Marantz DR-6000, MAR770, MAR775 service manual Ch1 Drain voltage Ch2 Drain current Ch3 Gate voltage

is switched off when the current sense level exceeds the level at the output of the error amplifier.

TimeON phase : A drain current will flow from the positive supply at pin 2 of the transformer through the transformer's primary winding, the MOSFET and Rsense to ground. As the positive voltage at pin 2 of the transformer is constant, the current will increase linearly and create a ramp dependent on the mains voltage and the inductance of the primary winding. A certain amount of energy is stored in the transformer in the form of a magnetic field. The polarity of the voltages at the secondary windings is opposite to the primary winding so that the diodes are non-conducting in this phase.

TimeDIODE phase : When the MOSFET is switched off, energy is no longer supplied to the transformer. The inductance of the tranformer now tries to maintain the current which has been flowing through it at a constant level. The polarity of the voltage from the transformer therefore reverses. This results in a current flow through the transformer's secondary winding via the now conducting diodes, electrolytic capacitors and the load. This current is also ramp shaped but decreasing.

TimeDEAD phase : when the stored energy has been supplied to the load, the current in the secondary windings stops flowing. At this point, the drain voltage of the MOSFET will drop to the voltage of C821 with a ringing caused by the drain-source capacitance with the primary inductance.

The oscillator will start a next cycle which consists of the above described three phases. The time of the different phases depends on the mains voltage and the load.

TimeDEAD is maximum with an input of 400VDC and a minimum load. It will be zero with an input of 100VDC and an overload.

V2

Vosc

V1

0

Vcomp

Vsense

Vgate

Vdrain

Idrain

Idiodes

Ton Tdiode Tdead

CL 96532076_034.eps 290799

Figure 8-15 ‘Regulation’

		CH1	2
		CH2
	PM3394B	CH3	2 V~ ALT MTB5.00us- 0.90dv ch1-
ch1	1
ch3
ch2	T
	3
	2

ch1 : Drain voltage

ch2 : Drain current

ch3 : Gate voltage

		CH1	1
	PM3394B	CH3	50mV~ ALT MTB5.00us- 0.90dv ch1-
ch1
ch3	1
	T
	3

ch1 : Drain voltage

ch2 : Oscillator voltage

	CH1	1
PM3394B	CH3	20mV~ ALT MTB5.00us- 0.90dv ch1-
ch1
1
ch3
T
3

ch1 : Drain voltage

ch3 : Sense voltageCL 96532076_033.eps 290799

Figure 8-16 ‘Oscillograms’

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