# Capacitor substitution and Inductor question

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#### lokeycmos

##### New Member
this is a 2 part question. both questions are about the attached schematic.

First off, there are 2 sets of three capacitors in parallel on the right side of the circuit. each individual cap is rated at 470nF. translation says that there can be 3 or 4 caps in parallel for each set. now if i go with 4 in each set, i get a total of 1.88uF. now i was able to salvage a bunch of 2.2uF pulse rated caps that match the voltage rating. my question is, will it be OK if i go a little higher on the value and go with 2.2uf instead of the 1.88uf?

second question is about the chokes on the input. translation is: 30 turns of 1.5mm(14awg) wire on a 6mm ferrite rod. im trying to find what the L value is of each coil, but there is no mention of permeability, AL, or anything to give me a clue as to the final value is. this is where i need your input. thank you for your time!

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#### ronsimpson

##### Well-Known Member
The L and C resonate at some frequency.
Changing the capacitors will effect the frequency. by square root of LC
You will need to run the IR2153 at a slightly different frequency.

When I made something like this; the maximum power was then the silicon switched near resonance. The minimum power was when the switching frequency was far away from the LC resonance.

The current in the capacitors can get very high.

#### lokeycmos

##### New Member
The L and C resonate at some frequency.
Changing the capacitors will effect the frequency. by square root of LC
You will need to run the IR2153 at a slightly different frequency.

When I made something like this; the maximum power was then the silicon switched near resonance. The minimum power was when the switching frequency was far away from the LC resonance.

The current in the capacitors can get very high.
so your saying it should work just fine, other than altering the frequency?

#### dr pepper

##### Well-Known Member
So long as the frequency doesnt go out of the range of the core, or cause saturation (which is a risk with lowering the freq), it'll probably be ok, and its only a minor change.
The circuit would probably be better with a trimmer to fine tune the freq o/p of the driver chip anyway, then you can 'find' the peak of the trans resonance with the caps.

I suspect that the input chokes were probably not 'designed' all that much, they do not so much play a critical part in the operation of the circuit, more to prevent switching noise from going back into the supply, or radiating from the supply wires.

#### lokeycmos

##### New Member
So long as the frequency doesnt go out of the range of the core, or cause saturation (which is a risk with lowering the freq), it'll probably be ok, and its only a minor change.
The circuit would probably be better with a trimmer to fine tune the freq o/p of the driver chip anyway, then you can 'find' the peak of the trans resonance with the caps.

I suspect that the input chokes were probably not 'designed' all that much, they do not so much play a critical part in the operation of the circuit, more to prevent switching noise from going back into the supply, or radiating from the supply wires.
It does have a frequency adjust comming off of pin 2

#### kubeek

##### Well-Known Member
The current in the capacitors can get very high.
..so you should check what current are your capacitors rated for. Or if you got eight of them you can series-parallel them to better share the dissipation.
Also I can translate from the original should you need it.