 Posted: Tue Nov 23, 2010 7:03 am Post subject: |
|
| Square waveform involves high frequency components and at such low rate and high frequencies I wonder if a solid state rely would do the trick. | |
| Posted: Thu Oct 28, 2010 8:22 am Post subject: |
|
| If you need current feedback to get a correct waveform through an inductive load, please take a look at the designs used in vertical deflection circuitry of TVs and monitors. The datasheet of any vertical output IC from the 80's or 90's will give you a lot of hints. A such design will be much simpler if you don't use a H-bridge topology but instead connect the "cold" end of the load to ground via a measurement shunt. The drawback of using a single-ended amplifier is that it will need twice the supply voltage of a bridge amplifier, and it will cause more ripple on the supply needing a better regulation or big filter capacitors that can withstand the ripple current. |
|
| Posted: Fri Oct 22, 2010 10:06 am Post subject: |
|
| Whilst most audio amplifiers have DC coupled outputs, very few if any will operate at DC since they are usually AC coupled at some stage in the signal path. Thus you should expect significant distortion of square waves at frequencies below about 10 Hz.A simple half or full bridge arrangement from the power supply might be more appropriate and easiest to do (Solid state relay idea of Gatomas). If you decide to go that way, ensure you use good (short and thick) wiring layout and diodes to catch any fly-back emf in the load is inductive _________________________________ |
|
| Posted: Tue Oct 19, 2010 2:14 pm Post subject: bocek ilaclama |
|
thanx  |
|
| Posted: Tue Oct 19, 2010 7:07 am Post subject: |
|
| I agree that square waveform involves high frequency. | |
| Posted: Mon Sep 27, 2010 7:27 pm Post subject: |
|||
You will need a quite sophisticated system to achieve that kind of output. It will need a control loop with current sensing. That would probably be more of a project than you’d want to take on. However, there is one simple option that you might try, assuming you can find a suitable power supply. If you get a PSU with current limiting, you could set the limit, at your required output, and use it with the full (H) bridge arrangement. Many bench power supplies have this facility but at the power levels you are looking at they will be expensive. However, this places the current limiting complexity in the power supply leaving the switching drive simple. The supply will also need to have a much higher maximum voltage output than for a resistive load. Inductive spikes at the switching transitions may present a problem and require suitable snubbing circuitry. |
|||
| Posted: Mon Sep 27, 2010 3:35 pm Post subject: |
|
| Hi JD406 I think the DC supply and the H-bridge will give a good bipolar ouput voltage but the current shape will not be good since I am driving an inductive load. My question: is there any kind of addition to this circuit to improve the shape of the current waveform? something like negative current feedback used in amplifiers or any other arrangement? What is importnat to me is that the current should be a square waveform. Many thanks |
|
| Posted: Wed Sep 22, 2010 6:28 pm Post subject: |
|||
A full bridge drive will provide bi-directional drive, i.e. it will drive current into a load in both directions and produce no drive (off). These three drive states can be applied to make bipolar drives. Depending on what you need and the nature of the load, there are various configurations that you could try. A half bridge (simplest) might be suitable if you have + & - supplies but if you only have a single supply then a full (H) bridge will probably be required. Note: Bridge arrangements can only provide fixed voltage outputs at the supply level (unless modulated which adds a lot of complexity - see digital amplifier [D-class]). This link is to a simple full bridge circuit that could be used as a starting point: http://www3.telus.net/chemelec/Projects/H-Bridge/H-Bridge-1.png [http://www3.telus.net/chemelec/Projects/H-Bridge/H-Bridge.htm] I did not design this circuit, not have I used it but I cannot see any major flaws in it. It is suitable for controlling the direction of motors/solenoids and similar. There is no current limit so it would be sensible to add a fuse in the supply line. Heatsinks will likely be necessary on the main MOSFETs and if the drive current is calculated to be close to the MOSFET limit then extra devices can be placed in parallel to share it. |
|||
| Posted: Wed Sep 22, 2010 12:18 pm Post subject: |
|
| Hi JD406 It sounds a good idea to use a bridge circuit with ssr. My question is : can this arrangement provide bipolar squarewave? Can you please decribe the circuit if it is possible. Thanks |
|
| Posted: Thu Sep 16, 2010 6:42 pm Post subject: |
|
| Can you be more specific about your application? Exactly what are you trying to drive? Whilst most audio amplifiers have DC coupled outputs, very few if any will operate at DC since they are usually AC coupled at some stage in the signal path. Thus you should expect significant distortion of square waves at frequencies below about 10 Hz. A simple half or full bridge arrangement from the power supply might be more appropriate and easiest to do (Solid state relay idea of Gatomas). If you decide to go that way, ensure you use good (short and thick) wiring layout and diodes to catch any fly-back emf in the load is inductive. Fir ideas on how to do bridge circuits check out the application notes and technical documents here: http://www.irf.com/indexnsw.html |
|