Re: gEDA-user: OT: help needed; asymmetric load after rectifier seems to disrupt its working.
Good point Rick, I should have explained that even though the larger inductance reduces the rms current in the primary significantly, the positive and negative peak currents are highly asymmetric. Simulating with a sinewave input, the positive peak current is about 110mA whilst the negative is about -390mA. Hence the transformer has to have a considerably higher peak current rating than the rms values might suggest. Robert originally said his input is bandlimited 15KHz to 28KHz but all his circuits include some form of discrete bandpass filtering. I suspect what Robert intends is that C1 and some combination of the transformer primary - as in his later posting - or a single inductance to ground or an additional series inductance - as in the original circuit posted - forms a bandpass filter centred on about 23kHz. In any case it is difficult to see how C1 can be removed without adding some sort of active buffer stage between the rectifiers and the filter, which then requires some sort of bootstrap supply to bring up the buffer to drive the rectifiers. Andy. signality.co.uk On 29 June 2011 23:54, rickman gnuarm.g...@arius.com wrote: The transformer allows a DC path to exist on the secondary side, but you still have the capacitor on the primary side of the circuit. If the positive and negative pulse currents are not equal, you will still have a problem on the primary side. You need to remove the cap C1. I still can't tell exactly what is going on in your circuit because you don't provide any labels on the o'scope diagrams. It would also be useful to see current waveforms from the simulations and waveforms from the loads. As was asked for previously, we still have not seen your requirements so I can't tell exactly what you are trying to do with this circuit. How large is the DC offset in the source? Why don't you include that in your simulation model? What voltage do you need out of this supply? I really can't tell what is needed in your design and what is just wrong. Rick On 6/24/2011 7:10 AM, myken wrote: This is strange in my simulation the attached circuit works fine. In real life it kinda works but the signals are distorted like you can see. I think that has something to do with the fact we used a pulse transformer to try the circuit. If we disconnect Vx the signals stay the same, so the distortion is in the transformer. If you say it doesn't work then why doesn't it work? On 22/06/11 22:39, Andy Fierman wrote: Sorry Robert, Both Wojciech and I are wrong. His suggestion about adding a choke is basically the same as mine of using a transformer. The idea of both is to add a dc path to ground at the rectifier inputs. The difference is that the transformer adds DC isolation - which if you include your bandpass filter - you do not need. Sounds like the thing to do but sadly, the simulations show the reality! A choke does not do what you want and neither does a simple 1:1 transformer. However, if you use a 1:1:1 transformer then it all comes together. You can use a transformer with a 1:2 turns ratio, centre tapped and keep to the original half wave rectifier scheme. If you use a three winding transformer of 1:1:1 then you can use two bridge rectifiers. Using bridge rectifiers doubles the ripple frequency so allows lower smoothing C for the same ripple voltage. The attached (not very good quality) pdf shows the non-working choke and 1:1 transformer ideas and the working 1:1:1 transformer versions. Note the 1u smoothing capacitor values. These were reduced to make the simulation reach a steady state sooner than with the original 100uF values. Andy. signality.co.uk On 22 June 2011 01:12, Wojciech Kazubski [1][1]w...@o2.pl wrote: Hello all, I would appreciate some expert advice. I have a system which rectifies a sine wave input signal of 20Khz after a LC filter (see Rectifier_sim.jpeg) Everything works fine if LOAD_1 and LOAD_2 are equal. Vx is then (almost) the same as Vin. And Vcc and Vss are equal to the positive or negative part of the sine wave (less the DC losses) (Vss = -Vin_top and Vcc = Vin_top). BUT if LOAD_1 and LOAD_2 are not equal (like in Rectifier_sim.jpeg) it seems that Vx is lifted (DC component added) and Vss moves to the 0V and Vcc is lifted to twice the value I would expect (Vss = 0 and Vcc = Vin_toptop) (see rectifiersmp.eps). Our real life prototype shows the same behaviour as the simulation. I need this set-up for my system to work and I can not guarantee that the two loads always will be equal. Vin can be anything between 10Vtt and 90Vtt. I have tried adding a resistor from Vx to ground and that seems to help but increases the current drawn from the source (V1) to a unacceptable level. It should be a low power solution. If I short-circuit C1 everything works fine again (V1 has a low resistance output) but of course will
Re: gEDA-user: OT: help needed; asymmetric load after rectifier seems to disrupt its working.
It's also hard to see how the circuit could work with C1 in series with the transformer current. Why is a capacitor needed if you use the transformer? Maybe there is some effect that will balance things out, but if the two currents are unequal, actually it would be the integral of the two currents that need to be equal, the peak value is unimportant, the voltage on the capacitor will grow without limit... until something limits it. In the circuit with the transformer, is there some effect that will balance the positive and negative currents in the primary? Rick On 6/30/2011 4:06 AM, Andy Fierman wrote: Good point Rick, I should have explained that even though the larger inductance reduces the rms current in the primary significantly, the positive and negative peak currents are highly asymmetric. Simulating with a sinewave input, the positive peak current is about 110mA whilst the negative is about -390mA. Hence the transformer has to have a considerably higher peak current rating than the rms values might suggest. Robert originally said his input is bandlimited 15KHz to 28KHz but all his circuits include some form of discrete bandpass filtering. I suspect what Robert intends is that C1 and some combination of the transformer primary - as in his later posting - or a single inductance to ground or an additional series inductance - as in the original circuit posted - forms a bandpass filter centred on about 23kHz. In any case it is difficult to see how C1 can be removed without adding some sort of active buffer stage between the rectifiers and the filter, which then requires some sort of bootstrap supply to bring up the buffer to drive the rectifiers. Andy. signality.co.uk On 29 June 2011 23:54, rickmangnuarm.g...@arius.com wrote: The transformer allows a DC path to exist on the secondary side, but you still have the capacitor on the primary side of the circuit. If the positive and negative pulse currents are not equal, you will still have a problem on the primary side. You need to remove the cap C1. I still can't tell exactly what is going on in your circuit because you don't provide any labels on the o'scope diagrams. It would also be useful to see current waveforms from the simulations and waveforms from the loads. As was asked for previously, we still have not seen your requirements so I can't tell exactly what you are trying to do with this circuit. How large is the DC offset in the source? Why don't you include that in your simulation model? What voltage do you need out of this supply? I really can't tell what is needed in your design and what is just wrong. Rick On 6/24/2011 7:10 AM, myken wrote: This is strange in my simulation the attached circuit works fine. In real life it kinda works but the signals are distorted like you can see. I think that has something to do with the fact we used a pulse transformer to try the circuit. If we disconnect Vx the signals stay the same, so the distortion is in the transformer. If you say it doesn't work then why doesn't it work? On 22/06/11 22:39, Andy Fierman wrote: Sorry Robert, Both Wojciech and I are wrong. His suggestion about adding a choke is basically the same as mine of using a transformer. The idea of both is to add a dc path to ground at the rectifier inputs. The difference is that the transformer adds DC isolation - which if you include your bandpass filter - you do not need. Sounds like the thing to do but sadly, the simulations show the reality! A choke does not do what you want and neither does a simple 1:1 transformer. However, if you use a 1:1:1 transformer then it all comes together. You can use a transformer with a 1:2 turns ratio, centre tapped and keep to the original half wave rectifier scheme. If you use a three winding transformer of 1:1:1 then you can use two bridge rectifiers. Using bridge rectifiers doubles the ripple frequency so allows lower smoothing C for the same ripple voltage. The attached (not very good quality) pdf shows the non-working choke and 1:1 transformer ideas and the working 1:1:1 transformer versions. Note the 1u smoothing capacitor values. These were reduced to make the simulation reach a steady state sooner than with the original 100uF values. Andy. signality.co.uk On 22 June 2011 01:12, Wojciech Kazubski [1][1]w...@o2.pl wrote: Hello all, I would appreciate some expert advice. I have a system which rectifies a sine wave input signal of 20Khz after a LC filter (see Rectifier_sim.jpeg) Everything works fine if LOAD_1 and LOAD_2 are equal. Vx is then (almost) the same as Vin. And Vcc and Vss are equal to the positive or negative part of the sine wave (less the DC losses) (Vss = -Vin_top and Vcc = Vin_top). BUT if LOAD_1 and LOAD_2 are not equal (like in Rectifier_sim.jpeg) it seems that Vx is lifted (DC component added) and Vss moves to the 0V and Vcc is lifted to twice the