**SLR half bridge DC/DC converter in low frequency**

**Concept of load resonant converters **

In these resonant converters ,an LC tank is used that results in oscillating load voltage and current and thus provided zero voltage ad/or zero current switchings.Each circuit in this catagory is analyzed with a load that is most practical for the converter topology being considered .Only the steady state operation is considered.

**SLR DC-DC converter**

Basic Definition:The series resonant tank is formed by Lr and Cr and current through the resonant tank circuit is full wave rectified at the output and feeds the output stage.Therefore as the name suggests the output load appears in series with the resonant tank.

**Modes of SLR DC-DC converter**

There are three possible modes of operation based on the ratio of switchingfrequency ws to the resonance frequency wo ,which determines if iL flows or discontinuously

1. Discontinuous condition mode with ws<1/2wo

2. Continuous conduction Mode with 1/2wo<ws<wo

3. Continuous Condition mode with ws>wo

**
Concept of Steady State Operating Chracteristics and Control of SLR
Dc-Dc Converters
**

**concept of steady state operating chracteristics :**
It is useful to know the relation of the peak and the average values of the
circuit volatge and currents to the operating condition(Vd,Vo,Io,wo etc).

A SLR DC- DC converter in the discontinuous conduction mode operates as a current source,that is io stays contant even through the load resistance & hence Vo may change.

**Control of SLR DC-DC Converters:**
In series resonant circuits, the resonant tank impedance depends on the
frequency of operation.Therefore,for a given applied inputs voltage Vd and
a load resistance Vo can be regulated by controlling the switching
frequency fs.

LOAD RESONENT CONVERTERs :

These converters consists of an LC resonant circuit.Oscillating voltage and
current ,due to LC resonance in the tank are applied to the load,and the
converter switches can be zero voltage and /or zero current.Either a series
LC or a parallel LC circuit can be used. In these converter circuits,the
power flow to the load is controlled by the resonent tank impedence ,w hich
in turn is controlled by the switching frequency f_{s} in
comparision to the resonent frequency f_{o} of the tank.

__Series loaded resonant (SLR) dc-dc converter :__

A half bridge configuration of the SLR converter is shown in the figure
below The waveforms and the operating pricniple are the same for the full
bridge configuration .A transformer can be included to provide the output
voltage of the desired magnitude as well as the electrical isolation
between the input and the outputThe series resonent tank is formed by Lr
and Cr ,and the current through the resonent tank circuit is full wave
rectified at the output and |i_{L}| feed the output stage.Therefore
the output load appears in series with the resonent tank.The filter
capacitor Cf at the output is usually very large ,and therefore the output
voltage across the capacitor can be assumed to be a dc voltage without any
ripple.The resistive power loss in the resonent circuit is assumed to be
negligible, which greatly simplifies the analysis.The output volatge V _{o} is reflected across the rectifier input as V_{B'B}
where V_{B'B} =V_{o} if i_{L} is positive and V _{B'B} = -V_{o} if _{ }i_{L} is negative

**
DISCONTINEOUS CONDUCTION MODE WITH w _{s}<w_{o}/2
**

**
CONTINEOUS CONDUCTION MODE WITH w _{o}/2<w_{s}<w _{o}
**

**
CONTINEOUS CONDUCTION MODE WITH w _{s}>w_{o}
**

**Steady state operating characteristics**

**Control of SLR dc-dc converters**