed controls use this control technique for exactly this reason.
Now for some new information to consider. Switching regulators come in two flavors, Pulse Width Modulation and Pulse Frequency Modulation, PWM and PFM respectively. PWM operates at a constant frequency and varies the duty cycle of the pulses. A classic servo signal is a PWM waveform with a frequency of 50Hz and a typical duty cycle of 2.5 to 12.5 % (corresponding to .5 ms to 2.5 ms with a nominal 20ms period.) PFM always delivers the same pulse width but varies the frequency at which the pulses are delivered to change the duty cycle. Typical 555 oscillator circuits are PFM as the discharge pulse is a constant width Td=0.693RaC, and the recharge is Tr=0.693(Ra+Rb)C. It is interesting to note that neither 0% nor 100% duty cycle are possibly with a PFM circuit.
You have indicated that your controlled load is to be a thermoelectric pile, aka a pelliteer block. You should research this on the web, specifically looking for application notes detailing TEC controllers. There is not much energy storage in a TEC and I know I have seen some specific TEC controller ICs that sort of bridge the gap between a switching and linear regulator. I don’t know that there will be any harm in using a PWM/PFM control to regulate one, but you should consider the effects of pulsing the heat transfer. If you are using a TEC to control the temperature of an overclocked CPU the heat density can both be very high and change very rapidly. It may not be a trivial design task to close that regulation loop, especially when you start to consider the thermal lag of your sense element.
Eddie posted a lot of great info. But just to briefly elaborate on this question as it relates to this thread:
In theory, you can get by with a 555, a big FET, a capacitor, and a load that is constant resistance. But there are issues like:
You make the cap big enough so that the output is clean, when you turn it on there is a big current surge to charge up the cap.
If the resistance of your load changes, the voltage changes.
The adjustment of the duty cycle might be ‘touchy’.
These sorts of issues are why switching power supplies are complex.
It doesn’t seem you read my post? (no offense) I did a google search. I always do a search before I ask a question. However, my search results were all about 555 PWM controllers for fans. Fans require very little current. Like 50-500mA. I am dealing with 10A here.
Perhaps you should use the google advanced search. Since PWM is usually associated with motor speed control (did you know that?), I did a google search for “pwm 555 motor” and the below link was at the top of the list. Looks like it could be good for up to 35A. Since you have decided on your own to use PWM with your gizmo, you are on your own there.
