A DC/DC converter 'chops' the currents - whether input or output. And independent from the converter's topology.

On the other hand, every power supply has a series resistance. Even if ever-so-small. So, what you observe is the effect of the change of input current on the series resistance.

Adding a capacitor reduces the ripple as a fraction of the changing currents is 'serviced' by the capacitor, but input ripple will never be 0 with 'real' devices.

Regards

Hi Paul,

I am not sure about the origin of the ripples, however, you may try these fixes. I have recently designed a Boost Converter circuit and I didn't notice any input ripples.

1. Add a capacitor at the input (two adjacently placed electrolytic capacitors and one ceramic capacitor to get rid of high-frequency noises)

2. Is your gate-driver circuit isolated from the converter circuit, i.e., are the converter grounds and PWM ground isolated? If not, use some optocoupler/optoisolator in your gate driver circuit.

Regards,

Mayank

Agreed with the answer given by Mayank

A DC/DC converter 'chops' the currents - whether input or output. And independent from the converter's topology.

On the other hand, every power supply has a series resistance. Even if ever-so-small. So, what you observe is the effect of the change of input current on the series resistance.

Adding a capacitor reduces the ripple as a fraction of the changing currents is 'serviced' by the capacitor, but input ripple will never be 0 with 'real' devices.

Regards

But some of them are of more than 25% magnitude. They are more like spikes. 

Which  converter is this, if you do not mind?

Looks like a boost converter. Or some other converter switching a choke to ground. Could be that the choke is beyond Saturation - which results in something looking similar to a short.

this is a dual input dual output boost converter.

In my college project of wireless power transfer, I had used boost converter at receiver side to boost up voltage. I faced same problem of ripple. I used capacitor to reduce that effect. However value of capacitor is important here.

The main problem of input ripple on the Dc Dc converter is the ripple on current input that drawn by the load. The acceptablr ripple voltage for input is about 1 to 2 %. As long as the ripple is equal to the standard value, I think you just don't care about it.

But, if you curious. You can add the input capasitor filter to stablize those ripple. Hope it answer your question. :)

The schematics look quite complicated and lack any capacitor on the input side. Thus your 'ripple' could be anything starting with overloading the power source Vin1 and ending with maybe switching inappriopriately.

What do you want to achieve with this topology ?

Hello Paul,

You can add the input capasitor filter to stablize these ripple. But adding a capacitor reduces the ripple as a fraction of the changing currents is 'serviced' by the capacitor, but input ripple will never be 0 with 'real' devices.

Ripples in input supply caused due to switching action of power electronics switches. These voltage ripples are reduced by using an extra cap at input side of converter.

However connection of extra capapcitor at input causes extra cost. The value of capacitor is decided by the ripple in voltage according to defined standard and losses caused due to ripples. For low value of ripple in voltage at input side, the value of cap will be large.

Each switch can be considered a capacitance when it is open. Therefore when a switch is turned off its capacitance has to charge to the Vdc level from the on state voltage. This will take spike currents even when there is no load connecetd to the dc-dc converter.

the principal cause is the quick variation of input current on the series resistance.

You should add low ESR capacitor between the D0/L node and ground. The path from  D1 out to motioned node through the  C1 and additional capacitor must be short as possible. These capacitors and S1 should connect star-wise to ground. Generally spices are generated by fast current edges on wires and components impedance

Best regards, Roman

These are the spikes during switching periods of converter. The probable solution is input capacitor, but if you are still getting problem then I think your switching frequency is high. So, to minimize this you have to design a snubber circuit for each switch which produced the transient during switching.

Hi , it seems that attachments can help you . Thanks

Rapid resolution is to add a capacitor in parallel to the DC voltage node.

A more sophisticated solution is to reduce the parasitic series resistance and apply high-quality inductors without mechanical movements, in DC source.

Adding a low ESR capacitor like MLCC(Multi-layer Ceramic Capacitor) at the input supply pin will help. If not for low ESR you may have to add N number of capacitors in parallel to keep the ESR low. This will add to cost and space constraints. You can prefer second order passive LC filter. But take care of damping. For critical damping you can prefer to add a small resistance in series with the inductor.